Squeezed tensor non-Gaussianity in non-attractor inflation

Abstract

We investigate primordial tensor non-Gaussianity in single field inflation, during a phase of nonattractor evolution when the spectrum of primordial tensor modes can be enhanced to a level detectable at interferometer scales. Making use of a tensor duality we introduced in [1], we analytically compute the full bispectrum of primordial tensor fluctuations during the non-attractor era. During this epoch the shape of the tensor bispectrum is enhanced in the squeezed limit, its amplitude can be amplified with respect to slow-roll models, and tensor non-Gaussianity can exhibit a scale dependence distinctive of our set-up. We prove that our results do not depend on the frame used for the calculations. Squeezed tensor non-Gaussianity induces a characteristic quadrupolar anisotropy on the power spectrum of the stochastic background of primordial tensor perturbations. As a step to make contact with gravitational wave experiments, we discuss the response function of a ground based Michelson interferometer to a gravitational wave background with such a feature.

Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem

“…Finally, notice that the non-Gaussian amplitudes (88) and (89) agree with those obtained in a kind of nonattractor inflation models, where tensor perturbations grow on superhorizon scales during inflation due to nonattractor dynamics of the non-minimally coupled inflaton [39]. This is because both our contracting models and the non-attractor phase of inflation are conformally equivalent to the matter-dominated contracting scenario.…”

Probing a stationary non-Gaussian background of stochastic gravitational waves with pulsar timing arrays

“…Possible ways out to these negative conclusions have been proposed, involving measurements of quantities only indirectly sensitive to graviton nG: the quadrupolar anisotropy of the SGWB power spectrum, an observable which depends on the squeezed limit of tensor non-Gaussian correlation functions[16][17][18]; and higher-order correlations among spatial anisotropies in the distribution function of the GW energy density[19] 3. The work[14] already pointed out that 3-point functions of GWs whose momenta are accurately aligned can avoid decorrelation effects.…”

Modern Topics in Scalar Field Cosmology

“…Their structure depends on nonminimal couplings of gravity to the scalar field driving inflation, and on the homogeneous scalar profile (see Subsection 3.2.2 and [202]). In the second 1 The quadratic action for tensor mode can be recasted into a canonical 'Einstein frame' action by applying a disformal and a conformal transformation to the system [200]. Nevertheless, all our results remain the same in any frame one uses, as anticipated in [123] and explained more at length in Section 3.…”

“…MACHOs are composed of visible matter but reflect little to no light, therefore they can be considered as dark matter candidates. Types of MACHOs include: neutrons stars, white dwarfs, brown dwarfs 1 . They can be detected as the result of gravitational lensing.…”

“…Chapter 3 consists of the paper [1] in which we discuss a specific type of inflation, dubbed as non-attractor inflation, which is a mechanism that enhances and amplifies the stochastic background primordial gravitational wave at frequencies and scales which allows them to be detected by interferometers and pulsar timing arrays. Moreover, non-attractor inflation also amplifies gravitational wave non-Gaussianities.…”