Positive and negative Hanbury-Brown and Twiss correlations in normal metal-superconducting devices

In the light of the recent analogs of the Hanbury--Brown and Twiss experiments in mesoscopic beam splitters, negative current noise correlations are recalled to be the consequence of an exclusion principle. Here, positive (bosonic) correlations are shown to exist in a fermionic system, composed of a superconductor connected to two normal reservoirs. In the Andreev regime, the correlations can either be positive or negative depending on the reflection coefficient of the beam splitter. For biases beyond the gap, the transmission of quasiparticles favors fermionic correlations. The presence of disorder enhances positive noise correlations. Potential experimental applications are discussed.Comment: 4 pages, 3 figures, RevTeX, revised versio

Towards single-valued polylogarithms in two variables for the seven-point remainder function in multi-Regge-kinematics

We investigate single-valued polylogarithms in two complex variables, which are relevant for the seven-point remainder function in N=4 super-Yang-Mills theory in the multi-Regge regime. After constructing these two-dimensional polylogarithms, we determine the leading logarithmic approximation of the seven-point remainder function up to and including five loops.Comment: 20 pages, 2 figures; v2: replaced with published versio

Generation of indistinguishable and pure heralded single photons with tunable bandwidth

We describe a new scheme to fully control the joint spectrum of paired photons generated in spontaneous parametric down-conversion. We show the capability of this method to generate frequency-uncorrelated photon pairs that are pure and indistinguishable, and whose bandwidth can be readily tuned. Importantly, the scheme we propose here can be implemented in any nonlinear crystal and frequency band of interest.Comment: 3 pages, 3 figure

Comparing supernova remnants around strongly magnetized and canonical pulsars

The origin of the strong magnetic fields measured in magnetars is one of the main uncertainties in the neutron star field. On the other hand, the recent discovery of a large number of such strongly magnetized neutron stars, is calling for more investigation on their formation. The first proposed model for the formation of such strong magnetic fields in magnetars was through alpha-dynamo effects on the rapidly rotating core of a massive star. Other scenarios involve highly magnetic massive progenitors that conserve their strong magnetic moment into the core after the explosion, or a common envelope phase of a massive binary system. In this work, we do a complete re-analysis of the archival X-ray emission of the Supernova Remnants (SNR) surrounding magnetars, and compare our results with all other bright X-ray emitting SNRs, which are associated with Compact Central Objects (CCOs; which are proposed to have magnetar-like B-fields buried in the crust by strong accretion soon after their formation), high-B pulsars and normal pulsars. We find that emission lines in SNRs hosting highly magnetic neutron stars do not differ significantly in elements or ionization state from those observed in other SNRs, neither averaging on the whole remnants, nor studying different parts of their total spatial extent. Furthermore, we find no significant evidence that the total X-ray luminosities of SNRs hosting magnetars, are on average larger than that of typical young X-ray SNRs. Although biased by a small number of objects, we found that for a similar age, there is the same percentage of magnetars showing a detectable SNR than for the normal pulsar population.Comment: 16 pages, 5 figures, Accepted for publication in MNRA

The effects of magnetic field, age, and intrinsic luminosity on Crab-like pulsar wind nebulae

We investigate the time-dependent behavior of Crab-like pulsar wind nebulae (PWNe) generating a set of models using 4 different initial spin-down luminosities ($L_0 =\{1,0.1,0.01,0.001\} \times L_{0, {\rm Crab}}$), 8 values of magnetic fraction ($\eta =$ 0.001, 0.01, 0.03, 0.1, 0.5, 0.9, 0.99, and 0.999, i.e., from fully particle dominated to fully magnetically dominated nebulae), and 3 distinctive ages: 940, 3000, and 9000 years. We find that the self-synchrotron Compton (SSC) contribution is irrelevant for $L_{SD}$=0.1, 1, and 10% of the Crab power, disregarding the age and the magnetic fraction. SSC only becomes relevant for highly energetic ($\sim 70$ of the Crab), particle dominated nebulae at low ages (of less than a few kyr), located in a FIR background with relatively low energy density. Since no pulsar other than Crab is known to have these features, these results clarify why the Crab Nebula, and only it, is SSC dominated. No young PWN would be detectable at TeV energies if the pulsar's spin-down power is 0.1% Crab or lower. For 1% of the Crab spin-down, only particle dominated nebulae can be detected by H.E.S.S.-like telescopes when young enough (with details depending on the precise injection and environmental parameters). Above 10% of the Crab's power, all PWNe are detectable by H.E.S.S.-like telescopes if they are particle dominated, no matter the age. The impact of the magnetic fraction on the final SED is varied and important, generating order of magnitude variations in the luminosity output for systems that are otherwise the same (equal $P$, $\dot P$, injection, and environment).Comment: Accepted for publication in MNRA

Is there room for highly magnetized pulsar wind nebulae among those non-detected at TeV?

We make a time-dependent characterization of pulsar wind nebulae (PWNe) surrounding some of the highest spin-down pulsars that have not yet been detected at TeV. Our aim is assessing their possible level of magnetization. We analyze the nebulae driven by J2022+3842 in G76.9+1.0, J0540-6919 in N158A (the Crab twin), J1400--6325 in G310.6--1.6, and J1124--5916 in G292.0+0.18, none of which have been found at TeV energies. For comparison we refer to published models of G54.1+0.3, the Crab nebula, and develop a model for N157B in the Large Magellanic Cloud (LMC). We conclude that further observations of N158A could lead to its detection at VHE. According to our model, a FIR energy density of 5 eV cm$^{-3}$ could already lead to a detection in H.E.S.S. (assuming no other IC target field) within 50 hours of exposure and just the CMB inverse Compton contribution would produce VHE photons at the CTA sensitivity. We also propose models for G76.9+1.0, G310.6--1.6 and G292.0+1.8 which suggest their TeV detection in a moderate exposure for the latter two with the current generation of Cherenkov telescopes. We analyze the possibility that these PWNe are highly magnetized, where the low number of particles explains the residual detection in X-rays and their lack of detection at TeV energies.Comment: Accepted for publication in MNRA

Integral Inequalities and their Applications to the Calculus of Variations on Time Scales

We discuss the use of inequalities to obtain the solution of certain variational problems on time scales.Comment: To appear in Mathematical Inequalities & Applications (http://mia.ele-math.com). Accepted: 14.01.201

Machine learning on deep neural networks and object tracking applied to motion of airplanes

The aim of this project is to understand the concepts underlying machine learning and how to implement those. To achieve this purpose, an exhaustive study of the origins of this technology has been made, describing the most popular types of neural networks, their history, and the architectures and subsequent implementations. Three implementations of neural networks are presented, using world-known datasets. In the last implementation, an exhaustive study has been realized to achieve the best performance algorithm taking into account different settings. In the second part of the project, Detectron2 has been used, an advanced machine learning program that performs object detection. We have worked with this program and executed a study of the motion of moving airplanes, implementing a new method to track objects given a set of images extracted from a given video