Inflationary gravitational waves in consistent D → 4 Einstein-Gauss-Bonnet gravity

We study the slow-roll single field inflation in the context of the consistent D -> 4 Einstein-Gauss-Bonnet gravity that was recently proposed in [1]. In addition to the standard attractor regime, we find a new attractor regime which we call the Gauss-Bonnet attractor as the dominant contribution comes from the Gauss-Bonnet term. Around this attractor solution, we find power spectra and spectral tilts for the curvature perturbations and gravitational waves (GWs) and also a model-independent consistency relation among observable quantities. The Gauss-Bonnet term provides a nonlinear k(4) term to the GWs dispersion relation which has the same order as the standard linear k(2) term at the time of horizon crossing around the Gauss-Bonnet attractor. The Gauss-Bonnet attractor regime thus provides a new scenario for the primordial GWs which can be tested by observations. Finally, we study non-Gaussianity of GWs in this model and estimate the nonlinear parameters f(NL, sq)(s1s2s3) and f(NL, sq)(s1s2s3) by fitting the computed GWs bispectra with the local-type and equilateral-type templates respectively at the squeezed limit and at the equilateral shape. For helicities (+ + +) and (- - -), f(NL, sq)(s1s2s3) is larger while f(NL, sq)(s1s2s3) is larger for helicities (+ + -) and (- -+).

Automated summary

The study focuses on slow-roll single field inflation in the context of consistent D -> 4 Einstein-Gauss-Bonnet gravity. Apart from the standard attractor regime, a new attractor regime known as the Gauss-Bonnet attractor is identified, providing insights into power spectra, spectral tilts, and consistency relations. The Gauss-Bonnet term introduces a nonlinear contribution to the gravitational waves dispersion relation, offering a new scenario for primordial gravitational waves that can be tested through observations. Furthermore, the analysis delves into the non-Gaussianity of gravitational waves and estimates nonlinear parameters for different helicities.