2025/04/14 by Arko Bhaumik, Bhaumik, Arko, Bhaswati Mandal +3 · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Cosmology and Gravitation Theories #Pulsars and Gravitational Waves Research
paper · pdf · doi:10.48550/arxiv.2504.10402
In the presence of spacetime torsion, any generic f(R) model of gravity is conformally dual to a scalar-tensor theory augmented with a second rank antisymmetric massless degree of freedom. We investigate the stochastic gravitational wave background (SGWB) that may be sourced directly at the second order by such a torsional field, treated perturbatively during an epoch of canonical, single-field, slow-roll inflation. The resulting second-order induced SGWB, which dominates over the primary inflationary GW background at all scales, peaks only at ultra-low frequencies, and is found to be extremely red-tilted with an effective tensor spectral index α\rm T∼-6 on matter-dominated scales. The signal is potentially within the reach of upcoming indirect GW probes on very large scales k\lesssim10-2 \textrmMpc-1, i.e., next-generation CMB experiments like the LiteBIRD. In the near future, observation of such a markedly red-tilted SGWB on CMB scales could hence provide a novel and unique clue in favour of torsional gravity during the inflationary era.