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Implications of Kaon Condensation in Dense Nuclear Matter for Recent Light Compact Star Observations

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Published: Feb 24, 2026
DOI: https://doi.org/10.12681/hnpsanp.8836
Keywords:
Neutron Stars Kaon Condensation Nuclear Matter
Martin Veselsky
Institute of Experimental and Applied Physics, Czech Technical University, Prague, 110 00, Czechia
https://orcid.org/0000-0002-7803-0109
Polichronis Koliogiannis
Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000, Zagreb, Croatia
https://orcid.org/0000-0001-9326-7481
Vlasios Petousis
Institute of Experimental and Applied Physics, Czech Technical University, Prague, 110 00, Czechia
Jozef Leja
Faculty of Mechanical Engineering, Slovak University of Technology in Bratislava, 812 31 Bratislava, Slovakia
Charalampos Moustakidis
Department of Theoretical Physics, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece
Abstract

Recent measurements of the compact star XTE J1814-338, with a mass of M=1.2-0.05+0.05 Mø and a radius of R=7-0.4+0.4 Km alongside those of HESS J1731-347, which has a mass of M=0.77-0.17+0.20 Mø and a radius of R=10.4-0.78+0.86 Km, provide compelling evidence for the potential existence of exotic matter in neutron star cores. These observations offer important insights into the equation of state of dense nuclear matter. In this study, we explore the presence of negatively charged kaons and neutral anti-kaons (K- and \bar{K0}) within neutron stars (NSs) using a Relativistic Mean Field (RMF) model with first order kaon condensate. To our knowledge, this is the first alternative approach aiming to simultaneously explain the observed properties of both XTE J1814-338 and HESS J1731-347 by invoking kaon condensation in dense matter. Furthermore, we compare our model with recent data from the pulsars PSR J0437-4715 and
PSR J1231-1411, and argue that a two-branch scenario, each representing a distinct form of nuclear matter, may be necessary to account for the diverse range of compact astrophysical objects.

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