A study of Wigner functions for discrete-time quantum walks

We perform a systematic study of the discrete time Quantum Walk on one dimension using Wigner functions, which are generalized to include the chirality (or coin) degree of freedom. In particular, we analyze the evolution of the negative volume in phase space, as a function of time, for different initial states. This negativity can be used to quantify the degree of departure of the system from a classical state. We also relate this quantity to the entanglement between the coin and walker subspaces.Comment: 16 pages, 8 figure

How many Ultra High Energy Cosmic Rays could we expect from Centaurus A?

The Pierre Auger Observatory has associated a few ultra high energy cosmic rays with the direction of Centaurus A. This source has been deeply studied in radio, infrared, X-ray and $\gamma$-rays (MeV-TeV) because it is the nearest radio-loud active galactic nuclei. Its spectral energy distribution or spectrum shows two main peaks, the low energy peak, at an energy of $10^{-2}$ eV, and the high energy peak, at about 150 keV. There is also a faint very high energy (E $\geq$ 100 GeV) $\gamma$-ray emission fully detected by the High Energy Stereoscopic System experiment. In this work we describe the entire spectrum, the two main peaks with a Synchrotron/Self-Synchrotron Compton model and, the Very High Energy emission with a hadronic model. We consider p$\gamma$ and $pp$ interactions. For the p$\gamma$ interaction, we assume that the target photons are those produced at 150 keV in the leptonic processes. On the other hand, for the pp interaction we consider as targets the thermal particle densities in the lobes. Requiring a satisfactory description of the spectra at very high energies with p$\gamma$ interaction we obtain an excessive luminosity in ultra high energy cosmic rays (even exceeding the Eddington luminosity). However, when considering pp interaction to describe the $\gamma$-spectrum, the obtained number of ultra high energy cosmic rays are in agreement with Pierre Auger observations. Moreover, we calculate the possible neutrino signal from pp interactions on a Km$^3$ neutrino telescope using Monte Carlo simulations.Comment: Accepted in Ap

Influence of Dislocations in Thomson's Problem

We investigate Thomson's problem of charges on a sphere as an example of a system with complex interactions. Assuming certain symmetries we can work with a larger number of charges than before. We found that, when the number of charges is large enough, the lowest energy states are not those with the highest symmetry. As predicted previously by Dodgson and Moore, the complex patterns in these states involve dislocation defects which screen the strains of the twelve disclinations required to satisfy Euler's theorem.Comment: 9 pages, 4 figures in gif format. Original PS files can be obtained in http://fermi.fcu.um.es/thomso

Continuity and variability in the parental involvement and advocacy beliefs of Latino families of young children

Parental involvement is an important component of children’s school success. Although the literature on parental involvement among Latino families is growing and moving from deficit-based perspectives, very few studies have examined the parental involvement beliefs and practices of Latino families who vary across demographic and sociocultural lines within the same school community. This qualitative study explored Latino parents’ beliefs about children’s education, their involvement and advocacy beliefs and practices, and their perceptions of feeling welcome at their children’s school. In-depth interviews were conducted with 12 parents of preschool and kindergarten children who attended a bilingual school. Qualitative descriptive analyses revealed that the majority of parents espoused the cultural value of educación, engaged in learning activities at home, and viewed themselves as living models of behavior for children, regardless of their education or immigrant status. Only first generation immigrant parents made explicit reference to children’s futures. All parents attributed supportive relationships with school personnel and a bilingual climate as the most important sources of feeling welcome at school. However, parents with more education valued what they perceived as an “open door policy” and were more vocal in critiquing policies. Findings have implications for the development of multicultural competence among teachers and for ways diverse Latino families might develop a shared voice within the school sector.Published versio

Revising the Solution of the Neutrino Oscillation Parameter Degeneracies at Neutrino Factories

In the context of neutrino factories, we review the solution of the degeneracies in the neutrino oscillation parameters. In particular, we have set limits to $\sin^2 2\theta_{13}$ in order to accomplish the unambiguous determination of $\theta_{23}$ and $\delta$. We have performed two different analysis. In the first, at a baseline of 3000 km, we simulate a measurement of the channels $\nu_e\to\nu_\mu$, $\nu_e\to\nu_\tau$ and $\bar{\nu}_\mu\to\bar{\nu}_\mu$, combined with their respective conjugate ones, with a muon energy of 50 GeV and a running time of five years. In the second, we merge the simulated data obtained at L=3000 km with the measurement of $\nu_e\to\nu_\mu$ channel at 7250 km, the so called 'magic baseline'. In both cases, we have studied the impact of varying the $\nu_\tau$ detector efficiency-mass product, $(\epsilon_{\nu_\tau}\times M_\tau)$, at 3000 km, keeping unchanged the $\nu_\mu$ detector mass and its efficiency. At L=3000 km, we found the existance of degenerate zones, that corresponds to values of $\theta_{13}$, which are equal or almost equal to the true ones. These zones are extremely difficult to discard, even when we increase the number of events. However, in the second scenario, this difficulty is overcomed, demostrating the relevance of the 'magic baseline'. From this scenario, the best limits of $\sin^2 2\theta_{13}$, reached at $3\sigma$, for $\sin^2 2\theta_{23}=0.95$, 0.975 and 0.99 are: 0.008, 0.015 and 0.045, respectively, obtained at $\delta=0$, and considering $(\epsilon_{\nu_\tau}\times M_\tau) \approx 125$, which is five times the initial efficiency-mass combination.Comment: 40 pages, 18 figures; added references, corrected typos, updated Eq (15c