Zeitschriftenartikel: „MODIFIED THEORIES“

1

Day, Charles. „Testing theories of modified gravity“. Physics Today 70, Nr. 3 (März 2017): 21. http://dx.doi.org/10.1063/pt.3.3485.

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BAMBA, KAZUHARU, CHAO-QIANG GENG und SHINJI TSUJIKAWA. „THERMODYNAMICS IN MODIFIED GRAVITY THEORIES“. International Journal of Modern Physics D 20, Nr. 08 (15.08.2011): 1363–71. http://dx.doi.org/10.1142/s0218271811019542.

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We demonstrate that there exists an equilibrium description of thermodynamics on the apparent horizon in the expanding cosmological background for a wide class of modified gravity theories with the Lagrangian density f(R,ϕ,X), where R is the Ricci scalar and X is the kinetic energy of a scalar field ϕ. This comes from a suitable definition of an energy momentum tensor of the "dark" component obeying the local energy conservation law in the Jordan frame. It is shown that the equilibrium description in terms of the horizon entropy S is convenient because it takes into account the contribution of the horizon entropy Ŝ in non-equilibrium thermodynamics as well as an entropy production term.

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Bamba, Kazuharu, und Sergei Odintsov. „Inflationary Cosmology in Modified Gravity Theories“. Symmetry 7, Nr. 1 (09.03.2015): 220–40. http://dx.doi.org/10.3390/sym7010220.

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4

Asada, Hideki. „Gravitational Microlensing in Modified Gravity Theories“. Progress of Theoretical Physics 125, Nr. 2 (Februar 2011): 403–10. http://dx.doi.org/10.1143/ptp.125.403.

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5

Bamba, Kazuharu, Chao-Qiang Geng und Shinji Tsujikawa. „Equilibrium thermodynamics in modified gravitational theories“. Physics Letters B 688, Nr. 1 (April 2010): 101–9. http://dx.doi.org/10.1016/j.physletb.2010.03.070.

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6

EASSON, DAMIEN A. „MODIFIED GRAVITATIONAL THEORIES AND COSMIC ACCELERATION“. International Journal of Modern Physics A 19, Nr. 31 (20.12.2004): 5343–50. http://dx.doi.org/10.1142/s0217751x04022578.

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Modified gravitational theories can provide alternatives to dark energy as an explaination for the observed late-time cosmic acceleration. Several examples of low-curvature corrections to the Einstein-Hilbert action are studied. These models generically contain unstable de Sitter solutions and, depending on the parameters of the theory, can exhibit late time accelerating attractor solutions.

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Bamba, Kazuharu. „Thermodynamic properties of modified gravity theories“. International Journal of Geometric Methods in Modern Physics 13, Nr. 06 (15.06.2016): 1630007. http://dx.doi.org/10.1142/s0219887816300075.

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We review thermodynamic properties of modified gravity theories, such as [Formula: see text] gravity and [Formula: see text] gravity, where [Formula: see text] is the scalar curvature and [Formula: see text] is the torsion scalar in teleparallelism. In particular, we explore the equivalence between the equations of motion for modified gravity theories and the Clausius relation in thermodynamics. In addition, thermodynamics of the cosmological apparent horizon is investigated in [Formula: see text] gravity. We show both equilibrium and nonequilibrium descriptions of thermodynamics. It is demonstrated that the second law of thermodynamics in the universe can be met, when the temperature of the outside of the apparent horizon is equivalent to that of the inside of it.

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Cruz-Dombriz, A. de la, A. Dobado und A. L. Maroto. „Black holes in modified gravity theories“. Journal of Physics: Conference Series 229 (01.05.2010): 012033. http://dx.doi.org/10.1088/1742-6596/229/1/012033.

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9

Felice, Antonio De, Shinji Tsujikawa, Joseph Elliston und Reza Tavakol. „Chaotic inflation in modified gravitational theories“. Journal of Cosmology and Astroparticle Physics 2011, Nr. 08 (23.08.2011): 021. http://dx.doi.org/10.1088/1475-7516/2011/08/021.

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10

Flanagan, Éanna É. „Khronometric Theories of Modified Newtonian Dynamics“. Astrophysical Journal 958, Nr. 2 (16.11.2023): 107. http://dx.doi.org/10.3847/1538-4357/ad003d.

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Abstract In 2011 Blanchet and Marsat suggested a fully relativistic version of Milgrom's modified Newtonian dynamics in which the dynamical degrees of freedom consist of the spacetime metric and a foliation of spacetime, the khronon field. This theory is simpler than the alternative relativistic formulations. We show that the theory has a consistent nonrelativistic or slow-motion limit. Blanchet and Marsat showed that in the slow motion limit, the theory reproduces stationary solutions of modified Newtonian dynamics. We show that these solutions are stable to khronon perturbations in the low acceleration regime, for the cases of spherical, cylindrical, and planar symmetry. For nonstationary systems in the low acceleration regime, we show that the khronon field generally gives an order unity correction to the modified Newtonian dynamics. In particular, there will be an order unity correction to the MOND version of Kepler's third law, potentially relevant to ongoing efforts to test MOND using GAIA observations of wide binaries.

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Capozziello, Salvatore, und Francesco Bajardi. „Gravitational waves in modified gravity“. International Journal of Modern Physics D 28, Nr. 05 (April 2019): 1942002. http://dx.doi.org/10.1142/s0218271819420021.

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Gravitational waves (GWs) in Modified Gravity are discussed and compared with General Relativity in view of possible detection of new modes. After a summary of some classes of modified theories, we recall GWs properties in General Relativity as the basic standard by which to compare any modified theory. Then, we discuss GWs in Extended Theories like [Formula: see text] gravity, scalar–tensor gravity, Gauss–Bonnet gravity and other gauge theories, as well as Teleparallel Equivalent General Relativity (TEGR), taking into account also torsion instead of curvature, to describe the gravitational field. As a general remark, all these theories lead to new polarizations in addition to the two standard modes of General Relativity. It is possible to show that, in 4 dimensions, the polarizations are at most 6. Theoretical and experimental implications of new modes are briefly discussed.

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Roshan, Mahmood, Indranil Banik, Neda Ghafourian, Ingo Thies, Benoit Famaey, Elena Asencio und Pavel Kroupa. „Barred spiral galaxies in modified gravity theories“. Monthly Notices of the Royal Astronomical Society 503, Nr. 2 (08.03.2021): 2833–60. http://dx.doi.org/10.1093/mnras/stab651.

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ABSTRACT When bars form within galaxy formation simulations in the standard cosmological context, dynamical friction with dark matter (DM) causes them to rotate rather slowly. However, almost all observed galactic bars are fast in terms of the ratio between corotation radius and bar length. Here, we explicitly display an 8σ tension between the observed distribution of this ratio and that in the EAGLE simulation at redshift 0. We also compare the evolution of Newtonian galactic discs embedded in DM haloes to their evolution in three extended gravity theories: Milgromian Dynamics (MOND), a model of non-local gravity, and a scalar–tensor–vector gravity theory (MOG). Although our models start with the same initial baryonic distribution and rotation curve, the long-term evolution is different. The bar instability happens more violently in MOND compared to the other models. There are some common features between the extended gravity models, in particular the negligible role played by dynamical friction − which plays a key role in the DM model. Partly for this reason, all extended gravity models predict weaker bars and faster bar pattern speeds compared to the DM case. Although the absence of strong bars in our idealized, isolated extended gravity simulations is in tension with observations, they reproduce the strong observational preference for ‘fast’ bar pattern speeds, which we could not do with DM. We confirm previous findings that apparently ‘ultrafast’ bars can be due to bar-spiral arm alignment leading to an overestimated bar length, especially in extended gravity scenarios where the bar is already fast.

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Munshi, Dipak. „The integrated bispectrum in modified gravity theories“. Journal of Cosmology and Astroparticle Physics 2017, Nr. 01 (24.01.2017): 049. http://dx.doi.org/10.1088/1475-7516/2017/01/049.

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14

Lin, Chunshan, und Shinji Mukohyama. „A class of minimally modified gravity theories“. Journal of Cosmology and Astroparticle Physics 2017, Nr. 10 (23.10.2017): 033. http://dx.doi.org/10.1088/1475-7516/2017/10/033.

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15

Tsujikawa, Shinji, Antonio De Felice und Shinji Mukohyama. „Cosmological Perturbations in General Modified Gravity Theories“. Progress of Theoretical Physics Supplement 190 (2011): 188–96. http://dx.doi.org/10.1143/ptps.190.188.

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Murayama, Hitoshi, und Elena Perazzi. „New theories with quantum modified moduli space“. Journal of High Energy Physics 2002, Nr. 05 (31.05.2002): 055. http://dx.doi.org/10.1088/1126-6708/2002/05/055.

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17

Geng, C. Q. „Gravitational Waves in Viable Modified Gravity Theories“. Journal of Physics: Conference Series 384 (13.09.2012): 012030. http://dx.doi.org/10.1088/1742-6596/384/1/012030.

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KILIÇARSLAN, Ercan. „On memory effect in modified gravity theories“. TURKISH JOURNAL OF PHYSICS 43, Nr. 1 (22.02.2019): 126–34. http://dx.doi.org/10.3906/fiz-1811-2.

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19

Saha, Dalia, Manas Chakrabortty und Abhik Kumar Sanyal. „Reconstructing Modified and Alternative Theories of Gravity“. Universe 10, Nr. 1 (17.01.2024): 44. http://dx.doi.org/10.3390/universe10010044.

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A viable radiation-dominated era in the early universe is best described by the standard (FLRW) model of cosmology. In this short review, we demonstrate reconstruction of the forms of F(R) in the modified theory of gravity and the metric compatible F(T) together with the symmetric F(Q) in alternative teleparallel theories of gravity, from different perspectives, primarily rendering emphasis on a viable FLRW radiation era. Inflation has also been studied for a particular choice of the scalar potential. The inflationary parameters are found to agree appreciably with the recently released observational data.

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Aviles, Alejandro, Jorge L. Cervantes-Cota und David F. Mota. „Screenings in modified gravity: a perturbative approach“. Astronomy & Astrophysics 622 (30.01.2019): A62. http://dx.doi.org/10.1051/0004-6361/201834383.

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We present a formalism to study screening mechanisms in modified theories of gravity through perturbative methods in different cosmological scenarios. We consider Einstein-frame posed theories that are recast as Jordan-frame theories, where a known formalism is employed, although the resulting nonlinearities of the Klein–Gordon equation acquire an explicit coupling between matter and the scalar field, which is absent in Jordan-frame theories. The obtained growth functions are then separated into screening and non-screened contributions to facilitate their analysis. This allows us to compare several theoretical models and to recognize patterns that can be used to distinguish models and their screening mechanisms. In particular, we find anti-screening features in the symmetron model. In contrast, chameleon-type theories in both the Jordan and Einstein frames always present a screening behaviour. Up to third order in perturbation, we find no anti-screening behaviour in theories with a Vainshtein mechanism, such as the Dvali Gabadadze Porrati braneworld model and the cubic Galileon.

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21

Gannouji, Radouane. „A primer on modified gravity“. International Journal of Modern Physics D 28, Nr. 05 (April 2019): 1942004. http://dx.doi.org/10.1142/s0218271819420045.

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In this first chapter of the Special Issue on Modified Theories of Gravity and Constraints Imposed by Recent GW Observations, we review observational constraints on gravity and the possibility to construct an alternative model to general relativity. For that, we motivate the study of theories beyond Einstein’s gravity, some of their phenomenology and the various ingredients to build a consistent model.

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Aksom, Herman, Oksana Zhylinska und Tetiana Gaidai. „Can institutional theory be refuted, replaced or modified?“ International Journal of Organizational Analysis 28, Nr. 1 (13.01.2020): 135–59. http://dx.doi.org/10.1108/ijoa-02-2019-1666.

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Purpose This paper aims to demonstrating that the former new institutional theory of isomorphism and decoupling cannot be extended, modified or refuted as it is a closed theory. By analyzing the structure of this former version of institutional theory and its numerous modern competitors (institutional entrepreneurship, institutional work and institutional logics theories) it is argued that these alternative theories demonstrate even less explanatory and predictive power and do not refute or extend their predecessor. The rise of new organizational theories can have no other effect on classic institutional theory than to limit the domain of its applicability. In turn, there are a number of principles and conditions that future theories should meet to be accepted as progressive advancements. Design/methodology/approach The paper provides a review of relevant organizational and philosophical literature on theory construction and scientific progress in organizational research and offers a set of principles and demands for those new theories that seek to challenge new institutionalism. Findings The authors show that the former institutional theory satisfies two main criteria that any scientific theory should conform with following it is useful and falsifiable in term of giving explanations and predictions while, at the same time, clearly specifying what can be observed and what cannot; what can happen and what is not likely to occur. Modern institutional theories cannot demonstrate this quality and they do not satisfy these criteria. Moreover, institutional isomorphism theory is a closed theory, which means it cannot be intervened with changes and modifications and all future theories should develop their theoretical propositions for other domains of applications while they should account for all empirical phenomena that institutional theory successfully explains. Originality/value Adopting instrumental view on organizational theories allowed reconstructing the logic and trajectory of organizational research evolution and defends its rationality and progressive nature. It is also outlined how existing dominant theory should be treated and how new theories should challenge its limitations and blind spots and which philosophical and methodological criteria should be met.

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Fring, Andreas, Takano Taira und Bethan Turner. „Higher Time-Derivative Theories from Space–Time Interchanged Integrable Field Theories“. Universe 10, Nr. 5 (28.04.2024): 198. http://dx.doi.org/10.3390/universe10050198.

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We compare a relativistic and a nonrelativistic version of Ostrogradsky’s method for higher-time derivative theories extended to scalar field theories and consider as an alternative a multi-field variant. We apply the schemes to space–time rotated modified Korteweg–de Vries systems and, exploiting their integrability, to Hamiltonian systems built from space–time rotated inverse Legendre transformed higher-order charges of these systems. We derive the equal-time Poisson bracket structures of these theories, establish the integrability of the latter theories by means of the Painlevé test and construct exact analytical period benign solutions in terms of Jacobi elliptic functions to the classical equations of motion. The classical energies of these partially complex solutions are real when they respect a certain modified CPT-symmetry and complex when this symmetry is broken. The higher-order Cauchy and initial-boundary value problem are addressed analytically and numerically. Finally, we provide the explicit quantization of the simplest mKdV system, exhibiting the usual conundrum of having the choice between having to deal with either a theory that includes non-normalizable states or spectra that are unbounded from below. In our non-Hermitian system, the choice is dictated by the correct sign in the decay width.

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Nozari, Kourosh, und Faeze Kiani. „Matter Instability in Theories with Modified Induced Gravity“. Advances in High Energy Physics 2012 (2012): 1–12. http://dx.doi.org/10.1155/2012/679156.

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Matter stability is a necessary condition to have a cosmologically viable model. Modified gravity in the spirit off(R)theories suffers from matter instability in some subdomains of the model parameter space. It has been shown recently that the late-time cosmic speedup can be explained through anf(R)-modified induced gravity program. In this paper, we study the issue of matter instability in a braneworld setup with modified induced gravity.

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Nashed, Gamal G. L. „Schwarzschild-dS Solution in Modified Teleparallel Gravity Theories“. Journal of the Physical Society of Japan 83, Nr. 4 (15.04.2014): 044003. http://dx.doi.org/10.7566/jpsj.83.044003.

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Bisabr, Yousef. „Cosmological Exact Solutions in Some Modified Gravitational Theories“. Gravitation and Cosmology 24, Nr. 2 (April 2018): 201–7. http://dx.doi.org/10.1134/s0202289318020032.

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Outhwaite, Christopher W., Miguel Molero und Lutful B. Bhuiyan. „Symmetrical Poisson–Boltzmann and modified Poisson–Boltzmann theories“. J. Chem. Soc., Faraday Trans. 87, Nr. 19 (1991): 3227–30. http://dx.doi.org/10.1039/ft9918703227.

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Nacir, D. López, F. D. Mazzitelli und C. Simeone. „Adiabatic renormalization in theories with modified dispersion relations“. Journal of Physics A: Mathematical and Theoretical 40, Nr. 25 (06.06.2007): 6895–900. http://dx.doi.org/10.1088/1751-8113/40/25/s36.

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29

Ter-Kazarian, Gagik. „Modified Theories of Gravitation behind the Spacetime Deformation“. Physics Research International 2015 (02.03.2015): 1–19. http://dx.doi.org/10.1155/2015/152846.

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In the framework of proposed theory of spacetime deformation/distortion, we have a way to deform the spacetime through a nontrivial choice of the distortion-complex, displaying different connections, which may reveal different post-Riemannian spacetime structures as corollary. We extend this theory to address, in particular, the gauge model of the most general metric-affine gravity carrying both nontrivial torsion and nonmetricity. This model is constructed in the framework of the first order Lagrangian expressed in terms of the gauge potentials and their first derivatives. The equations of the standard theory, which have no propagating modes for torsion, can be equivalently replaced in modified framework by the modified equations, which in the limit of reducing the affine group leads to the modified Einstein-Cartan theory with dynamical torsion and beyond. In testing the modified framework for various particular cases, we use the Lagrange multipliers for extinguishing nonmetricity and torsion.

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Kausar, Hafiza Rizwana. „Polarization states of gravitational waves in modified theories“. International Journal of Modern Physics D 26, Nr. 05 (April 2017): 1741010. http://dx.doi.org/10.1142/s0218271817410103.

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In this paper, we present polarization states of gravitational waves in modified theories. Particularly, we consider scalar–tensor theory and evaluate the extra polarization modes which appear other than the theory of general relativity. It is found that these metric theories present two extra states of polarization, the breathing massless transverse and massive longitudinal mode in the direction of propagation.

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Zubair, M., und M. Zeeshan. „Evolution of Collisional Matter in Modified Teleparallel Theories“. Journal of Physics: Conference Series 1557 (Mai 2020): 012007. http://dx.doi.org/10.1088/1742-6596/1557/1/012007.

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32

Cristofoli, Andrea. „Post-Minkowskian Hamiltonians in modified theories of gravity“. Physics Letters B 800 (Januar 2020): 135095. http://dx.doi.org/10.1016/j.physletb.2019.135095.

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Munshi, D., G. Pratten, P. Valageas, P. Coles und P. Brax. „Galaxy clustering in 3D and modified gravity theories“. Monthly Notices of the Royal Astronomical Society 456, Nr. 2 (24.12.2015): 1627–44. http://dx.doi.org/10.1093/mnras/stv2724.

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Gronke, M., C. Llinares, D. F. Mota und H. A. Winther. „Halo velocity profiles in screened modified gravity theories“. Monthly Notices of the Royal Astronomical Society 449, Nr. 3 (03.04.2015): 2837–44. http://dx.doi.org/10.1093/mnras/stv496.

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Chaubey, R., B. Tiwari, Anjani Kumar Shukla und Manoj Kumar. „Finsler–Randers Cosmological Models in Modified Gravity Theories“. Proceedings of the National Academy of Sciences, India Section A: Physical Sciences 89, Nr. 4 (26.09.2018): 757–68. http://dx.doi.org/10.1007/s40010-018-0534-2.

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Bernardo, Heliudson, Benjamin Bose, Guilherme Franzmann, Steffen Hagstotz, Yutong He, Aliki Litsa und Florian Niedermann. „Modified Gravity Approaches to the Cosmological Constant Problem“. Universe 9, Nr. 2 (20.01.2023): 63. http://dx.doi.org/10.3390/universe9020063.

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The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein’s general relativity could alleviate the different problems associated with it that result from the interplay of classical gravity and quantum field theory. We introduce a modern and concise language to describe the problems associated with its phenomenology, and inspect no-go theorems and their loopholes to motivate the approaches discussed here. Constrained gravity approaches exploit minimal departures from general relativity; massive gravity introduces mass to the graviton; Horndeski theories lead to the breaking of translational invariance of the vacuum; and models with extra dimensions change the symmetries of the vacuum. We also review screening mechanisms that have to be present in some of these theories if they aim to recover the success of general relativity on small scales as well. Finally, we summarize the statuses of these models in their attempts to solve the different cosmological constant problems while being able to account for current astrophysical and cosmological observations.

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Manolakos, George, Pantelis Manousselis und George Zoupanos. „Gauge Theories: From Kaluza–Klein to noncommutative gravity theories“. Symmetry 11, Nr. 7 (02.07.2019): 856. http://dx.doi.org/10.3390/sym11070856.

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First, the Coset Space Dimensional Reduction scheme and the best particle physics model so far resulting from it are reviewed. Then, a higher-dimensional theory in which the extra dimensions are fuzzy coset spaces is described and a dimensional reduction to four-dimensional theory is performed. Afterwards, another scheme including fuzzy extra dimensions is presented, but this time the starting theory is four-dimensional while the fuzzy extra dimensions are generated dynamically. The resulting theory and its particle content is discussed. Besides the particle physics models discussed above, gravity theories as gauge theories are reviewed and then, the whole methodology is modified in the case that the background spacetimes are noncommutative. For this reason, specific covariant fuzzy spaces are introduced and, eventually, the program is written for both the 3-d and 4-d cases.

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Petersen, Jonas, und Federico Lelli. „A first attempt to differentiate between modified gravity and modified inertia with galaxy rotation curves“. Astronomy & Astrophysics 636 (April 2020): A56. http://dx.doi.org/10.1051/0004-6361/201936964.

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The phenomenology of modified Newtonian dynamics (MOND) on galaxy scales may point to more fundamental theories of either modified gravity (MG) or modified inertia (MI). In this paper, we test the applicability of the global deep-MOND parameter Q which is predicted to vary at the 10% level between MG and MI theories. Using mock-observed analytical models of disk galaxies, we investigate several observational uncertainties, establish a set of quality requirements for actual galaxies, and derive systematic corrections in the determination of Q. Implementing our quality requirements to the SPARC database yields 15 galaxies, which are close enough to the deep-MOND regime as well as having rotation curves that are sufficiently extended and sampled. For these galaxies, the average and median values of Q seem to favor MG theories, albeit both MG and MI predictions are in agreement with the data within 1.5σ. Improved precision in the determination of Q can be obtained by measuring extended and finely-sampled rotation curves for a significant sample of extremely low-surface-brightness galaxies.

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Ho, Alex, Max Gronke, Bridget Falck und David F. Mota. „Probing modified gravity in cosmic filaments“. Astronomy & Astrophysics 619 (November 2018): A122. http://dx.doi.org/10.1051/0004-6361/201833899.

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Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing accuracy. In this work, we study the imprints of a particular class of models – “screened” modified gravity theories – on cosmic filaments. We have utilized the N-body code ISIS/RAMSES to simulate the symmetron model and the Hu–Sawicky f(R) model, and we post-process the output with DisPerSE to identify the filaments of the cosmic web. We investigated how the global properties of the filaments – such as their lengths, masses, and thicknesses – as well as their radial density and speed profiles change under different gravity theories. We find that filaments are, on average, shorter and denser in modified gravity models compared to in ΛCDM. We also find that the speed profiles of the filaments are enhanced, consistent with theoretical expectations. Overall, our results suggest that cosmic filaments can be an effective complementary probe of screened modified gravity theories on Mpc scales.

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Stavrinos, Panayiotis, Olivia Vacaru und Sergiu I. Vacaru. „Modified Einstein and Finsler like theories on tangent Lorentz bundles“. International Journal of Modern Physics D 23, Nr. 11 (Oktober 2014): 1450094. http://dx.doi.org/10.1142/s0218271814500941.

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In this paper, we study modifications of general relativity, GR, with nonlinear dispersion relations which can be geometrized on tangent Lorentz bundles. Such modified gravity theories, MGTs, can be modeled by gravitational Lagrange density functionals f(R, T, F) with generalized/modified scalar curvature R, trace of matter field tensors T and modified Finsler like generating function F. In particular, there are defined extensions of GR with extra dimensional "velocity/momentum" coordinates. For four-dimensional models, we prove that it is possible to decouple and integrate in very general forms the gravitational fields for f(R, T, F)-modified gravity using nonholonomic 2 + 2 splitting and nonholonomic Finsler like variables F. We study the modified motion and Newtonian limits of massive test particles on nonlinear geodesics approximated with effective extra forces orthogonal to the four-velocity. We compute the constraints on the magnitude of extra-accelerations and analyze perihelion effects and possible cosmological implications of such theories. We also derive the extended Raychaudhuri equation in the framework of a tangent Lorentz bundle. Finally, we speculate on effective modeling of modified theories by generic off-diagonal configurations in Einstein and/or MGTs and Finsler gravity. We provide some examples for modified stationary (black) ellipsoid configurations and locally anisotropic solitonic backgrounds.

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Bhuiyan, L. B. „Structure and thermodynamics in the linear modified Poisson-Boltzmann theories in restricted primitive model electrolytes“. Condensed Matter Physics 24, Nr. 2 (2021): 23801. http://dx.doi.org/10.5488/cmp.24.23801.

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Structure and thermodynamics in restricted primitive model electrolytes are examined using three recently developed versions of a linear form of the modified Poisson-Boltzmann equation. Analytical expressions for the osmotic coefficient and the electrical part of the mean activity coefficient are obtained and the results for the osmotic and the mean activity coefficients are compared with that from the more established mean spherical approximation, symmetric Poisson-Boltzmann, modified Poisson-Boltzmann theories, and available Monte Carlo simulation results. The linear theories predict the thermodynamics to a remarkable degree of accuracy relative to the simulations and are consistent with the mean spherical approximation and modified Poisson-Boltzmann results. The predicted structure in the form of the radial distribution functions and the mean electrostatic potential also compare well with the corresponding results from the formal theories. The excess internal energy and the electrical part of the mean activity coefficient are shown to be identical analytically for the mean spherical approximation and the linear modified Poisson-Boltzmann theories.

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Stavrinos, Panayiotis, und Emmanuel Saridakis. „Editorial of Modified Theories of Gravity and Cosmological Applications“. Universe 8, Nr. 8 (09.08.2022): 415. http://dx.doi.org/10.3390/universe8080415.

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General Relativity is a theory of gravity that describes some of the effects of gravity with high accuracy, such as solar system tests, gravitational lensing, gravitational waves, black holes, deflection angle, etc., in a definite framework of an homogeneous and isotropic space–time[...]

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Kuhfittig, Peter K. F. „A note on wormholes in slightly modified gravitational theories“. Advanced Studies in Theoretical Physics 7 (2013): 1087–93. http://dx.doi.org/10.12988/astp.2013.3998.

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SHEIKH-JABBARI, M. M. „ON IMPLICATIONS OF EQUIVALENCE PRINCIPLE FOR MODIFIED GRAVITY THEORIES“. International Journal of Modern Physics D 20, Nr. 14 (31.12.2011): 2839–45. http://dx.doi.org/10.1142/s0218271811020706.

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One of the manifestations of Einstein Equivalence Principle (EEP) is that a freely falling particle in a gravitational field is following a geodesic. In Einstein's general relativity (GR) this is built in the formulation by assuming the connection to be the Levi-Civita connection. The latter may, however, be demanded to be implied by the dynamics of a generic modified gravity theory, within the Palatini formulation. We show that for extensions of the Einstein GR which are described by a Lagrangian [Formula: see text], where gμν is the metric and Rμαβν is the Riemann curvature tensor, this manifestation of EEP is only fulfilled for a special class of Lagrangians, the Lovelock gravity theories. Our analysis also implies that within the above mentioned set of modified gravity theories only for Lovelock gravity theories metric and Palatini formulations are equivalent.

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EXIRIFARD, QASEM. „LUNAR SYSTEM CONSTRAINTS ON THE MODIFIED THEORIES OF GRAVITY“. International Journal of Modern Physics D 22, Nr. 09 (26.06.2013): 1350064. http://dx.doi.org/10.1142/s0218271813500648.

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The Modified Newtonian Dynamics (MOND) paradigm to the missing mass problem requires introducing a functional that is to be identified through observations and experiments. We consider the aquadratic Lagrangian theory as a realization of the MOND. We show that the accurate value of the Earth GM measured by the lunar laser ranging measurements and that by various artificial Earth satellites, including the accurate tracking of the LAGEOS satellites, constrain this functional such that some of the chosen/proposed functional are refuted.

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Pittordis, Charalambos, und Will Sutherland. „Testing modified-gravity theories via wide binaries and GAIA“. Monthly Notices of the Royal Astronomical Society 480, Nr. 2 (14.06.2018): 1778–95. http://dx.doi.org/10.1093/mnras/sty1578.

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Ziegler, Albert, und Heidrun Stoeger. „Research on a modified framework of implicit personality theories“. Learning and Individual Differences 20, Nr. 4 (August 2010): 318–26. http://dx.doi.org/10.1016/j.lindif.2010.01.007.

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Hernández-Aguayo, César, Jiamin Hou, Baojiu Li, Carlton M. Baugh und Ariel G. Sánchez. „Large-scale redshift space distortions in modified gravity theories“. Monthly Notices of the Royal Astronomical Society 485, Nr. 2 (20.02.2019): 2194–213. http://dx.doi.org/10.1093/mnras/stz516.

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Grinstein, Benjamín, und Detlef R. Nolte. „Systematic study of theories with quantum modified moduli. I“. Physical Review D 57, Nr. 10 (15.05.1998): 6471–82. http://dx.doi.org/10.1103/physrevd.57.6471.

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Siddiq, Muhammad Kamran, und Muhammad Ashraf. „Bioconvection of micropolar nanofluid with modified Cattaneo–Christov theories“. Advances in Mechanical Engineering 12, Nr. 5 (Mai 2020): 168781402092521. http://dx.doi.org/10.1177/1687814020925217.

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An incompressible, electrically conducting, bioconvective micropolar fluid flow between two stretchable disks is inspected. Modification versions of Fourier and Fick’s law are accounted through Cattaneo–Christov heat–mass theories. The nanofluid Buongiorno model is also utilized in constitutive equations. The influence of gyrotactic microorganism is also accounted through bioconvection. Similarity variables transform the fluid model into system of ordinary differential equations. The resultant model is then solved through bvp4c method. Results in pictorial and tabular ways are accomplished. It is found that stretching Reynolds number and magnetic parameter slows down the radial velocity at center of the plane. Motile microorganism field is reduced by Peclet number. Micropolar parameters can be useful in the enhancement of couple stresses and in reduction of shear stresses. A comparison is also elaborated with published work under limiting scenario for the validation of numerical scheme accuracy.

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