AbstractAbstract

[en] The stability of isothermal dark matter halos has been widely studied before. In this paper, we investigate the stability of non-isothermal fermionic dark matter halos. We show that in the presence of temperature gradient, the force due to the pressure has both inward and outward components. In some regions of halos, the inward force that provides stability is due to the pressure rather than gravity. Moreover, it is shown that higher temperature gradients lead to halos with lower mass and size. We prove that if the temperature is left as a free positive profile, one can place no phase-space lower bound on the mass of dark matter. For halos that are in the low degeneracy classic domain, we derive an analytic expression of their temperature in terms of their mass density and place an upper bound on the mass of dark matter by requiring that temperature is not negative. We then use the Burkert mass profile for the Milky Way to show that if the central temperature of the halo is a few Kelvins, the mass of dark matter cannot exceed a few keV.

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Available from: http://dx.doi.org/10.1140/epjc/s10052-020-08603-6; AID: 1076

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European Physical Journal. C, Particles and Fields (Online); ISSN 1434-6052; ; CODEN EPCFFB; v. 80(11); p. 1-16

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AbstractAbstract

[en] We replace general relativity (GR) and the cosmological constant (Λ) in the standard cosmology (SM-GR-Λ-CDM) with a Lorentz gauge theory of gravity (LGT) and show that the standard model (SM) neutrinos can be the cold dark matter (CDM) because (1.) the expansion of the universe at early times is not as sensitive to the amount of radiation as in the SM-GR-Λ-CDM and (2.) in LGT there exists a spin-spin long-range force that is very stronger than the Newtonian gravity and interacts with any fermion including neutrinos. Assuming that neutrinos as heavy as 1 eV are the cold dark matter, the lower bound on the dimensionless coupling constant of LGT is derived to be 10

^{-7}which is small enough to be consistent with the upper bound that can be placed by the electroweak precision tests. We also show that the vacuum energy does not gravitate in LGT and a decelerating universe shifts spontaneously to an accelerating one right at the moment that we expect. Therefore, current observations can be explained in our cosmological model (SM-LGT) with lesser assumptions than in the SM-GR-Λ-CDM. (orig.)Primary Subject

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Available from: http://dx.doi.org/10.1140/epjc/s10052-018-6104-6

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Journal Article

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European Physical Journal. C, Particles and Fields (Online); ISSN 1434-6052; ; v. 78(8); p. 1-7

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BOUND STATE, COSMIC NEUTRINOS, COSMOLOGICAL INFLATION, COSMOLOGY, COUPLING CONSTANTS, ELASTIC SCATTERING, GRAVITATION, GRAVITATIONAL INTERACTIONS, GRAVITONS, INFLATIONARY UNIVERSE, INTEGRAL CROSS SECTIONS, INTERACTION RANGE, J-J COUPLING, LORENTZ GROUPS, NONLUMINOUS MATTER, SCATTERING AMPLITUDES, STANDARD MODEL, VACUUM STATES, YANG-MILLS THEORY

AMPLITUDES, COSMIC RADIATION, COSMOLOGICAL MODELS, COUPLING, CROSS SECTIONS, DISTANCE, ELEMENTARY PARTICLES, FERMIONS, FIELD THEORIES, FUNDAMENTAL INTERACTIONS, GRAND UNIFIED THEORY, GRAVITATIONAL RADIATION, INTERACTIONS, INTERMEDIATE COUPLING, IONIZING RADIATIONS, LEPTONS, LIE GROUPS, MASSLESS PARTICLES, MATHEMATICAL MODELS, MATTER, NEUTRINOS, PARTICLE MODELS, POINCARE GROUPS, POSTULATED PARTICLES, QUANTUM FIELD THEORY, RADIATIONS, SCATTERING, SYMMETRY GROUPS, UNIFIED GAUGE MODELS

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Borzou, Ahmad, E-mail: ahmad_borzou@baylor.edu

AbstractAbstract

[en] Following the ideas of effective field theories, we derive classically effective field equations of the recently developed Lorentz gauge theory of gravity. It is shown that Newton’s gravitational constant emerges as an effective coupling parameter if an extremely small length is integrated out of the underlying theory. The linear version of the effective theory is shown to be fully consistent with the Newtonian gravity. We also derive a numerical solution for the interior of a star and show that in the nonlinear regions, the behavior of the effective theory deviates from the predictions of general relativity. (paper)

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Available from http://dx.doi.org/10.1088/0264-9381/33/23/235006; Country of input: International Atomic Energy Agency (IAEA)

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Borzou, Ahmad, E-mail: ahmad_borzou@baylor.edu

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[en] We present a Lorentz gauge theory of gravity in which the metric is not dynamical. Spherically symmetric weak field solutions are studied. We show that this solution contains the Schwarzschild spacetime at least to the first order of perturbation. Next, we present a special case of the theory where the Schwarzschild metric is an exact solution. It is also shown that the de Sitter space is an exact vacuum solution of this special case and as a result the theory is able to explain the expansion of the universe with no need for dark energy. Within this special case, quantization of the theory is also studied, the basic Feynman diagrams are derived and the renormalizability of the theory is studied using the power-counting method. We show that under a certain condition the theory is power-counting renormalizable. (paper)

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Available from http://dx.doi.org/10.1088/0264-9381/33/2/025008; Country of input: International Atomic Energy Agency (IAEA)

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Borzou, Ahmad; Lin, Kai; Wang, Anzhong, E-mail: ahmad_borzou@baylor.edu, E-mail: k_lin@baylor.edu, E-mail: anzhong_wang@baylor.edu

AbstractAbstract

[en] In this paper, we study electromeganetic static spacetimes in the nonrelativisitc general covariant theory of the Hořava-Lifshitz (HL) gravity, proposed recently by Hořava and Melby-Thompson, and present all the electric static solutions, which represent the generalization of the Reissner-Nordström solution found in Einstein's general relativity (GR). The global/local structures of spacetimes in the HL theory in general are different from those given in GR, because the dispersion relations of test particles now contain high-order momentum terms, so the speeds of these particles are unbounded in the ultraviolet (UV). As a result, the conception of light-cones defined in GR becomes invalid and test particles do not follow geodesics. To study black holes in the HL theory, we adopt the geometrical optical approximations, and define a horizon as a (two-closed) surface that is free of spacetime singularities and on which massless test particles are infinitely redshifted. With such a definition, we show that some of our solutions give rise to (charged) black holes, although the radii of their horizons in general depend on the energies of the test particles

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Available from http://dx.doi.org/10.1088/1475-7516/2012/02/025; Country of input: International Atomic Energy Agency (IAEA)

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Journal Article

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Journal of Cosmology and Astroparticle Physics; ISSN 1475-7516; ; v. 2012(02); p. 025

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Borzou, Ahmad; Lin, Kai; Wang, Anzhong, E-mail: ahmad_borzou@baylor.edu, E-mail: klin@baylor.edu, E-mail: anzhong_wang@baylor.edu

AbstractAbstract

[en] Detailed balance and projectability conditions are two main assumptions when Horava recently formulated his theory of quantum gravity - the Horava-Lifshitz (HL) theory. While the latter represents an important ingredient, the former often believed needs to be abandoned, in order to obtain an ultraviolet stable scalar field, among other things. In this paper, because of several attractive features of this condition, we revisit it, and show that the scalar field can be stabilized, if the detailed balance condition is allowed to be softly broken. Although this is done explicitly in the non-relativistic general covariant setup of Horava-Melby-Thompson with an arbitrary coupling constant λ, generalized lately by da Silva, it is also true in other versions of the HL theory. With the detailed balance condition softly breaking, the number of independent coupling constants can be still significantly reduced. It is remarkable to note that, unlike other setups, in this da Silva generalization, there exists a master equation for the linear perturbations of the scalar field in the flat Friedmann-Robertson-Walker background

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Available from http://dx.doi.org/10.1088/1475-7516/2011/05/006; Country of input: International Atomic Energy Agency (IAEA)

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Journal of Cosmology and Astroparticle Physics; ISSN 1475-7516; ; v. 2011(05); p. 006

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Borzou, Ahmad; Mirza, Behrouz, E-mail: ahmad_borzou@baylor.edu, E-mail: b.mirza@cc.iut.ac.ir

AbstractAbstract

[en] Lorentz gauge theory of gravity was recently introduced. We study the homogeneous and isotropic universe of this theory. It is shown that some time after the matter in the universe is diluted enough, at $z\sim 0.6$, the decelerating expansion shifts spontaneously to an accelerating one without a dark energy. We discuss that Lorentz gauge theory puts no constraint on the total energy content of the universe at present time and therefore the magnitude of vacuum energy predicted by field theory is not contradictory anymore. It is demonstrated that in this theory the limit on the number of relativistic particles in the universe is much looser than in GR. An inflationary mechanism is discussed as well. We show that the theory, unlike GR, does not require the slow-roll or similar conditions to drive the inflation at the beginning of the universe. (paper)

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Available from http://dx.doi.org/10.1088/1361-6382/aa7647; Country of input: International Atomic Energy Agency (IAEA)

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Borzou, Ahmad; Cleaver, Gerald; Mirza, Behrouz, E-mail: ahmad_borzou@baylor.edu, E-mail: gerald_cleaver@baylor.edu, E-mail: b.mirza@cc.iut.ac.ir

AbstractAbstract

[en] Lorentz gauge theory (LGT) is a feasible candidate for a theory of quantum gravity in which routine field theory calculations can be carried out perturbatively without encountering too many divergences. In LGT, the spin of matter also gravitates; spin-generated gravity is expected to be very much stronger than that generated by mass, and could be explored in current colliders. In this article, the signals of the theory observable in an electron–positron collider are investigated. We specifically study pair annihilation into two gravitons, and LGT corrections to processes like ${e}^{-}+{e}^{+}\to {\mu}^{-}+{\mu}^{+}$ and ${e}^{-}+{e}^{+}\to {e}^{-}+{e}^{+}$. (paper)

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Available from http://dx.doi.org/10.1088/1361-6382/aa8f7c; Country of input: International Atomic Energy Agency (IAEA)

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ANGULAR MOMENTUM, ANTILEPTONS, ANTIMATTER, ANTIPARTICLES, ELEMENTARY PARTICLES, FERMIONS, FIELD THEORIES, GRAVITATIONAL RADIATION, INTERACTIONS, INVARIANCE PRINCIPLES, LEPTONS, MASSLESS PARTICLES, MATTER, PARTICLE INTERACTIONS, PARTICLE PROPERTIES, POSTULATED PARTICLES, QUANTUM FIELD THEORY, RADIATIONS

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