Neutron Star Structure in Poincaré Gauge Gravity with Quadratic Torsion
Researchers have modeled static neutron stars within Poincaré gauge gravity incorporating quadratic torsion invariants, finding that torsion corrections produce more compact stars with lower maximum masses than predicted by general relativity. The work extends Einstein–Cartan theory by allowing the spin-spin interaction coefficient to vary with dimensionless torsion coupling parameters, rather than being fixed. These results constrain how modifications to spacetime geometry at the level of torsion could alter observable neutron star properties such as mass and radius.
A new preprint submitted to arXiv investigates how neutron stars behave when modeled within Poincaré gauge gravity, a framework that extends general relativity by incorporating quadratic torsion — a geometric property of spacetime linked to the intrinsic spin of matter. Because torsion is non-propagating in the algebraic sector studied, the contorsion equation can be solved directly in terms of the spin current, reducing the full field equations to modified Riemannian Einstein equations driven by an effective fluid with spin-squared corrections. The authors derive effective energy density and pressure components — both isotropic and anisotropic — and show that unlike in standard Einstein–Cartan theory, the spin-spin interaction coefficient is not fixed but depends on the quadratic-torsion coupling constants. Using the DD2 nuclear equation of state and modified Tolman–Oppenheimer–Volkoff equations solved numerically, they find that for the positive effective spin-spin coupling branch, torsion corrections make stellar configurations more compact, reduce the maximum mass, and lower binding energy relative to general-relativistic predictions. Notably, spin-correlation anisotropy has negligible impact on the mass–radius relation for the smooth, weakly polarized spin profiles considered.
What's missing
The study considers only the positive effective spin-spin coupling branch; results for the negative coupling branch are not presented, leaving open whether that regime produces qualitatively different or observationally distinguishable neutron star sequences. The work uses a single nuclear equation of state (DD2), so sensitivity to equation-of-state uncertainty is not assessed. As a preprint, the results have not yet undergone peer review.
What different sources said
- arXiv astro-phCenter
Neutron stars in Poincar\'e gauge gravity with quadratic torsion
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