Probing New Degrees of Freedom with the Universal Tail of Primordial Black Hole Mass Functions

Kaustubh Agashe; Jae Hyeok Chang; Steven J. Clark; Bhaskar Dutta; Yuhsin Tsai; Tao Xu

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arXiv · 2606.13788

Probing New Degrees of Freedom with the Universal Tail of Primordial Black Hole Mass Functions

Kaustubh Agashe·Jae Hyeok Chang·Steven J. Clark·Bhaskar Dutta·Yuhsin Tsai·Tao Xu

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Abstract

The primordial black hole (PBH) mass function today develops a low-mass evaporation tail whose shape is universal with respect to the initial PBH mass distribution. This universality is fixed by the continuity equation and the Hawking mass-loss rate, but the tail is distorted if additional particle degrees of freedom participate in Hawking evaporation. Since this tail controls high-energy PBH photon emission, such distortions leave characteristic features in the gamma-ray spectrum. We show that these features provide a robust probe of new degrees of freedom, even for subdominant PBHs, within reach of future experiments and independent of visible-sector couplings or relic abundance.

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Kaustubh Agashe, Jae Hyeok Chang, Steven J. Clark, Bhaskar Dutta, Yuhsin Tsai, Tao Xu. 2026-06-11. Probing New Degrees of Freedom with the Universal Tail of Primordial Black Hole Mass Functions. https://arxiv.org/abs/2606.13788

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