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In this lecture, we give a first introduction to neutron stars, based on fundamental physical principles. After outlining their outstanding macroscopic properties, as obtained from observations, we infer the extreme conditions of matter in…

High Energy Astrophysical Phenomena · Physics 2016-09-27 Pierre M. Pizzochero

We review some recent results about the mechanism of deconfinement of hadronic matter into quark matter in cold neutron stars and protoneutron stars. We discuss the role of finite size effects and the relevance of temperature and density…

High Energy Astrophysical Phenomena · Physics 2017-09-01 Germán Lugones

We study compact stars with hybrid equations of state consisting of a nuclear outer region and two nested quark phases, each separated from the lower density phase by a strong first-order phase transition. The stability of these models is…

High Energy Astrophysical Phenomena · Physics 2023-05-26 Peter B. Rau , Armen Sedrakian

In this work, we consider the consequences of phase transition in dense QCD on the properties of compact stars and implications for the observational program in gravitational wave and X-ray astrophysics. The key underlying assumption of our…

High Energy Astrophysical Phenomena · Physics 2023-01-27 Jia Jie Li , Armen Sedrakian , Mark Alford

We extract the equation of state of hot quark matter from a holographic 2+1 flavor QCD model, which could form the core of a stable compact star. By adding a thin hadron shell, a new type of hybrid star is constructed. With the temperature…

High Energy Physics - Phenomenology · Physics 2026-01-01 Le-Feng Chen , Heng-Yi Yuan , Meng-Hua Zhou , Kun Lu , Jing-Yi Wu , Kilar Zhang

In agreement with the constantly increasing gravitational wave events, new aspects of the internal structure of compact stars can be considered. A scenario in which a first order transition takes place inside these stars is of particular…

High Energy Astrophysical Phenomena · Physics 2023-02-07 Lazaros Tsaloukidis , P. S. Koliogiannis , A. Kanakis-Pegios , Ch. C. Moustakidis

We explore an alternative explanation for the low-mass ultra-compact star in the supernova remnant HESS~J1731-347 using a model-agnostic approach to construct hybrid equations of state. The hadronic part of the hybrid equation of state is…

High Energy Astrophysical Phenomena · Physics 2024-08-20 Mauro Mariani , Ignacio F. Ranea-Sandoval , Germán Lugones , Milva G. Orsaria

An equation of state is considered that, in superdense nuclear matter, results in a phase transition of the first kind from the nucleon state to the quark state with a transition parameter Lambda> 3/2. A calculation of the integrated…

Astrophysics · Physics 2014-10-13 G. B. Alaverdyan , A. R. Harutyunyan , Yu. L. Vartanyan

We study the rotational properties of inverted hybrid stars (also termed cross stars), which have been recently proposed as a possible new class of compact stars characterized by an outer layer of quark matter and a core of hadrons, in an…

High Energy Astrophysical Phenomena · Physics 2025-04-10 Rodrigo Negreiros , Chen Zhang , Renxin Xu

Using parametric equations of state (relativistic polytropes and a simple quark bag model) to model dense-matter phase transitions, we study global, measurable astrophysical parameters of compact stars such as their allowed radii and tidal…

High Energy Astrophysical Phenomena · Physics 2019-11-01 Magdalena Sieniawska , Władysław Turczański , Michał Bejger , Julian Leszek Zdunik

In the present study, we employ three distinct, physically motivated speed of sound bounds to construct hybrid models, where the high-density phase is described by the maximally stiff equation of state. In particular, we consider the bounds…

High Energy Astrophysical Phenomena · Physics 2025-02-05 P. Laskos-Patkos , G. A. Lalazissis , Sibo Wang , Jie Meng , Peter Ring , Ch. C. Moustakidis

We investigate a simple holographic model for cold and dense deconfined QCD matter consisting of three quark flavors. Varying the single free parameter of the model and utilizing a Chiral Effective Theory equation of state (EoS) for nuclear…

High Energy Astrophysical Phenomena · Physics 2019-01-30 Eemeli Annala , Christian Ecker , Carlos Hoyos , Niko Jokela , David Rodríguez Fernández , Aleksi Vuorinen

We construct a generalized EFT approach to dense compact-star matter that exploits the CCP for hadron-quark continuity at high density, hidden topology and hidden symmetries of QCD. No Landau-Ginzburg-Wilsonian-type phase transition is…

Nuclear Theory · Physics 2020-07-15 Yong-Liang Ma , Mannque Rho

The properties of neutron stars constituted of a crust of hadrons and an internal part of hadrons and kaon condensate are calculated within the quark-meson-coupling model. We have considered stars with nucleons only in the hadron phase and…

Astrophysics · Physics 2009-11-11 D. P. Menezes , P. K. Panda , C. Providencia

We investigate protoneutron star matter using the state-of-the-art perturbative equation of state for cold and dense QCD in the presence of a fixed lepton fraction in which both electrons and neutrinos are included. Besides computing the…

High Energy Physics - Phenomenology · Physics 2018-05-23 J. C. Jiménez , E. S. Fraga

This short review aims at giving a brief overview of the various states of matter that have been suggested to exist in the ultra-dense centers of neutron stars. Particular emphasis is put on the role of quark deconfinement in neutron stars…

Solar and Stellar Astrophysics · Physics 2014-08-04 Fridolin Weber , Gustavo A. Contrera , Milva G. Orsaria , William Spinella , Omair Zubairi

Based on a quasiparticle model for \beta stable and electrically neutral deconfined matter we address the mass-radius relation of pure quark stars. The model is adjusted to recent hot lattice QCD results for 2 + 1 flavors with almost…

Nuclear Theory · Physics 2009-12-17 R. Schulze , B. Kampfer

We study the equation state of strongly interacting quark matter within a NJL-like model in which the chiral condensates and the color superconducting gaps are computed self-consistently as a function of the baryon density. A vector…

Astrophysics · Physics 2008-11-26 G. Pagliara , J. Schaffner-Bielich

(abridged) We construct quark-diquark equations of state using the quark mass density-dependent formalism. A region inside a $2-D$ parameter space in which this matter is absolutely stable is identified. Motivated by the reported…

Astrophysics · Physics 2009-11-07 G. Lugones , J. E. Horvath

The nucleation process of quark matter in cold (T = 0) stellar matter is investigated using the microscopic Brueckner-Hartree-Fock approach to describe the hadronic phase, and the MIT bag model, the Nambu-Jona-Lasinio, and the Chromo…

Nuclear Theory · Physics 2015-06-04 Domenico Logoteta , Constança Providência , Isaac Vidana , Ignazio Bombaci