Research & Publications

We consider a Proca-Higgs model wherein a complex vector field gains mass via spontaneous symmetry breaking, by coupling to a real scalar field with a Higgs-type potential. This vector version of the scalar Friedberg-Lee-Sirlin model, can be considered as a UV completion of a complex Proca model with self-interactions. We study the flat spacetime and self-gravitating solitons of the model, that we dub Proca-Higgs balls and stars respectively, exploring the domain of solutions and describing some of their mathematical and physical properties. The stars reduce to the well-known (mini-)Proca stars in some limits. The full model evades the hyperbolicity problems of the self-interacting Proca models, offering novel possibilities for dynamical studies beyond mini-Proca stars.

In this work, we investigate the soliton scattering problem for anti-kink/kink and kink/anti-kink configurations. To this end, we employ two distinct methods, full simulation and collective coordinates, and compare them. We apply the collective coordinate approximation method to describe both scattering configurations in the hybrid model and show that, similar to the polynomial models ϕ4 and ϕ6, the method has limitations with respect to the initial scattering velocities. In such a way that, for certain initial velocities, the solution of collective coordinates agrees with the full simulation, and for other velocities, there is a discrepancy in the solutions obtained by these two methods. We investigate the time evolution for kink/anti-kink and anti-kink/kink scattering in the hybrid model, taking into consideration the null-vector problem. As an appendix, we performed the same inspection for kink/anti-kink scattering in the ϕ4 model.

A general formulation of the relativistic multipole moments in axistationary electrovac spacetimes is introduced in a closed analytical form. We give a complete description of how the Ernst potentials on the symmetry axis can be completely characterized by these arbitrary multipole moments. Some concrete applications are also developed.

The multipole moments of stationary axially symmetric vacuum or electrovacuum spacetimes can be expressed in terms of the power series expansion coefficients of the Ernst potential on the axis. In this paper we present a simpler, more efficient calculation of the multipole moments, applying methods introduced by Bäckdahl and Herberthson. For the nonvacuum electromagnetic case, our results for the octupole and higher moments differ from the results already published in the literature. The reason for this difference is that we correct an earlier unnoticed mistake in the power series solution of the Ernst equations. We also apply the presented method to directly calculate the multipole moments of a five-parameter charged magnetized generalization of the Kerr and Tomimatsu-Sato exact solutions.

In the present paper binary configurations of identical corotating Kerr-Newman black holes separated by a massless strut are derived and studied. After solving the axis conditions and establishing the absence of magnetic charges in the solution, one gets two 4-parametric corotating binary black hole models endowed with electric charge, where each source contains equal/opposite electric charge in the first/second configuration. Since the black hole horizons are given by concise expressions in terms of physical parameters, all their thermodynamical properties satisfying the Smarr relation for the mass are also obtained. We discuss the physical limits of both models.

University of Aveiro

Supervisors : Carlos Herdeiro, Eugen Radu

Dark matter remains a central mystery of modern-day science. The elusiveness of dark matter candidates in colliders suggests we further search for its true nature where it was first unveiled - in astrophysics via its gravitational effects. In particular, the new golden age in strong gravity - with the gravitational wave era and remarkable new electromagnetic observations of compact objects - is providing intriguing hints on fuzzy dark matter. Such phenomenological studies start from constructing appropriate compact objects where such fuzzy dark matter plays a key role, both new types of black holes and horizonless compact objects. This thesis aims to go beyond the simplest fuzzy dark matter models based on Abelian fields. A dark sector, like the visible one, may contain non-Abelian fields. The central goal of this thesis is the impact of such fields on the phenomenology of compact objects, connecting them to gravitational wave and electromagnetic observations.

University of Aveiro

Supervisors : Carlos Herdeiro, Eugen Radu

This project is divided into five interconnected parts, studying : 1) the theory of deviations from the Kerr paradigm, and, in particular, the construction of alternative models, both in modified gravity and in General Relativity in the presence of dark matter candidates, as ultralight bosons. 2) effects of light bending by BNs and their shadow, in these alternative models, making contact with the Event Horizon Telescope (EHT) observations. 3) gravitational waves emitted in different dynamic scenarios involving these alternative models, making contact with data from the LIGO-Virgo Scientific Collaboration. 4) other astrophysical phenomenological aspects of alternative models, namely orbits of stars. 5) on the theoretical front, concrete scenarios beyond the standard model of particle physics, where ultra-light dark matter models have theoretical support, considering the constraints of particle accelerators, namely the Large Hadron Collider (LHC).

University of São Paulo

Supervisor : Betti Hartmann

The construction of exact axisymmetric solutions of the Einstein-Maxwell equations possessing the prescribed physical properties means the obtaining of solutions in which different parameters would correspond to different relativistic multipole moments determining the structure of space-time. Associated with this, there are various solution-generating techniques based on integrable models that can be employed to obtain particular families of solutions from any suitable “seed” solution, one of them, known as Sbigatullin’s method, is applied. Sibgatullin’s method is fully revised and its parameters in the N-soliton solution are conected with Einstein-Maxwell multipoles moments.

University of São Paulo

Supervisor : Domingos Alves

We are a team of independent scientists from several Brazilian research institutions, highly motivated to contribute to the control of the coronavirus outbreak that took place in Brazil, based on the real-time monitoring of data provided by official sources on the spread of the virus in the country. Besides, we will use scientifically based analysis tools to help managers, authorities, and the population in general, to face this actual war against COVID-19. On the portal https://ciis.fmrp.usp.br/covid19/ , I am responsible for monitoring Brazil, updating the monitoring of daily cases and daily deaths with moving average, data projection for the next ten days based on exponential modeling of all capitals and states (and Brazil). I also wrote some opinion articles based on scientific evidence.

Federal University of Espírito Santo

 Supervisor : Gabriel Luchini

The Aharanov-Bohm effect is discussed in detail : from the introduction of fundamental concepts about electromagnetism as a gauge theory, the repercussions of this symmetry in quantum mechanics and its construction based on the Stokes theorem for the introduction of the geometric phase. In addition to the usual, more conceptual discussions about the effect, the problem of quantum electron scattering in a region with a confined magnetic field is made.

Federal University of Espírito Santo

 Supervisor : Gabriel Luchini

The so-called Heisenberg model describes magnetic systems very well in different situations of interest. In the continuous limit,with the imposition of a bond on the norm of this field, the dynamics of the spin field of the Heisenberg continuous model is equivalent to the static solutions of the two-dimensional non-linear sigma model. A study was carried out on the existence, stability and behaviour of solitons in different geometries, that is, in spaces with cylindrical symmetry, so that there is the ”coupling” of the spin with the geometry making the anisotropic model in a certain sense. By rewriting the equations of motion as Bogomol’nyi equations and including an axial symmetry ansatz for the spin field, it was possible to understand how to simplify the equations of motion and obtain analytical solutions for surfaces with axial symmetry.