Warm inflation and scalar perturbations of the metric (Q5932494)

The paper is devoted to the quantum fluctuations, which played an important role in the inflationary universe. A second-order expansion for the quantum fluctuations of the matter field is considered in the framework of the warm inflation scenario. The friction and Hubble parameters were expanded by means of a semiclassical approach. The fluctuations of the Hubble parameter generates fluctuations of the metric. These metric fluctuations produce an effective term of curvature. The power spectrum for the metric fluctuations can be calculated on the infrared sector. The author develops a formalism where the quantum field of matter \(\varphi \) interacts with other fields of a thermal bath at mean temperature \(\langle T_r\rangle <T_{\text{GUT}}\sim 10^{15}\operatorname {GeV}\). This lower temperature condition implies that the magnetic monopole suppression works effectively. In this model quantum fluctuations of the matter field \(\varphi \) lead to quantum fluctuations of the metric in addition to matter and radiation energy densities. It is considered a general case, where the inflation field has a nonzero mean value and an analysis is developed by using a consistent semiclassical expansion.