Adrià Delhom

Adrià Delhom
University of Valencia | UV · Theoretical physics

Physics

About

39
Publications
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504
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Introduction
During my PhD thesis I have worked in metric-affine theories of gravity with high-energy modifications to General Relativity. Concretely, I have done work both, in understanding their mathematical structure and their phenomenologyical implications that could serve to discriminate them from other alternatives. Currently, I am interested in exploring the fields of compact objects and/or cosmology as probes for the strong field and/or high energy regime gravitational interaction.

Publications

Publications (39)
Article
We consider the metric-affine formulation of bumblebee gravity, derive the field equations, and show that the connection can be written as Levi-Civita of a disformally related metric in which the bumblebee field determines the disformal part. As a consequence, the bumblebee field gets coupled to all the other matter fields present in the theory, po...
Preprint
Full-text available
In this contribution, we study the metric-affine bumblebee model coupled to fermions. Proceeding in a manner different from [1, 2], we find the exact result for the fermionic determinant in the Einstein frame, including all orders in the non-minimal coupling $\xi$. We demonstrate that the axial contributions are at least of second order in the pert...
Preprint
Full-text available
In this PhD thesis we deal with several theoretical and phenomenological apsects of metric-affine theories of gravity. Concretely, we first give a broad introduction to the necessary tools to understand the framework and elaborate on some subtleties of the minimal coupling prescription between geometry and matter in presence of torsion and nonmetri...
Chapter
The fact that the gravitational coupling constant is so weak compared to the other fundamental couplings may suggests that gravity plays a negligible role in physical scenarios where other fundamental forces are present, unless Planck scale processes are involved. This is actually not true, due to the fact that, unlike the other forces, the charge...
Chapter
We briefly review somo aspects of the cosmological dynamics of Palatini theories of gravity. In particular, we focus their theoretical viability in smoothing out the Big Bang singularity, the properties of different inflationary models, and the consequences of Palatini theories for background evolution and late-time acceleration. We also review cos...
Article
By using a novel technique that establishes a correspondence between general relativity and metric-affine theories based on the Ricci tensor, we are able to set stringent constraints on the free parameter of Born-Infeld gravity from the ones recently obtained for Born-Infeld electrodynamics by using light-by-light scattering data from ATLAS. We als...
Preprint
Full-text available
General Relativity and the $\Lambda$CDM framework are currently the standard lore and constitute the concordance paradigm. Nevertheless, long-standing open theoretical issues, as well as possible new observational ones arising from the explosive development of cosmology the last two decades, offer the motivation and lead a large amount of research...
Preprint
Full-text available
By using a novel technique that establishes a correspondence between general relativity and metric-affine theories based on the Ricci tensor, we are able to set stringent constraints on the free parameter of Born-Infeld gravity from the ones recently obtained for Born-Infeld electrodynamics by using light-by-light scattering data from ATLAS. We als...
Article
Full-text available
We consider the metric-affine formulation of bumblebee gravity, derive the field equations, and show that the connection can be written as Levi-Civita of a disformally related metric in which the bumblebee field determines the disformal part. As a consequence, the bumblebee field gets coupled to all the other matter fields present in the theory, po...
Article
Full-text available
Among the general class of metric-affine theories of gravity, there is a special class conformed by those endowed with a projective symmetry. Perhaps the simplest manner to realise this symmetry is by constructing the action in terms of the symmetric part of the Ricci tensor. In these theories, the connection can be solved algebraically in terms of...
Preprint
Full-text available
In this paper, we study the quantum aspects of the recently proposed \cite{Delhom:2019gxg} metric-affine version of the bumblebee gravity. We examine the one-loop corrections provided by minimally coupled spinor fields around a trivial as well as an arbitrary bumblebee background in the weak gravitational field limit. In this context, we examine th...
Preprint
We argue that several statements in Phys. Rev. Lett. 124, 081301 (2020) are not correct.
Article
Full-text available
We deal with the question of what it means to define a minimal coupling prescription in presence of torsion and/or non-metricity, carefully explaining while the naive substitution \(\partial \rightarrow \nabla \) introduces extra couplings between the matter fields and the connection that can be regarded as non-minimal in presence of torsion and/or...
Preprint
Among the general class of metric-affine theories of gravity, there is a special class conformed by those endowed with a projective symmetry. Perhaps the simplest manner to realise this symmetry is by constructing the action in terms of the symmetric part of the Ricci tensor. In these theories, the connection can be solved algebraically in terms of...
Article
Full-text available
We discuss the presence of ghostly instabilities for metric-affine theories constructed with higher order curvature terms. We mainly focus on theories containing only the Ricci tensor and show the crucial role played by the projective symmetry. The pathological modes arise from the absence of a pure kinetic term for the projective mode and the non-...
Article
Full-text available
We show that the definition of proper time for Weyl-invariant space-times given by Perlick naturally extends to spaces with arbitrary non-metricity. We then discuss the relation between this generalized proper time and the Ehlers–Pirani–Schild definition of time when there is arbitrary non-metricity. Then we show how this generalized proper time su...
Preprint
Full-text available
In this comment we clarify several aspects concerning four-dimensional Einstein-Gauss-Bonnet gravity. We argue that the limiting procedure outlined in [Phys. Rev. Lett. 124, 081301 (2020)] is not well defined as it generally produces divergent terms in the four dimensional field equations. Potential ways to circumvent this issue are discussed, alon...
Preprint
Full-text available
We discuss the presence of ghostly instabilities for metric-affine theories constructed with higher order curvature terms. We mainly focus on theories containing only the Ricci tensor and show the crucial role played by the projective symmetry. The pathological modes arise from the absence of a pure kinetic term for the projective mode and the non-...
Article
Full-text available
We show how minimally-coupled matter fields of arbitrary spin, when coupled to Ricci-based gravity theories, develop non-trivial effective interactions that can be treated perturbatively only below a characteristic high-energy scale \(\Lambda _{Q}\). We then use this interactions to set bounds on the high-energy scale \(\Lambda _{Q}\) that controls...
Preprint
We deal with the question of what are and what are not minimal coupling prescriptions in presence of torsion and/or non-metricity, carefully explaining while the naive substitution $\partial\to\nabla$ is not actually a minimal coupling prescritpion. We will also investigate whether minimal coupling prescriptions at the level of the action (MCPL) or...
Article
Full-text available
Projective invariance is a symmetry of the Palatini version of General Relativity which is not present in the metric formulation. The fact that the Riemann tensor changes nontrivially under projective transformations implies that, unlike in the usual metric approach, in the Palatini formulation this tensor is subject to a gauge freedom, which allow...
Preprint
Full-text available
We show that the definition of proper time for Weyl-invariant space-times given by Perlick naturally extends to spaces with arbitrary non-metricity. We then discuss the relation between this generalized proper time and the Ehlers-Pirani-Schild definition of time when there is arbitrary non-metricity. Then we show how this generalized proper time su...
Preprint
Full-text available
We consider the metric-affine formulation of bumblebee gravity, derive the field equations, and show that the connection can be written as Levi-Civita of a disformally related metric in which the bumblebee field determines the disformal part. As a consequence, the bumblebee field gets coupled to all the other matter fields present in the theory, po...
Article
Full-text available
A bstract We extend the correspondence between metric-affine Ricci-Based Gravity the- ories and General Relativity (GR) to the case in which the matter sector is represented by linear and nonlinear electromagnetic fields. This complements previous studies focused on fluids and scalar fields. We establish the general algorithm that relates the matte...
Article
Full-text available
A Weyl structure is usually defined by an equivalence class of pairs \((\mathbf{g}, {\varvec{\omega }})\) related by Weyl transformations, which preserve the relation \(\nabla \mathbf{g}={\varvec{\omega }}\otimes \mathbf{g}\), where \(\mathbf{g}\) and \({\varvec{\omega }}\) denote the metric tensor and a 1-form field. An equivalent way of defining...
Article
Full-text available
We disprove the widespread belief that higher order curvature theories of gravity in the metric-affine formalism are generally ghost-free. This is clarified by considering a sub-class of theories constructed only with the Ricci tensor and showing that the non-projectively invariant sector propagates ghost-like degrees of freedom. We also explain ho...
Preprint
We show how minimally-coupled matter fields of arbitrary spin, when coupled to Ricci-Based Gravity theories, develop non-trivial effective interactions that can be treated perturbatively only below a characteristic high-energy scale $\Lambda_Q$. Our results generalize to arbitrary matter fields those recently obtained for spin 1/2 fields in \cite{L...
Article
Using numerical methods, we investigate the absorption properties of a family of nonsingular solutions which arise in different metric-affine theories, such as quadratic and Born-Infeld gravity. These solutions continuously interpolate between Schwarzschild black holes and naked solitons with wormhole topology. The resulting spectrum is characteriz...
Preprint
Projective invariance is a symmetry of the Palatini version of General Relativity which is not present in the metric formulation. The fact that the Riemann tensor changes nontrivially under projective transformations implies that, unlike in the usual metric approach, in the Palatini formulation this tensor is subject to a gauge freedom and, as a co...
Preprint
We extend the correspondence between metric-affine Ricci-Based Gravity theories and General Relativity (GR) to the case in which the matter sector is represented by linear and nonlinear electromagnetic fields. This complements previous studies focused on fluids and scalar fields. We establish the general algorithm that relates the matter fields in...
Preprint
Full-text available
A Weyl structure is usually defined by an equivalence class of pairs (g, ω) related by Weyl transformations , which preserve the relation g = ω ⊗ g, where g and ω denote the metric tensor and a 1-form field. An equivalent way of defining such a structure is as an equivalence class of conformally related metrics with a unique affine connection Γω, w...
Preprint
Full-text available
Using numerical methods, we investigate the absorption properties of a family of nonsingular solutions {which arise in different metric-affine theories, such as quadratic and Born-Infeld gravity.} These solutions continuously interpolate between Schwarzschild black holes and naked solitons with wormhole topology. The resulting spectrum is character...
Preprint
Full-text available
A Weyl structure is usually defined by an equivalence class of pairs $({\bf g}, \boldsymbol{\omega})$ related by Weyl transformations, which preserve the relation $\nabla {\bf g}=\boldsymbol{\omega}\otimes{\bf g}$, where ${\bf g}$ and $\boldsymbol{\omega}$ denote the metric tensor and a 1-form field. An equivalent way of defining such a structure i...
Preprint
Full-text available
We disprove the widespread belief that higher order curvature theories of gravity in the metric-affine formalism are generally ghost-free. This is clarified by considering a sub-class of theories constructed only with the Ricci tensor and showing that the non-projectively invariant sector propagates ghost-like degrees of freedom. We also explain ho...
Preprint
Full-text available
We disprove the widespread belief that higher order curvature theories of gravity in the metric-affine formalism are generally ghost-free. This is clarified by considering a sub-class of theories constructed only with the Ricci tensor and showing that the non-projectively invariant sector propagates ghost-like degrees of freedom. We also explain ho...
Article
Full-text available
Relaxing the Riemannian condition to incorporate geometric quantities such as torsion and non-metricity may allow to explore new physics associated with defects in a hypothetical space-time microstructure. Here we show that non-metricity produces observable effects in quantum fields in the form of 4-fermion contact interactions, thereby allowing us...
Article
Full-text available
We demonstrate a coherence increase by six orders of magnitude of a standard quantum well semiconductor laser. Using a simple, optical-fiber-based feedback scheme, we stabilize the laser in a high-gain mode of a long external cavity. In a modified self-heterodyne measurement, we mix the high-gain mode with a strongly suppressed side mode and obtain...

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