Dissipative Dynamics of Inflation

Dissipative scalar quantum field theory is examined at zero temperature. Estimates of radiation production are given. Relevance of the results to supercooled and warm inflation are discussed. To appear in Proceeding, PASCOS-01, 2001 The basic picture of inflationary dynamics centers around a scalar field often called the inflaton. During the inflationary period, the potential energy of this field is pictured to dominate the energy density of the universe, thereby driving inflation-like accelerated expansion of the scale factor. The inflaton field also is required to interact with other fields, so as to allow transfer of energy from potential energy into radiation. Eventually the radiation energy density must dominate so that inflation can terminate into a standard hot big-bang radiation dominated regime. Although ultimately for inflationary dynamics to fit into a realistic particle physics scheme, the final models may be more elaborate, it is believed that these simple inflaton models contain all the essential features that must be found in any more realistic model. The most nontrivial aspect of the inflaton models is understanding the energy transfer dynamics from potential energy to radiation. A commonly followed picture is that dissipative effects of the inflaton field can be ignored throughout the inflation period, thus leading to a supercooled inflationary regime. However, from a thermodynamic perspective, this picture appears very restrictive. The point being, even if the inflaton were to allow a minuscule fraction of the energy to be released, say one part in 10, it still would constitute a significant radiation energy density component in the universe. For example, for inflation with vacuum (i.e. potential) energy at the GUT scale ∼ 10GeV, leaking one part in 10 of this energy into radiation corresponds to a temperature of 10GeV, which is nonnegligible. In fact, the most relevant lower bound that cosmology places on the temperature after inflation comes from the success of hot Big-Bang nucleosynthesis, which thus requires the universe to be within the radiation dominated regime by T > ∼ 1GeV. This limit can be met in the above example by dissipating as little as one part in 10 of the vacuum energy into radiation. Thus, from the perspective of both interacting field theory and basic notions of equipartition,