Kaon Production in Heavy-Ion Collisions and Maximum Mass of Neutron Stars

Abstract

We determine an 'empirical' kaon dispersion relation by analysing and fitting recent experimental data on kaon production in heavy-ion collisions. We then investigate its effects on hadronic equation of state at high densities and on neutron star properties. We find that the maximum mass of neutron stars can be lowered by about 0.4M⊙, once kaon condensation as constrained by our empirical dispersion relation is introduced. We emphasize the growing interplay between hadron physics, relativistic heavy-ion physics and the physics of compact objects in astrophysics. 25.75.Dw, 97.60.Jd, 26.60.+c, 24.10.Lx There is currently growing interplay between the physics of hadrons (especially the properties of hadrons in dense matter which might reflect spontaneous chiral symmetry breaking and its restoration), the physics of relativistic heavy-ion collisions (from which one might extract hadron properties in dense matter), and the physics of compact objects in astrophysics (which needs as inputs the information gained from the first two fields). A notable example is the kaon (K andK), which, being a Goldstone boson with strangeness, plays a special role in all of the three fields mentioned.Ever since the pioneering work of Kaplan and Nelson [1] on the possibility of kaon condensation in nuclear matter, much theoretical effort has been devoted to the study of kaon properties in dense matter. Brown et al.[2] have carried out a detailed study of free-space and in-medium kaon-nucleon scattering using chiral perturbation theory. Yuba et al. studied kaon in-medium properties based on phenomenological off-shell meson-nucleon interactions [3]. Weise and collaborators investigated this problem using the Nambu−Jona-Lasinio model, treating the kaon as a quark-antiquark excitation [4]. Recently they have extended the chiral perturbation calculation to include the coupled-channel effects which are important for the K − meson [5]. Another type of study, which is based on the extension of the Walecka meanfield model from SU(2) to SU(3), was pursued by Schaffner et al. [6] and Knorren et al. [7]. Although quantitatively results from these different models are not identical, qualitatively, a consistent picture has emerged; namely, in nuclear matter the K + feels a weak repulsive potential, whereas the K − feels a strong attractive potential. Measurements of kaon spectra and flow have been carried out in heavy-ion collisions at SIS (1-2 AGeV), AGS (10 AGeV), and SPS (200 AGeV) energies [8]. By comparing transport model predictions with experimental data, one can learn not only the global reaction dynamics, but more importantly, the kaon properties in dense matter. Of special interest is kaon production in heavy-ion collisions at SIS energies, as it has been shown that particle production at subthreshold energies is sensitive to its properties in dense matter [9]. Recently, high quality data concerning K + and K − production in heavy-ion collisions at SIS energies have been published by the KaoS collaboration at GSI [10]. The KaoS data show...

Third family of superdense stars in the presence of antikaon condensates

“…It was observed in previous calculations that antikaons experienced an attractive potential and kaons had a repulsive interaction in nuclear matter [30,[32][33][34][35][36]. The analysis of K − atomic data in the hybrid model [32] yielded the real part of the antikaon optical potential as large as UK = −180±20MeV at normal nuclear matter density but it was repulsive at low density in accordance with the low density theorem.…”

Ultra-Dense Neutron Star Matter, Strange Quark Stars, and the Nuclear Equation of State

“…Consequently, the collapsing core of a supernova, e.g. 1987A, if heavier than this value, should go into a black hole rather than forming a neutron star, as pointed out by Brown et al 30,59,60 This would imply the existence of a large number of low-mass black holes in our galaxy 30 . Thielemann and Hashimoto 64 deduced from the total amount of ejected 56 Ni in supernova 1987A a neutron star mass range of 1.43 − 1.52 M ⊙ .…”

Melting of antikaon condensate in protoneutron stars

“…They investigated the problem within the SU(3) L × SU(3) R chiral perturbation theory. Later detailed studies on antikaon condensation in neutron star interior were carried out in the chiral perturbation theory [9][10][11][12][13] as well as meson exchange models [2,7,[14][15][16][17][18][19][20][21]. The first order phase transition from nuclear matter to antikaon condensed matter was either studied using Maxwell construction or Gibbs' phase equilibrium rules.…”