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Register a new userEffect of reheating on predictions following multiple-field inflation
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We study the sensitivity of cosmological observables to the reheating phase following inflation driven by many scalar fields. We describe a method which allows semi-analytic treatment of the impact of perturbative reheating on cosmological perturbations using the sudden decay approximation. Focusing on $mathcal{N}$-quadratic inflation, we show how the scalar spectral index and tensor-to-scalar ratio are affected by the rates at which the scalar fields decay into radiation. We find that for certain choices of decay rates, reheating following multiple-field inflation can have a significant impact on the prediction of cosmological observables.
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The observational signatures of multi-field inflation will generally evolve as the Universe reheats. We introduce a general analytic formalism for tracking this evolution through perturbative reheating, applicable to two field models with arbitrary separable potentials. The various transitions, including the onset of scalar field oscillations and the reheating of each field, can happen in different orders and on arbitrary hypersurfaces. The effective equations of state of the oscillating fields are also arbitrary. Nevertheless, our results are surprisingly simple. Our formalism encapsulates and generalises a huge range of previous calculations including two-field inflation, spectator models, the inhomogeneous end of inflation scenario and numerous generalised curvaton scenarios.
We present constraints on the reheating era within the string Fibre Inflation scenario, in terms of the effective equation-of-state parameter of the reheating fluid, $w_{reh}$. The results of the analysis, completely independent on the details of the inflaton physics around the vacuum, illustrate the behavior of the number of $e$-foldings during the reheating stage, $N_{reh}$, and of the final reheating temperature, $T_{reh}$, as functions of the scalar spectral index, $n_s$. We analyze our results with respect to the current bounds given by the PLANCK mission data and to upcoming cosmological experiments. We find that large values of the equation-of-state parameter ($w_{reh}>1/3$) are particularly favored as the scalar spectral index is of the order of $n_ssim 0.9680$, with a $sigma_{n_s}sim 0.002$ error. Moreover, we compare the behavior of the general reheating functions $N_{reh}$ and $T_{reh}$ in the Fibre Inflation scenario with that extracted by the class of the $alpha$-attractor models with $alpha=2$. We find that the corresponding reheating curves are very similar in the two cases.
The simplest two-field completion of natural inflation has a regime in which both fields are active and in which its predictions are within the Planck 1-$sigma$ confidence contour. We show this for the original model of natural inflation, in which inflation is achieved through the explicit breaking of a U(1) symmetry. We consider the case in which the mass coming from explicit breaking of this symmetry is comparable to that from spontaneous breaking, which we show is consistent with a hierarchy between the corresponding energy scales. While both masses are comparable when the observable modes left the horizon, the mass hierarchy is restored in the last e-foldings of inflation, rendering the predictions consistent with the isocurvature bounds. For completeness, we also study the predictions for the case in which there is a large hierarchy of masses and an initial period of inflation driven by the (heavy) radial field.
Inflationary models involving more than one scalar field naturally produce isocurvature perturbations. However, while these are fairly well studied, less is known about their evolution through the reheating epoch, when the inflationary fields decay into the standard constituents of the present universe. In this paper, by modelling reheating perturbatively, we calculate the power spectrum of the non-adiabatic pressure perturbation in three different inflationary models. We show that the isocurvature can grow large initially, but decays faster than the pressure perturbations. When reheating ends, the isocurvature is negligible for the double quadratic and double quartic inflationary models. For the product exponential potential, which features large isocurvature at the end of inflation, the isocurvature decays during reheating and is around five orders of magnitudes smaller than the pressure perturbation at the end of reheating.
In this talk, I discuss the effects, viability, and predictions of the string-theory-motivated Kahler Moduli Inflation I (KMII) potential, coupled to a light scalar field $chi$, which can provide a possible source for todays dark energy density due to the potentials non-vanishing minimum. Although the model is consistent with the current measured Cosmic Microwave Background (CMB) data, tighter constraints from future observations are required to test the viability of the KMII potential with its minimum equivalent to the observed cosmological constants energy density $rho_{Lambda_{mathrm{obs}}}$. We implement a Markov Chain Monte Carlo (MCMC) sampling method to compute the allowed model parameter ranges and bounds on the inflatons mass $m_{phi}$ and reheating temperature $T_{mathrm{reh}}$. Additionally, our lattice simulations predict stochastic gravitational-wave backgrounds generated during the inflaton oscillations that would be observable today in the $10^{9}$-$10^{11} , mathrm{Hz}$ frequency range. All the results and details will be included in our upcoming paper with the same title.
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