Cosmology in the presence of diffeomorphism-violating, nondynamical background fields

Abstract

We consider diffeomorphism violation, which is parameterized by nondynamical background fields of the gravitational Standard-Model Extension (SME), and study its effects on the time evolution of the Universe. Our goal is to identify background field configurations that imply stages of accelerated expansion without exotic forms of matter and radiation present. Although our approach gives rise to a set of restrictive conditions, configurations are encountered that exhibit this property or show other interesting behaviors. The findings of our article, which is among the first to apply the SME to a cosmological setting, provide an initial understanding of how to technically incorporate background fields into the cosmological evolution equations and what their phenomenological impact may be.

Hubble tension as a guide for refining the early Universe: Cosmologies with explicit local Lorentz and diffeomorphism violation

“…In this section, we shall briefly review cosmological solutions based on the SME, which have recently been derived in Refs. [122,125]. Actually, these solutions, which involve nondynamical SME coefficients denoted as u, s µν , and s µν in the literature, address the role of local Lorentz and diffeomorphism symmetry violation in cosmological time evolution.…”

“…In parallel with the phenomenological articles, purely theoretical work has been done such as in Refs. [116][117][118][119][120][121][122][123][124][125][126][127] improving our understanding of symmetry violation in gravity. It is also worthwhile to mention the review paper [128] which, within the framework of the gravitational SME, presents a compilation of well-known tests of Lorentz symmetry violation.…”

“…Cosmological evolution based on different sectors of the gravitational SME has been on the focus in several very recent articles [111,122,124,125], which has ignited the emergence of a brand-new research direction. In the present work, this promising area is to be applied to the explanation of certain discrepancies in experimental data that cannot be accounted for in the context of ΛCDM.…”

“…In this regard, we take two cosmological scenarios [122,125] into account, which have recently been inspired by the gravitational SME. Given that results inferred from CMB data strongly depend on early-Universe physics, our objective is to investigate whether or not these two modified cosmologies related to the high-energy phase of the Universe are capable of explaining the HT.…”

Tree-level unitarity, causality and higher-order Lorentz and CPT violation

“…Radiative corrections have also been extensively studied within the SME [25]. Recently a sector of modified gravity has been cast in canonical form [26], and Lorentz-violating cosmology has been proposed [27].…”