Rozprawy doktorskie na temat „Big Bang Nucleosynthesis (BBN)”

The work presented in this thesis is focused on the experimental study of the two deuterium burning channels 2H(d,p)3H and 2H(d,n)3He in the Big Bang Nucleosynthesis (BBN) astrophysical scenario. In the beginning is presented this phase of the early universe and why the BBN model is still fine tuned with new results coming from observations and laboratory measurements. This model (if BBN is considered standard) can be adjusted such to have only a free parameter, the baryon to photon ratio of the universe eta at a certain time. Also the WMAP satellite results have been of great help to fix eta (and then all the others BBN numbers), but still persist some discrepancies, as for the lithium primordial abundances, between what is theoretically predicted and what is observed. The deuterium (and the reactions in which is involved) plays a key role in the evaluation of eta, thus for all BBN, so that is called the best baryometer. Then is explained that the need of new cross sections (and reaction rates) measurements for astrophysics can not be satisfied. This is because of the problems given by their measurements in the laboratory, as the presence of Coulomb barrier (that makes cross sections exponentially decrease in the energy range of interest) and the electron screening effect. For all these reasons the present measurements have been performed through the Trojan Horse Method (THM), an indirect method that allow to have a bare-nucleus cross section of the two-body reaction of astrophysical interest that is free of the Coulomb suppression. This is accomplished via the selection of the quasi-free mechanism in an appropriate three-body reaction, whose center-of-mass energy is greater than the Coulomb barrier. Two experimental runs have been carried out at the Nuclear Physics Institute of the Academy of Science of Czech Republic, in Rez (Prague). In the first one, with a 17 MeV 3He beam (in which only 2H(d,p)3H has been measured) the presence of quasi-free mechanism events has been ascertained. The result obtained is fair but not good enough for the error reduction needed for astrophysics. Instead, to optimize the result in the region relecant for astrophysics, a the second run (where the 3He beam energy was 18 MeV) has been performed. In particular for the first time the technique of measuring one of the two-body reactions participant ejectile and the spectator particle, in this case a proton, instead of both the ejectiles. This has also allowed the measure of the 2H(d,n)3He reaction without the complexity of the neutron detection, so with a very good precision. All the off-line analysis done until the S-factor extraction is detailed explained, including the MPWBA analysis by Dr. S. Typel. Also the screening potential has been evaluated, obtaining a value of 13.2±1.8 eV for 2H(d,p)3H and 11.7±1.6 eV for 2H(d,n)3He, very close to the adiabatic limit, as expected. A pole invariance test has been provided comparing present results with previous TH data, where the 6Li was used as TH nucleus. Reaction rates from present TH data for the two d+d channels, and from TH cross section of 3He(d,p)4He and 7Li(p,a)4He have been calculated. The new rates have been also compared with previous direct data compilations and with a new updated one that exclude questionable data sets. Using these new TH rates as input for the BBN code developed by prof. Bertulani, with eta fixed at the WMAP value, the primordial abundances have been obtained. These results are coherent with the whole model and will be soon compared with the observational results: a further analysis will provide stronger constraints on the values and a reduction of the involved uncertainties. This result reasserts that THM is a powerful tool for nuclear astrophysics and gives further validation to the BBN model.

Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of ${}^7$Li and ${}^6$Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to ${}^6$Li abundance and recently the $alpha$+d$ ightarrow$ ${}^6$Li + $gamma$ and the p+${}^6$Li$ ightarrow$${}^7$Be+$gamma$ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the ${}^6$Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and ${}^6$Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

Zwischen 10 und 1000 s nach dem Urknall bildeten sich während der Big Bang Nukleosynthese (BBN) die ersten leichten Elemente aus Protonen und Neutronen. Die primordialen Häufigkeiten dieser Elemente hingen von denWirkungsquerschnitten der beteiligten Kernreaktionen ab. Vergleiche zwischen den Ergebnissen nuklearer Netzwerkrechnungen mit astronomischen Beobachtungen bieten eine einzigartige Möglichkeit, etwas über das Universum zu dieser Zeit zu erfahren. Da es für die p(n,g)d-Reaktion, die eine Schlüsselreaktion der BBN ist, kaum Messungen im relevanten Energiebereich gibt, beruht deren Reaktionsrate in Netzwerkrechnungen auf theoretischen Berechnungen. Darin fließen auch experimentelle Daten der Nukleon-Nukleon-Streuung, des Einfangquerschnitts für thermische Neutronen sowie (nach Anwendung des Prinzips des detaillierten Gleichgewichts) der d(g,n)p-Reaktion mit ein. Diese Reaktion, die Photodissoziation des Deuterons, ist bei BBN-Energien (Tcm = 20–200 keV) ebenfalls kaum vermessen. Die großen experimentelle Unsicherheiten machen Vergleiche mit den präzisen theoretischen Berechnungen schwierig. In den letzten Jahren wurde die d(g,n)p-Reaktion und insbesondere der M1-Anteil des Wirkungsquerschnitts mit quasi-monoenergetischen g-Strahlen aus Laser-Compton-Streuung oder durch Elektrodesintegration untersucht. Üblicherweise verwendete man für Messungen des d(g,n)p-Wirkungsquerschnitts entweder die auf wenige diskrete Energien beschränkte Strahlung des g-Zerfalls oder Bremsstrahlung, für die aber eine genaue Photonenflussbestimmung sowie der Nachweis von einem der Reaktionsprodukte und dessen Energie nötig ist. Da diese Energie im Bereich der BBN relativ gering ist, gab es bisher noch keine absoluten Messung des d(g,n)p-Wirkungsquerschnitts bei Tcm < 5 MeV mit Bremsstrahlung. Das Ziel dieser Dissertation ist eine solche Messung mit einer Unsicherheit von 5 % im für die BBN relevanten Energiebereich und darüber hinaus bis Tcm ~ 2,5 MeV unter Verwendung gepulster Bremsstrahlung an der Strahlungsquelle ELBE. Dieser supraleitende Elektronenbeschleuniger befindet sich am Helmholtz-Zentrum Dresden-Rossendorf und stellte einen Elektronenstrahl hoher Intensität bereit. Die kinetische Elektronenenergie von 5 MeV wurde mit einem Browne-Buechner-Spektrometer präzise gemessen. Die Energieverteilung der in einer Niob-Folie erzeugten Bremsstrahlungsphotonen wurde berechnet. Die Photonenflussbestimmung nutzte die Kernresonanzstreuung an 27Al, das sich mit deuteriertem Polyethylen in einem mehrschichtigen Target befand. Die 27Al-Abregungen wurden mit abgeschirmten, hochreinen Germanium-Detektoren nachgewiesen, deren Effektivität mit GEANT4 simuliert und durch Quellmessungen normiert wurde. Die Messung der Energie der Neutronen aus der d(g,n)p-Reaktion erfolgte mittels deren Flugzeit in Plastikszintillatoren, die an zwei Seiten von Photoelektronenvervielfachern mit hoher Verstärkung ausgelesen wurden. Die Nachweiseffektivität dieser Detektoren wurde in einem eigenen Experiment in den Referenz-Neutronenfeldern der PTB Braunschweig kalibriert. Die Nachweisschwelle lag bei etwa 10 keV kinetischer Neutronenenergie.Wegen der guten Zeitauflösung der Neutronendetektoren und des ELBE-Beschleunigers genügte eine Flugstrecke von nur 1 m. Die Energieauflösung betrug im d(g,n)p-Experiment 1–2 %. Leider gingen viele Neutronen bereits durch Streuung in dem großen Target verloren oder sie wurden erst durch Teile des kompakten Experimentaufbaus in die Detektoren gestreut. Beide Effekte wurden mit Hilfe von FLUKA simuliert um einen Korrekturfaktor zu bestimmen, der aber bei niedrigen Energien relativ groß war. Der d(g,n)p-Wirkungsquerschnitts wurde daher nur im Bereich 0.7 MeV < Tcm < 2.5 MeV bestimmt. Die Ergebnisse stimmen mit anderen Messungen, Daten-Evaluierungen sowie theoretischen Rechnungen überein. Die Gesamtunsicherheit beträgt circa 6.5 % und kommt zu fast gleichen Teilen von den statistischen und systematischen Unsicherheiten. Die statistische Unsicherheit könnte durch eine längere FLUKA Simulation noch von 3–5 % auf 1 % verringert werden. Die systematische Unsicherheit von 4.5 % ist vorrangig auf die Photonenflussbestimmung, die Neutronen-Nachweiseffektivität und die Target-Zusammensetzung zurückzuführen.

For about 20 years now, observations of 6Li in several old metal-poor stars inside the halo of our galaxy have been reported, which are largely independent of the stars’ metallicity, and which point to a possible primordial origin. The observations exceed the predictions of the Standard Big-Bang Nucleosynthesis model by a factor of 500. In the relevant energy range, no directly measured S-factors were available yet for the main production reaction 2H(α,γ)6Li, while different theoretical estimations have an uncertainty of up to two orders of magnitude. The very small cross section in the picobarn range has been measured with a deuterium gas target at the LUNA acceler- ator (Laboratory for Underground Nuclear Astrophysics), located deep underground inside Laboratori Nazionali del Gran Sasso in Italy. A beam-induced, neutron-caused background in the γ-detector occurred which had to be analyzed carefully and sub- tracted in an appropriate way, to finally infer the weak signal of the reaction. For this purpose, a method to parameterize the Compton background has been developed. The results are a contribution to the discussion about the accuracy of the recent 6Li observations, and to the question if it is necessary to include new physics into the Standard Big-Bang Nucleosynthesis model.

For about 20 years now, observations of 6Li in several old metal-poor stars inside the halo of our galaxy have been reported, which are largely independent of the stars’ metallicity, and which point to a possible primordial origin. The observations exceed the predictions of the Standard Big-Bang Nucleosynthesis model by a factor of 500. In the relevant energy range, no directly measured S-factors were available yet for the main production reaction 2H(α,γ)6Li, while different theoretical estimations have an uncertainty of up to two orders of magnitude. The very small cross section in the picobarn range has been measured with a deuterium gas target at the LUNA acceler- ator (Laboratory for Underground Nuclear Astrophysics), located deep underground inside Laboratori Nazionali del Gran Sasso in Italy. A beam-induced, neutron-caused background in the γ-detector occurred which had to be analyzed carefully and sub- tracted in an appropriate way, to finally infer the weak signal of the reaction. For this purpose, a method to parameterize the Compton background has been developed. The results are a contribution to the discussion about the accuracy of the recent 6Li observations, and to the question if it is necessary to include new physics into the Standard Big-Bang Nucleosynthesis model.

The discovery of the Spite plateau in the abundances of 7Li for metal-poor stars led to the determination of an observationally deduced primordial lithium abundance. However, with the determination of the baryon density, Omega_B_h^2, from the Wilkinson Microwave Anisotropy Probe (WMAP) data, a discrepancy arose between observationally determined and theoretically determined abundances of 7Li. This is what has become known as the “lithium problem”. Of all the uncertain factors in determining a stellar Li abundance, the effective temperature is the most important. This thesis is concerned with determining an accurate effective temperature scale for metal-poor halo dwarfs, paying specific attention to eliminating any possible systematic errors. This is done by utilising the exponential term, Chi/T, of the Boltzmann equation. Two assumptions are adopted; firstly the simplifying assumptions of local thermodynamic equilibrium (LTE), and secondly the more sophisticated techniques of non-local thermodynamic equilibrium (NLTE). The temperature scales are compared to others derived using different techniques; a photometric scale, where I find comparable Teff in LTE and hotter temperatures by an average of ~ 150 K in NLTE; a scale derived using Balmer lines, for which I have comparable values in LTE and hotter Teff values, by typically 110 K – 160 K, in NLTE; and finally a scale derived using an infrared flux method (IRFM). Here I find their Teff values are hotter by ~ 250 K for LTE and ~ 190 K in NLTE. Lithium abundances are then calculated for the program stars and a mean Li abundance is derived. I find values ranging from A(Li) = 2.10 dex – 2.16 dex with the LTE scales and A(Li) = 2.19 dex – 2.21 dex for the NLTE scales. These mean Li abundances are compared to other observationally deduced abundances, for which I find comparable results in LTE and higher values in NLTE, and to the WMAP + big bang nucleosynthesis calculated Li abundance. I find that my new values are still considerably lower than the WMAP value and are therefore unable to reconcile the lithium problem. Second to this primary investigation, I use Ti as an independent test of the derived Teff values and log g’s. I find that Ti is not a useful constraint on the temperatures or, therefore, on the lithium problem. I also assess the impact of the new Teff scales on the different models of Galactic chemical evolution (GCE), comparing newly calculated abundances with GCE determined abundances. It was found that trends exist in several of the elements; however, these were not statistically relevant. Also a larger degree of scatter was found in the abundances compared to the Arnone et al. (2005). This scatter was not to the degree found in the Argast et al. (2000). Reasons for the differences have been discussed.

Le modèle standard de la physique des particules a été développé dans les années 1970. Malgré de grands succès expérimentaux, il présente des problèmes qui ne peuvent être résolus qu'avec des extensions du modèle. La supersymétrie est un candidat particulièrement intéressant, qui postule simplement une symétrie supplémentaire entre bosons et fermions. En plus d'apporter des réponses dans le domaine de la physique des particules, la supersymétrie trouve des applications intéressantes en cosmologie. Elle contient des candidats possibles à la matière noire, qui représente 25\% de la densité d'énergie de l'Univers et dont la nature est inconnue. Un autre problème cosmologique intéressant est celui des problèmes du lithium dans le cadre de la nucléosynthèse primordiale décrivant la production des éléments légers dans les premières secondes de l'Univers après le Big Bang. Les abondances de lithium prévues par la théorie sont incompatibles avec les observations. J'étudie ici un scénario où une particule supersymétrique, le gravitino, est un candidat à la matière noire et la production de cette particule par désintégration d'autres particules supersymétriques permet de résoudre les problèmes du lithium.

The dark matter is the most dominating matter candidate and a key driving force for the structure formation in the universe. Despite decade-long searches, the precise nature and particle properties of dark matter are still unknown. The standard cold dark matter candidate, the Weakly Interacting Massive Particle(WIMP) can successfully describe the large-scale features of the universe. However, when it comes to the scales comparable to a galaxy or a group of galaxies, it fails to explain the observations. The nature of the small-scale anomalies suggests a lower amount of dark matter at the scales of interest and can be tackled with different strategies. The simulation suites, used to produce the small-scale universe theoretically, can be equipped with varieties of baryonic phenomena, leading to a better agreement with observation. Another way is to use some new dark matter candidate altogether that reduces the small-scale power. Many such alternative dark matter candidates have been suggested and explored in the literature. The aim of the work presented in this thesis is to study the effects of small-scale power reduction due to new dark matter physics on different cosmological observables. In Chapter 2 of this thesis, we have discussed the particle physics properties of three dark matter candidates proposed as alternatives of the WIMP. The rst one is the Late Forming Dark Matter(LFDM), where dark matter is created due to a phase transition in the massless neutrino sector [1] long after the Big Bang Nucleosynthesis(BBN). Another candidate is the Ultra Light Axion Dark Matter(ULADM), which is born due to spontaneous symmetry breaking in the early universe and is stuck to its initial condition because of the Hubble drag. When the mass of the particle exceed the Hubble parameter, it decouples from the drag and starts behaving like dark matter [2], with a free-streaming length that is dependent on its mass. The last candidate we consider is the Charged Decaying Dark Matter (CHDM), which is born in iv the radiation dominated era, after an instantaneous decay of a massive charged particle [3]. All of these dark matter candidates suppress small-scale power, though because of different physical reasons. In the next three chapters, we have studied their e ects on various cosmological observables. The methods of study, along with the data used to validate the theoretical predictions and results are discussed below. Chapter 3: This chapter is based on the work performed in [4]. In this chapter, we focus on the LFDM and study its e ects on linear matter power spectra at both small and large scales. Method of Study: The LFDM model is speci ed by two parameters: The effective massless neutrino degrees of freedom(DOF) Ne and the redshift of formation zf . We have generated a set of matter power spectra using publicly available code CAMB for different sets of Ne and zf , and performed a 2 analysis using matter power spectrum data to constrain the model parameters. We have also considered a scenario, where a fraction flfdm of the total dark matter is LFDM and repeated the exercise. We have computed multi-parameter contours and posterior probabilities by marginalization over redundant parameters that allow us to estimate the model parameters. The Data: The two parameters|zf and Ne | affect the linear power spectrum at different scales. The main impact of changing Ne is to alter the MRE epoch, shifting the peak of the matter power spectrum, which is located at k ' 0:01hMpc􀀀1 in the standard model of cosmology. We use the SDSS DR7 data [5] for our analysis. As the SDSS data on the galaxy power spectrum gives the power at scales: k=0:02{0:1 h=Mpc, this data is sensitive to the variation of Ne . On the other hand, the main effect of formation redshift zf is to suppress the power at scales k > 0:1 h=Mpc. In this scales, we use the linear matter power spectrum, reconstructed from Lyman- forest power spectrum in the range: 0:2 < k < 4:8 h=Mpc from [6,7]. We use 45 band-powers from the SDSS galaxy data and 12 points from the reconstructed linear power spectrum from the Lyman- data. Results: Our results can be summarized as follows. If all the presently observed CDM is late forming, then both the data sets lead to upper limits on the redshift of formation of LFDM, with Lyman- data resulting in tighter bounds: zf < 3 106 at 99% con dence limit. On the other hand, if we allow only a fraction of the CDM to form at late times, then we improve the quality of t as compared to the standard CDM model for the Lyman- data. This is suggestive that the present data allows for a fraction 30% of the CDM to form at zf ' 105. Therefore, our result underlines the importance of the Lyman- data for studying the small-scale power spectrum in alternative dark matter regime. Chapter 4: This chapter is based on the work performed in [8]. Here, we have studied the e ects of small-scale power suppression on the Epoch of Reionization(EoR) and the evolution of collapsed fraction of gas at high redshift. We have considered two of the alternative dark matter candidates discussed in Chapter-2 in this chapter: the LFDM and the ULADM. Method of Study: Our method of constructing the reionization fi elds consists of three steps: (i) Generating the dark matter distribution at the desired redshift, (ii) Identifying the location and mass of collapsed dark matter halos within the simulation box, (iii) Generating the neutral hydrogen map using an excursion set formalism. The assumption here is that the hydrogen exactly traces the dark matter eld and the dark matter halos host the ionizing sources. Given the uncertainty of reionization history, we do not assume a particular model for reionization history xHI (z), where xHI is the fraction of neutral hydrogen in the universe. Instead, we xed the redshift at z = 8 and the ionization fraction at xHI = 0:5 and compared these models. We have produced Hi power spectra, and photon brightness temperature fluctuation( Tb) maps to compare the alternative models with the standard CDM model. We discard the models where no halo is formed to host the ionizing sources, or an absurdly high number of ionizing photon is necessary to make xHI = 0:5 at z = 8 successfully. The collapsed fraction, defined as the fraction of collapsed mass in haloes with masses larger than a threshold mass M at a redshift z, is sensitive to the mass function of the haloes. As obtaining the mass function from N-body simulation is numerically expensive, we integrate the Sheth-Tormen mass function above the density threshold of collapse at a given redshift for computing the collapsed fraction in case of LFDM models. For computing the collapsed fraction for ULADM models, we integrate the halo mass functions derived by [9]. The collapsed fractions are calculated for two threshold halo masses, 1010M and 5 1010M in the redshift range 2 < z < 5 and compared to observational data. Models that are unable to produce the observed collapsed fractions at high redshifts are discarded. The Data: From absorption studies of the Damped Lyman- (DLA) clouds, the evolution of average mass density of Hi in the universe can be inferred. Assuming that the collapsed fraction of baryons traces dark matter, this allows us to get an approximate measure of the minimum amount of collapsed fraction of the total matter in the redshift range 2 < z < 5. We have used the data of density of gas trapped in DLAs (HI ), at the mentioned redshift range from [10, 11] and converted them to collapsed fraction of gas. The re-constructed collapsed fractions are used to compare the theoretical predictions. Results: Our method predicts an `inside-out' reionization where the high-density regions are ionized rst. We fi nd that the Hi power for LFDM and ULADM models is greater than the CDM model over a large range of scales 0:1 < k < 4Mpc􀀀1. In the maps of Tb, there are two main differences between CDM and alternative models. The size of the ionized regions is larger in the LFDM (ULADM) models and the Hi elds have stronger density contrast. Checking the facts that halos are actually formed to host stars and a realistic number of ionizing photons are produced to achieve the desired level of ionization, we put a rough limit on zf 4 105 and ma ' 2:6 10􀀀23 eV as lower cut-o s. Comparing the estimated collapsed fraction with data we found weaker constraints on zf . 2 105 and ma . 10􀀀23 eV. All these constraints are in good agreement with previous constraints. Chapter 5: This chapter is based on the work performed in [12]. The observable of interest here is the spectral distortion in the Cosmic Microwave Background(CMB). Method of Study: The distortion on the CMB spectra can occur due to heating or cooling of the medium owing to several mechanisms at di erent times in the history of the universe. In this work, we consider heating due to the dissipation of acoustic waves, well-known as the Silk Damping. The fraction of energy injected into the photon bath is a function of the evolution of the fluctuation in gravitational potential and the CMB dipole 1. We have computed the evolution of and 1 for all the three dark matter candidates studied in Chapter 2, along with the WDM, using the publicly available code CMBFAST and axionCAMB. Using them, we estimate the evolution of the heating rate and integrate it to get the distortion parameters. The distortion parameters thus found are used to calculate the distorted CMB spectrum. The nal output is the percentage change of the distortion parameters for the alternative dark matter models with respect to the CDM model. Results: The two earlier spectral distortions, namely the - and the i-distortion, are not found to be affected due to new dark matter physics. The y-distortion is the only one that carries the signatures of small-scale power suppression. We conclude that, unless the constraints on the model parameters found in previous studies are violated, the change in the y-distortion parameter is not more than 14% compared to the standard model with identical spectral shapes. y-distortion occurring from later phenomena, i.e., structure formation and tSZ e ects in the galaxy clusters have orders of magnitude higher distortion parameters than the Silk Damping, again with the same spectral shape. Thus, unless these foregrounds are understood and cleared correctly, distinguishing between dark matter candidates which reduce small-scale power is next to impossible. Finally, our study shows that changing matter power at small scales can have noticeable impacts on other observables of the universe. However, to see the difference, the phenomena themselves are to be understood properly. The constraints found on the models using different probes are in good agreement with each other. In future, we will extend our research by investigating whether it is possible to accommodate an O(10 eV) particle as a dominating cold dark matter candidate, by exploring its effects on linear matter power spectrum and CMB spectral distortion.

We study the impact of long lived strongly interacting particles on primordial nuclear abundances. Particularly we look at the case of anti-squark quark bound states called mesinos. These mesinos are similar to massive nucleons in that they have the same spin and isospin. Like nucleons, the mesinos take part in nucleosynthesis and are bound into nuclei. We incorporate the mesinos into the various stages of BBN, from the QCD phase transition, to their capture of nucleons, to their eventual decay. We identify the mechanisms by which the mesinos could impact primordial abundances and show which actually do so. We nd that for the predicted mesino abundance, only one mechanism exists that has the potential of generating an observable signature.

The existence of charged electroweak-scale particles in the early universe can drastically affect the evolution of elemental abundances. Through the formation of Coulombic bound states with light nuclei, these exotic relic particles (hereafter referred to as X–) act to catalyze nuclear reactions by reducing their threshold energies. This thesis examines the properties of the X– bound states, and uses primordial element observations to constrain the abundance, lifetime, and mass of this exotic particle species. If the X– is a Dirac Fermion, its abundance relative to baryons is found to be YX- ~ 0.01, with a lifetime of 1500s ≤ τX- ≤ 3000s, and a mass of order 100 GeV. Assuming that the X– is a Scalar particle that decays into gravitinos, the resulting bounds become, 5x10-4 ≤ YX- ≤ 0.07, 1600s ≤ τX- ≤ 7000s, and 60GeV ≤ mX- ≤ 1000GeV. These ranges are consistent with Dark Matter constraints.

The Standard Model of Particle Physics has been verified to unprecedented precision in the last few decades. However there are still phenomena in nature which cannot be explained, and as such new theories will be required. Since terrestrial experiments are limited in both the energy and precision that can be probed, new methods are required to search for signs of physics beyond the Standard Model. In this dissertation, I demonstrate how these theories can be probed by searching for remnants of their effects in the early Universe. In particular I focus on three possible extensions of the Standard Model: the addition of massive neutral particles as dark matter, the addition of charged massive particles, and the existence of higher dimensions. For each new model, I review the existing experimental bounds and the potential for discovering new physics in the next generation of experiments. For dark matter, I introduce six simple models which I have developed, and which involve a minimum amount of new physics, as well as reviewing one existing model of dark matter. For each model I calculate the latest constraints from astrophysics experiments, nuclear recoil experiments, and collider experiments. I also provide motivations for studying sub-GeV mass dark matter, and propose the possibility of searching for light WIMPs in the decay of B-mesons and other heavy particles. For charged massive relics, I introduce and review the recently proposed model of catalyzed Big Bang nucleosynthesis. In particular I review the production of Li6 by this mechanism, and calculate the abundance of Li7 after destruction of Be7 by charged relics. The result is that for certain natural relics CBBN is capable of removing tensions between the predicted and observed Li6 and Li7 abundances which are present in the standard model of BBN. For extra dimensions, I review the constraints on the ADD model from both astrophysics and collider experiments. I then calculate the constraints on this model from Big Bang nucleosynthesis in the early Universe. I also calculate the bounds on this model from Kaluza-Klein gravitons trapped in the galaxy which decay to electron-positron pairs, using the measured 511 keV gamma-ray flux. For each example of new physics, I find that remnants of the early Universe provide constraints on the models which are complimentary to the existing constraints from colliders and other terrestrial experiments.

Above-barrier complete fusion cross-sections for reactions with light, weakly-bound nuclei such as 6,7Li and 9Be are suppressed relative to expectations from theory and experiment. This has been interpreted to be a result of the weakly-bound nucleus breaking up into its cluster constituents, reducing the probability of complete charge capture. However, experiments to probe mechanisms of breakup in below-barrier reactions of 9Be and 6,7Li with high atomic number targets have shown that breakup of unbound states formed following nucleon transfer dominates over direct breakup of the projectile into its cluster constituents. This thesis extends the study of breakup following transfer in interactions of 9Be and 7Li with light targets of 6 ≤ Z ≤ 28. Below-barrier coincidence measurements of breakup fragments produced in these reactions show a vanishing amount of direct breakup, and the dominance of transfer-triggered breakup. Since breakup can only suppress complete fusion if it occurs prior to the collision partners reaching the fusion barrier, the location of breakup is crucial. In turn, the location of breakup is intimately related to the lifetime of the unbound state populated. Nuclei produced in long-lived states cannot suppress complete fusion, since they will pass the barrier before breakup can occur. Conversely, nuclei produced in states with lifetimes comparable to the zeptosecond (10^−21 s) timescale of the collision may break up before reaching the fusion barrier. Through the use of experimental observables that are sensitive to the location of breakup, the importance of a realistic treatment of resonance lifetimes to correctly reproduce experimental results with theoretical modelling will be established. Below-barrier measurements of transfer-triggered breakup, where capture is minimised, are used to determine the breakup probability as a function of distance of closest approach for reactions of 7 Li and 9 Be with light targets of 13 ≤ Z ≤ 28, as well for reactions of 9Be with heavy targets of 62 ≤ Z ≤ 83. These probability functions are used as input into classical dynamical trajectory models to predict above-barrier complete and incomplete fusion cross-sections. These fusion cross-sections are found to be sensitive to the lifetime of the weakly-bound nucleus produced after transfer. When realistically modelled, the inclusion of lifetime leads to the conclusion that breakup alone cannot account for the observed suppression of complete fusion in reactions 9Be with 144Sm to 209Bi. Experimental groundwork is laid for measurement of the 7Be(d,p)8Be reaction at the Australian National University, relevant to Big Bang nucleosynthesis. The efficacy of using a large solid angle array and kinematic reconstruction techniques for such studies is demonstrated through a measurement of α particles produced in the mirror reaction 7Li(d,n)8Be. In this reaction, a high population of the broad 4+ resonance in 8Be is observed, totalling 69% of the coincidence yield after efficiency correction. It is therefore crucial to investigate the excitation of 8Be in the 7Be(d,p)8Be reaction. Test measurements of 7Be production via the 10B(6Li,7Be)9Be reaction are made using the SOLEROO RIB facility. Normalised secondary beam intensities above 10 4 cts/s/mg/cm^−2/μeA are achieved with beam purity of ∼ 96%.