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Nuclear pasta and crustal quasiperiodic oscillations in neutron stars

Vishal Parmar1,* and Ignazio Bombaci1,2

  • *Contact author: vishal.parmar@pi.infn.it
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Phys. Rev. D 114, 023009 – Published 6 July, 2026

DOI: https://doi.org/10.1103/qyqv-ldbd

Abstract

We investigate the impact of nuclear pasta on crustal structure and torsional oscillations using a Bayesian ensemble of unified neutron-star equations of state based on relativistic mean-field models constrained by nuclear experiments, empirical saturation properties, chiral effective field theory, and multimessenger observations. For each posterior sample, we compute the pasta sequence within a compressible liquid-drop model and quantify the onset density, thickness, and mass fraction of the pasta layers. We show that the appearance and extent of nuclear pasta are primarily controlled by the symmetry-energy slope parameter L, consistent with earlier studies and indicative of a universal trend. While spherical and rodlike pasta configurations are present for all equations of state, only a small fraction of the posterior supports slab, tube, or bubble geometries. The transition from spherical nuclei to rods is tightly constrained to occur at a density of ρsr=0.0588−0.0065+0.0045  fm−3. We further predict that the nuclear pasta layer occupies a relative radial thickness of ΔRpasta/ΔRc=0.140−0.036+0.025 and contributes a relative mass fraction of ΔMpasta/ΔMc=0.475−0.113+0.071. Using the resulting crust models, we present the quasiperiodic oscillations (QPOs) analysis based on a Bayesian posterior ensemble of neutron-star equations of state and systematically assess their compatibility with observed low-frequency quasiperiodic oscillations. We find that the predicted QPO frequencies are strongly correlated with the curvature of the symmetry energy evaluated at subsaturation density, Ksym(ρ0/2), and that uncertainties in the equation of state translate into a range of angular indices ℓ consistent with the observed frequencies.

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Phys. Rev. D 114, 023009– Published 6 July, 2026
  • Received 22 February 2026
  • Accepted 29 May 2026
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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.

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