http://arxiv.org/abs/1903.06344
We study unimodular gravity in the context of cosmology, particularly some interesting consequences that might be able to describe the background cosmology and the late cosmic acceleration. We focus our attention on the hypothesis of \textit{non conservation of the energy momentum tensor}. This characteristic has an interesting outcome: we can obtain a modified Friedmann equation along with the acceleration equation and also new fluid equations related to a third order derivative of the scale factor, known in cosmography as the jerk parameter. In addition, as a consequence of this theory, there appears that radiation and cosmological constant are intimately related, in agreement with what some authors have called the third coincidence problem. We show that the parameter that connect them is the $z_{ini}$, which has a that coincide with the reionization epoch. As a result, we are able to explain the late acceleration as a natural consequence of the equations, associating the new fluid to radiation and, thus, eliminating the need for another component (i.e. dark energy). Finally, we interpret the results and discuss the pros and cons to study the cosmological constant under the hypothesis of non conservation of the energy momentum tensor in the unimodular gravity scenario.
M. García-Aspeitia, C. Martínez-Robles, A. Hernández-Almada, et. al.
Mon, 18 Mar 19
70/102
Comments: 7 pages, 1 figure
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