Dissipative effects in the effective field theory of inflation

DIANA LOPEZ NACIR; RAFAEL A. PORTO; LEONARDO SENATORE; MATIAS ZALDARRIAGA

La cumbre, Córdoba

Conferencia; Conferencia de Relatividad y Gravitación (Grav11); 2011

FaMAF - Universidad Nacional de Córdoba

We generalize the effective field theory (EFT) of single field inflation to include dissipative effects. Working in the unitary gauge we couple new degrees of freedom in the effective action that are constrained solely by invariance under spatial diffeomorphisms. The addition of dissipation modifies the dynamics of the perturbations (`pions´), in particular the appearance of `friction´ and noise terms. Assuming certain locality properties for the Green´s functions of these new degrees of freedom, we show that there is a regime (large friction) in which the \zeta-correlators (\zeta=-H\pi) are dominated by the noise and the power spectrum can be significantly enhanced. The reason is twofold. Firstly, the energy scale of the fluctuations (for the canonically normalized pions, i.e. \pi_c =N_c^(1/2)\pi) is not related to the quantum vacuum and thus can be much bigger than Hubble, but also because the scale $N_c$ can be smaller than the case without dissipation. Among other examples we discuss a variation of the `trapped inflation´ scenario with local response functions and perform the matching with our EFT. As in the EFT for single field inflation, the non-linear realization of time diffeomorphisms imposes restrictions among different observables. We compute the three point function \langle \zeta\zeta\zeta\rangle for a wide class of models and discuss under which circumstances a large friction term leads to an increased level of non-gaussianities. In particular, if we assume that the only source of symmetry breaking is due to the existence of a preferred (scalar degree of freedom) clock that drives inflation, then strong dissipation \gamma\gg H together with the required (non-linear) realization of the symmetries, implies f_{NL}\sim\gamma/(c_s^2H) \gg 1. A detection of such signature would teach us a great deal about the early universe, and also extend the parameter space of inflationary models.