All Outputs (39)

Self-interactions and spontaneous black hole scalarization (2019)
Journal Article
Macedo, C. F., Sakstein, J., Berti, E., Gualtieri, L., Silva, H. O., & Sotiriou, T. P. (2019). Self-interactions and spontaneous black hole scalarization. Physical Review D, 99(10), 1-11. https://doi.org/10.1103/physrevd.99.104041

It has recently been shown that nontrivial couplings between a scalar and the Gauss-Bonnet invariant can give rise to black hole spontaneous scalarization. Theories that exhibit this phenomenon are among the leading candidates for testing gravity wit... Read More about Self-interactions and spontaneous black hole scalarization.

Multipole moments and universal relations for scalarized neutron stars (2019)
Journal Article
Pappas, G., Doneva, D. D., Sotiriou, T. P., Yazadjiev, S. S., & Kokkotas, K. D. (2019). Multipole moments and universal relations for scalarized neutron stars. Physical Review D, 99(10), Article 104014. https://doi.org/10.1103/physrevd.99.104014

In recent years there has been a surge of interest in what has come to be known as the “universal relations” between various global properties of neutron stars. These universal relations are equation of state independent relations between quantities... Read More about Multipole moments and universal relations for scalarized neutron stars.

Black holes and binary mergers in scalar Gauss-Bonnet gravity: Scalar field dynamics (2019)
Journal Article
Witek, H., Gualtieri, L., Pani, P., & Sotiriou, T. P. (2019). Black holes and binary mergers in scalar Gauss-Bonnet gravity: Scalar field dynamics. Physical Review D, 99(6), 1-24. https://doi.org/10.1103/physrevd.99.064035

We study the nonlinear dynamics of black holes that carry scalar hair and binaries composed of such black holes. The scalar hair is due to a linear or exponential coupling between the scalar and the Gauss-Bonnet invariant. We work perturbatively in t... Read More about Black holes and binary mergers in scalar Gauss-Bonnet gravity: Scalar field dynamics.

Stability of scalarized black hole solutions in scalar-Gauss-Bonnet gravity (2019)
Journal Article
Silva, H. O., Macedo, C. F., Sotiriou, T. P., Gualtieri, L., Sakstein, J., & Berti, E. (2019). Stability of scalarized black hole solutions in scalar-Gauss-Bonnet gravity. Physical Review D, 99(6), 1-9. https://doi.org/10.1103/physrevd.99.064011

Scalar-tensor theories of gravity where a new scalar degree of freedom couples to the Gauss-Bonnet invariant can exhibit the phenomenon of spontaneous black hole scalarization. These theories admit both the classic black hole solutions predicted by g... Read More about Stability of scalarized black hole solutions in scalar-Gauss-Bonnet gravity.

Dynamical obstruction to perpetual motion from Lorentz-violating black holes (2018)
Journal Article
Benkel, R., Bhattacharyya, J., Louko, J., Mattingly, D., & Sotiriou, T. P. (2018). Dynamical obstruction to perpetual motion from Lorentz-violating black holes. Physical Review D, 98(2), Article 024034. https://doi.org/10.1103/PhysRevD.98.024034

Black holes in Lorentz-violating theories have been claimed to violate the second law of thermodynamics by perpetual motion energy extraction. We revisit this question for a Penrose splitting process in a spherically symmetric setting with two specie... Read More about Dynamical obstruction to perpetual motion from Lorentz-violating black holes.

Spontaneous scalarization of black holes and compact stars from a Gauss-Bonnet coupling (2018)
Journal Article
Silva, H. O., Sakstein, J., Gualtieri, L., Sotiriou, T. P., & Berti, E. (2018). Spontaneous scalarization of black holes and compact stars from a Gauss-Bonnet coupling. Physical Review Letters, 120(13), Article 131104. https://doi.org/10.1103/PhysRevLett.120.131104

We identify a class of scalar-tensor theories with coupling between the scalar and the Gauss-Bonnet invariant that exhibit spontaneous scalarization for both black holes and compact stars. In particular, these theories formally admit all of the stati... Read More about Spontaneous scalarization of black holes and compact stars from a Gauss-Bonnet coupling.

Revisiting the cuscuton as a Lorentz-violating gravity theory (2018)
Journal Article
Bhattacharyya, J., Coates, A., Colombo, M., Gümrükçüoğlu, A. E., & Sotiriou, T. P. (2018). Revisiting the cuscuton as a Lorentz-violating gravity theory. Physical Review D, 97(6), https://doi.org/10.1103/PhysRevD.97.064020

The cuscuton is a scalar field with infinite speed of propagation. It was introduced in the context of cosmology but it has also been claimed to resemble Horava gravity in a certain limit. Here we revisit the cuscuton theory as a Lorentz-violating gr... Read More about Revisiting the cuscuton as a Lorentz-violating gravity theory.

Constructing neutron stars with a gravitational Higgs mechanism (2018)
Journal Article
Franchini, N., Coates, A., & Sotiriou, T. P. (2018). Constructing neutron stars with a gravitational Higgs mechanism. Physical Review D, 97(6), https://doi.org/10.1103/PhysRevD.97.064013

In scalar-tensor theories, spontaneous scalarization is a phase transition that can occur in ultradense environments such as neutron stars. The scalar field develops a non-trivial configuration once the stars exceeds a compactness threshold. We recen... Read More about Constructing neutron stars with a gravitational Higgs mechanism.

Detecting Lorentz violations with gravitational waves from black hole binaries (2018)
Journal Article
Sotiriou, T. P. (2018). Detecting Lorentz violations with gravitational waves from black hole binaries. Physical Review Letters, 120(4), https://doi.org/10.1103/PhysRevLett.120.041104

Gravitational wave observations have been used to test Lorentz symmetry by looking for dispersive effects that are caused by higher order corrections to the dispersion relation. In this Letter I argue on general grounds that, when such corrections ar... Read More about Detecting Lorentz violations with gravitational waves from black hole binaries.

Gravitational Higgs mechanism in neutron star interiors (2017)
Journal Article
Coates, A., Horbatsch, M. W., & Sotiriou, T. P. (2017). Gravitational Higgs mechanism in neutron star interiors. Physical Review D, 95(8), Article 084003. https://doi.org/10.1103/PhysRevD.95.084003

We suggest that nonminimally coupled scalar fields can lead to modifications of the microphysics in the interiors of relativistic stars. As a concrete example, we consider the generation of a non-zero photon mass in such high-density environments. Th... Read More about Gravitational Higgs mechanism in neutron star interiors.

Black hole hair formation in shift-symmetric generalised scalar-tensor gravity (2017)
Journal Article
Benkel, R., Sotiriou, T. P., & Witek, H. (2017). Black hole hair formation in shift-symmetric generalised scalar-tensor gravity. Classical and Quantum Gravity, 34(6), Article 064001. https://doi.org/10.1088/1361-6382/aa5ce7

A linear coupling between a scalar field and the Gauss–Bonnet invariant is the only known interaction term between a scalar and the metric that: respects shift symmetry; does not lead to higher order equations; inevitably introduces black hole hair i... Read More about Black hole hair formation in shift-symmetric generalised scalar-tensor gravity.

Dynamical scalar hair formation around a Schwarzschild black hole (2016)
Journal Article
Benkel, R., Sotiriou, T. P., & Witek, H. (2016). Dynamical scalar hair formation around a Schwarzschild black hole. Physical Review D, 94(12), https://doi.org/10.1103/PhysRevD.94.121503

Scalar fields coupled to the Gauss-Bonnet invariant evade the known no-hair theorems and have nontrivial configurations around black holes. We focus on a scalar field that couples linearly to the Gauss-Bonnet invariant and hence exhibits shift symmet... Read More about Dynamical scalar hair formation around a Schwarzschild black hole.

Uninvited guest in mixed derivative Hořava gravity (2016)
Journal Article
Coates, A., Colombo, M., Gümrükçüoğlu, A. E., & Sotiriou, T. P. (2016). Uninvited guest in mixed derivative Hořava gravity. Physical Review D, 94(8), Article 84014. https://doi.org/10.1103/PhysRevD.94.084014

We revisit the mixed-derivative extension of Hořava gravity which was designed to address the naturalness problems of the standard theory in the presence of matter couplings. We consider the minimal theory with mixed-derivative terms that contain two... Read More about Uninvited guest in mixed derivative Hořava gravity.

Extrinsic curvature in two-dimensional causal dynamical triangulation (2016)
Journal Article
Glaser, L., Sotiriou, T. P., & Weinfurtner, S. (2016). Extrinsic curvature in two-dimensional causal dynamical triangulation. Physical Review D, 94(6), Article 64014. https://doi.org/10.1103/PhysRevD.94.064014

Causal dynamical triangulation (CDT) is a nonperturbative quantization of general relativity. Hořava-Lifshitz gravity, on the other hand, modifies general relativity to allow for perturbative quantization. Past work has given rise to the speculation... Read More about Extrinsic curvature in two-dimensional causal dynamical triangulation.

Low energy ghosts and the Jeans’ instability (2016)
Journal Article
Gümrükçüoğlu, A. E., Mukohyama, S., & Sotiriou, T. P. (2016). Low energy ghosts and the Jeans’ instability. Physical Review D, 94(6), Article 64001. https://doi.org/10.1103/PhysRevD.94.064001

We show that a massless canonical scalar field minimally coupled to general relativity can become a tachyonic ghost at low energies around a background in which the scalar’s gradient is spacelike. By performing a canonical transformation we demonstra... Read More about Low energy ghosts and the Jeans’ instability.

Slowly rotating black holes in Einstein-æther theory (2016)
Journal Article
Barausse, E., Sotiriou, T. P., & Vega, I. (2016). Slowly rotating black holes in Einstein-æther theory. Physical Review D, 93(4), Article 44044. https://doi.org/10.1103/PhysRevD.93.044044

We study slowly rotating, asymptotically flat black holes in Einstein-æther theory and show that solutions that are free from naked finite area singularities form a two-parameter family. These parameters can be thought of as the mass and angular mome... Read More about Slowly rotating black holes in Einstein-æther theory.

Hořava gravity with mixed derivative terms: powercounting renormalizability with lower order dispersions (2015)
Journal Article
Colombo, M., Gümrükçüoğlu, A. E., & Sotiriou, T. P. (2015). Hořava gravity with mixed derivative terms: powercounting renormalizability with lower order dispersions. Physical Review D - Particles, Fields, Gravitation and Cosmology, 92(6), Article 064037. https://doi.org/10.1103/PhysRevD.92.064037

It has been argued that Hořava gravity needs to be extended to include terms that mix spatial and time derivatives in order to avoid unacceptable violations of Lorentz invariance in the matter sector. In an earlier paper we have shown that including... Read More about Hořava gravity with mixed derivative terms: powercounting renormalizability with lower order dispersions.

Multipole moments in scalar-tensor theory of gravity (2015)
Journal Article
Pappas, G., & Sotiriou, T. P. (2015). Multipole moments in scalar-tensor theory of gravity. Physical Review D - Particles, Fields, Gravitation and Cosmology, 91, 1-12. https://doi.org/10.1103/PhysRevD.91.044011

Stationary, asymptotically flat spacetimes in general relativity can be characterized by their multipole moments. The moments have proved to be very useful tools for extracting information about the spacetime from various observables and, more recent... Read More about Multipole moments in scalar-tensor theory of gravity.

Black hole hair in generalized scalar-tensor gravity (2014)
Journal Article

The most general action for a scalar field coupled to gravity that leads to second-order field equations for both the metric and the scalar—Horndeski’s theory—is considered, with the extra assumption that the scalar satisfies shift symmetry. We show... Read More about Black hole hair in generalized scalar-tensor gravity.