arXiv subjects

José Ferreira

Publications and source records attributed to José Ferreira.

8 recordsLinked to original sources

arXiv2026

Spontaneous spherical symmetry breaking of black holes with resonant hair

Black holes with resonant hair are static, spherical, electrically charged solutions of the Einstein-Maxwell-(gauged-)scalar system. Scalar self-interactions are mandatory for their existence. Initial dynamical studies restricted to spherical symmetry suggested stability; more recently, fully non-spherical dynamical studies revealed instabilities, at least for a particular class of self-interactions. Here, we provide a more detailed study of this instability together with a different decay channel, depending on the chosen solutions. Moreover, considering a second model, we provide evidence that the instabilities may be generic for different classes of self-interactions. We conclude these solutions are dynamically unstable and split into a bosonic lump and a bald black hole (via fission) or implode to the latter (via absorption). In both cases, the non-spherical dynamics seems to be key.

gr-qc↗

arXiv2026

Electromagnetic duality degeneracy in dynamical black hole mergers

Electromagnetic duality is a symmetry of the source-free Einstein-Maxwell equations that rotates electric and magnetic fields while leaving the stress-energy tensor invariant. We present the first fully nonlinear realization of this symmetry in dynamical strong-gravity regimes by performing numerical relativity simulations of charged black hole mergers across a continuous duality family. Starting from electrically charged binaries, we generate dyonic and magnetically charged configurations via duality rotations and evolve them within a common numerical framework. We find that all dual configurations exhibit identical spacetime dynamics, while the emitted electromagnetic radiation is related by a rotation of its polarization equal to the duality angle. Our results demonstrate a degeneracy of gravitational observables under electromagnetic duality and provide a concrete mapping between dual configurations at the level of radiation, establishing electromagnetic duality as an organizing principle for dynamical Einstein-Maxwell solutions.

gr-qc↗

arXiv2026

Splitting the Gravitational Atom: Instabilities of Black Holes with Synchronized or Resonant Hair

Black holes (BHs) with synchronized bosonic hair challenge the Kerr paradigm, linking superradiance from ultralight fields -- creating gravitational atoms -- to bosonic stars across parameter space. In the ''very hairy'' regime, where a small horizon lies inside a bosonic star containing most of the energy, they deviate sharply from Kerr, but their dynamics remain unexplored. We show that for such solutions the horizon gets naturally ejected from the center of its scalar environment, and observe a similar dynamics in a cousin model of BHs with resonant scalar hair, albeit with a different fate. This dynamical splitting is likely to be generic for sufficiently hairy BHs in the broader class of models with synchronized or resonant hair, but possible exceptions may exist.

gr-qc↗

arXiv2023

Testing $Λ$-Free f(Q) Cosmology

We study a model of Symmetric Teleparallel gravity that is able to account for the current accelerated expansion of the universe without the need for dark energy component. We investigate this model by making use of dynamical system analysis techniques to identify the regions of the parameter space with viable cosmologies and constrain it using type Ia supernova (SnIa), cosmic microwave background (CMB) data and make forecasts using standard siren (SS) events. We conclude that this model is disfavored with respect to $Λ$CDM and forthcoming standard siren events can be decisive in testing the viability of the model.

astro-ph.CO↗

arXiv2023

Constraining f(Q) Cosmology with Standard Sirens

In this dissertation, we study two cosmological models based on $f(Q)$ gravity. We resort to mock catalogs of standard siren (SS) events to see whether data from future gravitational wave (GWs) observatories will be able to distinguish these models from $Λ$CDM. The first model is the most general $f(Q)$ formulation that replicates a $Λ$CDM background, with deviations appearing only at the perturbative level. It has one additional free parameter compared to $Λ$CDM, $α$, which when set to zero falls back to $Λ$CDM. We show that LIGO-Virgo is unable to constrain $α$, due to the high error and low redshift of the measurements, whereas LISA and the ET will, with the ET outperforming LISA. The catalogs for both LISA and LIGO-Virgo show non-negligible statistical fluctuations, where we consider three representative catalogs (the best, median and worst), whereas for the ET, only a single catalog is considered, as the number of events is large enough for statistical fluctuations to be neglected. The best LISA catalog is the one with more low redshift events, while the worst LISA catalog features fewer low redshift events. Additionally, if we are to observe a bad LISA catalog, we can rely on data from LIGO-Virgo to improve the quality of the constrains, bringing it closer to a median LISA catalog. The second model attempts to replace dark energy by making use of a specific form of the function $f(Q)$. We study this model resorting to dynamical system techniques to show the regions in parameter space with viable cosmologies. Using model selection criteria, we show that no number of SS events is, by itself, able to tell this model and $Λ$CDM apart. We then show that if we add current type Ia Supernova (SnIa) data, tensions in this model arise when compared to the constrains set by the SS events.

astro-ph.CO↗

arXiv2023

Software-based security approach for networked embedded devices

As the Internet of Things (IoT) continues to expand, data security has become increasingly important for ensuring privacy and safety, especially given the sensitive and, sometimes, critical nature of the data handled by IoT devices. There exist hardware-based trusted execution environments used to protect data, but they are not compatible with low-cost devices that lack hardware-assisted security features. The research in this paper presents software-based protection and encryption mechanisms explicitly designed for embedded devices. The proposed architecture is designed to work with low-cost, low-end devices without requiring the usual changes on the underlying hardware. It protects against hardware attacks and supports runtime updates, enabling devices to write data in protected memory. The proposed solution is an alternative data security approach for low-cost IoT devices without compromising performance or functionality. Our work underscores the importance of developing secure and cost-effective solutions for protecting data in the context of IoT.

cs.CR↗

arXiv2022

Forecasting F(Q) cosmology with $Λ$CDM background using standard sirens

Forecast constraints for a Symmetric Teleparallel Gravity model with a $Λ$CDM background are made using forthcoming ground and space based gravitational waves observatories. A Bayesian analysis resorting to generated mock catalogs shows that LIGO is not expected to be able to distinguish this model from $Λ$CDM, while both LISA and the ET will, with the ET outperforming LISA. We also show that low redshift events are favored in order to improve the quality of the constrains.

astro-ph.CO↗

arXiv2017

Time-resolved monitoring of polycyclic aromatic hydrocarbons adsorbed on atmospheric particles

Real-time monitoring of individual particles from atmospheric aerosols was performed by means of a specifically developed single-particle fluorescence spectrometer (SPFS). The observed fluorescence was assigned to particles bearing polycyclic aromatic hydrocarbons (PAH). This assignment was supported by an intercomparison with classical speciation on filters followed by gas chromatography-mass spectrometry (GC-MS) analysis. As compared with daily-averaged data, our time resolved approach provided information about the physicochemical dynamics of the particles. In particular, distinctions were made between background emissions related to heating, and traffic peaks during rush hours. Also, the evolution of the peak fluorescence wavelength provided an indication of the aging of the particles during the day.

physics.ao-ph↗