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Universe 2018, 4(9), 94; https://doi.org/10.3390/universe4090094

Two Novel Approaches to the Hadron-Quark Mixed Phase in Compact Stars

1
Laboratory for Information Technologies, Joint Institute for Nuclear Research, Joliot-Curie Street 6, Dubna 141980, Russia
2
Bogoliubov Laboratory for Theoretical Physics, Joint Institute for Nuclear Research, Joliot-Curie Street 6, Dubna 141980, Russia
3
Institute of Theoretical Physics, University of Wroclaw, Max Born Place 9, 50-204 Wroclaw, Poland
4
National Research Nuclear University (MEPhI), Kashirskoe Shosse 31, Moscow 115409, Russia
5
Department of Physics, Yerevan State University, Alek Manukyan Str. 1, Yerevan 0025, Armenia
*
Authors to whom correspondence should be addressed.
Received: 23 July 2018 / Revised: 31 August 2018 / Accepted: 31 August 2018 / Published: 5 September 2018
(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram)
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Abstract

First-order phase transitions, such as the liquid-gas transition, proceed via formation of structures, such as bubbles and droplets. In strongly interacting compact star matter, at the crust-core transition but also the hadron-quark transition in the core, these structures form different shapes dubbed “pasta phases”. We describe two methods to obtain one-parameter families of hybrid equations of state (EoS) substituting the Maxwell construction that mimic the thermodynamic behaviour of pasta phase in between a low-density hadron and a high-density quark matter phase without explicitly computing geometrical structures. Both methods reproduce the Maxwell construction as a limiting case. The first method replaces the behaviour of pressure against chemical potential in a finite region around the critical pressure of the Maxwell construction by a polynomial interpolation. The second method uses extrapolations of the hadronic and quark matter EoS beyond the Maxwell point to define a mixing of both with weight functions bounded by finite limits around the Maxwell point. We apply both methods to the case of a hybrid EoS with a strong first order transition that entails the formation of a third family of compact stars and the corresponding mass twin phenomenon. For both models, we investigate the robustness of this phenomenon against variation of the single parameter: the pressure increment at the critical chemical potential that quantifies the deviation from the Maxwell construction. We also show sets of results for compact star observables other than mass and radius, namely the moment of inertia and the baryon mass. View Full-Text
Keywords: quark-hadron phase transition; pasta phases; speed of sound; hybrid compact stars; mass-radius relation; GW170817 quark-hadron phase transition; pasta phases; speed of sound; hybrid compact stars; mass-radius relation; GW170817
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Abgaryan, V.; Alvarez-Castillo, D.; Ayriyan, A.; Blaschke, D.; Grigorian, H. Two Novel Approaches to the Hadron-Quark Mixed Phase in Compact Stars. Universe 2018, 4, 94.

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