Cosmological constraints on dissipative models of inflation

Abstract

We study dissipative inflation in the regime where the dissipative term takes a specific form,Γ = Γ(ϕ), analyzing two models in the weak and strong dissipative regimes with a supersymmetrybreaking potential. This system introduces three new parameters: two for the potential andone for the dissipative term. After developing intuition about the predictionsfrom these models through analytic approximations, we compute the predictedcosmological observables through full numerical evolution of the equations of motion,relating the mass scale and scale of dissipation to the characteristic amplitude andshape of the primordial power spectrum. We then use Markov chain Monte Carlotechniques to constrain a subset of the models with cosmological data from the cosmicmicrowave background (Wilkinson Microwave Anisotropy Probe three-year data)and large scale structure (Sloan Digital Sky Survey luminous red galaxy powerspectrum). We find that the primordial dissipative parameters are uncorrelatedwith the ‘late-time’ cosmological parameters which describe the contents andexpansion rate of the universe; the latter show no significant shift from the standardΛCDM (cold dark matter) concordance cosmology and possess close to Gaussian posteriorprobability distributions. In contrast, the posterior distributions of the dissipativeparameters are highly non-Gaussian and their allowed ranges agree well with theexpectations obtained using analytic approximations. In the weak regime, onlythe mass scale is tightly constrained; conversely, in the strong regime, only thedissipative coefficient is tightly constrained. A lower limit is seen on the inflationscale: a sub-Planckian inflaton is disfavored by the data. In both weak and strongregimes, we reconstruct the limits on the primordial power spectrum and show thatthese models prefer a red spectrum, with no significant running of the index.Despite having one extra degree of freedom in the fit compared to the standardΛCDM model, the data does not display a preference for any of the dissipative models; thegoodness of fit is comparable to that of the latter. We calculate the reheat temperature andshow that the gravitino problem can be overcome with large dissipation, which in turnleads to large levels of non-Gaussianity: if dissipative inflation is to evade the gravitinoproblem, the predicted level of non-Gaussianity might be seen by the Plancksatellite.