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arXiv · 2410.10111

Constraints on primordial black holes from $N_{\text{eff}}$ : scalar induced gravitational waves as an extra radiation component

Jing-Zhi Zhou·Yu-Ting Kuang·Zhe Chang·H. Lü
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Abstract

In June 2023, multiple pulsar timing array collaborations provided evidence for the existence of a stochastic gravitational wave background. Scalar induced gravitational waves (SIGWs), as one of the most likely sources of stochastic gravitational waves, have received widespread attention. When primordial curvature perturbations on small scales are sufficiently large, \acp{PBH} inevitably form, concurrently producing SIGWs with significant observable effects. These SIGWs can serve as an additional radiation component, influencing the relativistic degrees of freedom $N_{\text{eff}}$. Taking into account primordial non-Gaussianity, we study the energy density spectrum of SIGWs up to the third order and use the current observational data of $N_{\text{eff}}$ to constrain small-scale primordial curvature perturbations and the abundance of \acp{PBH}.

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Jing-Zhi Zhou, Yu-Ting Kuang, Zhe Chang, H. Lü. 2024-10-14. Constraints on primordial black holes from $N_{\text{eff}}$ : scalar induced gravitational waves as an extra radiation component. https://arxiv.org/abs/2410.10111

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