1,236 research outputs found

    Primordial Neutrinos: Hot in SM-GR-Λ\Lambda-CDM, Cold in SM-LGT

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    We replace general relativity (GR) and the cosmological constant (Λ\Lambda) in the standard cosmology (SM-GR-Λ\Lambda-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 (i) the expansion of the universe at early times is not as sensitive to the amount of radiation as in the SM-GR-Λ\Lambda-CDM and (ii) 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 1eV are the cold dark matter, the lower bound on the dimensionless coupling constant of LGT is derived to be 10710^{-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\Lambda-CDM.Comment: 7 pages, 1 figur

    On the Stability of Fermionic Non-Isothermal Dark Matter Halos

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    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.Comment: 15 pages, 14 figures, computer software to solve the most general stability equation. Comments are welcom
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