XIIIth International Symposium on Nuclear Symmetry Energy (NuSym25)

Disentangling symmetry energy and surface properties of warm nuclear matter for binary neutron star mergers equation of state

9 Sept 2025, 16:50

2h 10m

Auditorium (8F) (Integrated Innovation Building (IIB), RIKEN Kobe Campus)

8. Theory of compact stars, including neutron star mergers and supernovae NuSym Poster Session

Speaker

Guilherme Grams (University of Potsdam)

Description

The properties of neutron star matter in the low-density regime, where nucleonic clusters coexist with a neutron fluid, remain rather uncertain, but are essential for the accurate modelling of neutron star mergers. We systematically explore how nuclear physics inputs, particularly those related to the symmetry energy and the treatment of finite-size effects, impact the properties of warm, inhomogeneous matter.
We start by comparing zero-temperature models: compressible liquid-drop, extended Thomas-Fermi (ETF), and ETF with shell corrections, highlighting their different treatment of surface tension and quantum effects, and their consequences for crustal composition [1]. Then, we assess how chiral Effective Field Theory and Skyrme interactions diverge in predictions for the neutron star crusts [2], emphasizing the role of pure neutron matter and the symmetry energy. At finite temperatures, we contrast compressible liquid-drop and temperature-dependent ETF approaches, revealing agreements in thermodynamics but discrepancies in cluster composition and neutron skin thickness [3].
We will present new results with different Skyrme parametrizations that demonstrate how variations in the symmetry energy at T > 0 alter the crust-core transition, cluster populations (A, Z), pressure, and sound speed—key ingredients for merger simulations.
We conclude by discussing open questions: Should one prioritize symmetry energy constraints, surface energy descriptions, or both? How do these choices affect gravitational-wave observables and kilonova signals?
Our work provides a benchmark for constructing a unified equation of state at finite temperatures, clarifying where simplified models are sufficient and where microscopic treatments are necessary for multi-messenger astronomy.

[1] G. Grams, J. Margueron, R. Somasundaram, N. Chamel, and, S. Goriely, J Phys: Conf.Seri, 2340, 012030 (2022).
[2] G. Grams, J. Margueron, R. Somasundaram, and S. Reddy, Eur. Phys. J. A 58, 56 (2022).
[3] G. Grams, N.N. Shchechilin, T. Diverres, A.F. Fantina, N. Chamel, F. Gulminelli, Universe, 11, 172 (2025).