Cross-correlations as a diagnostic tool for primordial gravitational waves

Abstract

We explore and corroborate, by working out explicit examples, the effectiveness of cross-correlating stochastic gravitational wave background anisotropies with CMB temperature fluctuations as a way to establish the primordial nature of a given gravitational wave signal. We consider the case of gravitational wave anisotropies induced by scalar-tensor-tensor primordial non-Gaussianity. Our analysis spans anisotropies exhibiting different angular behaviours, including a quadrupolar dependence. We calculate the expected uncertainty on the non-linearity parameter FNL obtained as a result of cross-correlation measurements for several proposed experiments such as the ground-based Einstein Telescope, Cosmic Explorer, and the space-based Big-Bang Observer. As a benchmark for future survey planning, we also calculate the theoretical, cosmic-variance-limited, error on the non-linearity parameter.

Primordial non-Gaussianity in supersolid inflation

“…While in solid inflation their size is similar, for a supersolid the monopole gets enhanced by a factor 1/c 3 s2 for small c s2 . This leads a characteristic signature of supersolid inflation: the non-linear and local corrections to the tensor PS that becomes rather different from solid inflation, as discussed in [36] where TTS predictions for the standard solid inflation [10] scenario are compared with another "isotropic" (in the sense that the f TTS gives a monopole) model [37].…”

“…The former could leave a signature in LSS next-generation experiments, giving a specific imprint 22 on the distribution of galaxies [33,48,49], while the latter could play a crucial role in the generation of anisotropies of the gravitational waves background [36,37,50,51].…”

Probing pre-Recombination Physics by the Cross-Correlation of Stochastic Gravitational Waves and CMB Anisotropies

“…Their cross-correlation with CMB temperature anisotropies has instead first been considered in Refs. [37,38] and used to forecast constraints on primordial non-Gaussian signals originated by scalar-tensor-tensor interactions.…”

Cross-correlating Astrophysical and Cosmological Gravitational Wave Backgrounds with the Cosmic Microwave Background

“…Forecasts of detection prospects for this monopole signal with ground and space-based detectors were shown in, e.g., [5,[11][12][13][14][15][16][17]. Such backgrounds are however also expected to display anisotropies (direction dependence) in the GW energy density Ω GW (f, n), which can be generated either at the time of their production [18][19][20][21][22][23][24] or during their propagation in our perturbed universe [25][26][27][28]. While the former generation mechanism is source/model-dependent, the latter is model-independent and ubiquitous for all the SGWB sources.…”

“…In our analysis we have neglected the instrumental noise of CMB experiment, since it is well known that at the multipoles we are interested in ( 100), available CMB data are completely cosmic variance dominated. On the interferometer side, we have instead considered the expected noise levels of LISA and BBO, following [24,56]; for BBO, we have only considered the two units of aligned detectors in the star-of-David [57,58]. The corresponding noise angular power-spectra are plotted in Figure 6 in Appendix B.…”