Nonconservative unimodular gravity : a viable cosmological scenario?
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2022
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In this work we review the issue of imposing the
conservation of the energy–momentum tensor as a necessary
condition to recover the equivalence between the unimod-
ular gravity and General Relativity (GR) equipped with a
cosmological constant. This procedure is usually interpreted
as an ad hoc imposition on the unimodular theory’s struc-
ture. Whereas the consequences of avoiding the conserva-
tion of the total energy–momentum tensor has been already
introduced in the literature, it has been not widely explored
so far. We study an expanding universe sourced by a sin-
gle effective perfect fluid such that the null divergence of
its energy–momentum tensor is not imposed. As we shall
show, in this scheme, the unimodular theory has its own
conservation equation obtained from the Bianchi identities.
We explore the evolution of the homogeneous and isotropic
expanding background and show that a viable cosmologi-
cal scenario exists. Also, we consider scalar perturbations
with particular attention given to the gauge issue. We show
that contrary to the traditional unimodular theory where the
synchronous and longitudinal (newtonian) gauge for cosmo-
logical perturbations are not permitted, if the conservation
of the energy–momentum is relaxed the scalar perturbations
in the synchronous condition survive and present a growing
mode behavior. We study therefore a new cosmological sce-
nario in which the dynamics of the universe transits from the
radiative phase directly to a accelerated one but allowing thus
for structure formation.
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FABRIS, J. C. et al. Nonconservative unimodular gravity: a viable cosmological scenario?. The European Physical Journal C, v. 82, artigo 522, 2022. Disponível em: <https://link.springer.com/article/10.1140/epjc/s10052-022-10470-2>. Acesso em: 06 jul. 2023.