Observations of Cygnus X-1 in the MeV band by the INTEGRAL imager

The spectrum of the MeV tail detected in the black-hole candidate Cygnus X-1 remains controversial as it appeared much harder when observed with the INTEGRAL Imager IBIS than with the INTEGRAL spectrometer SPI or CGRO. We present an independent analysis of the spectra of Cygnus X-1 observed by IBIS in the hard and soft states. We developed a new analysis software for the PICsIT detector layer and for the Compton mode data of the IBIS instrument and calibrated the idiosyncrasies of the PICsIT front-end electronics. The spectra of Cygnus X-1 obtained for the hard and soft states with the INTEGRAL imager IBIS are compatible with those obtained with the INTEGRAL spectrometer SPI, with CGRO, and with the models that attribute the MeV hard tail either to hybrid thermal/non-thermal Comptonisation or to synchrotron emission.Comment: 6 pages, 7 figure

Low Energy Effective Field Theories of Sp(4) Spin systems

We study the classical and quantum phase transitions of Sp(4) spin systems on three dimensional stacked square and triangular lattices. We present general Ginzburg-Landau field theories for various types of Sp(4) spin orders with different ground state manifolds such as CP(3), S^7/Z_2, Grassmann manifold G_{2,5}, G_{2,6} and so on, based on which the nature of the classical phase transitions are studied, and a global phase diagram is presented. The classical phase transitions close to quantum phase transitions toward spin liquid states are also discussed based on renormalization group (RG) flow. Our results can be directly applied to the simplest Sp(4) and SU(4) Heisenberg models which can be realized using spin-3/2 atoms and Alkaline earth atoms trapped in optical lattice.Comment: 8 pages, 4 figure

Large scale behaviour of 3D continuous phase coexistence models

We study a class of three dimensional continuous phase coexistence models, and show that, under different symmetry assumptions on the potential, the large-scale behaviour of such models near a bifurcation point is described by the dynamical $\Phi^p_3$ models for $p \in \{2,3,4\}$. This result is specific to space dimension $3$ and does not hold in dimension $2$

A new three-parameter correlation for gamma-ray bursts with a plateau phase in the afterglow

Gamma ray bursts (GRBs) have great advantages for their huge burst energies, luminosities and high redshifts in probing the Universe. A few interesting luminosity correlations of GRBs have been used to test cosmology models. Especially, for a subsample of long GRBs with known redshifts and a plateau phase in the afterglow, a correlation between the end time of the plateau phase (in the GRB rest frame) and the corresponding X-ray luminosity has been found. In this paper, we re-analyze the subsample and found that a significantly tighter correlation exists when we add a third parameter, i.e. the isotropic $\gamma$-ray energy release, into the consideration. Additionally, both long and intermediate duration GRBs are consistent with the same three-parameter correlation equation. It is argued that the new three-parameter correlation is consistent with the hypothesis that the subsample of GRBs with a plateau phase in the afterglow be associated with the birth of rapidly rotating magnetars, and that the plateau be due to the continuous energy-injection from the magnetar. It is suggested that the newly born millisecond magnetars associated with GRBs might provide a good standard candle in the Universe.Comment: 11 pages, 3 figures, 1 table; A&A, in pres

Toy models for gravitational and scalar QED decoherence

We investigate the dynamics of two quantum mechanical oscillator system-bath toy models obtained by dimensionally truncating linearized gravity coupled to a massive scalar field and scalar QED. The scalar-gravity toy model maps onto the phase damped oscillator, while the scalar QED toy model approximately maps onto an oscillator system subject to two-photon damping. The toy models provide potentially useful insights into solving for open system quantum dynamics relevant to the full scalar QED and weak gravitational field systems, in particular the decoherence of initial scalar field system superposition states

Mixing Rates of Random Walks with Little Backtracking

Many regular graphs admit a natural partition of their edge set into cliques of the same order such that each vertex is contained in the same number of cliques. In this paper, we study the mixing rate of certain random walks on such graphs and we generalize previous results of Alon, Benjamini, Lubetzky and Sodin regarding the mixing rates of non-backtracking random walks on regular graphs.Comment: 31 pages; to appear in the CRM Proceedings Series, published by the American Mathematical Society as part of the Contemporary Mathematics Serie