We investigate how the production of gravitational waves (GWs) is affected by the GW velocity (cT) during preheating after inflation. For instance, we simulate the production of GWs after λϕ4 chaotic inflation, and find that GW spectrum is enhanced for cT<1, but distorted (suppressed at low frequency, but enhanced at high frequency) for cT>1.
@article{arxiv.2102.03084,
title = {Gravitational Waves from Preheating with Modified Gravitational-wave Propagation},
author = {Ke Wang and Qing-Guo Huang},
journal= {arXiv preprint arXiv:2102.03084},
year = {2021}
}