Light clusters in warm stellar matter: calibrating the cluster couplings
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Regular Article - Theoretical Physics
Light clusters in warm stellar matter: calibrating the cluster couplings Tiago Custódio1, Alexandre Falcão1, Helena Pais1,a , Constança Providência1, Francesca Gulminelli2 , Gerd Röpke3,4 1
CFisUC, Department of Physics, University of Coimbra, 3004-516 Coimbra, Portugal ENSICAEN, UNICAEN, CNRS/IN2P3, LPC Caen, Normandie University, 14000 Caen, France 3 Institut für Physik, Universität Rostock, 18051 Rostock, Germany 4 National Research Nuclear University (MEPhI), 115409 Moscow, Russia
2
Received: 29 September 2020 / Accepted: 6 November 2020 / Published online: 23 November 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Communicated by David Blaschke
Abstract The abundances of light clusters within a formalism that considers in-medium effects are calculated using several relativistic mean-field models, with both densitydependent and density-independent couplings. Clusters are introduced as new quasiparticles, with a modified coupling to the scalar meson field. A comparison with experimental data from heavy ion collisions allows settling the model dependence of the results and the determination of the couplings of the light clusters to the meson fields. We find that extra experimental constraints at higher density are needed to convincingly pin down the density associated to the melting of clusters in the dense nuclear medium. The role of neutron rich clusters, such as 6 He, in asymmetric matter is discussed.
1 Introduction Below saturation density, nuclear matter is supposed to undergo a liquid-gas phase transition [1–3]. Since in physical systems nuclear matter is electrically charged, the phase separation will produce clusterized matter. This behavior is directly reflected in several astrophysical sites, like corecollapse supernovae [4–8], neutron star (NS) mergers [9– 11], and the inner crust of neutron stars [12–14]. The form of the clusterized matter depends on temperature and isospin asymmetry. In cold catalysed beta-equilibrium matter, as the one occuring in neutron stars, spherical clusters are found in almost the whole inner crust region, and close to the crust-core transition, the competition between surface and Coulomb forces gives rise to cluster configurations of different geometries coined “pasta phases” [12]. These types of clusters may survive even at finite temperature [15–20]. a e-mail:
Light clusters, i.e. light nuclei like deuterons or α−particles, will form in warm stellar matter as found in core-collapse supernova matter, proto-neutron stars or binary neutron star mergers, and may also coexist with heavy clusters at densities above 10−2 fm−3 , if the temperature does not overcome a few MeV. The presence of light clusters affects the rates of the reactions involving the weak force, and therefore, may impact the supernova dynamics [4,21]. In the NS merger evolution, the α particles play an important role on the dissolution of the remnant torus of accreted matter that surrounds the central high-mass NS f
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