Constraining ΩM\Omega_M and Dark Energy with Gamma-Ray Bursts

An $E_{\gamma,{\rm jet}}\propto {E'_p}^{1.5}$ relationship with a small scatter for current $\gamma$-ray burst (GRB) data was recently reported, where $E_{\gamma,{\rm jet}}$ is the beaming-corrected $\gamma$-ray energy and $E'_p$ is the $\nu F_\nu$ peak energy in the local observer frame. By considering this relationship for a sample of 12 GRBs with known redshift, peak energy, and break time of afterglow light curves, we constrain the mass density of the universe and the nature of dark energy. We find that the mass density $\Omega_M=0.35\pm^{0.15}_{0.15}$ (at the $1\sigma$ confident level) for a flat universe with a cosmological constant, and the $w$ parameter of an assumed static dark-energy equation of state $w=-0.84\pm^{0.57}_{0.83}$ ($1\sigma$). Our results are consistent with those from type Ia supernovae. A larger sample established by the upcoming {\em Swift} satellite is expected to provide further constraints.Comment: 8 pages including 4 figures, to appear in ApJ Letters, typos correcte

On the Inelastic Collapse of a Ball Bouncing on a Randomly Vibrating Platform

We study analytically the dynamics of a ball bouncing inelastically on a randomly vibrating platform, as a simple toy model of inelastic collapse. Of principal interest are the distributions of the number of flights n_f till the collapse and the total time \tau_c elapsed before the collapse. In the strictly elastic case, both distributions have power law tails characterised by exponents which are universal, i.e., independent of the details of the platform noise distribution. In the inelastic case, both distributions have exponential tails: P(n_f) ~ exp[-\theta_1 n_f] and P(\tau_c) ~ exp[-\theta_2 \tau_c]. The decay exponents \theta_1 and \theta_2 depend continuously on the coefficient of restitution and are nonuniversal; however as one approches the elastic limit, they vanish in a universal manner that we compute exactly. An explicit expression for \theta_1 is provided for a particular case of the platform noise distribution.Comment: 32 page

Three-loop HTL gluon thermodynamics at intermediate coupling

We calculate the thermodynamic functions of pure-glue QCD to three-loop order using the hard-thermal-loop perturbation theory (HTLpt) reorganization of finite temperature quantum field theory. We show that at three-loop order hard-thermal-loop perturbation theory is compatible with lattice results for the pressure, energy density, and entropy down to temperatures $T\simeq3\;T_c$. Our results suggest that HTLpt provides a systematic framework that can used to calculate static and dynamic quantities for temperatures relevant at LHC.Comment: 24 pages, 13 figs. 2nd version: improved discussion and fixing typos. Published in JHE

Mott transition and suppression of orbital fluctuations in orthorhombic 3d1d^{1} perovskites

Using $t_{2g}$ Wannier-functions, a low-energy Hamiltonian is derived for orthorhombic $3d^{1}$ transition-metal oxides. Electronic correlations are treated with a new implementation of dynamical mean-field theory for non-cubic systems. Good agreement with photoemission data is obtained. The interplay of correlation effects and cation covalency (GdFeO$_{3}$-type distortions) is found to suppress orbital fluctuations in LaTiO$_{3},$ and even more in YTiO$_{3}$, and to favor the transition to the insulating state.Comment: 4 pages, 3 figures; revised manuscrip

W Plus Multiple Jets at the LHC with High Energy Jets

We study the production of a W boson in association with n hard QCD jets (for n>=2), with a particular emphasis on results relevant for the Large Hadron Collider (7 TeV and 8 TeV). We present predictions for this process from High Energy Jets, a framework for all-order resummation of the dominant contributions from wide-angle QCD emissions. We first compare predictions against recent ATLAS data and then shift focus to observables and regions of phase space where effects beyond NLO are expected to be large.Comment: 19 pages, 9 figure

Comparative study of correlation effects in CaVO3 and SrVO3

We present parameter-free LDA+DMFT (local density approximation + dynamical mean field theory) results for the many-body spectra of cubic SrVO3 and orthorhombic CaVO3. Both systems are found to be strongly correlated metals, but not on the verge of a metal-insulator transition. In spite of the considerably smaller V-O-V bond angle in CaVO3 the LDA+DMFT spectra of the two systems for energies E<E_F are very similar, their quasiparticle parts being almost identical. The calculated spectrum for E>E_F shows more pronounced, albeit still small, differences. This is in contrast to earlier theoretical and experimental conclusions, but in good agreement with recent bulk-sensitive photoemission and x-ray absorption experiments.Comment: 15 pages, 6 figure

Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets

In the CERN NA63 collaboration we have addressed the question of the potential inadequacy of the commonly used Migdal formulation of the Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20 and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference target, Ta. For each target and energy, a comparison between simulated values based on the LPM suppression of incoherent bremsstrahlung is shown, taking multi-photon effects into account. For these targets and energies, we find that Migdal's theoretical formulation is adequate to a precision of better than about 5%, irrespective of the target substance.Comment: 8 pages, 13 figure

Momentum-resolved spectral functions of SrVO3_3 calculated by LDA+DMFT

LDA+DMFT, the merger of density functional theory in the local density approximation and dynamical mean-field theory, has been mostly employed to calculate k-integrated spectra accessible by photoemission spectroscopy. In this paper, we calculate k-resolved spectral functions by LDA+DMFT. To this end, we employ the Nth order muffin-tin (NMTO) downfolding to set up an effective low-energy Hamiltonian with three t_2g orbitals. This downfolded Hamiltonian is solved by DMFT yielding k-dependent spectra. Our results show renormalized quasiparticle bands over a broad energy range from -0.7 eV to +0.9 eV with small ``kinks'', discernible in the dispersion below the Fermi energy.Comment: 21 pages, 8 figure

Electronic Structure, Local Moments and Transport in Fe_2VAl

Local spin density approximation calculations are used to elucidate electronic and magnetic properties of Heusler structure Fe_2VAl. The compound is found to be a low carrier density semimetal. The Fermi surface has small hole pockets derived from a triply degenerate Fe derived state at Gamma compensated by an V derived electron pocket at the X point. The ideal compound is found to be stable against ferromagnetism. Fe impurities on V sites, however, behave as local moments. Because of the separation of the hole and electron pockets the RKKY interaction between such local moments should be rapidly oscillating on the scale of its decay, leading to the likelihood of spin-glass behavior for moderate concentrations of Fe on V sites. These features are discussed in relation to experimental observations of an unusual insulating state in this compound.Comment: 16 pages, RevTeX, 5 figure

Anomalous diffusion and generalized Sparre-Andersen scaling

We are discussing long-time, scaling limit for the anomalous diffusion composed of the subordinated L\'evy-Wiener process. The limiting anomalous diffusion is in general non-Markov, even in the regime, where ensemble averages of a mean-square displacement or quantiles representing the group spread of the distribution follow the scaling characteristic for an ordinary stochastic diffusion. To discriminate between truly memory-less process and the non-Markov one, we are analyzing deviation of the survival probability from the (standard) Sparre-Andersen scaling.Comment: 5 pages, 3 figure