A Nearly Massless Graviton in EinsteinGaussBonnet Inflation with Linear Coupling Implies Constantroll for the Scalar Field
Abstract
The striking GW170817 event indicated that the graviton is nearly massless, since the gamma rays emitted from the two neutron stars merging arrived almost simultaneously with the gravitational waves. Thus, the graviton must also be massless during the inflationary and postinflationary era, since there is no obvious reason to believe otherwise. In this letter we shall investigate the theoretical implications of the constraint that the graviton is massless to an EinsteinGaussBonnet theory with linear coupling of the scalar field to the four dimensional GaussBonnet invariant. As we show, the constraint of having gravitational wave speed of the primordial gravitational waves equal to one, severely restricts the dynamics of the scalar field, imposing a direct constantroll evolution on it. Also, as we show, the spectral index of the primordial scalar perturbations for the GW170817compatible EinsteinGaussBonnet theory with linear coupling is different in comparison to the same theory with nonlinear coupling. Thus the phenomenology of the model is expected to be different, and we briefly discuss this issue too. In addition, the constantroll condition is always related to nonGaussianities, thus it is interesting that the imposition of a massless graviton in an EinsteinGaussBonnet theory with linear coupling may lead to nonGaussianities, so we briefly discuss this issue too.
 Publication:

arXiv eprints
 Pub Date:
 July 2020
 arXiv:
 arXiv:2007.11915
 Bibcode:
 2020arXiv200711915O
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Theory
 EPrint:
 EPL Accepted