Tracing Primordial Gravitational Waves via non-Gaussian Signatures of Halo Bias

TL;DR

This paper explores how primordial gravitational waves induce non-Gaussian signatures in halo bias, offering a new way to probe inflationary physics through large-scale structure observations.

Contribution

It introduces a novel method to detect primordial gravitational waves by analyzing their unique non-Gaussian imprint on halo bias in large-scale structure.

Findings

Percent-level bias correction for massive low-redshift halos.

Potential for an order-one modulation in high-redshift halos at z=7.

Distinct scale dependence not captured by standard PNG templates.

Abstract

Primordial gravitational waves (PGWs) generate scalar density perturbations at second order. Since the induced density contrast is quadratic in the tensor field, it is intrinsically non-Gaussian. We study the imprint of this tensor-induced non-Gaussianity (NG) on the large-scale clustering of dark matter halos through its correction to halo bias. Focusing on inflationary scenarios with a peaked primordial tensor spectrum, we derive the leading scale-dependent contribution sourced by the bispectrum of the induced density field. While yielding a percent-level bias correction for massive low-redshift halos, this effect can reach an $\mathcal{O}(1)$ modulation for rare, high-redshift halos at $z=7$. Notably, the resulting signature exhibits a distinct scale dependence that is not captured by standard primordial non-Gaussianity (PNG) templates. Our results establish halo bias as a novel probe of PGWs through their imprint on the large-scale structure, providing a complementary window into the inflationary epoch.