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arXiv · 2504.07063

Non-Gaussianity of Tensor Induced Density Perturbations

Mariam Abdelaziz·Pritha Bari·Sabino Matarrese·Angelo Ricciardone
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Abstract

We investigate the non-Gaussianity of second-order matter density perturbations induced by primordial gravitational waves (GWs). These tensor-induced scalar modes arise from local fluctuations in the GWs energy density, which is quadratic in tensor perturbations. The resulting second-order density contrast follows a chi-squared distribution, naturally exhibiting significant non-Gaussianity. We compute the bispectrum of these tensor-induced scalar modes and analyze its dependence on various primordial GWs power spectra, including scale-invariant, blue-tilted, Gaussian-bump, and monochromatic sources. We find that the bispectrum shape is inherently sensitive to the underlying GWs spectrum by construction. In particular, Gaussian-bump and monochromatic sources produce a strong signal peaking in the equilateral configuration, similar to the effect of scalar-induced tensor modes. Our findings reveal a new way to probe primordial GWs via galaxy surveys and highlight a unique feature of tensor-induced density perturbations, otherwise mimicking linear ones on sub-horizon scales.

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Mariam Abdelaziz, Pritha Bari, Sabino Matarrese, Angelo Ricciardone. 2025-04-09. Non-Gaussianity of Tensor Induced Density Perturbations. https://doi.org/10.1103/bb22-pq2m

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