Transition into a low temperature superconducting phase of unconventional pinning in Sr_2RuO_4

We have found a sharp transition in the vortex creep rates at a temperature T^\ast=0.05 T_c in a single crystal of Sr_2RuO_4 (T_{c}=1.03 K) by means of magnetic relaxation measurements. For T<T^\ast, the initial creep rates drop to undetectable low levels. One explanation for this transition into a phase with such extremely low vortex creep is that the low-temperature phase of Sr_2RuO_4 breaks time reversal symmetry. In that case, degenerate domain walls separating discreetly degenerate states of a superconductor can act as very strong pinning centers.Comment: 3 pages, 2 figure

The guarantee of the data subject rights within data sharing with third parties : comparative analyses under the scope of the GDPR and the LED

This dissertation sets its objective into the analyze of the data sharing with third parties and the guarantee of the data subject rights in the perspective of the Data Protection Regulation and the Directive 2016/680. In this analyzes the responsible for the data sharing will be a private company and the third parties, the competent authorities, in particular the judicial authorities. We will start by analyzing, in a comparative perspective, the rights in the regime of the Data Protection Regulation and the Directive 2016/608, in this context we will analyze the data sharing between private companies and the judicial authorities defining which law will regulate, and at what stage, this sharing. Finally, we will analyze the point of confrontation of the two regimes in the scope of the rights, emphasizing the right of access and the fundamental role that it occupies in this problem.A presente dissertação tem como objetivo a análise da partilha de dados com terceiros e a garantia dos direitos na perspectiva do Regulamento de Proteção de Dados e na Diretiva 2016/608. Nesta análise o responsável pela partilha de dados configura a figura da empresa privada e os terceiros, as autoridades competentes, em específico, as autoridades judiciais. Iremos começar por analisar, numa perspectiva comparada, os direitos no regime do Regulamento de Proteção de Dados e da Diretiva 2016/680, nesse âmbito vamos partir para a análise da partilha de dados entre as empresas privadas e as autoridades judicias definindo qual a lei que regula, e em que fase, esta partilha. Por último, iremos analisar o ponto de confronto dos dois regimes no âmbito dos direitos desta partilha, dando ênfase ao direito de acesso e ao papel fundamental que ocupa nesta problemática

Cosmic voids in modified gravity scenarios

Modified gravity (MG) theories aim to reproduce the observed acceleration of the Universe by reducing the dark sector while simultaneously recovering General Relativity (GR) within dense environments. Void studies appear to be a suitable scenario to search for imprints of alternative gravity models on cosmological scales. Voids cover an interesting range of density scales where screening mechanisms fade out, which reaches from a density contrast $\delta \approx -1$ close to their centers to $\delta \approx 0$ close to their boundaries. We present an analysis of the level of distinction between GR and two modified gravity theories, the Hu-Sawicki $f(R)$ and the symmetron theory. This study relies on the abundance, linear bias, and density profile of voids detected in n-body cosmological simulations. We define voids as connected regions made up of the union of spheres with a {\it \textup{mean}} density given by $\overline\rho_v=0.2\,\overline\rho_m$, but disconnected from any other voids. We find that the height of void walls is considerably affected by the gravitational theory, such that it increases for stronger gravity modifications. Finally, we show that at the level of dark matter n-body simulations, our constraints allow us to distinguish between GR and MG models with $|f_{R0}| > 10^{-6}$ and $z_{SSB} > 1$. Differences of best-fit values for MG parameters that are derived independently from multiple void probes may indicate an incorrect MG model. This serves as an important consistency check.Comment: 15 pages, 12 figure

Klein-Gordon oscillator in a topologically nontrivial space-time

In this study, we analyze solutions of the wave equation for scalar particles in a space-time with nontrivial topology. Solutions for the Klein--Gordon oscillator are found considering two configurations of this space-time. In the first one, it is assumed the $S^{1}\times R^{3}$ space where the metric is written in the usual inertial frame of reference. In the second case, we consider a rotating reference frame adapted to the circle S1. We obtained compact expressions for the energy spectrum and for the particles wave functions in both configurations. Additionally, we show that the energy spectrum of the solution associated to the rotating system has an additional term that breaks the symmetry around $E = 0$

Momentum Space Regularizations and the Indeterminacy in the Schwinger Model

We revisited the problem of the presence of finite indeterminacies that appear in the calculations of a Quantum Field Theory. We investigate the occurrence of undetermined mathematical quantities in the evaluation of the Schwinger model in several regularization scenarios. We show that the undetermined character of the divergent part of the vacuum polarization tensor of the model, introduced as an {\it ansatz} in previous works, can be obtained mathematically if one introduces a set of two parameters in the evaluation of these quantities. The formal mathematical properties of this tensor and their violations are discussed. The analysis is carried out in both analytical and sharp cutoff regularization procedures. We also show how the Pauli Villars regularization scheme eliminates the indeterminacy, giving a gauge invariant result in the vector Schwinger model.Comment: 10 pages, no figure