AN INFLATIONARY MODEL WITHOUT INFLATONS

Abstract

In the inflationary cosmology, the most popular and successful models are those of the slow-roll variety, which satisfy the required conditions to solve the classical problems of the standard cosmology. However, these models require the existence of fundamental scalar fields, such as the inflaton, that have not been observed yet in nature. Besides this 'difficulty", these models require almost flat potentials to generate inflation. In this paper, we build an inflationary model motivated by the difficulties presented by the slow-roll model. In this model, we consider our Universe at large scales as a perfect fluid composed of vacuum or cosmological constant Λ (in which case this is the only dominant component) and radiation. The accelerated expansion of the Universe, for this model, is driven by the transfer of energy from vacuum to radiation (in the case that the vacuum energy is not transferred to radiation, a successful inflationary epoch will not be generated) without the need for fundamental scalar fields such as the inflaton. As the transition happens, the energy density associated with the vacuum will exponentially decay to radiation energy density, modifying the energy content of the Universe and, consequently, the evolution equations that describe this inflationary stage. From the dynamics of the model, exact analytical solutions for the Hubble and expansion parameters are obtained. The amount of inflation is calculated, and the necessary conditions to solve the flatness, horizon, and unwanted relics problem are established. In addition, the temperature at the end of this inflationary period, which is called post-inflationary temperature, is calculated.