Finite-time Singularities in Swampland-related Dark Energy Models

Abstract

In this work we shall investigate the singularity structure of the phase space corresponding to an exponential quintessence dark energy model recently related to swampland models. The dynamical system corresponding to the cosmological system is an autonomous polynomial dynamical system, and by using a mathematical theorem we shall investigate whether finite-time singularities can occur in the dynamical system variables. As we demonstrate, the solutions of the dynamical system are non-singular for all cosmic times and this result is general, meaning that the initial conditions corresponding to the regular solutions, belong to a general set of initial conditions and not to a limited set of initial conditions. As we explain, a dynamical system singularity is not directly related to a physical finite-time singularity. Then, by assuming that the Hubble rate with functional form \(H(t)=f_1(t)+f_2(t)(t-t_s)^{\alpha}\), is a solution of the dynamical system, we investigate the implications of the absence of finite-time singularities in the dynamical system variables. As we demonstrate, Big Rip and a Type IV singularities can always occur if \(\alpha<-1\) and \(\alpha>2\) respectively. However, Type II and Type III singularities cannot occur in the cosmological system, if the Hubble rate we quoted is considered a solution of the cosmological system.