Primordial gravitational waves for universality classes of pseudoscalar inflation

Abstract

Current bounds from the polarization of the CMB predict the scale-invariant gravitational wave (GW) background of inflation to be out of reach for upcoming GW interferometers. This prospect dramatically changes if the inflaton is a pseudoscalar, in which case its generic coupling to any abelian gauge field provides a new source of GWs, directly related to the dynamics of inflation. This opens up new ways of probing the scalar potential responsible for cosmic inflation. Dividing inflation models into universality classes, we analyze the possible observational signatures. One of the most promising scenarios is Starobinsky inflation, which may lead to observational signatures both in direct GW detection as well as in upcoming CMB detectors. In this case, the complementarity between the CMB and direct GW detection, as well as the possibility of a multi-frequency analysis with upcoming ground and space based GW interferometers, may provide a first clue to the microphysics of inflation.

PBH dark matter from axion inflation

“…to larger scales. This is consistent with the physical intuition: For larger values of α/Λ the increase in the spectrum arises earlier (see also [40]), for larger values of ς the subsequent suppression due to the non-canonically normalized kinetic term takes effect at earlier times. Moreover, increasing ς we reduce the field excursion during inflation, leading to a suppression of ξ over a broad range of N -values.…”

“…the Starobinsky-like class 28 with p = 2). As shown in [40], in the context of higher-dimensional couplings with Abelian 26 Higgs inflation corresponds to h(φ) = φ 2 . 27 However, it is crucial to stress that these expressions for n s − 1 and r only hold for large values of N .…”

“…As in the context of direct GW observations it is customary to express quantities in terms of the frequency f = k/(2π), it is useful to introduce the relation between f and the number of e-foldings N [31,40]: 15) where k CMB = 0.002 Mpc −1 and N CMB 50 − 60. Following the convention used throughout this work, the number of e-foldings N decreases during inflation, reaching N = 0 at the end of inflation and we will set N CMB = 60.…”

“…The arguably simplest axion inflation model employs the cosine potential (A.5). 40 Note that inflation models based on such an oscillatory potential are models of large-field inflation: the slow-roll conditions are satisfied for φ m p . As the potential is periodic, this implies that the period needs to take super-Planckian values,…”

“…This can be realized by coupling the axion to a 3-form theory [109][110][111]. To be explicit, consider the theory of an axion φ and a 3-form C νρσ with corresponding field strength F µνρσ = 4∂ [µ C νρσ] described by 40 The inflationary potential is obtained from eq. the following Lagrangian density:…”