Centaurus A as the Source of ultra-high energy cosmic rays?

We present numerical simulations for energy spectra and angular distributions of nucleons above 10^{19} eV injected by the radio-galaxy Centaurus A at a distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the sub-micro Gauss range. We show that field strengths B~0.3 micro Gauss, as proposed by Farrar and Piran, cannot provide sufficient angular deflection to explain the observational data. A magnetic field of intensity ~1 micro Gauss could reproduce the observed large-scale isotropy and could marginally explain the observed energy spectrum. However, it would not readily account for the E=320 plusminus 93 EeV Fly's Eye event that was detected at an angle 136 degrees away from Cen-A. Such a strong magnetic field also saturates observational upper limits from Faraday rotation observations and X-ray bremsstrahlung emission from the ambient gas (assuming equipartition of energy). This scenario may already be tested by improving magnetic field limits with existing instruments. We also show that high energy cosmic ray experiments now under construction will be able to detect the level of anisotropy predicted by this scenario. We conclude that for magnetic fields B~0.1-0.5 micro Gauss, considered as more reasonable for the local Supercluster environment, in all likelihood at least a few sources within ~10 Mpc from the Earth should contribute to the observed ultra high energy cosmic ray flux.Comment: 7 latex pages, 7 postscript figures included; for related numerical simulations see also http://www.iap.fr/users/sigl/r2e.htm

On the spectrum of the transfer operators of a one-parameter family with intermittency transition

We study the transfer operators for a family $F_r:[0,1] \to [0,1]$ depending on the parameter $r\in [0,1]$, which interpolates between the tent map and the Farey map. In particular, considering the action of the transfer operator on a suitable Hilbert space, we can define a family of infinite matrices associated to the operators and study their spectrum by numerical methods.Comment: 6 pages, 3 figure

The correlation between soft and hard X-rays component in flares: from the Sun to the stars

In this work we study the correlation between the soft (1.6--12.4 keV, mostly thermal) and the hard (20--40 and 60--80 keV, mostly non-thermal) X-ray emission in solar flares up to the most energetic events, spanning about 4 orders of magnitude in peak flux, establishing a general scaling law and extending it to the most intense stellar flaring events observed to date. We used the data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, a NASA Small Explorer launched in February 2002. RHESSI has good spectral resolution (~1 keV in the X-ray range) and broad energy coverage (3 keV--20 MeV), which makes it well suited to distinguish the thermal from non-thermal emission in solar flares. Our study is based on the detailed analysis of 45 flares ranging from the GOES C-class, to the strongest X-class events, using the peak photon fluxes in the GOES 1.6--12.4 keV and in two bands selected from RHESSI data, i.e.20--40 keV and 60--80 keV. We find a significant correlation between the soft and hard peak X-ray fluxes spanning the complete sample studied. The resulting scaling law has been extrapolated to the case of the most intense stellar flares observed, comparing it with the stellar observations. Our results show that an extrapolation of the scaling law derived for solar flares to the most active stellar events is compatible with the available observations of intense stellar flares in hard X-rays.Comment: 9 pages, 10 figures. To be published in Astronomy and Astrophysic

Statistics of energy levels and zero temperature dynamics for deterministic spin models with glassy behaviour

We consider the zero-temperature dynamics for the infinite-range, non translation invariant one-dimensional spin model introduced by Marinari, Parisi and Ritort to generate glassy behaviour out of a deterministic interaction. It is shown that there can be a large number of metatastable (i.e., one-flip stable) states with very small overlap with the ground state but very close in energy to it, and that their total number increases exponentially with the size of the system.Comment: 25 pages, 8 figure

Neutrino self-energy in a magnetized medium in arbitrary ξ\xi-gauge

We calculate the one-loop neutrino self-energy in a magnetized plasma to all orders in the magnetic field. The calculation is done in a general gauge. We obtain the dispersion relation and effective potential for neutrinos in a CP-symmetric plasma under various conditions, and show that, while the self-energy depends on the gauge parameter $\xi$, the dispersion relation and effective potential to leading order are independent of it.Comment: 13 pages, RevTeX, epsfig, axodra

On the leading eigenvalue of transfer operators of the Farey map with real temperature

We study the spectral properties of a family of generalized transfer operators associated to the Farey map. We show that when acting on a suitable space of holomorphic functions, the operators are self-adjoint and the positive dominant eigenvalue can be approximated by means of the matrix expression of the operators.Comment: 9 pages, 3 figure

Power Corrections in Charmless B Decays

In this paper, we focus on the role of power corrections in QCD factorization(QCDF) method in charmless two-body nonleptonic $B$ meson decays. We use the ratio of the branching fraction of $B^+ \to \pi^+ K^{\ast 0}$ to that of $B^0 \to \pi^- \rho^+$, for which the theoretical uncertainties are greatly reduced, to show clearly that the power corrections in charmless B decays are probably large. With other similar ratios considered, for example, for the $B^0 \to K^- \rho^+$ decay, it is very likely that, among various sources of power corrections, annihilation topology plays an indispensable role at least for penguin dominated $\rm PV$ channels. We also consider some selective ratios of direct CP asymmetries. Among these, we find that, if power corrections other than the chirally enhanced power corrections and annihilation topology were negligible, QCDF would predict the direct CP asymmetry of $B \to \pi^+ \pi^-$ to be about 3 times larger than that of $B \to \pi^\pm K^\mp$, with opposite sign. Experimentally any significant deviation from this prediction would suggest either new physics or possibly the importance of long-distance rescattering effects.Comment: references and note added, to appear in Phys. Rev.