Perturbative reheating after multiple-field inflation: The impact on primordial observables

Abstract

We study the impact of perturbative reheating on primordial observables in models of multiplefield inflation. By performing a sudden decay calculation, we derive analytic expressions for the local-type non-linearity parameter f local NL , the scalar spectral index n ζ , and the tensor-to-scalar ratio rT as functions of the decay rates of the inflationary fields. We compare our analytic results to a fully numerical classical field theory simulation, finding excellent agreement. We find that the sensitivity of fNL, n ζ , and rT to the reheating phase depends heavily on the underlying inflationary model. We quantify this sensitivity, and discuss conditions that must be satisfied if observable predictions are to be insensitive to the dynamics of reheating. We demonstrate that upon completion of reheating, all observable quantities take values within finite ranges, the limits of which are determined completely by the conditions during inflation. Furthermore, fluctuations in both fields play an important role in determining the full dependence of the observables on the dynamics of reheating. By applying our formalism to two concrete examples, we demonstrate that variations in fNL, n ζ , and rT caused by changes in reheating dynamics are well within the sensitivity of Planck, and as such the impact of reheating must be accounted for when making predictions for models of multiple-field inflation. Our final expressions are very general, encompassing a wide range of two-field inflationary models, including the standard curvaton scenario. We show that the curvaton scenario is a limiting case of two-field inflation, and recover the standard curvaton results in the appropriate limit. Our results allow a much more unified approach to studying two-field inflation including the effects of perturbative reheating. As such, entire classes of models can be studied together, allowing a more systematic approach to gaining insight into the physics of the early universe through observation.

Comprehensive analysis of the simplest curvaton model

“…This is in agreement with the predictions of Nflation [35][36][37], and hence may be considered as a special, twofield case of that scenario. It is also the same as the predictions of inflation driven by two quadratic fields which decay at the same time [9,33,38]. Finally, note that if one took an equal prior range for ϕ Ã and σ Ã then the inflating curvaton would be much more common than the standard curvaton scenario, since it can occur for a much larger range of initial σ Ã values.…”

“…A particular example of the latter class is the curvaton model [4], and there have been several reports on the status of those models in the light of Planck satellite results [5][6][7][8][9]. In this work we carry out an analysis of the simplest curvaton model [10], aiming at an exhaustive study of parameter space while minimizing the set of usual assumptions.…”

Probing the scale dependence of non-Gaussianity with spectral distortions of the cosmic microwave background

“…Here, the f nl parameter is evaluated roughly at the log-midpoints of the y-and µ-distortion k intervals, which defines the y-and µ-distortion pivot wavenumbers k y 7 Mpc −1 and k µ 740 Mpc −1 , respectively. Although the scale-dependence of f nl is often modeled in the literature as a power law in wavenumber k, this parametrization does not accommodate the possibility, which arises in curvaton and multi-field models [34,[38][39][40], that f nl may change sign with scale. The above parametrization is therefore more general.…”

Testing supersymmetric Higgs inflation with non-Gaussianity

“…See, e.g., Ref. [67] for a recent study on the relation between the primordial observables and the decay process.…”