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1
Neshatpour, Siavash. "Recent B-decay implications beyond the Standard Model." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2013. http://tel.archives-ouvertes.fr/tel-00847404.
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Des progr ès exp erimentaux importants sont en cours dans l' étude des d ésint égrations rares de m ésons contenant un quark beau et impliquant un quark étrange et une paire de leptons. Le travail pr ésent mesure la port ée indirecte de ces progr ès sur des extensions supersym etriques du mod èle standard. Même dans des mod èles contraints, les limites indirectes ainsi obtenues peuvent dans certains cas être plus fortes que celles provenant de la recherche directe de particules supersym étriques. La pr écision gagn ée par les facteurs de forme et les corrections d'ordre sup érieur nouvellement impl ément és dans le programme public "SuperIso" montrent alors leur importance.
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Hansen, Christian. "Neutrino Oscillations and Charged Higgs Bosons – Experimental Projects for Physics beyond the Standard Model." Doctoral thesis, Uppsala University, Department of Nuclear and Particle Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5778.
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This thesis is based on work done in two different experimental projects.
The first project, the Tau RICH, is a previously proposed τ-neutrino appearance experiment for the CERN neutrino beam at the Gran Sasso laboratory in Italy. The proposed experimental concept is based on the use of focusing RICH detectors with liquid radiator (C6F14). Simulations made with a Geant4 code show that in the proposed experimental set-up, Cherenkov light from delta electrons will constitute a severe background that in practice would render the experiment unfeasible.
The second project, ATLAS, is a general purpose detector at the CERN 14 TeV proton-proton collider LHC which will start operation in 2007. To make the reconstruction and selection of the events in ATLAS more accurate, complete and up-to-date information on the interaction of the produced particles with the detector is needed. A service program code, the Material Integration Service (MIS), has been developed which makes use of the detector descriptions already available in a Geant4 code and which uses a novel algorithm, based on line integrals evaluated within small volume elements that build up the detector. This code is demonstrated to constitute a practically useful tool of satisfactory performance and accuracy.
The charged Higgs boson production in the gluon-bottom quark mode, gb → tH±, followed by charged Higgs decays into a chargino and a neutralino, is studied for a specific choice of values for the Minimal Supersymmetric Standard Model (MSSM) parameters. It is shown, using a Monte Carlo code to simulate the ATLAS detector and the assumed MSSM physics model, that for an integrated luminosity of 300 fb-1, in the intermediate region 4 < tanβ < 10 where H± decays to SM particles cannot be used for H± discovery, charged Higgs decays to non-SM particles can be used for Higgs discovery at the 5 σ significance level.
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Opferkuch, Toby Oliver [Verfasser]. "Sarah Goes Left and Right Looking Beyond the Standard Model and Meets Susy / Toby Oliver Opferkuch." Bonn : Universitäts- und Landesbibliothek Bonn, 2017. http://d-nb.info/1140525891/34.
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Opferkuch, Toby [Verfasser]. "Sarah Goes Left and Right Looking Beyond the Standard Model and Meets Susy / Toby Oliver Opferkuch." Bonn : Universitäts- und Landesbibliothek Bonn, 2017. http://d-nb.info/1140525891/34.
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Birkel, Michael. "Astroparticle physics beyond the standard model." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388826.
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Quevillon, Jérémie. "Higgs Physics Beyond the Standard Model." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01070196.
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On the 4th of July 2012, the discovery of a new scalar particle with a mass of order 125 GeV was announced by the ATLAS and CMS collaborations. An important era is now opening: the precise determination of the properties of the produced particle. This is of extreme importance in order to establish that this particle is indeed the relic of the mechanism responsible for the electroweak symmetry breaking and to pin down effects of new physics if additional ingredients beyond those of the Standard Model are involved in the symmetry breaking mechanism. In this thesis we have tried to understand and characterize to which extent this new scalar field is the Standard Model Higgs Boson and set the implications of this discovery in the context of Supersymmetric theories and dark matter models.In a first part devoted to the Standard Model of particle physics, we discuss the Higgs pair production processes at the LHC and the main output of our results is that they al-low for the determination of the trilinear Higgs self-coupling which represents a first important step towards the reconstruction of the Higgs potential and thus the final verifica-tion of the Higgs mechanism as the origin of electroweak symmetry breaking.The second part is about Supersymmetric theories. After a review of the topics one of our result is to set strong restrictions on Supersymmetric models after the Higgs discov-ery. We also introduce a new approach which would allow experimentalists to efficiently look for supersymmetric heavy Higgs bosons at current and next LHC runs.The third part concerns dark matter. We present results which give strong constraints on Higgs-portal models. We finally discuss alternative non-thermal dark matter scenario. Firstly, we demonstrate that there exists a tight link between the reheating temperature and the scheme of the Standard Model gauge group breaking and secondly we study the genesis of dark matter by a Z' portal.
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Csáki, Csaba 1963. "Beyond the minimal supersymmetric standard model." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42615.
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García, Isabel García. "Naturalness in beyond the standard model physics." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:76889f57-7120-422b-af27-e33c59292a3a.
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Being consistent with every experimental measurement made to date, the current paradigm of particle physics, the Standard Model, remains a successful parametrization of nature. Together, the Standard Model plus the theory of General Relativity seem to provide a consistent picture of physics at all scales, yet there is plenty of room to believe the story is incomplete. Puzzles that remain unanswered within the context of the Standard Model include (i) an explanation of the origin of Dark Matter, which accounts for no less than ~ 25% of the Universe's energy budget, (ii) a meaningful answer to the question of electroweak naturalness, (iii) a rationale for the absence of anti-matter in our observable patch of the Universe, (iv) a dynamical picture of the vast hierarchies we observe in fermion masses, and (v) a resolution to the strong CP problem. With the exception of the Dark Matter mystery, all other objections to the Standard Model listed here take the guise of a 'hierarchy' problem: why is some quantity (either a scale or coupling) so small? This work addresses two of the objections to the Standard Model: the necessity of an explanation to the origin of Dark Matter, and the question of naturalness as a guiding principle in nature, understood as the necessity for a dynamical mechanism behind unexplained hierarchies. Chapters 1 and 2 introduce the topics of naturalness and Dark Matter respectively. The former makes an emphasis on the electroweak hierarchy problem, and a particular class of theories that provide a solution to this puzzle: models based on the Twin Higgs mechanism. Chapters 3 and 4 are based on work published in [1] and [2], where novel theories of Dark Matter, and their phenomenology, are explored in the context of Twin Higgs models. Chapter 5 explores structural aspects of a particular mechanism - the so-called 'clockwork' - for generating hierarchies in parameters in a way that can be considered natural, and it is based on [3]. Finally, chapter 6 summarizes our conclusions and future outlook. Other work published during my time as a graduate student include [4 - 7], but those publications are not the focus of this thesis.
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Setford, Jack. "Strongly coupled physics beyond the standard model." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/77429/.
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This thesis is concerned with strongly coupled extensions to the Standard Model. The majority of the thesis is dedicated to the study of Composite Higgs models, which are a proposed solution to the hierarchy problem of the electroweak scale. In these models the Higgs is a composite pseudo-Nambu Goldstone boson which forms a part of a new strongly interacting sector. There are many different variations on the basic Composite Higgs theme { the current status of some of these variations is assessed in light of results from the Large Hadron Collider. A new kind of Composite Higgs model is presented and studied, which features an alternative mechanism for the breaking of electroweak symmetry. A mechanism for deforming one model into another is also discussed, which might find application to the UV completion of Composite Higgs models. The formalism used in the Composite Higgs literature is also applied to the study of inflation, where the inflaton is assumed to be a pseudo-Nambu Goldstone boson arising from strongly coupled dynamics. A study of the inflaton potential is performed and its cosmological implications discussed. A different extension to the Standard Model with interesting phenomenological consequences is also studied. Quirks are strongly interacting particles whose masses are significantly higher than their confining scale. If produced in colliders, they leave unusual tracks which current searches are mostly blind to. A new search strategy for these hypothetical particles is proposed.
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Fok, Ricky. "Scenarios of Physics Beyond the Standard Model." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11940.
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xviii, 124 p. : ill. (some col.)This dissertation discusses three topics on scenarios beyond the Standard Model. Topic one is the effects from a fourth generation of quarks and leptons on electroweak baryogenesis in the early universe. The Standard Model is incapable of electroweak baryogenesis due to an insufficiently strong enough electroweak phase transition (EWPT) as well as insufficient CP violation. We show that the presence of heavy fourth generation fermions solves the first problem but requires additional bosons to be included to stabilize the electroweak vacuum. Introducing supersymmetric partners of the heavy fermions, we find that the EWPT can be made strong enough and new sources of CP violation are present. Topic two relates to the lepton avor problem in supersymmetry. In the Minimal Supersymmetric Standard Model (MSSM), the off-diagonal elements in the slepton mass matrix must be suppressed at the 10-3 level to avoid experimental bounds from lepton avor changing processes. This dissertation shows that an enlarged R-parity can alleviate the lepton avor problem. An analysis of all sensitive parameters was performed in the mass range below 1 TeV, and we find that slepton maximal mixing is possible without violating bounds from the lepton avor changing processes: μ [arrow right] eγ; μ [arrow right] e conversion, and μ [arrow right] 3e. Topic three is the collider phenomenology of quirky dark matter. In this model, quirks are particles that are gauged under the electroweak group, as well as a \dark" color SU (2) group. The hadronization scale of this color group is well below the quirk masses. As a result, the dark color strings never break. Quirk and anti-quirk pairs can be produced at the LHC. Once produced, they immediately form a bound state of high angular momentum. The quirk pair rapidly shed angular momentum by emitting soft radiation before they annihilate into observable signals. This dissertation presents the decay branching ratios of quirkonia where quirks obtain their masses through electroweak symmetry breaking. This dissertation includes previously published and unpublished co-authored material.
Committee in charge: Dr. Davison Soper: Chair; Dr. Graham Kribs: Advisor; Dr. Ray Frey: Member; Dr. Michael Kellman: Outside Member
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Newby, Christopher. "Tool for Physics Beyond the Standard Model." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20472.
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The standard model (SM) of particle physics is a well studied theory, but there are hints that the SM is not the final story. What the full picture is, no one knows, but this thesis looks into three methods useful for exploring a few of the possibilities.
To begin I present a paper by Spencer Chang, Nirmal Raj, Chaowaroj Wanotayaroj, and me, that studies the Higgs boson. The scalar particle first seen in 2012 may be the vanilla SM version, but there is some evidence that its couplings are different than predicted. By means of increasing the Higgs' coupling to vector bosons and fermions, we can be more consistent with the data.
Next, in a paper by Spencer Chang, Gabriel Barello, and me, we elaborate on a tool created to study dark matter (DM) direct detection. The original work by Anand. {\em et al.} focused on elastic dark matter, whereas we extended this work to include the inelastic case, where different DM mass states enter and leave the collision. We also examine several direct detection experiments with our new framework to see if DAMA's modulation can be explained while avoiding the strong constraints imposed by the other experiments. We find that there are several operators that can do this.
Finally, in a paper by Spencer Chang, Gabriel Barello, and me, we study an interesting phenomenon know as kinetic mixing, where two gauge bosons can share interactions with particles even though these particles aren't charged under both gauge groups. This, in and of itself, is not new, but we discuss a different method of obtaining this mixing where instead of mixing between two Abelian groups one of the groups is Nonabelian. Using this we then see that there is an inherent mass scale in the mixing strength; something that is absent in the Abelian-Abelian case. Furthermore, if the Nonabelian symmetry is the SU$(2)_L$ of the SM then the mass scale of the physics responsible for the mixing is about 1 TeV, right around the sweet spot for detection at the LHC.
This dissertation includes previously published and unpublished co-authored material.
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Aranda, Alfredo. "Topics in physics beyond the Standard model." W&M ScholarWorks, 2001. https://scholarworks.wm.edu/etd/1539623373.
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In this dissertation we address three issues related to physics beyond the Standard model: flavor and the use of discrete gauge symmetries, the dynamical breaking of electroweak symmetry, and the addition of a U(1) gauge symmetry to the Standard model in order to suppress proton decay. We present: (i) A model of flavor based on the double tetrahedral group that leads to acceptable quark and lepton masses as well as mixing angles. Furthermore it gives solutions for the atmospheric and solar neutrino problems. (ii) A model of bosonic topcolor in which the breaking of electroweak symmetry occurs dynamically through the vacuum expectation value of a composite field, generated by some strong dynamics that affects third generation fields only. The mass of the top quark is also generated by this vev. All other light quarks acquire their masses through the vev of a fundamental scalar also present in the theory. (iii) Models in which baryon number has been gauged to eliminate operators that lead to rapid proton decay. We study the phenomenology of the gauge boson associated with the new U(1). In one model we investigate the possibility of having a light leptophobic gauge boson with mass in the 1--10 GeV range. In another model, constructed in the framework of extra dimensions, we explore the phenomenology of the leptophobic gauge boson and its Kaluza-Klein excitations.
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Shaheen, Matloob H. "Neutral currents beyond the standard model." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6334/.
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The electroweak standard model (Salam-Weinberg) is well-known to be a satisfactory and consistent theoretical description of all the experimental data we have obtained so far. In this thesis, we discuss possible phenomenology which goes beyond the standard model, with particular emphasis on the neutral current effects. First of all, the left-right symmetric extension of the standard model is discussed and we find limits on its parameters. We show that this model cannot explain certain newly reported and highly speculative events at the CERN collider [3], which in principle could be caused by the decay into two W's of a new heavy Z. We then discuss composite models where there is a strong expectation that there should be two neutral Z's of similar mass. We study the effects of these on neutral current phenomenology and show that in general the extra Z would be very hard to detect. A comparison of our model with a particular superstring model [6] is also made.
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Wizansky, Tommer. "Colliders, cosmology and physics beyond the standard model /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Glover, Brian Audley. "Topics in particle physics beyond the Standard Model." W&M ScholarWorks, 2009. https://scholarworks.wm.edu/etd/1539623541.
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We present new models of particle physics beyond the Standard Model. These models include extensions to the ideas of extra dimensions, deconstruction, supersymmetry, and Higgsless electroweak symmetry breaking. Besides introducing new models and discussing their consequences, we also discuss how galaxy cluster surveys can be used to constrain new physics beyond the Standard Model.;We find that an ultraviolet completion of gauge theories in the Randall-Sundrum model can be found in a deconstructed theory. The warping of the extra dimension is reproduced in the low energy theory by considering a general potential for the link fields with translational invariance broken only by boundary terms. The mass spectrum for the gauge and link fields is found to deviate from the Randall-Sundrum case after the first couple modes. By extending this model to a supersymmetric theory space, we find that supersymmetry is broken by the generation of a cosmological constant. Unless the theory is coupled to gravity or messenger fields, the spectrum remains supersymmetric.;We also present a hybrid Randall-Sundrum model in which an infinite slice of warped space is added to the extra dimension of the original theory. The hybrid model has a continuous gravitational spectrum with resonances at the Kaluza-Klein excitations of the original orbifolded model. A similar model is considered where the infinite space is cutoff by the addition of a negative tension brane. SU(2)L x SU(2)R x U(1)B-L gauge fields are added to the bulk of our hybrid model and we find that electroweak symmetry is broken with an appropriate choice of boundary conditions. By varying the size of the extra dimension, we find that the S parameter can be decreased by as much as 60%.;Finally we review models of structure formation and discuss the possibility of constraining new physics with galaxy cluster surveys. We find that for a large scatter in the luminosity-temperature relation, the cosmological parameters favored by galaxy cluster counts from the 400 Square Degree ROSAT survey are in agreement with the values found in the WMAP-3 year analysis. We explain why X-Ray surveys of galaxy cluster number counts are insensitive to new physics that would produce a dimming mechanism.
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Kahn, Yonatan Frederick. "Forces and gauge groups beyond the standard model." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99311.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 145-162).
The discovery of the Higgs boson in 2012 completed the particle content of the Standard Model, but brought into sharp relief two outstanding problems: why is the Higgs so light, and what is the identity of 80% of the matter content of the universe? Neither appears to have an answer within the Standard Model. This thesis attempts to address these problems with the introduction of new forces and gauge groups. I investigate a model where dark matter interacts through a new massive U(1) gauge boson which kinetically mixes with the photon, and show how this model can be tested at neutrino experiments. Supersymmetry may explain the smallness of the Higgs mass compared to the Planck scale, but reconciling the measured value of 126 GeV with the absence of super-partners at colliders is difficult. By gauging various global symmetries of the Standard Model, I show that a variant of Higgsed gauge mediation called auxiliary gauge mediation can provide acceptable supersymmetric spectra. Finally, the astrophysical dark sector may be complicated, with many kinds of allowed interactions, and I describe techniques to diagnose the presence of dark matter at direct-detection experiments independent of its velocity distribution.
by Yonatan Frederick Kahn.
Ph. D.
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Skiba, Witold. "Strong dynamics in theories beyond the standard model." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42622.
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Boudjemaa, Salima. "Physics beyond the standard model : moduli stabilisation and neutrino physics." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/161213/.
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We look at models of neutrino mass and mixing which represent an important aspect of physics beyond the Standard Model (SM). We derive approximate analytic formulae for the neutrino mixing angles in general SD involving NLO and NNLO corrections. These expressions, which are given in terms of input see-saw parameters, provide a useful guide for unified model building. We then evaluate these formulae in the cases of CSD and PCSD for two numerical GUT inspired models in order to measure the effect of NLO and NNLO corrections. In addition to this, we analyse the effects of charged lepton corrections and Renormalisation Group (RG) running on neutrino mixing angles and various sum rules, in models where tri-bimaximal mixing is exactly achieved at high energy scale. We find the RG corrections to neutrino sum rules to be typically small for the case of hierarchical neutrinos. Another aspect of physics beyond the Standard Model concerns the search for viable four dimensional string models. We look at moduli stabilisation in the framework of four dimensional models arising from heterotic and type IIA string theories. The superpotentials in these models involve ux and non-perturbative terms. We consider a set of conditions which lead to moduli solutions for Minkowski minima of the scalar potential. Following this procedure, we correct models presented in the literature and uplift the at directions. We also study inflation in the framework of these models. We find that it is successfully achieved along the axionic directions of the moduli fields for values of the initial conditions within substantial regions of parameter space. A very interesting structure of the potential is obtained when considering the evolution of two axionic directions in one of the models in the presence of a gaugino condensate term. This structure, which involves the existence of multiple local minima surrounding the global one, represents a perfect background for realising in ation.
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Colburn, Russell J. III. "Beyond the Standard Model: Dark Matter and Collider Physics." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1507215920939059.
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Yuan, Yao. "Beyond the Standard Model: New scalars and new leptons." W&M ScholarWorks, 1993. https://scholarworks.wm.edu/etd/1539623845.
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Physics that might lie beyond the standard model is discussed, with special emphasis on two possible extensions of the standard model: multi-Higgs extension, and the fourth generation leptons.;In multi-Higgs-boson extensions of the standard model, tree-level flavor-changing neutral currents exist naturally. It is often believed that the presence of the tree-level FCNC in this model is fatal, unless a discrete symmetry is added, since it requires the exchanged scalar to be extremely heavy. This follows, however, from the assumption that the flavor-changing coupling is quite large. Using a more natural value for the flavor-changing coupling, much smaller bounds were obtained. Unlike previous calculations, we calculate the bounds on the flavor-changing couplings of an additional scalar for the processes involving the third generation fields. We find that in the quark sector the strongest bound comes from {dollar}B - \=B{dollar} mixing and in the lepton sector, surprisingly, from {dollar}\mu \to e\gamma{dollar}. It is then noted that flavor-changing coupling in the quark sector are related to those in the lepton sector in many grand unified theories. Comparing flavor-changing B decays with rare {dollar}\tau{dollar} decays, we find that rare B decays provide the strongest bounds and the most promising decay models are {dollar}B \to K\mu\tau{dollar} and {dollar}B\sb{lcub}s{rcub} \to \mu\tau{dollar}.;If a fourth generation of leptons exists, both the neutrino and the charged lepton must have masses in excess of 45 GeV. It is certainly possible that the neutrino will be heavier than, or comparable in mass to, the charged lepton. In this case, the charged lepton can only decay through mixing with lighter generations, and might thus be extremely long-lived. First, we investigate the implications of very long-lived charged leptons for cosmology and astrophysics. We calculate the bounds on the mass and lifetime of long-lived charged particles which arise from terrestrial and cosmology. The strongest bounds come from the requirement that the decay products not unacceptably distort the cosmic microwave background. Phenomenological implications are also briefly discussed. Second, we study the production cross-sections and signatures for the SSC and LHC. Four models are considered. Two are fourth-generation extensions of the standard model in which the right-handed heavy leptons are either isosinglets or in an isodoublet; the other two are motivated by the aspon model of CP violation. The detection methods for these heavy leptons are also discussed.
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Gelzer, Zechariah John. "Lattice gauge theories within and beyond the Standard Model." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5757.
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The Standard Model of particle physics has been very successful in describing fundamental interactions up to the highest energies currently probed in particle accelerator experiments. However, the Standard Model is incomplete and currently exhibits tension with experimental data for interactions involving $B$~mesons. Consequently, $B$-meson physics is of great interest to both experimentalists and theorists. Experimentalists worldwide are studying the decay and mixing processes of $B$~mesons in particle accelerators. Theorists are working to understand the data by employing lattice gauge theories within and beyond the Standard Model. This work addresses the theoretical effort and is divided into two main parts.
In the first part, I present a lattice-QCD calculation of form factors for exclusive semileptonic decays of $B$~mesons that are mediated by both charged currents ($B \to \pi \ell \nu$, $B_s \to K \ell \nu$) and neutral currents ($B \to \pi \ell^+ \ell^-$, $B \to K \ell^+ \ell^-$). The results are important for constraining or revealing physics beyond the Standard Model. This work uses MILC's $(2+1+1)$-flavor ensembles, with the HISQ action for the up, down, strange, and charm sea and valence quarks, and the clover action in the Fermilab interpretation for the $b$~quark. Simulations are carried out on five ensembles at three lattice spacings down to $\approx 0.088$~fm, with both physical and unphysical sea-quark masses. I present results for correlation-function fits and describe the chiral-continuum extrapolation and $z$~expansion of the form factors.
In the second part, I present the status of an ongoing lattice calculation of $SU(3)$ gauge theory with eight and $12$ fundamental fermions, in which I search for the endpoint of the line of first-order phase transitions in the mass--coupling plane. The results are important for understanding the phase diagram of these models, with possible applications to physics beyond the Standard Model. This work uses the staggered action and the nHYP-improved staggered action for the fermions, as well as the Wilson action in the fundamental and fundamental--adjoint representations for the gauge bosons. With the unimproved actions, I present results for a small lattice and describe the ongoing effort on larger lattices. I also discuss the shift symmetry on lattices with and without improved actions.
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Blinov, Nikita. "Phase transitions : applications to physics beyond the Standard Model." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54340.
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Despite their phenomenological successes, the Standard Models (SMs) of particle physics and cosmology remain incomplete. Several theoretical and observational problems cannot be explained within this framework, including the hierarchy problem, dark matter (DM), and the baryon asymmetry of the Universe. The objective of this thesis is to investigate phenomenological and theoretical aspects of the solutions to these issues. We consider two kinds of phase transitions that can occur in the early or late Universe in extensions of the SM, that can be either responsible for dark matter and/or baryon asymmetry production or may be used to constrain possible models of new physics.
In the first part we analyze string theory-inspired models where the Universe transitions from
matter- to radiation-dominated evolution just before Big Bang Nucleosynthesis through out-of-equilibrium decays of a scalar modulus field. We employ these decays to produce DM and for baryogenesis. We study the phenomenology of these scenarios and its implications for high-scale physics. The second part of this thesis is dedicated to thermodynamic and quantum phase transitions in the early and late Universe, respectively. In the former case, we investigate the dynamics of the electroweak phase transition when the electroweak symmetry is broken down to electromagnetism in the Inert Doublet Model, a simple extension of the SM that can account for DM. Such transitions can generate the baryon asymmetry in a process called electroweak baryogenesis. Some extensions of the SM also predict similar transitions through quantum tunneling that break the colour and electromagnetic symmetries, indicating that our ground state is unstable. We use these arguments to put new constraints on the Minimal Supersymmetric Standard Model.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Hsieh, Ken. "Physics beyond the standard model supersymmetry and extra dimensions /." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6779.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Shuhmaher, Natalia. "Aspects of cosmology from physics beyond the standard model." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18460.
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The interface of Cosmology and High Energy physics is a forefront area of research which is constantly undergoing development. This thesis makes various contributions to this endeavor. String-inspired cosmology is the subject of the first part of the thesis, where we propose both a new inflationary and a new alternative cosmological model. The second part of the thesis concentrates on the problems of integrating cosmology with particle physics beyond the Standard Model. Inspired by new opportunities due to stringy degrees of freedom, we propose a non-inflationary resolution of the entropy and horizon problems. In this string-inspired scenario, 'our' dimensions expand while the extra dimensions first expand and then contract, before eventually stabilizing. The equation of state of the bulk matter (which consists of branes) is negative. Hence, there is a net gain in the total energy of the universe during the pre-stabilization phase. At the end of this phase, the energy stored in the branes is converted into radiation. The result is a large and dense 3-dimensional universe. Making use of similar ideas, we propose a not-fine-tuned model of brane inflation. In this scenario the brane separation, playing the role of the inflaton, is the same as the overall volume modulus. The bulk matter provides an initial expansion phase which drives the inflaton up its potential, so that the conditions for inflation are realized. The specific choice of the inflationary potential nicely fits the cosmological observations. Another aspect of this research concentrates on the cosmological moduli problem: namely, the existence of weakly coupled particles those decay is late enough to interfere with Big Bang Nucleosynthesis. As a solution, we suggest parametric and tachyonic resonances to shorten the decay time. Even heavy moduli are dangerous for cosmology if they cause the overproduction of gravitinos. We find that tachyonic decay channels help to transfer most of the energy of thesL'interface entre la Cosmologie et la Physique des hautes énergies est un sujet de recherche d'avant-plan en constant développement. La cosmologie inspirée par la théorie des cordes est le sujet de la première partie de cette thèse, dans laquelle nous proposons d'une part un nouveau mécanisme pour l'inflation et d'autre part une nouvelle alternative de modèle cosmologique. Dans la seconde partie nous nous concentrons sur les problèmes reliés à l'intégration de la cosmologie dans un modèle de physique des particules au-delà du Modèle Standard. Motivés par les nouvelles possibilités venant des degrés de liberté de la théorie des cordes, nous proposons une résolution non-inflationiste aux problèmes d'entropie et d'horizon. Selon notre scenario fondé sur la théorie des cordes, les trois dimensions spatiales habituelles ainsi que les dimensions supplémentaires s'étendent, mais ces dernières se contractent eventuellement avant de se stabiliser. L'équation d'état de la matière du bulk, qui consiste de branes, est négative. Il y a donc un net gain dans l'énégie totale de l'univers durant la phase de pré-stabilisation. A la fin de cette phase, l'énergie stockée dans les branes est convertie en radiation. Le résultat est un univers tri-dimensionel large et dense. En utilisant des idées similaires, nous proposons un modèle d'inflation qui ne requiert pas d'ajustements fins. Dans ce scénario, la séparation entre les branes, qui joue le rôle de l'inflaton, est la même que le module du volume global. La matière du bulk fournit une phase d'expansion initiale qui pousse l'inflaton vers le haut de son potentiel, réalisant ainsi les conditions pour l'inflation. Le choix spécifique du potentiel de l'inflaton est en accord avec observations cosmologiques. Un autre aspect de ma these adresse le problème cosmologique des champs de module: c'est-à-dire l'existence de particules faiblement couplées dont la désintégration a li
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Rinaldi, Enrico. "Non-perturbative aspects of physics beyond the Standard Model." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8301.
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The Large Hadron Collider (LHC) and the four major experiments set up along its 27 kilometers of circumference (ATLAS, CMS, ALICE and LHCb), have recently started to explore the high–energy frontier at √s = 8 TeV, and will move to even higher energy in just about 2 years. The aim of physics searches at LHC experiments was to complete the picture of the Standard Model (SM) of elementary particles with the discovery of the Higgs boson and to look for specific signatures of models extending the current understanding of particle interactions, at zero and non–zero temperature. In 2012, the official discovery of the Higgs boson, the only missing particle of the StandardModel, was announced by ATLAS and CMS. Other important results include the measurement of rare decay modes in heavy quarks systems, and indications of CP violation in charm decays by LHCb. Signatures of beyond the Standard Model (BSM) physics are currently being looked for in the experimental data, and this often requires the knowledge of quantities that can be computed only with non–perturbative methods. This thesis focuses on some possible extensions of the SM and the analysis of interesting physical observables, like masses or decay rates, calculated using non– perturbative lattice methods. The approach followed for the main part of this work is to model BSM theories as effective field theories defined on a lattice. This lattice approach has a twofold advantage: it allows us to explore non– renormalizable gauge theories by imposing an explicit gauge–invariant cutoff and it allows us to go beyond perturbative results in the study of strongly interacting systems. Some of the issues of the SM that we will try to address include, for example, the hierarchy problem and the origin of dynamical electroweak symmetry breaking (DEWSB). We investigate non–perturbatively the possibility that the lightness of the mass for an elementary scalar field in a four–dimensional quantum field theory might be due to a higher–dimensional gauge symmetry principle. This idea fits in the Gauge–Higgs unification approach to the hierarchy problem and the results we present extend what is known from perturbative expectations. Extra dimensional models are also often used to approach DEWSB. Another approach to DEWSB implies a new strongly interacting gauge sector that extends the SM at high energies and it is usually referred to as Technicolor. The phenomenological consequences of Technicolor can only be studied by non– perturbative methods at low energy since the theory is strongly coupled at large distances. We perform a comprehensive lattice study of fermionic and gluonic scalar bound states in one of the candidate theories for Technicolor BSM physics. We relate our findings to the nature of the newly discovered Higgs boson. New physics is also commonly believed to be hidden in the flavour sector of the SM. In this sector, lattice calculations of non–perturbative input parameters are needed in order to make precise predictions and extract signals of possible new physics. In particular, heavy quark physics on the lattice is still in development and it is important to understand the relevant discretisation errors. We describe a preliminary study of the mixing parameter of heavy–light mesons oscillations in a partially–quenched scenario, using staggered dynamical fermions and domain wall valence fermions.
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Gigg, Martyn Anthony. "Monte Carlo simulations of physics beyond the standard model." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2301/.
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The Large Hadron Collider, currently under construction at CERN, will give direct access to physics at the TeV scale for the first time. The lack of certainty over the type of physics that will be revealed has produced a wealth of ideas for so-called Beyond the Standard Model physics, all with the aim of solving the problems possessed by the Standard Model. The oldest and most well studied is supersymmetry but new ideas based on extra dimensions and collective symmetry breaking have been proposed more recently. In order to study these models most effectively, we argue that they must be implemented within the framework of a Monte Carlo event generator so that their signals can be studied in a real world setting. In this thesis we develop a general approach for the simulation of new physics models with the aim of reducing the effort in implementing a new model into the Herwig++ event generator. The approach is based upon the external spin structures of production and decay matrix elements so that the amount of information required to input a new model is simply a set of Feynman rules and mass spectrum. The first method uses an on-shell approximation throughout but this is later refined to include the effects of finite widths, as these are found to be important when processes occur close to threshold. In all of the discussions regarding our new approach we make specific reference to two models of new physics, the Minimal Supersymmetrie Standard Model and the Minimal Universal Extra Dimensions model. Our general matrix elements and approach to finite widths are all demonstrated and tested using examples from these two models. The concluding discussion makes use of a third model, the Littlest Higgs model with T-parity, such that signals from the three models are compared and contrasted using the general framework developed here.
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SANTOS, FABIO ALEX PEREIRA DOS. "PHENOMENOLOGY OF NEUTRINOS AND PHYSICS BEYOND THE STANDARD MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=20782@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Com o avanço na medida dos parâmetros responsáveis por oscilação de neutrinos, podemos dizer que hoje a física de neutrinos está entrando na era da precisão, o que nos permite explorar cenários além de massas e misturas de três sabores de neutrinos, ou seja, podemos procurar uma nova física que cause algum efeito subdominante, que não pode ser explicado por oscilação usual. Podemos citar a anomalia de antineutrinos de reator e anomalia de Gálio, ambas serão explicadas posteriormente no capítulo 3. Propomos uma solução alternativa para estas duas anomalias, baseado em um cenário com grandes dimensões extras. Exploramos também a capacidade de um experimento com neutrinos ultramonocromáticos produzidos via efeito Mossbauer, de detectar ou vincular alguns cenários de nova física além do modelo padrão. Os cenários que consideramos nesta tese são: neutrinos esteréis, estes sendo a extensão mais simples do modelo de três sabores; o cenário com grandes dimensões espaciais extras; descoerência quântica como física não padrão; e por último e não menos importante o cenário com neutrinos de massa variável. Mostramos também o impacto, se assumimos a existência destes cenários, na determinação dos parâmetros de oscilação Delta m2 31 e Teta 13.
With advances in the measurements of the neutrino oscillation parameters, we can assume that neutrino physics is going to a precision era, as a consequence we can explore new scenarios beyond the standard mass and mixing with three neutrino flavors , that is, we can look for a new physics that affects in a subleading way and that can not be explained by the standard oscillation framework. For instance, the reactor antineutrino and Gallium anomalies, both anomalies will be discussed in chapter 3. We propose an explanation for these anomalies based on a scenario with large extra dimension. We also explore the capability of an experiment with ultramonochromatic neutrinos based on M ossbauer effect detects or constrains some new physics scenarios beyond the standard model. In this thesis we consider: sterile neutrinos, large extra dimensions, non standard quantum decoherence and mass varying neutrinos. We also show the impact on the determination of the standard oscillation parameters delta m2 31 and teta 13 if we assume non standard physics scenarios.
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Denis, Malika. "Probing physics beyond the standard model in diatomic molecules." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30059/document.
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De nos jours, l'incomplétude du modèle standard des particules est largement reconnue. L'une de ses failles les plus évidentes est le manque d'explication de l'énorme excédent de matière par rapport à l'antimatière dans l'univers, que l'on appelle l'asymétrie baryonique de l'univers. De nouvelles violations de CP (conjugaison de charge et parité spatiale) absentes dans le modèle standard sont supposées être responsables de cette asymétrie. Une telle violation pourrait être observée dans la matière ordinaire à travers un ensemble d'interactions violant les symétries de parité et de renversement du temps (impaires pour P,T) dont les prépondérantes sont les interactions du moment dipolaire électrique de l'électron (eEDM), électron-nucléon scalaire-pseudoscalaire (enSPS) et du moment quadripolaire magnétique nucléaire (nMQM). Ainsi, une preuve expérimentale d'une constante d'interaction impaire pour P,T serait une preuve de cette nouvelle physique au-delà du modèle standard. Le calcul des paramètres moléculaires correspondants est réalisé en utilisant une approche d'interaction de configurations relativiste à quatre composantes dans des molécules diatomiques polaires contenant un actinide, qui sont des systèmes particulièrement appropriés pour les expèriences eEDM, tels que ThO qui a permis d'assigner à l'eEDM la borne supérieure la plus contraignante et ThF+ qui sera utilisé dans une expérience à venir. Ces résultats sont d'une importance cruciale dans l'interprétation des mesures puisque les constantes fondamentales ne peuvent être évaluées que si l'on associe les mesures de décalages énergétiques et les paramètres moléculaires théoriquesNowadays, the incompleteness of the Standard Model of particles is largely acknowledged. One of its most obvious shortcomings is the lack of explanation for the huge surplus of matter over antimatter in the universe, the so-called Baryon Asymmetry of the Universe. New CP (Charge conjugation and spatial Parity) violations absent in the SM are assumed to be responsible for this asymmetry. Such a violation could be observed in ordinary matter through a set of interactions violating both parity and time-reversal symmetries (P,T-odd), among which the preponderant ones are the electron Electric Dipole Moment (eEDM), the electron-nucleon scalar-pseudoscalar (enSPS) and the nuclear magnetic quadrupole moment (nMQM) interactions. Hence, an experimental evidence of a non-zero P,T-odd interaction constant would be a probe of this New Physics beyond the Standard Model. The calculation of the corresponding molecular parameters is performed by making use of an elaborate four-component relativistic configuration interaction approach in polar diatomic molecules containing an actinide, that are particularly adequate systems for eEDM experiments, such as ThO that allowed for assigning the most constraining upper bound on the eEDM and ThF+ that will be used in a forthcoming experiment. Those results will be of crucial importance in the interpretation of the measurements since the fundamental constants can only be evaluated if one combines both experimental energy shift measurements and theoretical molecular parameters
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Wang, Peng Wise Mark B. Wise Mark B. Ramsey-Musolf Michael. "Neutrino mass implications for physics beyond the Standard Model /." Diss., Pasadena, Calif. : California Institute of Technology, 2007. http://resolver.caltech.edu/CaltechETD:etd-05312007-144931.
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Riad, Stella. "Studies of effective theories beyond the Standard Model." Licentiate thesis, KTH, Teoretisk partikelfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154048.
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The vast majority of all experimental results in particle physics can be described by the Standard Model (SM) of particle physics. However, neither the existence of neutrino masses nor the mixing in the leptonic sector, which have been observed, can be described within this model. In fact, the model only describes a fraction of the known energy in the Universe. Thus, we know there must exist a theory beyond the SM. There is a plethora of possible candidates for such a model, such as supersymmetry, extra dimensional theories, and string theory. So far, there are no evidence in favor of these models. These theories often reside at high energies, and will therefore be manifest as effective theories at the low energies experienced here on Earth. A first example in extra-dimensional theories. From our four-dimensional point of view, particles which propagate through the extra dimensions will effectivel be perceived as towers of heavy particles. In this thesis we consider an extra-dimensional model with universal extra dimensions, where all SM particles are allowed to propagate through the extra dimensions. Especially, we place a bound on the range of validity for this model. We study the renormalization group running of the leptonic parameters as well as the Higgs self-coupling in this model with the neutrino masses generated by a Weinberg operator. Grand unified theories, where the gauge couplings of the SM are unified into a single oe at some high energy scale, are motivated by the electroweak unification. The unification must necessarily take place at energies many orders of magnitude greater than those that ever can be achieved on Earth. In order to make sense of the theoru, ehich is given at the grand unified scale, at the electroweak scale, the symmetry at the grand unified scale is broken down to the SM symmetry. Within these models the SM is considered as an effective field theory. We study renormalization group running of the leptonic parameters in a non-supersymmetric SO(10) model which is broken in two steps via the Pati-Salam group. Finally, the discovery of the new boson at the LHC provides a new opportunity to search for physics beyond the SM. We consider an effective model where the magnitudes of the couplings in the Higgs sector are scaled by so-called coupling scale factors. We perform Bayesian parameter inference based on the LHC data. Furthermore, we perform Bayesian model comparison, comparing models where one or several of the Higgs couplings are allowed, to the SM, where the couplings are fixed.QC 20141020
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Rosa, Joao P. T. G. "Aspects of beyond the Standard Model string phenomenology." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:5e21fba9-9211-4adb-9c73-d27e98910f30.
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String theory is currently the best-known candidate for a theory of quantum gravity, having the necessary ingredients to describe all known elementary particles and interactions. It also includes several novel features, arising, for instance, from the additional six compact dimensions required for its internal consistency, making it the natural arena to construct extensions of the Standard Model. In this thesis, we analyze some of the new phenomenological aspects introduced by string theory within the framework of low energy effective theories, focusing on their applications to cosmology, astrophysics and collider experiments. We first consider a particular realization of the brane-world scenario in branonium bound states, showing that the orbital motion of a probe antibrane about a central brane stack leads to a resonant amplification of its world-volume scalar modes. We analyze the cosmological development of this process and also its potential relevance for either dark or baryonic matter generation in the early universe. We then focus on the spectrum of quark and lepton string excitations in warped compactifications, modeled by an effective 5-dimensional Randall- Sundrum throat. Motivated by the observed fermion mass hierarchy, we show that the spin-3/2 Regge excitation of the right-handed top quark is the lightest of such resonances in a significant region of parameter space, possibly lying below the TeV scale, and discuss its potential signatures at the Tevatron and at the LHC. Finally, we study the emission of sub-eV scalar particles by maximally rotating Kerr black holes, motivated by the recent string axiverse proposal. We focus on the spectrum of unstable scalar bound states in the superradiant regime, leading to an exponentially large axion cloud around astrophysical black holes, and analyze two semi-analytical methods for computing the growth rate of this instability, comparing the obtained results with previous analytical and numerical analyses.
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Chen, Chien-Yi. "New Physics Beyond the Standard Model with Weakly Interacting Particles." Research Showcase @ CMU, 2012. http://repository.cmu.edu/dissertations/118.
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In this thesis, two of the most exciting areas in high energy physics nowadays are studied: neutrino physics and collider physics, which play important roles in the intensity and energy frontiers, respectively.
For neutrino physics, assuming that the neutrino mass matrix is dominated by a term with the permutation symmetry S2, it is possible to explain neutrino data only if the masses are quasi-degenerate. A sub-dominant term with an approximate μ−τ symmetry leads to an approximate tri-bimaximal form. Experimental consequences are discussed.
In this thesis several channels that contain missing-energy signal in the final states will be investigated with minimal model assumptions. Channels of this type are very challenging to analyze at the Large Hadron Collider (LHC), since this approach offers only a few kinematical handles. I start with a channel that has a clean signal of two leptons and missing energy. This signature generally arises from pair production of heavy charged particles which each decay into a lepton and a weakly interacting stable particle. This class of processes is analyzed with minimal model assumptions by considering all possible combinations of spin 0, ½ or 1, and of weak iso-singlets, -doublets, or -triplets for the new particles. Adding to existing work on mass and spin measurements, two new variables for spin determination and an asymmetry for the determination of the couplings of the new particles are introduced. It is shown that these observables allow one to independently determine the spin and the couplings of the new particles, except for a few cases that turn out to be indistinguishable at the LHC. These findings are corroborated by results of an alternative analysis strategy based on an automated likelihood test.
I then study decays of the form C → ℓ+ℓ−A (ℓ = e, μ), including the possibility that this three-body decay is preceded by an additional decay step D → jC. Here A, C and D are heavy new-physics particles and j stands for a quark jet. It is assumed that A escapes direct detection in a collider experiment, so that one cannot kinematically reconstruct the momenta of the new particles. Instead, information about their properties can be obtained from invariant-mass distributions of the visible decay products, i. e. the di-lepton (ℓℓ) and jet-lepton (jℓ) invariant-mass distributions. All possible spin configurations and renormalizable couplings of the new particles are considered, and explicit expressions for the invariant-mass distributions are derived, in a formulation that separates the coupling parameters from the spin and kinematic information. In a numerical analysis, it is shown how these properties can be determined independently from a fit to the mℓℓ and mjℓ distributions.
Finally, I will take a model-independent approach to searching for new physics involving the top quark. The experimental signatures for new physics involving top quarks at the LHC may be characteristic, yet challenging to disentangle. I systematically parameterize generic interactions of a new particle that couples to the top quark and optimize the search strategy for the new particles at the LHC and propose the study for their properties. Several variables are proposed and a detailed numerical study is performed for the determination of spins and couplings of new heavy particles.
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Merchand, Medina Marco Antonio. "Study Of Scalar Extensions For Physics Beyond The Standard Model." W&M ScholarWorks, 2020. https://scholarworks.wm.edu/etd/1616444546.
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In this thesis we investigate the phenomenology of beyond the Standard Model scenarios with extra scalar fields. A review and motivation of extended electroweak symmetry breaking is presented. Then we address observational evidence of new physics such as possible lepton flavor violating processes and the relic abundance of dark matter by implementing models with three Higgs doublets. The complementarity between theoretical restrictions and experimental bounds on some of the predicted signals is leveraged to sharpen the allowed parameter space. After that we study embeddings of two-Higgs doublets into the Randall-Sundrum model with emphasis on the scalar fluctuations of the metric tensor and the stabilization mechanism: i) the viability of Higgs-radion unification is reappraised as well as some amendments to it, ii) additionally, kinetic mixing between radion and two Higgs doublets is explored. Theoretical predictions are tested against the most current experimental data and new avenues of discovery are highlighted. We devote the last part of this thesis to study how the axion solution to the strong CP problem can be unified with the dynamical flavor symmetry explanation for the huge hierarchies observed on the fermions.
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Conroy, Justin M. "Modifications of spacetime and particle physics beyond the standard model." W&M ScholarWorks, 2005. https://scholarworks.wm.edu/etd/1539623481.
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In this dissertation we consider spacetime modifications that result in new physics beyond the standard model. We investigate various collider implications of a particular Lorentz-conserving formulation of QED in which spacetime coordinates are noncommuting. We also consider collider implications of Universal Extra Dimensions. Specifically, we address the possible formation of bound states involving the first quark KK-modes, i.e. KK-quarkonium. In addition, we consider the use of boundary conditions in extra dimensions to break gauge symmetries in unified theories. These boundary conditions can be related to a boundary Higgs sector that decouples from the theory. This technique of "Higgsless" symmetry breaking is applied to several models based on the trinified gauge group GT = SU(3)C x SU(3) L x SU(3)R. In addition, we analyze various phenomenological issues such as coupling unification and proton decay.
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Vantalon, Thibaud. "Probing beyond the Standard Model physics using effective field theory." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/565736.
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Ara que el LHC ha proporcionat 120 fb-1 de dades, l'evidència d'una diferència d'energia entre el model estàndard (SM) i la nova física ha augmentat. Això fa que la teoria de camps efectiva (EFT) sigui un mètode versàtil per restringir la nova física amb una dependència mínima del model. En aquesta tesi, basada en el meu treball realitzat durant la meva candidatura a doctorat [1-4], fem ús de la tècnica EFT en diversos estudis. Comencem per estudiar l'extracció de acoblament trilineal del Higgs en els col·lisionadors actuals i futurs de leptons, utilitzant correccions de següent ordre en la producció de Higgs i producció de Higgs doble. Els nostres anàlisis minimitzen la dependència del model gràcies a l'ús de l'EFT. Argumentem que per restringir les diferents possibles desviacions al Model Estàndard, un ajust global amb la inclusió de tants observables com sigui possible és necessari. Hem trobat que la inclusió del trilineal en els processos únics d'Higgs tindrà un efecte marginal a LHC aconseguint una precisió d'ordre ú. La situació és diferent els futurs col·lisionadors de leptons, on l'alta precisió i la diferent energia de centre de masses poden donar el 50% de precisió. A continuació, ampliem l'EFT afegint un singlet escalar per estudiar les propietats del CP de la partícula que podria haver estat amagada després de l'infame excés de di-fotons a 750 GeV. Definim les asimetries sensibles al CP, tant en els canals de fusió de vectors com gluons, i estudiem el seu poder de diferenciar entre el CP imparell o fins i tot les hipòtesis. Finalment, ens movem de l'EFT i considerem un model simplificat de Higgs compost per comparar les mesures a baixa energia procedents
de la mesura del dipol elèctric (EDM) de neutrons i electrons, amb les cerques al LHC. La teoria de camps efectiva no està completament absent, ja que calculem les correccions de dos loops al EDM de quarks i leptons lleugers que coincideixen amb el nostre model simplificat per als operadors de dimensions superiors i obtenim límits per al nostre model.
A continuació, adaptem les cerques de l'LHC i comparem els límits actuals i futurs
Hem trobat que el límit actual és competitiu amb el que proveeix la cerca directa de LHC, que és d'uns quants TeV. La futura actualització de l'experiment que permetrà mesurar el moment dipolar d'electrons ha de portar els límits al rang de 5-10 TeV.Now the LHC has provided 120 fb−1 of data, the evidence for an energy gap between the Standard Model (SM) and new physics has grown strong. This makes effective field the- ory (EFT) a versatile method to constrain new physics with minimal model dependence. In this thesis, based on work done during my PhD candidature [1–4], we make use of EFT techniques in a variety of studies. We start by exploring the prospect of extracting the Higgs trilinear self-coupling at current hadron and future lepton colliders, using both higher order corrections to the single-Higgs process and di-Higgs production. Our anal- ysis minimizes model dependence thanks to the use of EFT. We argue that in order to constrain the different possible deviations to the Standard Model, a global fit with the inclusion of as many observables as possible is needed. We found that the inclusion of the trilinear correction in single-Higgs processes has a marginal effect at the LHC and will give a bound on the trilinear of order one. The situation is different at lepton col- liders, where the high precision and different running energies can give bound of order 50%. We then extend our EFT by adding a scalar singlet to study the CP properties of the particle which could have been behind the infamous 750 GeV di-photon excess. We define the CP sensitive asymmetries, in both the vector and gluon fusion channels, and study their power to differentiate between the CP odd or even hypotheses. Finally, we move somewhat away from EFT, and use a simplified model to compare the constraints on composite Higgs models coming from low energy neutron and electron electric dipole moment (EDM) measurements and LHC searches. Effective field theory is not completely absent, since we compute the two loop corrections of the light quarks and leptons EDM to match our simplified model to the higher dimensional operators of a low energy effective Lagrangian, and obtain bounds for our model. We then recast LHC searches and compare the present and future bounds. We found that the current bounds are competitive with the one coming from the LHC direct search and are of order a few TeV. The future upgrade of the experiment measuring the electron dipole moment should bring the bounds to the 5-10 TeV range.
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Frost, James Alexander. "Exploring physics beyond the standard model with the ATLAS detector." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608579.
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Zhang, Huanian, and Huanian Zhang. "Direct and Indirect Searches for New Physics beyond Standard Model." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621580.
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The search for new physics beyond the Standard Model can follow one of two tracks: direct searches for new particles at the collider or indirect probes for new physics from precision measurements. In the direct searches for third generation squarks in SUSY at the LHC, the common practice has been to assume a 100% decay branching fraction for a given search channel. In realistic MSSM scenarios, there is often more than one signicant decay mode present, which signicantly weakens the current search limits on third generation squarks at the LHC. On the other hand, the combination of multiple decay modes as well as the new open decay modes offer alternative discovery channels for third generation squarks searches. In this work, we present the third generation squarks decay and the collider signatures in a few representative mass parameter scenarios. We then analyze the reach of the stop/sbottom signal for the pair production in QCD at the 14 TeV LHC with 300 fb⁻¹ integrated luminosity and of the 100 TeV future collider with 3000 fb⁻¹ integrated luminosity in a few representative scenarios. In the scenario of Bino LSP with Wino NLSP, we investigate stop/sbottom pair production at the LHC with one stop/sbottom decaying via t̃ --> t𝑥[0 1], t𝑥[0 2]/b̃ --> b𝑥[0 1], b𝑥[0 2], and the other one decaying via t̃ --> b𝑥[± 1]/b̃ -->t𝑥[± 1]. With the gaugino subsequent decaying to gauge bosons or a Higgs boson 𝑥[0 2] --> 𝑍𝑥[0 1], h𝑥[0 1] and 𝑥[± 1]--> 𝑊±𝑥[0 1], leading to 𝑏𝑏𝑏𝑏𝑗𝑗𝓁 Ɇᴛ final states for the Higgs channel and 𝑏𝑏𝑗𝑗𝑗𝑗𝓁𝓁Ɇᴛ final states for the 𝑍 channel, we study the reach of those signals at the 14 TeV LHC with 300 fb⁻¹ integrated luminosity. Because the sbottom and stop signals in the same SUSY parameter scenario have indistinguishable final states, they are combined to obtain optimal sensitivity, which is about 150 GeV better than the individual reaches of the sbottom or stop. In the scenario of Bino LSP with Higgsino NLSP. The light stop pair production at the 14 TeV LHC, with stops decaying via t̃₁ --> t𝑥[0 2]/𝑥[0 3] and the neutralino subsequently decaying to a gauge boson or a Higgs boson 𝑥[0 2]/𝑥[0 3] --> 𝑥[0 1]h/𝑍, leads to tt̄hh Ɇᴛ, tt̄h𝑍 Ɇᴛ or tt̄𝑍𝑍 Ɇᴛ final states. The above decay channels give rise to final states containing one or more leptons, therefore our search strategy is to divide the signal regions based on the multiplicity of leptons. We find that the one lepton signal region of channel tt̄h𝑍 Ɇᴛ has the best reach sensitivity of light stop searches at the 14 TeV LHC with 300 fb⁻¹ integrated luminosity. We then combine all the signal regions for a given decay channel or combine all the decay channels for a given signal region to maximize the reach sensitivity of the stop search. For the light stop pair production at the √s = 100 TeV future machine with 3000 fb⁻¹ integrated luminosity, we find that a stop with a mass up to 6 TeV can be discovered at 5𝜎 signicance, while a mass up to 6.8 TeV can be excluded at 95% C.L. for the combined results of all three channels. In the indirect probes for new physics, we utilize the 𝑍-pole Oblique Parameters 𝑆,𝑇, 𝑈 and Higgs precision measurements complementarily in the framework of the Two Higgs Doublet Model at current and future colliders. The 𝑆, 𝑇 , 𝑈 is not that sensitive to the rotation angle 𝛽-𝛼, while the Higgs precision measurements set strong constrains on 𝛽-𝛼. Also the 𝑇 is very sensitive to the mass difference of Higgs bosons, leading to the mass of charged Higgs (H±) aligning either along with the mass of neutral Higgs 𝐻 or 𝐴. As for the Higgs precision measurements, we consider the tree level corrections to Higgs coupling constants as well as the radiative corrections to Higgs coupling constants at one loop level for the future collider. The combination of 𝑍-pole precision measurements and Higgs precision measurements complementarily set strong constraints on the parameter space of the 2HDM, especially in the future 𝑒⁺𝑒⁻ circular collider compared to the current collider due to much cleaner backgrounds and higher luminosity.
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Thomas, Marc. "Beyond standard model collider phenomenology of Higgs physics and supersymmetry." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/379264/.
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In this thesis I study the collider phenomenology of BSM physics at the LHC, concentrating on the Higgs boson and supersymmetery. The implications and effects on cross sections of the loss of unitarity in scattering processes involving multiple vector bosons and/or the Higgs, when the Higgs couplings to the W and the Z are non-SM, is studied using an effective Lagrangian. Subsequently methods to remove unwanted background from transversely polarised vector bosons are explored, which enable an estimation of the potential to measure the Higgs couplings to weak bosons in a model-independent way via vector boson fusion. MSSM effects on Higgs production and decay are also considered, concentrating on the effects due to light stops, sbottoms and staus. Amongst other things, we find that light 3rd generation squarks generally produce asymmetrical alteration in signal strengths of different production channels, generally causing μV BF μggF > 1. Finally we extend some ATLAS analyses in the low ∆m = m˜t − m˜x01 region, extending the excluded masses of light stops. This enables us to limit the maximum effects of light stops on the Higgs, and further limits the parameter space where the light stop scenario of electroweak baryogenesis is viable.
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Brown, Matthew. "Higgs and collider phenomenology of physics beyond the standard model." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/365147/.
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This thesis explores three classes of beyond-the-Standard Model (BSM) theories: Minimal Universal Extra Dimensions (MUED), the 4D Composite Higgs Model (4DCHM) and Technicolor. In particular, Higgs boson data from the Large Hadron Collider (LHC) is used to test the viability of these models and constrain their parameter spaces. It turns out that this provides a valuable constraint for MUED, requiring that the compactification scale R-1 of the theory be greater than 500 GeV. More direct searches for MUED are also considered, and the creation of a software implementation of MUED in CalcHEP is discussed. This implementation is used to determine that the tri-lepton final state is the most promising discovery signature due to the high lepton multiplicity in MUED and that the exclusion reach of MUED using this signature is up to R-1 = 1200 GeV with 20 fb-1 of data from the 8 TeV LHC. The 4DCHM is also analysed in light of the Higgs data. It is found that, once direct detection constraints are applied, the model is actually a slightly better fit to Higgs data than the Standard Model for most points in the 4DCHM parameter space considered. Finally, various Technicolor models are tested against Higgs data using a more sophisticated statistical analysis and it is found that most provide viable Higgs boson candidates with broadly Standard-Model like couplings.
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Jenkins, Alejandro Wise Mark B. "Topics in particle physics and cosmology beyond the standard model /." Diss., Pasadena, Calif. : Caltech, 2006. http://resolver.caltech.edu/CaltechETD:etd-06022006-145211.
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Spencer-Smith, Alexander Fraser. "Higgs Vacuum Stability, Inflation & Physics Beyond the Standard Model." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/15512.
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The discovery of the Higgs particle, simultaneous measurement of it's mass and subsequent confirmation of it's status as the Standard Model (SM) Higgs represents the completion of the theory in it's original guise. Armed with all necessary inputs of the theory at the weak scale, it is now possible to extrapolate the parameters of the theory up to the Planck scale. We complement the current state of the art renormalisation group (RG) studies performed in the MS bar scheme with an analogous study performed in an explicitly mass-dependant scheme. The necessary renormalisation and construction of the mass-dependent beta--functions is performed. We then RG evolve the SM parameters up to the planck scale and, in parallel to the current studies, find the electroweak (EW) symmetry breaking Higgs vacuum to be metastable, but with increased statistical significance as compared to those studies, we also find a reduction of the errors in the theoretical determination of the critical values of the Higgs and top pole masses required for absolute stability of the SM Higgs vacuum. An ever-growing body of evidence supports the idea of a period of exponential inflation in the early history of the universe. The non-flat spacetime geometry during inflation gives rise to new decay mechanisms not considered in the flat spacetime analysis of SM Higgs vacuum decay. We re-examine stability of the SM Higgs vacuum during inflation, finding new instantons with no flat-spacetime analogue dominate in the decay. Under the assumption of no new physics beyond the SM and forcing the requirement that inflation should proceed, we are able to place a bound upon the inflationary rate. Combining our results with the most likely value of the rate of inflation suggested by combination of the Planck and BICEP2 measurements of the CMB temperature anisotropy, we find the SM Higgs vacuum could not have survived inflation, providing new evidence for physics beyond the SM Motivated by the need for new physics which should stabilise the Higgs potential, we discuss the effect of adding new degrees of freedom and interactions to the SM, first in a general context, but then looking at concrete examples, focussing on the effect of models which could explain the mechanism of neutrino mass generation. We find the parameter space in type-II seesaw models to be the least constrained by the requirement of vacuum stability, thanks to the introduction of new bosonic, rather than fermionic, degrees of freedom. Finally, we consider the apparently accidental near criticality of the Higgs potential and find that it is possible to provide an explanation for this phenomenon using the framework of classically scale invariant models. We construct an explicit example of such a model, finding the symmetries of the theory permit a reduction in the number of free parameters of the SM by one.
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Vryonidou, Eleni. "Phenomenology of the standard model and beyond at hadron colliders." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648273.
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Bonnefoy, Quentin. "Topics beyond the Standard Model : axions, supersymmetry, string theory." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLX034/document.
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Cette thèse a pour but l'étude de théories diverses, toutefois interconnectées, décrivant la nouvelle physique au-delà du modèle standard de la physique des particules. Ces sont des théories d'un nouveau type de particules, les axions, d'un nouveau principe de symétrie, la supersymétrie, et d'une nouvelle description des degrés de liberté fondamentaux, la théorie des cordes. Les progrès instrumentaux et théoriques constamment fait au fil des ans ont confirmé que ces théories sont des candidates privilégiées pour une description de la physique au-delà du modèle standard.Les axions sont d'abord examinés et étudiés d'un point de vue phénoménologique: nous présentons des modèles qui désenchevêtrent les différentes échelles qui décrivent l'espace des paramètres des modèles d'axions, et nous discutons les axions présents dans des modèles de saveur. Inspirés par les recherches autour du swampland, nous nous imposons l'utilisation de symétries de jauge, et non globales, en tant que point de départ pour la construction de modèles.Notre intérêt se porte ensuite sur la supersymétrie. Nous étudions sa brisure, à la fois dans des modèles explicites dans l'ultraviolet qui génèrent une échelle de brisure de supersymétrie basse à partir de matière à haute échelle, et au niveau des théories effectives à l'aide de la supersymétrie non-linéaire. En ce qui concerne ce dernier thème, nous nous restreignons à l'approche des superchamps contraints. Enfin, nous présentons des solutions classiques exactes d'un modèle supersymétrique dont la portée est grande, le modèle de Wess-Zumino d'un superchamp chiral.Finalement, nous nous intéressons à la théorie des cordes. Nous calculons des spectres de cordes en guise d'illustration de la structure de la théorie et de point de départ pour le calcul d'amplitudes du vide à une boucle. Celles-ci nous permettent de tester l'une des conjectures du swampland, qui désigne la gravité comme la plus faible des forces, dans une configuration de théorie des cordes où la supersymétrie est brisée. Enfin, les axions en théorie des cordes sont analysés, en particulier lorsqu'ils sont chargés sous une symétrie de jauge abélienne anormaleThe aim of this thesis is to study various but interconnected theories for new physics beyond the standard model of particle physics. Those are theories of a new kind of particles, axions, a new symmetry principle, supersymmetry, and a new description of fundamental degrees of freedom, string theory. Constant instrumental and theoretical progresses made over the years maintain those already old subjects as leading BSM candidates.Axions are first reviewed and studied from a phenomenological perspective: we present models which disentangle the different scales which define the axion parameter space, and we discuss axions which arise in models of flavour physics. Motivated by swampland considerations, we insist on using gauge, and not global, symmetries as model building inputs.The focus then shifts to supersymmetry. We study its breaking, both in explicit ultraviolet models which generate a low supersymmetry breaking scale from high-scale matter, and at the effective field theory level using non-linearly realized supersymmetry. In our study of the latter topic, we focus on the constrained superfield approach. Finally, we present exact classical solutions of a supersymmetric model with broad application scope, the Wess-Zumino model of a chiral superfield.Last, we discuss string theory. We compute string spectra as illustrations of the structure of the theory and as starting points to compute one-loop vacuum amplitudes. Those are used to understand supersymmetry breaking in string theory, as well as brane interactions. Then, the latter enable us to test one of the swampland criteria, the weak gravity conjecture, in a string theory setup with broken supersymmetry. Finally, axions in string theory are scrutinized, in particular when they are charged under an anomalous abelian factor of the gauge group
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Brännström, Hanna. "Di-Higgs Production in the Standard Model and Beyond." Thesis, Stockholms universitet, Fysikum, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-194419.
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This thesis examines how the kinetic properties of pair-produced Higgs bosons depend on whether the process is mediated by particles in the Standard Model or a simplified supersymmetric model. The analysis is based on simulated data made using MadGraph. The examination within this thesis is split into two parts, one performed on the output of MadGraph (parton level) and the second performed on the output of a simplified simulation of the ATLAS detector response (reconstruction level). The first part also contains a section showing that the supersymmetric model results are consistent with the Standard Model results in cases where no supersymmetric particles are present in the di-Higgs production and decay, and a section detailing the minor differences in kinematics of the Higgs bosons depending on the mass of the supersymmetric partner of the top quark. The second part of the thesis covers the decay of the Higgs boson into bottom and anti-bottom quarks, and includes a section showing that there is no difference if the decay is done using the MadSpin module or the Pythia module for MadGraph, before exploring the kinematics of the jets produced. Both when studying Higgs bosons at the parton level and when studying b-jets at the reconstruction level, it is found that there are clear differences in the kinematics between the Standard Model and the supersymmetric model. At both levels, a neural network has been designed, trained and tested. For the parton level neural network 59 % of all events are classified correctly, while at the reconstruction level 51 % of all events are classified correctly. These neural network results show that it is possible to train a neural network to learn on data like this, and that with enough di-Higgs events detected, their kinematic properties could be used to indirectly infer the presence of physics beyond the Standard Model.
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Athron, Peter. "Aspects of electroweak symmetry breaking in physics beyond the standard model." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/513/.
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Fine tuning in the Standard Model (SM) is the basis for a widespread expectation that the minimal model for electroweak symmetry breaking, with a single Higgs boson, is not realised in nature and that new physics, in addition to (or instead of) the Higgs, will be discovered at the Large Hadron Collider (LHC). However constraints on new physics indicate that many models which go beyond the SM (BSM) may also be fine tuned (although to a much lesser extent). To test this a reliable, quantitative measure of tuning is required. We review the measures of tuning used in the literature and propose an alternative measure. We apply this measure to several toy models and a constrained version of the Minimal Supersymmetric Standard Model. The Exceptional Supersymmetric Standard Model (E6SSM) is another BSM motivated by naturalness. As a supersymmetric theory it solves the SM hierarchy problem and by breaking a new gauged U(1) symmetry it also solves the μ-problem of the MSSM. We investigate the Renormalisation Group Evolution of the model and test for radiative electroweak symmetry breaking in two versions of the model with different high scale constraints. First we briefly look at scenarios with non-universal Higgs masses at the GUT scale and present a particle spectrum that could be observed at the LHC. Secondly we study the constrained E6SSM (CE6SSM), with universal scalar (m0), trilinear (A0) and gaugino (M) masses. We reveal a large volume of CE6SSM parameter space where the correct breakdown of the gauge symmetry can be achieved and all experimental constraints can be satisfied. We present benchmark points corresponding to different patterns of the particle spectrum. A general feature of the benchmark spectra is a light sector of SUSY particles consisting of a light gluino, two light neutralinos and a light chargino. Although the squarks, sleptons and Z′ boson are typically much heavier, the exotic color triplet charge 1/3 fermions as well as the lightest stop can be also relatively light leading to spectacular new physics signals at the LHC.
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Cano, Victor Manuel Peralta. "Phenomenology of Vector-like Fermions in Physics Beyond the Standard Model." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06122017-083800/.
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The Standard model of particle physics provides a successful theory to understand the experimental results of the electroweak and strong interactions. However, it does not have a satisfactory explanation for the hierarchy problem. Many extensions of the Standard Model that solve the hierarchy problem result in new particles. We will study the phenomenology of vector-like fermions resulting in theories where the Higgs boson is typically a pseudo-Nambu-Goldstone boson. In these theories we study the case where a heavy fermion will be heavier than a heavy gluon, and then the channel of a heavy fermion decaying into a color octet is considered. We study this phenomenology at high energy colliders, both the LHC as well as future machines.O modelo padrão de física de partículas fornece uma teoria bem-sucedida para entender os resultados experimentais das interações eletrofracas e fortes. No entanto, não tem uma explicação satisfatória para o problema de hierarquia. Muitas extensões do Modelo Padrão que resolvem o problema hierarquia resultam em novas partículas. Estudaremos a fenomenologia de férmions vetoriais resultando em teorias onde o bóson de Higgs é tipicamente um bóson pseudo-Nambu-Goldstone. Nessas teorias, estudaremos o caso em que um férmion pesado será mais pesado do que um glúon pesado, e então o canal de um férmion pesado decaindo em um octeto de cor é considerado. Estudamos esta fenomenologia em colisores de alta energia, tanto para o LHC quanto as futuras máquinas.
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Kile, Jennifer Wise Mark B. "Constraints on physics beyond the Standard Model and its observable effects /." Diss., Pasadena, Calif. : California Institute of Technology, 2007. http://resolver.caltech.edu/CaltechETD:etd-05282007-034337.
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Baumgart, Stefan [Verfasser]. "Effective Field Theories for Physics Beyond the Standard Model / Stefan Baumgart." Mainz : Universitätsbibliothek Mainz, 2020. http://d-nb.info/1205348328/34.
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Chaurasia, Shikha. "Beyond the Standard Model: Flavor Symmetry, Nonperturbative Unification, Quantum Gravity, and Dark Matter." W&M ScholarWorks, 2019. https://scholarworks.wm.edu/etd/1563898980.
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Despite the vast success of the Standard Model of particle physics, it is no secret that is also has its shortcomings, thus providing incentive to look beyond the Standard Model for solutions. In this thesis we focus in particular on a model of horizontal flavor symmetry, unification via a universal Landau pole, emergent gravity, and dark matter. First we explain the observed hierarchies in the elementary fermion mass spectrum via a model based on the double tetrahedral group, the smallest discrete subgroup of SU(2), while relaxing previous assumptions of supersymmetry. A sequential symmetry breaking process results in a hierarchy in the Yukawa couplings. Just as the Standard Model raises questions on the origin of the fermion mass spectrum, it similarly raises questions on the origins of its gauge couplings. We have to look beyond the Standard Model for the possibility of a unified description of the electromagnetic, weak and strong forces. As an alternative to conventional unification, we assume the existence of a universal Landau pole in which the gauge couplings blow up at a common scale in the ultraviolet. We consider extensions of the minimal scenario, to see if there are cases that might be probed at a future hadron collider. Next we focus on gravity, the fourth fundamental force that has yet to be embedded in the Standard Model. We consider a model where gravity is an emergent phenomenon in which the graviton appears as a bound state of scalars. We show how this approach can accommodate an arbitrary metric. Lastly we turn to the issue of dark matter, a hypothetical form of matter believed to account for a large portion of the universe but with no place in the Standard Model. We specifically focus on fermionic dark matter that is charged under the simplest non-Abelian dark gauge group. Exotic, vector-like leptons that also transform under the dark gauge group group can mix with standard model leptons and serve as a portal between the dark and visible sectors. We present a framework based on symmetries that allows the mixing between the dark and visible sectors to be non-negligible, while simultaneously suppressing unwanted flavor-changing processes. By extending the particle content and symmetries of the Standard Model, we can solve its various issues. In this thesis we seek to explain the observed hierarchies in the fermion mass spectrum, provide a unified description of the three gauge couplings, generalize a model of emergent gravity, and create a model that gives rise to dark matter via a vector-like fermion portal.
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Wouda, Glenn. "Phenomenology of Higgs Bosons Beyond the Standard Model." Doctoral thesis, Uppsala universitet, Högenergifysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-240617.
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After a long history of searches, a Higgs boson H was discovered by the ATLAS and the CMS experiments at the Large Hadron Collider (LHC) in 2012. Its properties fit well the ones predicted by the Standard Model (SM) of particle physics. However, the SM can not explain other established properties of Nature, such as the existence of Dark Matter. For this reason, models beyond the SM should be considered. Such models often predict the existence of several Higgs bosons and this thesis explores some of those models. In particular, the possibility to discover a charged Higgs boson, which would be a clear sign of physics beyond the SM, is studied. A commonly studied extension of the SM is the framework of two-Higgs-doublet models (2HDMs), where there are five Higgs bosons. By confronting the parameter spaces of some 2HDMs with publically available data from the LHC, the prospects for finding the 2HDM Higgs bosons is presented through the calculation of production cross sections and decay branching ratios in various channels. A new kind of 2HDM, called the Stealth Doublet Model is presented and the properties of the Higgs bosons are studied. In this model, it is shown that in particular the properties of the charged Higgs boson H± have new features not exhibited in earlier studied models. Within the parameter space compatible with the LHC results, the production cross section for H± can be sizeable enough to be experimentally observed. Finally, the discovery prospects at the LHC, for a H± in the pp → tH± process, with the decays H± → HW± and H → bb, is studied in various models beyond the Standard Model. It is shown that for the supersymmetric models, this channel is beyond the discovery reach of the LHC. In some of the other studied models, in particular the Aligned 2HDM, the situation is improved and the channel is feasible.