Speed of sound and scalar spectral index: Reconstructing inflation and reheating in a non-canonical theory

Abstract

In this article we analyze the reconstruction of inflation in the framework of a non-canonical theory. In this sense, we study the viability of reconstructing the background variables assuming a non-lineal kinetic term given by $K(X,\varphi )=X+g(\varphi )X^2$, with $X$ the standard kinetic term associated to the scalar field $\varphi$ and $g(\varphi )$ an arbitrary coupling function. In order to achieve this reconstruction in the context of inflation, we assume the slow-roll approximation together with the parametrization of the scalar spectral index $n_s$ and the speed of sound $c_s$ as a function of the number of $e-$folds $N$. By assuming the simplest parametrizations for $n_s-1=-2/N$ and $c_s\propto N^{-\beta }$ with $\beta$ a constant, we find the reconstruction of the effective potential $V(\varphi )$ and the coupling function $g(\varphi )$ in terms of the scalar field. Besides, we study the reheating epoch by considering a constant equation of state parameter, where we determine the temperature and number of $e-$folds during the reheating epoch in terms of the reconstructed variables and the observational parameters. In this way, the parameter-space related to the reconstructed inflationary model are constrained during the epochs of inflation and reheating by assuming the current astronomical data from Planck and BICEP/Keck results.

20 pages and 5 figures. Accepted by Physics of the Dark Universe