Inflation in the general Poincar\'e gauge cosmology

Abstract

The general Poincar\'e gauge cosmology given by a nine-parameter gravitational Lagrangian with ghost- and tachyon-free conditions is studied from the perspective of field theory. By introducing new variables for replacing two (pseudo-) scalar torsions, the Poincar\'e gauge cosmological system can be recast into a gravitational system coupled to two-scalar fields with a potential up to quartic-order. We discussed the possibility of this system producing two types of inflation without any extra inflatons. The hybrid inflation with a first-order phase transition can be ruled out, while the slow rollover can be achieved. The numerical analysis shows that the two-scalar fields system evolved in a potential well processes spontaneously four stages: "pre-inflation", slow-roll inflation with large enough e-folds, "pre-reheating" and reheating. We also studied the stableness of this system by setting large values of initial kinetic energies. The results show that even if the system evolves past the highest point of the potential well, the scalar fields can still return to the potential well and cause inflation. The general Poincar\'e gauge cosmology provides us with a self-consistent candidate of inflation.