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Register a new userFloquet analysis of self-resonance in single-field models of inflation
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Added by
Krzysztof Turzynski
Publication date
2018
fields
Physics
and research's language is
English
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We review 51 models of single-field inflation, paying special attention to the possibility that self-resonance of the unstable inflaton perturbations leads to reheating. We compute Floquet exponents for the models that are consistent with current cosmological data. We find five models that exhibit a strong instability, but only in one of them -- KKLT inflation -- the equation of state efficiently approaches that of radiation.
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Using the latest release from WMAP, I find that for a reasonable number of e-folds the tree-level potential with self coupling power p=3 is now excluded from the 2-sigma region, the axion monodromy model with the power alpha=2/3 is now excluded from the 1-sigma confidence region for N=47 e-folds and for N=61. alpha=2/5 is also excluded from the 2-sigma region for N=61. I also find that since the upper bound on the running has been reduced, a significant abundance of PBHs requires fractional powers of self-coupling in the Hilltop-type model.
In this paper we summarise the status of single field models of inflation in light of the WMAP 7 data release. We find little has changed since the 5 year release, and results are consistent with previous findings. The increase in the upper bound on the running of the spectral index impacts on the status of the production of Primordial Black Holes from single field models. The lower bound on the equilateral configuration of the non-gaussianity parameter is reduced and thus the bounds on the theoretical parameters of (UV) DBI single brane models are weakened. In the case of multiple coincident branes the bounds are also weakened and the two, three or four brane cases will produce a tensor-signal that could possibly be observed in the future.
Short baseline neutrino experiments, like LSND and MiniBooNE experiments, pointed towards the existence of eV mass scale sterile neutrinos. To reconcile sterile neutrinos with cosmology self interaction between sterile neutrinos has been studied. We analysed Planck cosmic microwave background (CMB) data with self-interacting sterile neutrino (SI$ u$) and study their impact on inflation models. The fit to the CMB data in SI$ u$ model is as good as the fit to $Lambda$CDM model. We find that the spectral index ($n_s$) values shift to $0.9361pm 0.0055$ in SI$ u$ model. This has significant impact on the validity of different inflation models. For example the Starobinsky and quartic hilltop model, which were allowed within $Lambda$CDM cosmology, are ruled out. On the other hand some models like natural and Coleman-Weinberg inflation are now favoured. Therefore, the existence of self interacting sterile neutrinos with eV order of mass will play an important role in the selection of correct inflation model.
We initially consider two simple situations where inflationary slow roll parameters are large and modes no longer freeze out shortly after exiting the horizon, treating both cases analytically. We then consider applications to transient phases where the slow roll parameters can become large, especially in the context of the common `fast-roll inflation frequently used as a mechanism to explain the anomalously low scalar power at low $l$ in the CMB. These transient cases we treat numerically. We find when $epsilon$, the first slow roll parameter, and only $epsilon$ is large, modes decay outside the horizon, and when $delta$, the second slow roll parameter, is large, modes grow outside the horizon. When multiple slow roll parameters are large the behavior in general is more complicated, but we nevertheless show in the fast-roll inflation case, modes grow outside the horizon.
We revisit the notion of slow-roll in the context of general single-field inflation. As a generalization of slow-roll dynamics, we consider an inflaton $phi$ in an attractor phase where the time derivative of $phi$ is determined by a function of $phi$, $dotphi=dotphi(phi)$. In other words, we consider the case when the number of $e$-folds $N$ counted backward in time from the end of inflation is solely a function of $phi$, $N=N(phi)$. In this case, it is found that we need a new independent parameter to properly describe the dynamics of the inflaton field in general, in addition to the standard parameters conventionally denoted by $epsilon$, $eta$, $c_s^2$ and $s$. Two illustrative examples are presented to discuss the non-slow-roll dynamics of the inflaton field consistent with observations.
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