Diffeomorphism Invariance Breaking in Gravity and Cosmological Evolution
| Autor: | Aydemir, Ufuk, Elbistan, Mahmut |
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| Rok vydání: | 2024 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | Breaking diffeomorphism invariance has been motivated in the literature in several contexts, including emergent General Relativity (GR). For this to be an admissible possibility, GR augmented with minor violations of general covariance must yield only slight deviations from the outcomes of GR. In this paper, the cosmological evolution of the scale factor in gravity with explicitly broken general covariance is investigated in the (modified) Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) spacetime. The model augments the GR Lagrangian with all of the diffeomorphism-breaking (but Lorentz invariant) terms in the leading order, the terms involving two derivatives. The magnitudes of (minor) violations are kept general modulo the conditions for a healthy linearized version of the model. The analytic solutions of the scale factor in the full non-linear theory for the single-component universes are attempted; the radiation and vacuum solutions are found analytically, whereas the matter solution is worked out numerically since an analytic solution does not exist in the required form. It is observed that the solutions smoothly connect to those of GR in the limit of vanishing symmetry-breaking. The more realistic, two-component, and three-component universes are numerically studied, and no sign of unhealthy behavior is observed: minor diffeomorphism violating modifications to GR do not cause instabilities in the evolution of the scale factor. Comment: 31 pages, 12 figures; references added, typos fixed, minor changes made |
| Databáze: | arXiv |
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