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We study how rapid rotation influences the relation between the normalized moment of inertia $\bar{I}$ and quadrupole moment $\bar{Q}$ for scalarized neutron stars. The questions one has to answer are whether the EOS universality is…

General Relativity and Quantum Cosmology · Physics 2015-06-22 Daniela D. Doneva , Stoytcho S. Yazadjiev , Kalin V. Staykov , Kostas D. Kokkotas

We present the field equations governing the equilibrium of rapidly rotating neutron stars in scalar-tensor theories of gravity, as well as representative numerical solutions. The conditions for the presence of a nontrivial scalar field and…

General Relativity and Quantum Cosmology · Physics 2014-02-25 Daniela D. Doneva , Stoytcho S. Yazadjiev , Nikolaos Stergioulas , Kostas D. Kokkotas

In the scalar-tensor theories with a massive scalar field the coupling constants, and the coupling functions in general, which are observationally allowed, can differ significantly from those in the massless case. This fact naturally…

General Relativity and Quantum Cosmology · Physics 2016-04-27 Stoytcho S. Yazadjiev , Daniela D. Doneva , Dimitar Popchev

We construct models of slowly rotating, perfect-fluid neutron stars by extending the classical Hartle-Thorne formalism to generic scalar-tensor theories of gravity. Working at second order in the dimensionless angular momentum, we compute…

General Relativity and Quantum Cosmology · Physics 2014-07-15 Paolo Pani , Emanuele Berti

Binary pulsar observations and gravitational wave detections seriously constrained scalar-tensor theories with massless scalar field allowing only small deviations from general relativity. If we consider a nonzero mass of the scalar field,…

General Relativity and Quantum Cosmology · Physics 2018-08-15 Kalin V. Staykov , Dimitar Popchev , Daniela D. Doneva , Stoytcho S. Yazadjiev

We consider a universal relation between moment of inertia and quadrupole moment of arbitrarily fast rotating neutron stars. Recent studies suggest that this relation breaks down for fast rotation. We find that it is still universal among…

General Relativity and Quantum Cosmology · Physics 2014-06-30 Sayan Chakrabarti , Térence Delsate , Norman Gürlebeck , Jan Steinhoff

We present the first numerical models of differentially rotating stars in alternative theories of gravity. We chose a particular class of scalar-tensor theories of gravity that is indistinguishable from GR in the weak field regime but can…

General Relativity and Quantum Cosmology · Physics 2018-12-05 Daniela D. Doneva , Stoytcho S. Yazadjiev , Nikolaos Stergioulas , Kostas D. Kokkotas

We are investigating universal relations between different normalisations of the moment of inertia and the compactness of neutron stars in slow rotation approximation. We study the relations in particular class of massive scalar-sensor…

General Relativity and Quantum Cosmology · Physics 2019-03-27 Dimitar Popchev , Kalin V. Staykov , Daniela D. Doneva , Stoytcho S. Yazadjiev

We perform the first study of the oscillation frequencies of rapidly rotating neutron stars in alternative theories of gravity, focusing mainly on the fundamental $f$-modes. We concentrated on a particular class of alternative theories -…

General Relativity and Quantum Cosmology · Physics 2017-09-13 Stoytcho S. Yazadjiev , Daniela D. Doneva , Kostas D. Kokkotas

Recently it was shown that slowly rotating neutron stars exhibit an interesting correlation between their moment of inertia $I$, their quadrupole moment $Q$, and their tidal deformation Love number $\lambda$ (the I-Love-Q relations),…

General Relativity and Quantum Cosmology · Physics 2014-03-31 George Pappas , Theocharis A. Apostolatos

As some of the most compact stellar objects in the universe, neutron stars are unique cosmic laboratories. The study of neutron stars provides an ideal theoretical testbed for investigating both physics at supra-nuclear densities as well as…

High Energy Astrophysical Phenomena · Physics 2023-05-29 Grigorios Papigkiotis , George Pappas

We are investigating universal relations between different normalisations of the moment of inertia and the compactness of neutron and strange stars. Slowly rotating as well as rapidly rotating models are studied in General Relativity,…

General Relativity and Quantum Cosmology · Physics 2016-04-13 Kalin V. Staykov , Daniela D. Doneva , Stoytcho S. Yazadjiev

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

It was shown recently, that normalized relations between the moment of inertia (I), the quadrupole moment (Q) and the tidal deformability (Love number) exist and for slowly-rotating neutron stars they are almost independent of the equation…

General Relativity and Quantum Cosmology · Physics 2014-02-25 Daniela D. Doneva , Stoytcho S. Yazadjiev , Nikolaos Stergioulas , Kostas D. Kokkotas

Neutron stars (NSs) in scalar-tensor theories of gravitation with the phenomenon of spontaneous scalarization can develop significant deviations from general relativity. Cases with a massless scalar were studied widely. Here we compare the…

General Relativity and Quantum Cosmology · Physics 2025-04-01 Zexin Hu , Yong Gao , Rui Xu , Lijing Shao

$f(R)$ theories of gravity are one of the most popular alternative explanations for dark energy and therefore studying the possible astrophysical implications of these theories is an important task. In the present paper we make a…

General Relativity and Quantum Cosmology · Physics 2015-06-23 Stoytcho S. Yazadjiev , Daniela D. Doneva , Kostas D. Kokkotas

A number of hadronic equations of state for neutron stars have been investigated for the purpose of the present paper, considering the fact that at sufficiently high density, heavy baryons and quark phases may appear. The observational…

Nuclear Theory · Physics 2026-02-04 Sujan Kumar Roy , Gargi Chaudhuri

We provide accurate universal relations that allow to estimate the moment of inertia $I$ and the ratio of kinetic to gravitational binding energy $T/W$ of uniformly rotating neutron stars from the knowledge of mass, radius, and moment of…

General Relativity and Quantum Cosmology · Physics 2024-01-17 Christian J. Krüger , Sebastian H. Völkel

We investigated universal relations for compact stars rotating at the Keplerian (mass-shedding) limit, which is highly relevant for understanding the rapidly rotating objects formed in the aftermath of a neutron star-neutron star merger.…

High Energy Astrophysical Phenomena · Physics 2025-10-15 Pion Sudarshan Yeasin , Stefanos Tsiopelas , Armen Sedrakian , Jia-Jie Li

Recently, general relations among the quadrupole moment (Q), the moment of inertia (I), and the tidal deformability (Love number) of a neutron star were shown to exist. They are nearly independent of the nuclear matter equation of state and…

Solar and Stellar Astrophysics · Physics 2014-06-27 Brynmor Haskell , Riccardo Ciolfi , Francesco Pannarale , Luciano Rezzolla
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