Spontaneous Spin Polarization in Dense Quark Matter Reexamined
Abstract
The phase structure of strongly interacting matter at high baryon density remains an open problem in QCD, with important implications for the internal structure and magnetic properties of neutron stars. We reexamine the emergence of a quark spin-polarized (QSP) phase in cold, dense quark matter within the two-flavor Nambu-Jona-Lasinio model with tensor interactions, focusing on its dependence on regularization. We compare the traditional regularization scheme (TRS), where a sharp momentum cutoff is applied to both vacuum and medium contributions, with the medium separation scheme (MSS), where ultraviolet-divergent vacuum terms are isolated while finite medium-dependent phase-space contributions remain cutoff free. The two prescriptions lead to qualitatively different results. In TRS, the QSP condensate eventually collapses at high chemical potential, leading to nonmonotonic thermodynamic behavior and, for some couplings, violations of causality. In MSS, the QSP condensate instead increases monotonically with density, the equation of state remains causal, and the associated spontaneous magnetization grows toward high density. The persistence of spin polarization at high density may provide a microscopic contribution to the strong magnetic fields of compact stars, including magnetars. An exploratory hybrid-star construction further shows that the QSP phase can significantly modify the equation of state, stability trends, and mass-radius relations. These results highlight the importance of a consistent treatment of medium phase space and demonstrate the potential impact of a persistent spin-polarized quark phase on neutron-star physics.
Related
- Perturbative QCD correction to the nonleptonic weak rate in dense quark matter
- Evidence for a Continuous Hadron--Quark Transition in Cold Dense Matter
- Dense and Cold Magnetized Quark Matter: A Review of Magnetic-Field-Independent Regularization and the Medium Separation Scheme
- How Neutron Star Radii Encode the Dense-Matter Equation of State and Hadron-Quark Transition
- MUSES workflows for pQCD constraints on dense matter with finite quark masses
BibTeX
@misc{miller2026spontaneous,
title = {{Spontaneous Spin Polarization in Dense Quark Matter Reexamined}},
author = {Carlisson Miller and Rodolfo Casana and Manoel M. Ferreira and Gastão Krein},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.04160},
eprint = {2610.04160},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.04160},
}
RIS
TY - UNPB
TI - Spontaneous Spin Polarization in Dense Quark Matter Reexamined
AU - Carlisson Miller
AU - Rodolfo Casana
AU - Manoel M. Ferreira
AU - Gastão Krein
PY - 2026
DA - 2026/10/03
PB - arXiv
DO - 10.48550/arxiv.2610.04160
UR - https://arxiv.org/abs/2610.04160
AB - The phase structure of strongly interacting matter at high baryon density remains an open problem in QCD, with important implications for the internal structure and magnetic properties of neutron stars. We reexamine the emergence of a quark spin-polarized (QSP) phase in cold, dense quark matter within the two-flavor Nambu-Jona-Lasinio model with tensor interactions, focusing on its dependence on regularization. We compare the traditional regularization scheme (TRS), where a sharp momentum cutoff is applied to both vacuum and medium contributions, with the medium separation scheme (MSS), where ultraviolet-divergent vacuum terms are isolated while finite medium-dependent phase-space contributions remain cutoff free. The two prescriptions lead to qualitatively different results. In TRS, the QSP condensate eventually collapses at high chemical potential, leading to nonmonotonic thermodynamic behavior and, for some couplings, violations of causality. In MSS, the QSP condensate instead increases monotonically with density, the equation of state remains causal, and the associated spontaneous magnetization grows toward high density. The persistence of spin polarization at high density may provide a microscopic contribution to the strong magnetic fields of compact stars, including magnetars. An exploratory hybrid-star construction further shows that the QSP phase can significantly modify the equation of state, stability trends, and mass-radius relations. These results highlight the importance of a consistent treatment of medium phase space and demonstrate the potential impact of a persistent spin-polarized quark phase on neutron-star physics.
ER -