Tunneling probability for the birth of universes with radiation, cosmological constant and an ad hoc potential

Abstract: In this work we study the birth of Friedmann-Lema^{\i}tre-Robertson-Walker (FLRW) models with zero ($k=0$) and negative ($k=-1$) curvatures of the spatial sections. The material content of the models is composed of a radiation perfect fluid and a positive cosmological constant. The models also have the presence of an ad hoc potential which origin is believed to be of geometrical nature. In order to describe the birth of these universes, we quantize them using quantum cosmology. Initially, we obtain the Wheeler-DeWitt equations and solve them using the WKB approximation. We notice that the presence of the ad hoc potential produces a barrier for any value of $k$. It means that we may describe the birth of the universe through a tunneling mechanism, for any curvature of the spatial sections, not only for the usual case $k=1$. We, explicitly, compute the tunneling probabilities for the birth of the different models of the universe and compare these tunneling probabilities.