Finite-Temperature Axion-Admixed Neutron Stars in a Quarkyonic Crossover Framework
Abstract
We analyze the effect of axion contribution on the mass, radius and dimensionless deformability of a neutron star (NS) at finite temperature. Although the cooling of an NS is mainly due to the emission of neutrinos, additional cooling cannot be ruled out due to the emission of axions. The existence of an axion is needed for addressing the strong CP problem within the standard model. The Peccei-Quinn (PQ) symmetry breaking mechanism generates axions. They are pseudo-Nambu-Goldstone bosons. Their mass is extremely small but non-zero. This naturally resolves the fine-tuning problem of the strong CP-violating parameter θ ≲ 10−10. We propose that a finite temperature NS feature a quark core surrounded by a baryonic medium admixed with the axions, which are pseudo scalar Goldstone bosons and are considered as strong candidates for the dark matter (DM). Unlike the original quarkyonic model, we formulate a quarkyonic-inspired smooth crossover equation of state (EoS) at finite temperatures. This smooth crossover avoids thermodynamic instabilities found in sharp first-order constructions. We add the axionic EoS to the finite temperature quarkyonic one and solve the Tolman-Oppenheimer-Volkoff equations to estimate the properties of the NS both with and without taking the axion into account at different temperatures. We find that the production of axions is maximum within a radius of 5−11 km in the star's interior; however, the impact on the mass is significant, i.e., ∼ 60% of axion mass concentrated in the central region of the star. We also find that the effect of temperature on the mass of NS is marginal unlike the radius. In general, the influence of axions is significant for the observational properties of NS. These results highlight the pivotal role of axion physics in neutron star phenomenology.
Related
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BibTeX
@misc{patra2026finitetemperature,
title = {{Finite-Temperature Axion-Admixed Neutron Stars in a Quarkyonic Crossover Framework}},
author = {S. K. Patra and D. Dey and Jeet Amrit Pattnaik and R. N. Panda},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28555},
eprint = {2609.28555},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28555},
note = {CC0},
}
RIS
TY - UNPB
TI - Finite-Temperature Axion-Admixed Neutron Stars in a Quarkyonic Crossover Framework
AU - S. K. Patra
AU - D. Dey
AU - Jeet Amrit Pattnaik
AU - R. N. Panda
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.28555
UR - https://arxiv.org/abs/2609.28555
AB - We analyze the effect of axion contribution on the mass, radius and dimensionless deformability of a neutron star (NS) at finite temperature. Although the cooling of an NS is mainly due to the emission of neutrinos, additional cooling cannot be ruled out due to the emission of axions. The existence of an axion is needed for addressing the strong CP problem within the standard model. The Peccei-Quinn (PQ) symmetry breaking mechanism generates axions. They are pseudo-Nambu-Goldstone bosons. Their mass is extremely small but non-zero. This naturally resolves the fine-tuning problem of the strong CP-violating parameter θ ≲ 10^−10. We propose that a finite temperature NS feature a quark core surrounded by a baryonic medium admixed with the axions, which are pseudo scalar Goldstone bosons and are considered as strong candidates for the dark matter (DM). Unlike the original quarkyonic model, we formulate a quarkyonic-inspired smooth crossover equation of state (EoS) at finite temperatures. This smooth crossover avoids thermodynamic instabilities found in sharp first-order constructions. We add the axionic EoS to the finite temperature quarkyonic one and solve the Tolman-Oppenheimer-Volkoff equations to estimate the properties of the NS both with and without taking the axion into account at different temperatures. We find that the production of axions is maximum within a radius of 5−11 km in the star's interior; however, the impact on the mass is significant, i.e., ∼ 60% of axion mass concentrated in the central region of the star. We also find that the effect of temperature on the mass of NS is marginal unlike the radius. In general, the influence of axions is significant for the observational properties of NS. These results highlight the pivotal role of axion physics in neutron star phenomenology.
ER -