Big-Bounce in projectively invariant Nieh-Yan models: the Bianchi I case

• DOI: 10.48550/arxiv.2111.03338
• Publication Date: 2023-01-24
• Authors: Bombacigno, Flavio; Boudet, Simon; Olmo, Gonzalo J.; Montani, Giovanni
• Keywords: 0103 physical sciences; FOS: Physical sciences; General Relativity and Quantum Cosmology (gr-qc); 01 natural sciences; General Relativity and Quantum Cosmology

We show that the Nieh-Yan topological invariant breaks projective symmetry and loses its topological character in presence of non vanishing nonmetricity. The notion of the Nieh-Yan topological invariant is then extended to the generic metric-affine case, defining a generalized Nieh-Yan term, which allows to recover topologicity and projective invariance, independently. As a concrete example a class of modified theories of gravity is considered and its dynamical properties are investigated in a cosmological setting. In particular, bouncing cosmological solutions in Bianchi I models are derived. Finite time singularities affecting these solutions are analysed, showing that the geodesic completeness and the regular behavior of scalar perturbations in these space-times are not spoiled.<br/>To appear in the Proceedings of the 16th Marcel Grossmann meeting (5-10 July, 2021)<br/>