Recent results from the Pierre Auger Observatory

The results obtained after the first decade of operation of the Pierre Auger Observatory are reviewed.Comment: Proceedings X SILAFAE Medellin-201

Results from the Pierre Auger Observatory

I describe some of the results on ultrahigh-energy cosmic rays that have been obtained with the Pierre Auger Observatory. These include measurements of the spectrum, composition and anisotropies. Possible astrophysical scenarios that account for these results are discussed.Comment: Proceedings of the 7th Roma International Conference on Astroparticle Physic

Electron neutrino opacity in magnetised media

We study the effects of strong magnetic fields ($B> 10^{13}$~G) in the cross section for $\nu_e n\to p e$ scattering in the presence of a degenerate electron background. This can be relevant for the $\nu_e$ propagation in the proto-neutron star stage after supernovae collapse. We find that for field strengths $B> 10^{16}$~G$(E_\nu/10$ MeV$)^2$ the $\nu_e$ opacity is sizeably affected by the magnetic field and can lead to a shift in the location of the electron neutrino sphere towards lower densities. We discuss the implications that this may have for scenarios proposed to explain the observed pulsar velocities

Microlensing searches of dark matter

The evolution of the observational results of microlensing towards the LMC and some of the suggested interpretations to account for them are discussed. It is emphasized that the results at present are indicative of a lensing population of white dwarfs, possibly in the spheroid (not dark halo) of the Galaxy, together with the more standard backgrounds of stellar populations in the Magellanic Clouds and in the Galaxy. This is also hinted by dynamical estimates of the spheroid mass and by recent direct searches of old white dwarfs.Comment: 9 pp., Lecture given at Silafae III Conference (april 2000

Optimal synchronization deep in the quantum regime: resource and fundamental limit

We develop an analytical framework to study the synchronization of a quantum self-sustained oscillator to an external signal. Our unified description allows us to identify the resource on which quantum synchronization relies, and to compare quantitatively the synchronization behavior of different limit cycles and signals. We focus on the most elementary quantum system that is able to host a self-sustained oscillation, namely a single spin 1. Despite the spin having no classical analogue, we first show that it can realize the van der Pol limit cycle deep in the quantum regime, which allows us to provide an analytical understanding to recently reported numerical results. Moving on to the equatorial limit cycle, we then reveal the existence of an interference-based quantum synchronization blockade and extend the classical Arnold tongue to a snake-like split tongue. Finally, we derive the maximum synchronization that can be achieved in the spin-1 system, and construct a limit cycle that reaches this fundamental limit asymptotically.Comment: 15 pages, 9 figures, equivalent to published versio

Magnetic diffusion effects on the Ultra-High Energy Cosmic Ray spectrum and composition

We discuss the effects of diffusion of high energy cosmic rays in turbulent extra-galactic magnetic fields. We find an approximate expression for the low energy suppression of the spectrum of the different mass components (with charge $Z$) in the case in which this suppression happens at energies below $\sim Z$ EeV, so that energy losses are dominated by the adiabatic ones. The low energy suppression appears when cosmic rays from the closest sources take a time comparable to the age of the Universe to reach the Earth. This occurs for energies $E< Z\, {\rm EeV}\,(B/{{\rm G}})\sqrt{l_c/{\rm Mpc}}(d_s/70\ {\rm Mpc})$ in terms of the magnetic field RMS strength $B$, its coherence length $l_c$ and the typical separation between sources $d_s$. We apply this to scenarios in which the sources produce a mixed composition and have a relatively low maximum rigidity ($E_{max}\sim (2$--$10) Z$ EeV), finding that diffusion has a significant effect on the resulting spectrum, the average mass and on its spread, in particular reducing this last one. For reasonable values of $B$ and $l_c$ these effects can help to reproduce the composition trends observed by the Auger Collaboration for source spectra compatible with Fermi acceleration

E sub 6 leptoquarks and the solar neutrino problem

The possibility that non-conventional neutrino oscillations take place in the superstring inspired E sub 6 models is considered. In this context, the influence of leptoquark mediated interactions of the neutrinos with nucleons in the resonant flavor conversion is discussed. It is shown that this effect can be significant for v sub e - v sub tau oscillations if these neutrinos have masses required in the ordinary Mikheyev-Smirnov-Wolfenstein (MSW) effect, and may lead to a solution of the solar neutrino problem even in the absence of vacuum mixings. On the other hand, this model cannot lead to a resonant behavior in the sun if the neutrinos are massless

Solving the scattering of N photons on a two-level atom without computation

We propose a novel approach for solving the scattering of light onto a two-level atom coupled to a one-dimensional waveguide. We first express the physical quantity of interest in terms of Feynman diagrams and treat the atom as a non-saturable linear beamsplitter. By using the atomic response to our advantage, a relevant substitution is then made that captures the nonlinearity of the atom, and the final result is obtained in terms of simple integrals over the initial incoming wavepackets. The procedure is not limited to post-scattering quantities and allows for instance to derive the atomic excitation during the scattering event.Comment: 15 pages, 4 figure