# Propagating speed of primordial gravitational waves

@article{Giar2020PropagatingSO,
title={Propagating speed of primordial gravitational waves},
author={William Giar{\'e} and Fabrizio Renzi},
journal={Physical Review D},
year={2020},
volume={102}
}
• Published 8 July 2020
• Physics
• Physical Review D
Primordial Gravitational Waves, i.e. a background of metric perturbations sourced by the quantum inflationary fluctuations, if measured, could both provide a substantial evidence for primordial inflation and shed light on physics at extremely high energy scales. In this work we focus on their propagating speed. Using an effective field theory approach we introduce a time-dependent propagating speed $c_{\rm T}(t)$ showing that also small deviations from the General Relativity (GR) prediction $c_… 11 Citations ## Figures and Tables from this paper • Physics • 2020 Primordial null energy condition (NEC) violation would imprint a blue-tilted spectrum on gravitational wave background (GWB). However, its implications on the GWB might be far richer than expected. The NANOGrav pulsar timing array experiment recently reported evidence for a stochastic common-spectrum process affecting pulsar timing residuals in its 12.5-year dataset, which might be interpreted A violation of the null energy condition (NEC) during inflation in a single-field inflation model will naturally enhance the amplitude of the parity violation effect (defined by$\Delta\chi\$) of
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Higher-curvature corrections to the effective gravitational action may leave signatures in the spectrum of primordial tensor perturbations if the inflationary energy scale is sufficiently high. In

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