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Tripling Fluctuations and Peaked Sound Speed in Fermionic Matter

Hiroyuki Tajima1,2,3, Kei Iida4,2,5, Toru Kojo6, and Haozhao Liang1,7,3

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Phys. Rev. Lett. 135, 042701 – Published 23 July, 2025

DOI: https://doi.org/10.1103/4ywp-752m

Abstract

A crossover involving three-fermion clusters is relevant to the hadron-quark crossover, which, if occurring in a neutron star, could naturally reproduce the dense-matter equation of state recently deduced from simultaneous observations of neutron-star masses and radii. To understand the crossover mechanism, we examine the role of tripling fluctuations induced by the formation of three-fermion clusters. The phase-shift representation of fluctuations manifests an interplay of bound and scattering states, leading to nonmonotonic momentum distributions of baryonlike clusters and peaked sound speed at finite densities. We demonstrate them by applying our approach to a nonrelativistic system of one-dimensional three-color fermions analogous to the hadron-quark matter.

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Phys. Rev. Lett. 135, 042701– Published 23 July, 2025
  • Received 6 December 2024
  • Revised 7 May 2025
  • Accepted 27 June 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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