All Outputs (49)

Prospects for fundamental physics with LISA (2020)
Journal Article

In this paper, which is of programmatic rather than quantitative nature, we aim to further delineate and sharpen the future potential of the LISA mission in the area of fundamental physics. Given the very broad range of topics that might be relevant... Read More about Prospects for fundamental physics with LISA.

Onset of spontaneous scalarization in generalized scalar-tensor theories (2020)
Journal Article

In gravity theories that exhibit spontaneous scalarization, astrophysical objects are identical to their general relativistic counterpart until they reach a certain threshold in compactness or curvature. Beyond this threshold, they acquire a nontrivi... Read More about Onset of spontaneous scalarization in generalized scalar-tensor theories.

Black holes, gravitational waves and fundamental physics: A roadmap (2019)
Journal Article

© 2019 IOP Publishing Ltd. The grand challenges of contemporary fundamental physics-dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem-all involve gravity as a key component. And o... Read More about Black holes, gravitational waves and fundamental physics: A roadmap.

Spontaneous scalarization in generalized scalar-tensor theory (2019)
Journal Article

Spontaneous scalarization is a mechanism that endows relativistic stars and black holes with a nontrivial configuration only when their spacetime curvature exceeds some threshold. The standard way to trigger spontaneous scalarization is via a tachyon... Read More about Spontaneous scalarization in generalized scalar-tensor theory.

Classification of shift-symmetric Horndeski theories and hairy black holes (2019)
Journal Article

No-hair theorems for scalar-tensor theories imply that the trivial scalar field configuration is the unique configuration around stationary black hole spacetimes. The most basic assumption in these theorems is that a constant scalar configuration is... Read More about Classification of shift-symmetric Horndeski theories and hairy black holes.

Self-interactions and spontaneous black hole scalarization (2019)
Journal Article

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

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

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

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.

Causal structure of black holes in shift-symmetric Horndeski theories (2018)
Journal Article

In theories with derivative (self-)interactions, the propagation of perturbations on nontrivial field configurations is determined by effective metrics. Generalized scalar-tensor theories belong in this class and this implies that the matter fields a... Read More about Causal structure of black holes in shift-symmetric Horndeski theories.

Dynamical obstruction to perpetual motion from Lorentz-violating black holes (2018)
Journal Article

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

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

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

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

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.

Ho?ava gravity after GW170817 (2018)
Journal Article

The recent detection of gravitational wave GW170817 has placed a severe bound on the deviation of the speed of gravitational waves from the speed of light. We explore the consequences of this detection for Ho?ava gravity.

Black hole horizons at the extremal limit in Lorentz-violating gravity (2017)
Journal Article

Lorentz-violating gravity theories with a preferred foliation can have instantaneous propagation. Nonetheless, it has been shown that black holes can still exist in such theories and the relevant notion of an event horizon has been dubbed “universal... Read More about Black hole horizons at the extremal limit in Lorentz-violating gravity.

Gravitational Higgs mechanism in neutron star interiors (2017)
Journal Article

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

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

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.