Naturally large tensor-to-scalar ratio in inflation

Abstract

Recently, BICEP2 measurements of the cosmic microwave background (CMB) B-mode polarization at degree angular scales has indicated the presence of tensor modes with a high tensor-to-scalar ratio of r = 0.2 when assuming nearly scale-invariant tensor and scalar spectra, although the signal may be contaminated by dust emission as implied by the recent Planck polarization data. This result is in conflict with the Planck best-fit Lambda Cold Dark Model with r < 0.11. Due to the fact that inflaton has to be interacting with other fields so as to convert its potential energy into radiation to reheat the Universe, the interacting inflaton may result in a suppression of the scalar spectrum at large scales. This suppression has been used to explain the observed low quadrupole in the CMB anisotropy. In this paper, we show that a combination of the tensor modes measured by BICEP2 and the large-scale suppressed scalar modes contributes to the CMB anisotropy in such a way that the resultant CMB anisotropy and polarization power spectra are consistent with both Planck and BICEP2 data. We also project our findings to cases in which r may become reduced in future CMB polarization measurements.

Warm inflation dissipative effects: Predictions and constraints from the Planck data

“…the data prefers a tiny negative value n s = −0.0084 ± 0.0082 (68% CL, TT+lowP), with a small improvement of the maximum likelihood with respect to a powel-law spectrum (∆χ = −0.8) [2]. The data give also the possibility of a small running of the running, 25) and in this case, at 68% CL using the TT+lowP data, the values obtained for a ΛCDM+n s + n s model are n s = 0.9569 ± 0.0077, n s = 0.011 ± 0.014, n s = 0.029 ± 0.015, which seems to produce a better fit to the temperature spectrum at low multipoles according to the Planck results, such that ∆χ = −4.8 [2]. The positive constraints on n s takes a particularly relevance since, for single field slow-roll CI models, the running of the running is expected to be progressively smaller, and usually negative.…”

“…[21,22]). Dissipative and stochastic processes typically involved in the WI dynamics [10,12,13,[23][24][25][26][27] are able to produce a strongly modified dynamics, both at the background and the fluctuations levels, leading to many distinguished predictions with respect to the CI scenario. In particular, in WI the primary source of density fluctuations comes from thermal fluctuations originated in the radiation bath and transported to the inflaton field as adiabatic curvature perturbations [28,29], while in CI the density perturbations are due to quantum fluctuations of the inflaton field [30].…”

Role of four-fermion interaction and impurity in the states of two-dimensional semi-Dirac materials

“…According to the standard procedures of RG framework [54,55,61,62,[64][65][66][76][77][78][79][80][81][82][83], we need to integrate out the fields in the momentum shell bΛ < k < Λ with b < 1 to derive the evolutions of interaction parameters, where Λ represents the energy scale and the variable parameter b can be written as b = e −l with a running energy scale l > 0 [54,61,62,[76][77][78].…”

“…For instance, there are in all five one-loop diagrams contributing to the fermion interacting coupling u 0 as shown in figure 2, whose contributions are displayed in equations (A.1)-(A.4) of appendix A.1. Thereafter, summarizing all of these related one-loop contributions [54,61,62,77,78,[80][81][82][83] forthrightly gives rise to…”

Eternal inflation in a dissipative and radiation environment: Heated demise of eternity

“…We know from many recent studies [28][29][30][31][32][33][34] that dissipation and stochastic noise effects are able to strongly modify the inflationary dynamics. This in turn can lead to very different predictions for observational quantities, like for the tensor-to-scalar ratio, the spectral index, and nongaussianities, when compared to the cold inflation case.…”