Our studies are novel in that the stochastic gravitational wave (GW) signals of torsion during the reheating stage are investigated for the first time. We construct the phenomenological interaction vertex describing the coupling between a single inflaton and four fermions based on the effective theory of torsion within the first-order formalism for gravity and fermions. Subsequently, we compute the resulting GW spectrum arising from torsion-induced five-body decay, assuming a perturbative decay process in which the inflaton decays into two pairs of fermions along with the emission of a single graviton. Our results uncover that the dimensionless amplitude of the GW background from torsion-induced five-body decay is of the same order of magnitude as that generated by the standard three-body perturbative inflaton decay via Yukawa interactions. These findings suggest that future high-frequency GW detectors, such as resonant cavities, may have the potential to detect such signals in the GHz range, offering valuable insights into the twisted geometric structure of the early Universe’s spacetime.

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• Gravitational waves
• Particle astrophysics