Our latest study (2407.18845) investigates the possibility of generating gravitational waves (GWs) from a curvature-induced phase transition of a non-minimally coupled scalar field acting as dark matter, with a portal interaction to the Higgs field. This analysis is conducted within a dynamical spacetime framework, specifically during the transition from inflation to kination, while also...
The collapse of domain wall networks in the early universe could have left observable signatures in the form of gravitational waves and primordial black holes. This motivates a detailed study of the dynamics of these topological defects. In this talk, I will discuss how their effective description can predict singularities in the worldvolume of the walls and how this catastrophic evolution is...
The CVOS model is a thermodynamical framework designed to describe the evolution of a network of current‐carrying cosmic strings, where energy loss due to loop formation is incorporated phenomenologically. In this work, I investigate the stability of these configurations by analytically manipulating and examining the microscopic equations of the model. Subsequently, I analyze the evolution of...
Cosmic strings can be produced during phase transitions in the very
early universe. They are particularly interesting objects since they
emit gravitational waves contributing to the stochastic gravitational
wave background (SGWB). This gives us possibility to connect
gravitational waves experiments to unknown physics scenarios of the very
distant past. In the early stages of cosmic string...
We introduce new simple analytical approximations for quintessence solutions covering both tracking (asymptotically inverse power-law potentials) and thawing slow-roll models. From an observational perspective the remarkable accuracy of the approximations makes numerical calculations superfluous when assessing observational constraints. We will then discuss ongoing work on generalisations for...
The wide range of modified gravity theories proposed to address the limitations of General Relativity (GR) presents a challenge in distinguishing between them. In particular, the Geometric Trinity of Gravity - comprising General Relativity, based on curvature; Teleparallel Gravity, which relies on torsion and Symmetric Teleparallel Gravity, which is formulated in terms of nonmetricity- are...
The canonical cosmological model to explain the recent acceleration of the universe relies on a cosmological constant, and most dynamical dark energy and modified gravity model alternatives are based on scalar fields. Still, further alternatives are possible. One of these involves vector fields: under certain conditions, they can lead to accelerating universes while preserving large-scale...
The elusive cosmological redshift drift — predicted by General Relativity as a direct signature of the universe's accelerated expansion — remains one of the most ambitious goals in observational cosmology. In this study, we take the first steps toward detecting this effect using the Lyman-α forest of bright quasars as tracers of the expanding cosmos. Focusing on the brightest quasar,...
There has been recent interest in the cosmological consequences of energy-momentum-powered-gravity models, in which the matter side of Einstein’s equations includes a term proportional to some power, n, of the energy-momentum tensor, in addition to the canonical linear term. Previous works have suggested that these models can lead to a recent accelerating universe without a cosmological...
This work explores the viability of Hyperconical Modified Gravity (HMG) as a relativistic alternative to the Modified Newtonian Dynamics (MOND) in explaining the dynamics of galaxy clusters, radial accelerations and galaxy rotation curves. By using five datasets (including high-resolution X-ray data and weak-lensing observations), we test HMG's predictions for hydrostatic equilibrium in galaxy...
The accelerated expansion of the Universe is canonically attributed to the Dark Energy (DE), encapsulated in the Lambda factor in the Einstein field equations of gravity, but its nature is still not understood. While observations supply strong evidence in favor of the standard model of cosmology Lambda-CDM, a plethora of different modified gravity models (MG) can still arise and describe...
The next generation of galaxy surveys will provide unprecedented data, leading to accurate tests of gravity on cosmological scales. To fully exploit the nonlinear information encoded in the large-scale structure of the Universe, we propose to leverage cutting-edge deep learning algorithms, such as diffusion models, to efficiently generate 3D density fields conditioned on cosmological...
The $f(\mathcal{G},T)$ theory of gravity is recast in terms of the $\phi$ and $\psi$ fields within the scalar-tensor formulation, where $\mathcal{G}$ is the Gauss-Bonnet term and $T$ denotes the trace of the energy-momentum tensor. The general aspects of the introduced reformulation are discussed and the reconstruction of the cosmological scenarios is presented, focusing on the so-called...
A new exact time-dependent Kerr-like black hole solution is found on a Randall-Sundrum brane world spacetime. The solution is also valid on the Wick-rotated Euclidean counterpart space, so represents equally well a gravitational instanton, i.e. a bump in spactime. Because the $r$-dependent part is determined by a first order differential equation, one conjectures that the solution is a...
I will present expansions of the metric and its derivative near a conformal gauge singularity (also known as isotropic singularities) for Bianchi I symmetric massless solutions of the Einstein-Vlasov and Einstein-Boltzmann system with a magnetic field. We will discuss how this can be related to our universe. This is work in collaboration with Ho Lee, John Stalker and Paul Tod.
In the quest to understand the accelerated expansion of the universe, f(Q) gravity offers a promising alternative to General Relativity (GR) by incorporating non-metricity into the gravitational framework. Unlike GR, which relies on spacetime curvature, f(Q) gravity modifies the Einstein-Hilbert action by replacing the Ricci scalar R with a function f(Q), where Q represents the non-metricity...
It has been argued that realistic models of (singularity-free) black holes (BHs) embedded within an expanding Universe are coupled to the large-scale cosmological dynamics, with striking consequences, including pure cosmological growth of BH masses. In this pilot study, we examine the consequences of this growth for the stochastic gravitational wave background (SGWB) produced by inspiraling...
It is well known that alternative theories to the Standard Model allow and sometimes require fundamental constants, such as the fine-structure constant, α, to vary in spacetime. We demonstrate that one way to investigate these variations is through the Mass-Radius relation of compact astrophysical objects, which is inherently affected by α variations. We start by considering the model of a...
We explore a minimal scenario where the Standard-Model Higgs is responsible for reheating the Universe after inflation and produces a significant background of gravitational waves. The characteristic features of such signal can be directly correlated to the classical stability of the electroweak vacuum, thus offering a novel connection between the inflationary scale and the top quark mass at...
If reheating occurs at sufficiently low temperatures (below $20$ MeV), neutrinos--assuming they are populated only through weak interactions--do not have enough time to reach thermal equilibrium before decoupling. We present an updated analysis of cosmological models with very low reheating scenarios, including a more precise computation of neutrino distribution functions, leveraging the...
The de Sitter Swampland Conjectures are used to test some inflationary models compatible with CMBdata. We find that warm inflationary models, with one or more scalar fields, and the Claplygin-inspired models for some class of potentials satisfy the de Sitter Swampland Conjectures. Inflationary models in the context of theories of gravity that couple non-minimally curvature and matter are shown...
We study classical background electric fields and the Schwinger effect in de Sitter space. We show that having a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current which affect its IR behaviour. To study this we recompute the Schwinger current in de Sitter space for...
We develop and analyse a novel mechanism based on Warm Little Inflaton models that allows for production of scalar particles $\chi$ during the slow-roll regime due to a narrow parametric resonance. We show that an appreciable energy density of $\chi$ particles can be generated through this mechanism without it becoming the dominant contribution to the Friedmann equation, thus preserving the...
The QCD axion is a well-motivated candidate for new physics and a primary focus of an ambitious global experimental program. It offers a compelling solution to both the strong CP and the dark matter problems within a narrow region of its parameter space, known as the QCD axion band. Nevertheless, rich theoretical frameworks lead us to expect that the axion is not the only exotic scalar...
Axion-like particles (ALPS), radiated from a network of cosmic strings, may be a large part of Dark Matter (DM). In the era of precision cosmology, it is possible to characterize the effect of such particles - which almost scale invariant distribution function spans many orders of magnitudes in momentum - on the observables. In this work, we employ the CLASS code and Planck 2018 data to place...
The nature of dark matter is one of the most important unsolved questions in science. Some dark matter candidates do not have sufficient nongravitational interactions to be probed in laboratory or accelerator experiments. It is thus important to develop astrophysical probes which can constrain or lead to a discovery of such candidates. I illustrate this using state-of-the-art measurements of...
Over 80–85% of the matter in the universe is dark matter (DM), with most of it classified as Cold Dark Matter (CDM), composed of collisionless, heavy particles. However, there is no fundamental reason to assume that the dark sector consists of only one type of particle. Recently, the existence of Light Massive Relics (LiMRs), which act like hot dark matter, has received renewed attention....
According to the von Laue condition, the volume integral of the proper pressure inside isolated particles with a fixed structure and finite mass vanishes in the Minkowski limit of general relativity. We explore this condition considering a simple illustrative example: non-standard static global monopoles with finite energy, for which the von Laue condition is satisfied when the proper pressure...
I will discuss how the effective geometry seen by photons propagating on a non-trivial electromagnetic background within Born-Infeld theory corresponds to an asymmetric wormhole. I will explain some interesting properties of the generated geometry such as the behaviour of null geodesics. Interestingly, the wormhole effective geometry arises for the background fields created by a charged...
The Penrose process consists of transferring energy from a black hole to infinity. This process can be studied in a combined description with the Bañados-Silk-West (BSW) mechanism, which uses collisions of ingoing particles at the event horizon of a black hole to locally produce large amounts of energy. In this talk, the blending of the Penrose process with BSW mechanism is described for a $d$...
We present two nonlinear electromagnetic black hole solutions belonging to the Kerr-Newman-AdS-NUT family, referred to as cubic potential and quartic potential. These solutions are characterized by mass, angular momentum, electric and magnetic charge, the NUT parameter, the cosmological constant, and a nonlinear parameter. We provide the necessary electromagnetic potentials to generate these...
This work explores the extraction of energy from electrostatic black holes through the decay or splitting of electrically charged particles. We establish the energetic criteria for viable extraction, deriving a general expression for the efficiency that depends on black hole and particle parameters. Focusing on Reissner-Nordström (RN) and Reissner-Nordström-de Sitter (RNdS) black holes, we...
We considered the generation of gravitational waves by the binary system associated with a wormhole. In the Newtonian limit, the gravitational potential of a wormhole requires the effective mass of the wormhole taking into account radial tension effects. This definition allows us to derive gravitational wave production in homogeneous and heterogeneous binary systems. Therefore, we studied...
The present work investigates a new model of the gravastar in a framework of 5-Dimensional (5D) Einstein-Gauss-Bonnet (EGB) grav- itational theory. Adopting the approach of Mazur and Mottala, we divide the geometry of the stellar spherical object into three differ- ent portions, as follows (i) interior portion (ii) intermediate spherical thin shell and (iii) exterior portion. The interior...
The symmetry group of general relativity is the group of diffeomorphisms (Diff), which means that the form of the physical equations remains invariant under general coordinate transformations. We discuss the cosmological implications of breaking the Diff invariance down to transverse diffeomorphisms (TDiff) invariance in the matter sector. We show that even simple cases, like a minimally...
Observations from the James Webb Space Telescope (JWST) have unveiled an unexpectedly high abundance of massive galaxies at early times, further challenging ΛCDM predictions. I will discuss our pioneering solutions for these tensions and their implications for the future of cosmology.
Several studies in the literature have found a discrepancy between Baryon Acoustic Oscillation (BAO) measurements derived from two distinct methodologies, i.e. the two-dimensional (2D, angular) and the three-dimensional (3D, anisotropic) BAO. Since these probes play a key role in building the inverse distance ladder, this inconsistency affects discussions on the Hubble tension and its...
