Exploring Chern-Simons gravity from a metric-affine perspective: black holes, cosmology and gravitational waves
We discuss the latest results in metric-affine Chern-Simons gravity, a recent generalization of the standard metric theory, where projective invariance is recovered by supplementing the Pontryagin density with homothetic curvature terms. We present perturbative and non-perturbative solutions for different physical scenarios, outlining how torsion and non-metricity can lead to peculiar phenomenological signatures. We review, in the first istance, the role of a non-trivialmetric-affine geometry in quasinormal modes emission for Schwarzschild blackholes. Then, we explore Friedmann-Robertson-Walker dynamics and the propagation of gravitational waves on curved cosmological backgrounds. In particular, we show how gravitational torsional waves can interact with metric perturbations, resulting in the appearance of frequency and amplitude birefringence, which, in turn, can trigger Landau damping for tensor modes in the presence of matter.