TY  - JOUR
AU  - Boudet, S.
AU  - Bombacigno, F.
AU  - Moretti, F.
AU  - Olmo, G. J.
PY  - 2023
DA  - 2023//
TI  - Torsional birefringence in metric-affine Chern-Simons gravity: gravitational waves in late-time cosmology
T2  - J. Cosmol. Astropart. Phys.
JO  - Journal of Cosmology and Astroparticle Physics
SP  - 026
EP  - 28pp
VL  - 01
IS  - 1
PB  - IOP Publishing Ltd
KW  - Gravitational waves in GR and beyond: theory
KW  - modified gravity
KW  - Cosmological perturbation theory in GR and beyond
KW  - Exact solutions
KW  - black holes and black hole thermodynamics in GR and beyond
AB  - In the context of the metric-affine Chern-Simons gravity endowed with projective invariance, we derive analytical solutions for torsion and nonmetricity in the homogeneous and isotropic cosmological case, described by a flat Friedmann-Robertson-Walker metric. We discuss in some details the general properties of the cosmological solutions in the presence of a perfect fluid, such as the dynamical stability and the emergence of big bounce points, and we examine the structure of some specific solutions reproducing de Sitter and power law behaviours for the scale factor. Then, we focus on first-order perturbations in the de Sitter scenario, and we study the propagation of gravitational waves in the adiabatic limit, looking at tensor and scalar polarizations. In particular, we find that metric tensor modes couple to torsion tensor components, leading to the appearance, as in the metric version of Chern-Simons gravity, of birefringence, characterized by different dispersion relations for the left and right circularized polarization states. As a result, the purely tensor part of torsion propagates like a wave, while nonmetricity decouples and behaves like a harmonic oscillator. Finally, we discuss scalar modes, outlining as they decay exponentially in time and do not propagate.
SN  - 1475-7516
UR  - https://arxiv.org/abs/2209.14394
UR  - https://doi.org/10.1088/1475-7516/2023/01/026
DO  - 10.1088/1475-7516/2023/01/026
LA  - English
N1  - WOS:001090397800016
ID  - Boudet_etal2023
ER  -