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arXiv · 2608.18649

Broadband Chiral Primordial Gravitational Waves from Constant-roll Inflation in Parity-violating Symmetric Teleparallel Gravity

Xu Zhang·Chang Liu·Chengjie Fu
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Abstract

We investigate primordial gravitational waves (GWs) generated during constant-roll inflation in a parity-violating extension of symmetric teleparallel gravity. The parity-violating interactions leave the background evolution and linear scalar perturbations unchanged, while inducing velocity birefringence in the tensor sector. Consequently, one of the two circular polarization states undergoes tachyonic amplification, producing a strongly blue and nearly fully chiral tensor spectrum from the cosmic microwave background (CMB) to interferometer scales. We identify viable constant-roll parameter regions consistent with current CMB constraints and determine the largest coupling strength compatible with both CMB B-mode measurements and the LIGO-Virgo-KAGRA (LVK) O1--O4a bound on the stochastic GW background. The predicted CMB B-mode spectra may be detectable by LiteBIRD, while the enhanced high-frequency signal could be accessible to the LISA--Taiji network and LVK O5 run. The model also predicts nonvanishing TB and EB correlations. These results highlight the potential of combining CMB and multi-band GW observations to test parity-violating gravity during inflation.

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Xu Zhang, Chang Liu, Chengjie Fu. 2026-08-19. Broadband Chiral Primordial Gravitational Waves from Constant-roll Inflation in Parity-violating Symmetric Teleparallel Gravity. https://arxiv.org/abs/2608.18649

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