Scale-dependent gravitational waves from a rolling axion

Abstract

Abstract. We consider a model in which a pseudo-scalar field σ rolls for some e-folds during inflation, sourcing one helicity of a gauge field. These fields are only gravitationally coupled to the inflaton, and therefore produce scalar and tensor primordial perturbations only through gravitational interactions. These sourced signals are localized on modes that exit the horizon while the roll of σ is significant. We focus our study on cases in which the model can simultaneously produce (i) a large gravitational wave signal, resulting in observable B-modes of the CMB polarizations, and (ii) sufficiently small scalar perturbations, so to be in agreement with the current limits from temperature anisotropies. Different choice of parameters can instead lead to a localized and visible departure from gaussianity in the scalar sector, either at CMB or LSS scales.arXiv:1509.07521v1 [astro-ph.CO]

Propagating speed of primordial gravitational waves and inflation

“…Thus n T > 0 requires either the superinflation [9][10], also [11] [12], which breaks the null energy condition (NEC), or an anisotropic stress source during inflation, e.g., the particle production [13] [14][15] [16]. During the superinflation, the primordial GWs come from the amplification of vacuum tensor perturbations.…”

de Sitter symmetries and inflationary correlators in parity violating scalar-vector models

“…Some criticism on this model have raised due to the validity of its perturbative expansion and about the consistency of this mechanism to produce sizable primordial gravitational waves without contradict current observational limits [69,70]. Nevertheless, by using the perturbative approach, it was shown that the model have an available parameter window, that is in agreement with the current observational constraints [55,71].…”

“…We consider a scenario with a scalar field driving the inflationary expansion, and a vector field, which is partly responsible fro the generation of the primordial curvature perturbation and is a source of statistical anisotropies. Several models of this type has been studied in the literature [32,35,37,38,40,[43][44][45][46][47][48][49][50][51][52][53][54][55][56]. The interest for those models has been diverse and it has evolved over the years.…”

“…It is worthwhile to mention the Ratra model [32], which has a rich and interesting phenomenology in the context of primordial magnetogenesis scenario [36,[57][58][59][60] and later used as a source of sizable statistical anisotropies which doesn't dilute with the inflationary evolution [29,[33][34][35]37]. Aside of this, there is a rich literature about models whit an axion/pseudoscalar coupling of the form φFF which allows for interesting phenomenology and source of nonvacuum gravitational waves, chiral gravitational waves, large tensor non-gaussianities among other interesting effects [38,47,49,52,55]. In this paper we consider a mixture of this two scenarios which can be encompassed in the following model:…”

“…Its relevance, in the context of inflationary physics, has been a matter of interest and debate, in particular, this model offer a mechanism to enhance the production of gravitational waves during the inflationary period (see for instance Ref. [55]). Some criticism on this model have raised due to the validity of its perturbative expansion and about the consistency of this mechanism to produce sizable primordial gravitational waves without contradict current observational limits [69,70].…”