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PreprintarXiv licencearXiv

Direct Urca process facilitated by non-Fermi-liquid quantum criticality

  • Hao-Fu Zhu
  • Guo-Zhu Liu
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Abstract

Conventional Fermi-liquid theories of dense nuclear matter predict that the direct Urca process requires a proton fraction above a threshold of Yp ≈ 0.11--$0.15$, which is rarely reached in low-mass neutron stars. Here we show that this stringent kinematic constraint is drastically relaxed by the non-Fermi liquid behavior arising from superfluid and superconducting quantum criticality in neutron stars. In the non-Fermi-liquid regimes, nucleons have a smooth momentum occupation without a sharp Fermi surface, and their chemical potentials develop a logarithmic temperature dependence. These intrinsic features fundamentally alter the standard β-equilibrium relation. Consequently, direct Urca neutrino emission can be activated even at low nuclear densities. This modifies the long-standing Urca-threshold paradigm and indicates that direct Urca process has the opportunity to occur in low-mass neutron stars.

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Cite

BibTeXRIS
BibTeX
@misc{zhu2026direct,
  title = {{Direct Urca process facilitated by non-Fermi-liquid quantum criticality}},
  author = {Hao-Fu Zhu and Guo-Zhu Liu},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.28023},
  eprint = {2610.28023},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.28023},
}
RIS
TY  - UNPB
TI  - Direct Urca process facilitated by non-Fermi-liquid quantum criticality
AU  - Hao-Fu Zhu
AU  - Guo-Zhu Liu
PY  - 2026
DA  - 2026/10/20
PB  - arXiv
DO  - 10.48550/arxiv.2610.28023
UR  - https://arxiv.org/abs/2610.28023
AB  - Conventional Fermi-liquid theories of dense nuclear matter predict that the direct Urca process requires a proton fraction above a threshold of Y_p ≈ 0.11--$0.15$, which is rarely reached in low-mass neutron stars. Here we show that this stringent kinematic constraint is drastically relaxed by the non-Fermi liquid behavior arising from superfluid and superconducting quantum criticality in neutron stars. In the non-Fermi-liquid regimes, nucleons have a smooth momentum occupation without a sharp Fermi surface, and their chemical potentials develop a logarithmic temperature dependence. These intrinsic features fundamentally alter the standard β-equilibrium relation. Consequently, direct Urca neutrino emission can be activated even at low nuclear densities. This modifies the long-standing Urca-threshold paradigm and indicates that direct Urca process has the opportunity to occur in low-mass neutron stars.
ER  -