Constraining Modified Einstein-Gauss-Bonnet Inflation with GW170817
F Khairunnisa (a*), G. Hikmawan (a), F P Zen (a,b)

(a) Theoretical Physics Laboratory, Department of Physics, Institut Teknologi Bandung, Jl. Ganesha 10 Bandung,Indonesia
*fkhairunnisa96[at]students.itb.ac.id
(b) Indonesia Center for Theoretical and Mathematical Physics (ICTMP), Institut Teknologi Bandung, Jl. Ganesha 10 Bandung, 40132, Indonesia

Abstract

The GW170817 event manifests that gravitational wave velocity is close to the speed of light. As a result, several theories of gravity are no longer applicable, including Einstein-Gauss-Bonnet (EGB) inflation. However, a constraint equation could be applied so that the theory could produce a viable result. In this study, the EGB inflation is being extended by adding a non-minimal coupling (NMC) and a non-minimal derivative coupling (NMDC). Free parameters values were evaluated to obtained viability with observational indices. We use power law and exponential Gauss-Bonnet coupling functions. Each model provides observational values of \(n_s\) and \(r\) that are compatible with the observations and has its characteristic. It specifies the free parameter that controls the alteration of \(n_s\) and \(r\) values. The power-law model is controlled by the power \(m\) of the Gauss-Bonnet coupling function and the potential integration constant, \(V_2\). While the exponential model is controlled by the potential integration constant \(c\) and the power \(m\) of the exponential function. Some approximations do not hold true so that the models need to be rectified. Apparently, the rectified power-law model is violating null energy condition (NEC), so we also provide the non-violating NEC power-law model.

Keywords: Einstein-Gauss-Bonnet- Inflation- Cosmology- Gravitational Wave- Effective Field Theory

Topic: Theoretical High Energy Physics