Measurement of parity violation in the early universe using gravitational-wave detectors

Abstract

A stochastic gravitational-wave background (SGWB) is expected to arise from the superposition of many independent and unresolved gravitational-wave signals, of either cosmological or astrophysical origin. Some cosmological models (characterized, for instance, by a pseudo-scalar inflaton, or by some modification of gravity) break parity, leading to a polarized SGWB. We present a new technique to measure this parity violation, which we then apply to the recent results from LIGO to produce the first upper limit on parity violation in the SGWB, assuming a generic power-law SGWB spectrum across the LIGO sensitive frequency region. We also estimate sensitivity to parity violation of the future generations of gravitational-wave detectors, both for a power-law spectrum and for a model of axion inflation. This technique offers a new way of differentiating between the cosmological and astrophysical sources of the isotropic SGWB, as astrophysical sources are not expected to produce a polarized SGWB. PACS numbers:Introduction.-A stochastic gravitational-wave background (SGWB) is expected to arise from the superposition of gravitational waves (GWs) from many uncorrelated and unresolved sources. Numerous cosmological SGWB models have been proposed, including inflationary models [1][2][3][4], models based on cosmic (super)strings [5,6], and models of alternative cosmologies [7]. Furthermore, various astrophysical models have been proposed based on integrating contributions from astrophysical objects across the universe, such as compact binary coalescences of binary neutron stars and/or black holes [8,9], magnetars [10,11], or rotating neutron stars [12]. Several searches for the unpolarized isotropic [13][14][15] and anisotropic SGWB [16,17] have been conducted using data acquired by interferometric GW detectors LIGO [18,19] and Virgo [20]. These searches have established upper limits on the energy density in the SGWB, and have started to constrain some of the proposed models [6,9,21].

A review of axion inflation in the era of Planck

“…A more detailed study was performed in ref. [73]. It was shown there that, for a quadratic inflaton potential, the forthcoming second generation gravity waves experiments (Advanced LIGO, VIRGO, and Kagra) can probe ξ * > ∼ 2.2 (at 95% CL, based on flat priors on ξ), while third generation experiments can improve the limit to ξ * > ∼ 1.9.…”

Inflation and String Theory

“…It is therefore conceivable for the signal to be small on CMB scale, but detectable on scales accessible to terrestrial interferometers. In [770] it was estimated that ξ > 2.2 could be probed with Advanced LIGO.…”

PBH dark matter from axion inflation

“…16 Moreover, during the last years it was realized that the introduction of a nonminimal coupling between the inflaton and gravity (in the Jordan frame) can provide a mechanism to "flatten" the inflationary potential (in the Einstein frame) [42,44,[50][51][52][53][54][55][56][57][58][59]70] leading to predictions for the scalar spectral index n s and the tensor-to-scalar-ratio r that lie right in the sweet spot of the constraints set by CMB observations [61]. For 14 For details on methods to detect the chirality of GW background see [68]. 15 To ease the notation, in Secs.…”