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We study the axial quasi-normal modes of neutron stars in scalar-tensor theories with massive scalar field including a self-interacting term in the potential. Various realistic equations of state including nuclear, hyperonic and hybrid…

General Relativity and Quantum Cosmology · Physics 2019-05-08 Zahra Altaha Motahar , Jose Luis Blázquez-Salcedo , Daniela D. Doneva , Jutta Kunz , Stoytcho S. Yazadjiev

Diffferentially rotating stars can support significantly more mass in equilibrium than nonrotating or uniformly rotating stars, according to general relativity. The remnant of a binary neutron star merger may give rise to such a…

Astrophysics · Physics 2009-10-31 Stuart L. Shapiro

Binary neutron star mergers, which can lead to less massive black holes relative to other known astrophysical channels, have the potential to probe modifications to general relativity that arise at smaller curvature scales compared to more…

General Relativity and Quantum Cosmology · Physics 2022-11-29 William E. East , Frans Pretorius

Scalar-tensor theories are well studied extensions of general relativity that offer deviations which are yet within observational boundaries. We present the time evolution equations governing the perturbations of a nonrotating scalarized…

General Relativity and Quantum Cosmology · Physics 2021-07-06 Christian J. Krüger , Daniela D. Doneva

There has been a recent revival in understanding the spontaneous scalarization phenomenon in scalar-tensor gravity as a phase transition. Using the tools of the Landau theory, we now know that first-order transitions where scalarization…

General Relativity and Quantum Cosmology · Physics 2026-04-24 Kalin V. Staykov , Fethi M. Ramazanoğlu , Daniela D. Doneva , Stoytcho S. Yazadjiev

We study torsional oscillations of neutron stars in the scalar-tensor theory of gravity using the relativistic Cowling approximation. We compute unperturbed neutron star models adopting realistic equations of state for the neutron star's…

General Relativity and Quantum Cosmology · Physics 2014-12-24 Hector O. Silva , Hajime Sotani , Emanuele Berti , Michael Horbatsch

We investigate the dynamical stability of relativistic, differentially rotating, quasi-toroidal models of neutron stars through hydrodynamical simulations in full general relativity. We find that all quasi-toroidal configurations studied in…

High Energy Astrophysical Phenomena · Physics 2019-08-21 Pedro L. Espino , Vasileios Paschalidis , Thomas W. Baumgarte , Stuart L. Shapiro

We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can form in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both…

We present a full 3D numerical evolution code to study neutron stars in massive-scalar-tensor theories. The code is embedded in the Einstein Toolkit framework and its implementation constitutes a modified version of the…

General Relativity and Quantum Cosmology · Physics 2026-05-19 José Carlos Olvera M. , Daniela D. Doneva , Pablo Cerdá-Durán , José A. Font , Stoytcho S. Yazadjiev

The main features of the gravitational dynamics of binary neutron star systems are now well established. While the inspiral can be precisely described in the post-Newtonian approximation, fully relativistic magneto-hydrodynamical…

High Energy Astrophysical Phenomena · Physics 2020-10-23 Matteo Lucca , Laura Sagunski , Federico Guercilena , Christian M. Fromm

As we showed in previous work, the dynamics and gravitational emission of binary neutron star systems in certain scalar-tensor theories can differ significantly from that expected from General Relativity in the coalescing stage. In this…

General Relativity and Quantum Cosmology · Physics 2015-04-22 Marcelo Ponce , Carlos Palenzuela , Enrico Barausse , Luis Lehner

We study the solution space of general relativistic, axisymmetric, equilibria of differentially rotating neutron stars with realistic, nuclear equations of state. We find that different types of stars, which were identified by earlier works…

High Energy Astrophysical Phenomena · Physics 2019-05-08 Pedro Espino , Vasileios Paschalidis

We present our study of stability of differentially rotating, axisymmetric neutron stars described by a polytropic equation of state with $\Gamma = 2$. We focus on quasi-toroidal solutions with a degree of differential rotation $\widetilde…

High Energy Astrophysical Phenomena · Physics 2024-02-29 Paweł Szewczyk , Dorota Gondek-Rosińska , Pablo Cerdá-Durán

We study static, spherically symmetric neutron stars in a class of scalar-tensor theories with non-canonical kinetic terms (K-essence) obeying all causality and hyperbolicity conditions. These models have non-trivial dynamics that lead to a…

General Relativity and Quantum Cosmology · Physics 2025-09-12 Mark P. Hertzberg , Oleksandr S. Stashko

The merger of binary neutron stars is likely to lead to differentially rotating remnants. In this paper, we survey several cold nuclear equations of state (EOSs) and numerically construct models of differentially rotating neutron stars in…

Astrophysics · Physics 2009-11-10 Ian A. Morrison , Thomas W. Baumgarte , Stuart L. Shapiro

We study the main astrophysical properties of differentially rotating neutron stars described as stationary and axisymmetric configurations of a moderately stiff $\Gamma=2$ polytropic fluid. The high level of accuracy and of stability of…

High Energy Astrophysical Phenomena · Physics 2017-03-08 Dorota Gondek-Rosinska , Izabela Kowalska , Loic Villain , Marcus Ansorg , Marcin Kucaba

Modified theories of gravity that offer viable models for dark energy often rely on mechanisms that screen their effects in high density environments. From this perspective, it would appear that, once solar system constraints are satisfied,…

General Relativity and Quantum Cosmology · Physics 2020-07-24 Bernardo F. de Aguiar , Raissa F. P. Mendes

We consider the effect of scalarization on static and slowly rotating neutron stars for a wide variety of realistic equations of state, including pure nuclear matter, nuclear matter with hyperons, hybrid nuclear and quark matter, and pure…

General Relativity and Quantum Cosmology · Physics 2017-09-28 Zahra Altaha Motahar , Jose Luis Blázquez-Salcedo , Burkhard Kleihaus , Jutta Kunz

Scalar-tensor gravity models are among the prime candidates to explain cosmic acceleration, and compact stars provide unique laboratories for testing such theories. Predictions of scalar-tensor gravity in compact stars can be examined…

High Energy Astrophysical Phenomena · Physics 2025-10-08 Fahimeh Rahimi , Zeinab Rezaei , Adamu Issifu

The stability properties of rotating relativistic stars against prompt gravitational collapse to a black hole are rather well understood for uniformly rotating models. This is not the case for differentially rotating neutron stars, which…

General Relativity and Quantum Cosmology · Physics 2018-01-12 Lukas R. Weih , Elias R. Most , Luciano Rezzolla