The very faint hard state of the persistent neutron star X-ray binary SLX 1737-282 near the Galactic centre

We report on a detailed study of the spectral and temporal properties of the neutron star low mass X-ray binary SLX 1737-282, which is located only ~1degr away from Sgr A. The system is expected to have a short orbital period, even within the ultra-compact regime, given its persistent nature at low X-ray luminosities and the long duration thermonuclear burst that it has displayed. We have analysed a Suzaku (18 ks) observation and an XMM-Newton (39 ks) observation taken 7 years apart. We infer (0.5-10 keV) X-ray luminosities in the range 3-6 x10^35erg s-1, in agreement with previous findings. The spectra are well described by a relatively cool (kTbb = 0.5 keV) black body component plus a Comptonized emission component with {\Gamma} ~1.5-1.7. These values are consistent with the source being in a faint hard state, as confirmed by the ~ 20 per cent fractional root mean square amplitude of the fast variability (0.1 - 7 Hz) inferred from the XMM-Newton data. The electron temperature of the corona is >7 keV for the Suzaku observation, but it is measured to be as low as ~2 keV in the XMM-Newton data at higher flux. The latter is significantly lower than expected for systems in the hard state. We searched for X-ray pulsations and imposed an upper limit to their semi-amplitude of 2 per cent (0.001 - 7 Hz). Finally, we investigated the origin of the low frequency variability emission present in the XMM-Newton data and ruled out an absorption dip origin. This constraint the orbital inclination of the system to 65 degr unless the orbital period is longer than 11 hr (i.e. the length of the XMM-Newton observation).Comment: 7 pages, 4 figures, 1 table. Accepted for publication in MNRA

TeV Burst of Gamma-Ray Bursts and Ultra High Energy Cosmic Rays

Some recent experiments detecting very high energy (VHE) gamma-rays above 10-20 TeV independently reported VHE bursts for some of bright gamma-ray bursts (GRBs). If these signals are truly from GRBs, these GRBs must emit a much larger amount of energy as VHE gamma-rays than in the ordinary photon energy range of GRBs (keV-MeV). We show that such extreme phenomena can be reasonably explained by synchrotron radiation of protons accelerated to \sim 10^{20-21} eV, which has been predicted by Totani (1998a). Protons seem to carry about (m_p/m_e) times larger energy than electrons, and hence the total energy liberated by one GRB becomes as large as \sim 10^{56} (\Delta \Omega / 4 \pi) ergs. Therefore a strong beaming of GRB emission is highly likely. Extension of the VHE spectrum beyond 20 TeV gives a nearly model-independent lower limit of the Lorentz factor of GRBs, as \gamma \gtilde 500. Furthermore, our model gives the correct energy range and time variability of ordinary keV-MeV gamma-rays of GRBs by synchrotron radiation of electrons. Therefore the VHE bursts of GRBs strongly support the hypothesis that ultra high energy cosmic rays observed on the Earth are produced by GRBs.Comment: Final version to appear in ApJ Lett. Emphasizing that the extremely large energy required in this model is not theoretically impossible if GRB emission is strongly beamed. References update

Closure of the Monte Carlo dynamical equation in the spherical Sherrington-Kirkpatrick model

We study the analytical solution of the Monte Carlo dynamics in the spherical Sherrington-Kirkpatrick model using the technique of the generating function. Explicit solutions for one-time observables (like the energy) and two-time observables (like the correlation and response function) are obtained. We show that the crucial quantity which governs the dynamics is the acceptance rate. At zero temperature, an adiabatic approximation reveals that the relaxational behavior of the model corresponds to that of a single harmonic oscillator with an effective renormalized mass

Quintessence and the Swampland: The Parametrically Controlled Regime of Moduli Space

We provide evidence that slow roll is not possible in any parametrically controlled regime of the moduli space of string theory. This is proven in full generality in the asymptotic limit of the moduli space of type II and heterotic Calabi-Yau compactifications for the dilaton and any number of Kähler moduli. Our results suggest that in order to build quintessence into string theory one must work in the interior of moduli space where numerical, even if not parametric, control could still be achieved

The good, the bad and the ugly .... of Horava gravity

I review the good, the bad and the ugly of the non-projectable versions of Horava gravity. I explain how this non-relativistic theory was constructed and why it was touted with such excitement as a quantum theory of gravity. I then review some of the issues facing the theory, explaining how strong coupling occurs and why this is such a problem for both phenomenology and the question of renormalisability. Finally I comment on possible violations of Equivalence Principle, and explain why these could be an issue for Blas et al's "healthy extension". This paper was presented as a talk at PASCOS 2010 in Valencia.Comment: 7 page

Galaxy Clusters in the Line of Sight to Background Quasars: I. Survey Design and Incidence of MgII Absorbers at Cluster Redshifts

We describe the first optical survey of absorption systems associated with galaxy clusters at z= 0.3-0.9. We have cross-correlated SDSS DR3 quasars with high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. We have found 442 quasar-cluster pairs for which the MgII doublet might be detected at a transverse (physical) distance d<2 Mpc from the cluster centers. To investigate the incidence (dN/dz) and equivalent-width distribution n(W) of MgII systems at cluster redshifts, two statistical samples were drawn out of these pairs: one made of high-resolution spectroscopic quasar observations (46 pairs), and one made of quasars used in MgII searches found in the literature (375 pairs). The results are: (1) the population of strong MgII systems (W_0>2.0 Ang.) near cluster redshifts shows a significant (>3 sigma) overabundance (up to a factor of 15) when compared with the 'field' population; (2) the overabundance is more evident at smaller distances (d<1 Mpc) than larger distances (d<2 Mpc) from the cluster center; and, (3) the population of weak MgII systems (W_0<0.3 Ang.) near cluster redshifts conform to the field statistics. Unlike in the field, this dichotomy makes n(W) in clusters appear flat and well fitted by a power-law in the entire W-range. A sub-sample of the most massive clusters yields a stronger and still significant signal. Since either the absorber number density or filling-factor/cross-section affects the absorber statistics, an interesting possibility is that we have detected the signature of truncated halos due to environmental effects. Thus, we argue that the excess of strong systems is due to a population of absorbers in an overdense galaxy environment, and the lack of weak systems to a different population, that got destroyed in the cluster environment. (Abridged)Comment: Accepted for publication in the Astrophysical Journa

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.Comment: 44 pages, Latex, epsfig, 18 figures, to appear on the Report of the Workshop on Physics at LEP2, CERN 96-01, vol. 1, 199