All Outputs (40)

Shadows and properties of spin-induced scalarized black holes with and without a Ricci coupling (2024)
Journal Article

In this work, we explore the properties and shadows of spin-induced scalarized black holes, as well as investigate how a Ricci coupling influences them. Our findings reveal significant deviations from the Kerr metric in terms of the location and geod... Read More about Shadows and properties of spin-induced scalarized black holes with and without a Ricci coupling.

Using machine learning to optimise chameleon fifth force experiments (2024)
Journal Article

The chameleon is a theorised scalar field that couples to matter and possess a screening mechanism, which weakens observational constraints from experiments performed in regions of higher matter density. One consequence of this screening mechanism is... Read More about Using machine learning to optimise chameleon fifth force experiments.

Higgs-induced screening mechanisms in scalar-tensor theories (2023)
Journal Article

We consider the theory of a light conformally coupled scalar field, that is, one that is coupled directly to the Ricci scalar of the gravitational sector. This theory can be written equivalently as one of a light scalar that is coupled to the Standar... Read More about Higgs-induced screening mechanisms in scalar-tensor theories.

Spinning black holes with axion hair (2023)
Journal Article

In this work we construct and analyze non-perturbative stationary and axially-symmetric black hole solutions in general relativity coupled to an electromagnetic and an axion field. The axion field is coupled to the electromagnetic field, which leads... Read More about Spinning black holes with axion hair.

Chameleon screening in cosmic voids (2022)
Journal Article

A key goal in cosmology in the upcoming decade will be to form a better understanding of the accelerated expansion of the Universe. Upcoming surveys, such as the Vera C. Rubin Observatory's 10-year Legacy Survey of Space and Time (LSST), Euclid and t... Read More about Chameleon screening in cosmic voids.

Dark sector domain walls could explain the observed planes of satellites (2022)
Journal Article

The observed 'planes of satellites' around the Milky Way and other nearby galaxies are notoriously difficult to explain under the ΛCDM paradigm. Here, we propose an alternative solution: domain walls arising in theories with symmetry-breaking scalar... Read More about Dark sector domain walls could explain the observed planes of satellites.

Chameleon screening depends on the shape and structure of NFW halos (2022)
Journal Article

Chameleon gravity is an example of a model that gives rise to interesting phenomenology on cosmological scales while simultaneously possessing a screening mechanism, allowing it to avoid solar system constraints. Such models result in non-linear fiel... Read More about Chameleon screening depends on the shape and structure of NFW halos.

Charting galactic accelerations - II: How to ‘learn’ accelerations in the solar neighbourhood (2022)
Journal Article

Gravitational acceleration fields can be deduced from the collisionless Boltzmann equation, once the distribution function is known. This can be constructed via the method of normalizing flows from data sets of the positions and velocities of stars.... Read More about Charting galactic accelerations - II: How to ‘learn’ accelerations in the solar neighbourhood.

SELCIE: a tool for investigating the chameleon field of arbitrary sources (2021)
Journal Article

The chameleon model is a modified gravity theory that introduces an additional scalar field that couples to matter through a conformal coupling. This `chameleon field' possesses a screening mechanism through a nonlinear self-interaction term which al... Read More about SELCIE: a tool for investigating the chameleon field of arbitrary sources.

Fifth-force screening around extremely compact sources (2021)
Journal Article

Many non-linear scalar field theories possess a screening mechanism that can suppress any associated fifth force in dense environments. As a result, these theories can evade local experimental tests of new forces. Chameleon-like screening, which occu... Read More about Fifth-force screening around extremely compact sources.

Charting galactic accelerations: when and how to extract a unique potential from the distribution function (2021)
Journal Article

The advent of data sets of stars in the Milky Way with 6D phase-space information makes it possible to construct empirically the distribution function (DF). Here, we show that the accelerations can be uniquely determined from the DF using the collisi... Read More about Charting galactic accelerations: when and how to extract a unique potential from the distribution function.

φenics: Vainshtein screening with the finite element method (2021)
Journal Article

Within the landscape of modified theories of gravity, progress in understanding the behaviour of, and developing tests for, screening mechanisms has been hindered by the complexity of the field equations involved, which are nonlinear in nature and ch... Read More about φenics: Vainshtein screening with the finite element method.

Massive Galileons and Vainshtein screening (2021)
Journal Article

The Vainshtein screening mechanism relies on nonlinear interaction terms becoming dominant close to a compact source. However, theories displaying this mechanism are generally understood to be low-energy theories: it is unclear that operators emergin... Read More about Massive Galileons and Vainshtein screening.

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.

Open quantum dynamics induced by light scalar fields (2019)
Journal Article

We consider the impact of a weakly coupled environment comprising a light scalar field on the open dynamics of a quantum test mass, resulting in a master equation for the test mass that features corrections to the coherent dynamics, as well as decohe... Read More about Open quantum dynamics induced by light scalar fields.

Influence functionals, decoherence and conformally coupled scalars (2019)
Journal Article

Some of the simplest modifications to general relativity involve the coupling of additional scalar fields to the scalar curvature. By making a Weyl rescaling of the metric, these theories can be mapped to Einstein gravity with the additional scalar f... Read More about Influence functionals, decoherence and conformally coupled scalars.

Experiment to Detect Dark Energy Forces Using Atom Interferometry (2019)
Journal Article

The accelerated expansion of the universe motivates a wide class of scalar field theories that modify General Relativity (GR) on large scales. Such theories require a screening mechanism to suppress the new force in regions where the weak field limit... Read More about Experiment to Detect Dark Energy Forces Using Atom Interferometry.

Stellar kinematics from the symmetron fifth force in the Milky Way disk (2018)
Journal Article

It has been shown that the presence of nonminimally coupled scalar fields giving rise to a fifth force can noticeably alter dynamics on galactic scales. Such a fifth force must be screened in the Solar System but if unscreened it can have similar obs... Read More about Stellar kinematics from the symmetron fifth force in the Milky Way disk.

Tests of chameleon gravity (2018)
Journal Article

Theories of modified gravity, where light scalars with non-trivial self-interactions and non-minimal couplings to matter—chameleon and symmetron theories—dynamically suppress deviations from general relativity in the solar system. On other scales, th... Read More about Tests of chameleon gravity.

The shape dependence of chameleon screening (2018)
Journal Article

Chameleon scalar fields can screen their associated fifth forces from detection by changing their mass with the local density. These models are an archetypal example of a screening mechanism, and have become an important target for both cosmological... Read More about The shape dependence of chameleon screening.