A Parton Model for Inclusive Semileptonic B Meson Decays

The parton model for semileptonic B meson decays is studied with special attention to the decay distributions. We find that the spectra show dramatic variations when we introduce cuts on the hadronic energy or invariant mass of hadrons. Results for both $b\rightarrow u$ and $b\rightarrow c$ decays are presented. The detailed spectra may help to separate the two types of decays.Comment: 9 pages, DO-TH 93/29, OHSTPY-HEP-T-93-011, September 199

Spectra of Modular and Small-World Matrices

We compute spectra of symmetric random matrices describing graphs with general modular structure and arbitrary inter- and intra-module degree distributions, subject only to the constraint of finite mean connectivities. We also evaluate spectra of a certain class of small-world matrices generated from random graphs by introducing short-cuts via additional random connectivity components. Both adjacency matrices and the associated graph Laplacians are investigated. For the Laplacians, we find Lifshitz type singular behaviour of the spectral density in a localised region of small $|\lambda|$ values. In the case of modular networks, we can identify contributions local densities of state from individual modules. For small-world networks, we find that the introduction of short cuts can lead to the creation of satellite bands outside the central band of extended states, exhibiting only localised states in the band-gaps. Results for the ensemble in the thermodynamic limit are in excellent agreement with those obtained via a cavity approach for large finite single instances, and with direct diagonalisation results.Comment: 18 pages, 5 figure

Second and third season QUaD CMB temperature and polarization power spectra

We report results from the second and third seasons of observation with the QUaD experiment. Angular power spectra of the Cosmic Microwave Background are derived for both temperature and polarization at both 100 GHz and 150 GHz, and as cross frequency spectra. All spectra are subjected to an extensive set of jackknife tests to probe for possible systematic contamination. For the implemented data cuts and processing technique such contamination is undetectable. We analyze the difference map formed between the 100 and 150 GHz bands and find no evidence of foreground contamination in polarization. The spectra are then combined to form a single set of results which are shown to be consistent with the prevailing LCDM model. The sensitivity of the polarization results is considerably better than that of any previous experiment -- for the first time multiple acoustic peaks are detected in the E-mode power spectrum at high significance.Comment: 24 pages, 23 figures, updated to reflect published versio

Observing many body effects on lepton pair production from low mass enhancement and flow at RHIC and LHC energies

The $\rho$ spectral function at finite temperature calculated using the real-time formalism of thermal field theory is used to evaluate the low mass dilepton spectra. The analytic structure of the $\rho$ propagator is studied and contributions to the dilepton yield in the region below the bare $\rho$ peak from the different cuts in the spectral function are discussed. The space-time integrated yield shows significant enhancement in the region below the bare $\rho$ peak in the invariant mass spectra. It is argued that the variation of the inverse slope of the transverse mass ($M_T$) distribution can be used as an efficient tool to predict the presence of two different phases of the matter during the evolution of the system. Sensitivity of the effective temperature obtained from the slopes of the $M_T$ spectra to the medium effects are studied

Probing in-medium vector meson decays by double-differential di-electron spectra in heavy-ion collisions at SIS energies

Within a transport code simulation for heavy-ion collisions at bombarding energies around 1 AGeV, we demonstrate that double-differential di-electron spectra with suitable kinematical cuts are useful to isolate (i) the $\rho$ meson peak even in case of strong broadening, and (ii) the in-medium $\omega$ decay contribution. The expected in-medium modifications of the vector meson spectral densities can thus be probed in this energy range via the di-electron channel

Ghost-free and Modular Invariant Spectra of a String in SL(2,R) and Three Dimensional Black Hole Geometry

Spectra of a string in $SL(2,R)$ and three dimensional (BTZ) black hole geometry are discussed. We consider a free field realization of ^sl (2,R) different from the standard ones in treatment of zero-modes. Applying this to the string model in SL(2,R), we show that the spectrum is ghost-free. The essence of the argument is the same as Bars' resolution to the ghost problem, but there are differences; for example, the currents do not contain logarithmic cuts. Moreover, we obtain a modular invariant partition function. This realization is also applicable to the analysis of the string in the three dimensional black hole geometry, the model of which is described by an orbifold of the SL(2,R) WZW model. We obtain ghost-free and modular invariant spectra for the black hole theory as well. These spectra provide examples of few sensible spectra of a string in non-trivial backgrounds with curved time and, in particular, in a black hole background with an infinite number of propagating modes.Comment: 18 pages, Latex; typos and some terminology correcte