We analyse in all generality beyond Horndeski theories of shift symmetry in a static and spherically symmetric spacetime. By introducing four auxiliary functions, we write the field equations in a particularly compact form. We show that assuming additionally parity symmetry renders the system directly integrable giving multiple families of black-hole solutions. These have typically an...

We present explicit black holes endowed with primary scalar hair within the shift-symmetric subclass of Beyond Horndeski theories. These solutions depend, in addition to the conventional mass parameter, on a second free parameter encoding primary scalar hair. The properties and characteristics of the solutions at hand are analyzed with varying scalar charge. We observe that when the scalar...

In this work, we embark on the thermodynamic investigation concerning a family of primary charged black holes within the context of shift and parity symmetric Beyond Horndeski gravity. Employing the Euclidean approach, we derive the functional expression for the free energy and derive the first thermodynamic law, offering a methodology to address the challenge of extracting the thermal...

Spherical Proca Stars (PSs) are regarded as the ground state amongst the family of PSs. In accordance, spherical PSs are thought to have a fundamental branch of stable solutions. In this Letter, we provide energetic, morphological and dynamical evidence that spherical PSs are actually excited states. The ground state is shown to be a family of static, non-spherical, in fact prolate, PSs. The...

Deviations from General Relativity can be probed with black hole spectroscopy, as the quasi-normal mode (QNM) frequency spectrum of a black hole with additional ‘hair’ is expected to differ from that of a Kerr black hole. We construct an effective field theory scheme for QNMs to capture deviations from Kerr for black holes in theories with a coupling between a shift-symmetric scalar and the...

In general relativity, dynamical black holes generically have non-smooth horizons. One can study the properties of the non-smooth structures that are stable under perturbations of the horizon. This analysis does not make use of the Einstein equations, and hence is potentially relevant to higher-derivative theories of gravity. We describe the possible non-smooth structures and discuss some...

In the last few years the contribution of higher-curvature terms in modified gravity has received quite a lot of attention. This is due to the discovery of a 4-dimensional limit of Einstein-Gauss-Bonnet theory that has non-trivial contributions from the Gauss-Bonnet invariant. The theory is a very interesting phenomenological competitor to General Relativity insofar as it passes all...

We consider higher-order derivative gauge field corrections that arise in the fundamental context of dimensional reduction of String Theory and Lovelock-inspired gravities and obtain an exact and asymptotically flat

black-hole solution, in the presence of non-trivial dilaton configurations. Specifically, by considering the gravitational theory of Euler-Heisenberg non-linear electrodynamics...

In modified theories of gravity, the question of well-posedness of their equations underlies any attempts at numerical simulations. These in turn are crucial for comparison with experimental data and possible confirmation of the theory’s predictions. In this talk, we will concentrate on ghost-free massive gravity, notable for being a genuine IR modification of general relativity. Through a...

There are a few unanswered questions about standard cosmological model. An open question to answer is if we can use gravitational waves (GWs) to probe beyond General Relativity? Due to their weak interaction with matter, we hope to observe Primordial GWs which can give us a better understanding of the physics of the early Universe. Primordial GWs come in the form of a stochastic background...

I discuss sensitivity of black hole thermodynamics to certain boundary terms in the gravitational action. In some cases, boundary terms can alter not only the black hole entropy but even its thermodynamic temperature. Remarkably, this behaviour is confirmed by both covariant phase space (Iyer-Wald) and Euclidean (Brown-York) methods. I demonstrate our results on the example of 4D scalar-tensor...

It is well established that black holes satisfying some quite general set of assumptions are always surrounded by a light ring. These are a special set of bound null orbits. Such orbits are of particular relevance when entering the new era of precision test of General Relativity, as they leave imprints on both gravitational wave observations, and on the black hole shadows, the two main new...

General relativity (GR) exists in different formulations. They are equivalent in pure gravity but generically lead to distinct predictions once matter is included. After a brief overview of various versions of GR, I will focus on metric-affine gravity, which avoids any assumption about the vanishing of curvature, torsion, or nonmetricity. With a view toward the Standard Model, we can construct...

Based on: 2311.03308

Authors: Stefano Massai, Alejandro Ruiperez, Matteo Zatti

Abstact: We find solutions of the heterotic string effective action describing the first-order alpha prime corrections to two-charge black holes at finite temperature. Making explicit use of these solutions, we compute the corrections to the thermodynamic quantities: temperature, chemical potentials, mass,...

We study the first law for non-stationary perturbations of a stationary black hole whose event horizon is a Killing horizon, that relates the first-order change in the mass and angular momentum to the change in the entropy of an arbitrary horizon cross-section. Recently, Hollands, Wald and Zhang [1] have shown that the dynamical black hole entropy that satisfies this first law, for general...

Various recent works have explored the emergence and properties of compact object solutions including black holes, in models with a metric tensor and a scalar field within the Horndeski framework of theories. Studying the quasinormal mode (QNM) spectrum of hairy black holes is particularly useful when considering the potential of observing hairy solutions in nature. In this talk we discuss how...

A key science target for LISA is testing General Relativity by measuring extreme-mass-ratio inspirals. Modelling such binaries with numerical relativity is not viable due to the disparate length scales. Perturbation theory comes to the rescue: leveraging the disparate length scales, we can model the binary using the self-force approach. Great effort is being expounded in pursuing high-accuracy...

We present an introduction to cosmic inflation in the framework of Palatini gravity, which provides an intriguing alternative to the conventional metric formulation of gravity. In the latter, only the metric specifies the spacetime geometry, whereas in the former, the metric and the spacetime connection are independent variables-an option that can result in a gravity theory distinct from the...

In this talk I will present some classification results of higher-curvature gravities (in generic spacetime dimensions) satisfying a quite remarkable property: the differential order of their equations of motion gets reduced when considered on certain specific backgrounds. First, I will consider those higher-order gravities whose equations of motion become second-order (or less) on top of...

The covariant position-space propagators for GR in the Euclidean AdS background have been known for more than 25 years (partially even before the AdS/CFT). However, due to the complicated bi-tensorial structure of these quantities, no such explicit formulas have been presented in the literature for gravitational theories beyond GR. In this talk, I will describe a new method of construction of...

In this talk, we will focus on describing features of the C-metric in 2+1 dimensions. Starting from a general ansatz we construct three classes of geometries which can be interpreted by studying their physical parameters. From these, we identify stationary, accelerating point particles; one-parameter extensions of the BTZ family resembling an accelerating black hole; and a novel “accelerating...

We study the interplay between higher curvature terms and the backreaction of quantum fluctuations in 3-dimensional massive gravity in asymptotically (Anti-)de Sitter space. We focus on the theory at the special point of the parameter space where the two maximally symmetric vacua coincide. In the case of positive cosmological constant, this corresponds to the partially massless point, at which...

Black hole superradiance has proven being very valuable in several realms of gravitational physics, and holds a promising discovery potential. In this talk I will show how it can sheed light on a long

standing problem in physics, the quest for magnetic monopoles in the Universe. Placing them in the interior of primordial rotating black holes, which act as natural amplifiers, I will show that...

Black holes are not unique in higher dimensions. It is well known that, in five dimensions, stationary, biaxisymmetric black holes with the horizon of $S^3$-topology and $S^2 \times S^1$-topology can exist for the same asymptotic charges, in contrast to the black holes in four dimensions where the horizon must have $S^2$-topology.

In this talk, we aim to demonstrate that even if the horizon...

The Galactic Center of the Milky Way can serve as a test bench to investigate physical phenomena at the edge of astrophysics and fundamental physics. As such, it offers a unique laboratory to probe General Relativity, modified theories of gravity, different paradigms of dark matter, and black hole mimickers. I will provide a general overview of the results achieved in recent years emphasizing...