b-quark decay in the collinear approximation

The semileptonic decay of a b-quark, b--> c l nu, is considered in the relativistic limit where the decay products are approximately collinear. Analytic results for the double differential lepton energy distributions are given for finite charm-quark mass. Their use for the fast simulation of isolated lepton backgrounds from heavy quark decays is discussed.Comment: 7 pages, 1 figure, submitted to Phys.Rev.

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It has long been established that the appropriate way of reslicing volume MR images is to use the method of sinc interpolation [2, 4]. We have recently needed to implement this method ourselves and have found, like other authors before us, that large convolution kernels are needed in order to produce accurate reslice data, suitable for subtraction. This requirement has led many groups to investigate the use of specialised hardware and software in order to perform data analysis within sensible timescales. However, we have found that the major component of the error introduced from interpolation with small kernels, is actually due to a first order normalisation problem introduced by truncation. In this paper we demonstrate the characteristics of this problem on real data and show how it can be eliminated, so that accurate reslice data can be obtained with small kernels. Unlike other recent suggestions for correcting such effects [3], the required changes in computation are simple and significantly reduce the processing requirement for a given interpolation accuracy. Renormalised Sinc Interpolation. There are several techniques that one can adopt to solve the problem of image interpolation. One is to assume a particular prior functional model for a local region of the image data, estimate the function parameters from a maximum likelihood metric and then recompute intermediate sites from the functiona

Hadron masses and decay constants in quenched QCD

We present results for the mass spectrum and decay constants using non-perturbatively O(a) improved Wilson fermions. Three values of $\beta$ and 30 different quark masses are used to obtain the chiral and continuum limits. Special emphasis will be given to the question of taking the chiral limit and the existence of non-analytic behavior predicted by quenched chiral perturbation theory.Comment: LATTICE99(spectrum), 3 pages, 6 figure

Effective viscosity from cloud-cloud collisions in three-dimensional global SPH simulations

Analytic estimates of the viscous time-scale due to cloud-cloud collisions have been as high as thousands of Gyr. Consequently, cloud collisions are widely ignored as a source of viscosity in galactic disks. However, capturing the hydrodynamics of discs in simple analytic models is a challenge, both because of the wide dynamic range and importance of 2D and 3D effects. To test the validity of analytic models we present estimates for the viscous time-scale that are measured from three dimensional SPH simulations of disc formation and evolution. We have deliberately removed uncertainties associated with star-formation and feedback thereby enabling us to place lower bounds on the time-scale for this process. We also contrast collapse simulations with results from simulations of initially stable discs and examine the impact of numerical parameters and assumptions on our work, to constrain possible systematics in our estimates. We find that cloud-collision viscous time-scales are in the range of 0.6-16 Gyr, considerably shorter than previously estimated. This large discrepency can be understood in terms of how the efficiency of collisions is included in the analytical estimates. We find that the viscous time-scale only depends weakly on the number of clouds formed, and so while the viscous time-scale will increase with increasing resolution, this effect is too weak to alter our conclusions.Comment: 11 pages, accepted to MNRA

Exotic meson spectroscopy from the clover action at beta = 5.85 and 6.15

We repeat our original simulations of the hybrid meson spectrum using the clover action, as a check on lattice artifacts. Our results for the 1-+ masses do not substantially change. We present preliminary results for the wave function of the 1-+ state in Coulomb gauge.Comment: LATTICE98(spectrum) 3 latex pages and two postscript figures. Contribution to lattice 9

Smoothed Particle Hydrodynamics for Relativistic Heavy Ion Collisions

The method of smoothed particle hydrodynamics (SPH) is developped appropriately for the study of relativistic heavy ion collision processes. In order to describe the flow of a high energy but low baryon number density fluid, the entropy is taken as the SPH base. We formulate the method in terms of the variational principle. Several examples show that the method is very promising for the study of hadronic flow in RHIC physics.Comment: 14 pages, 8figure

String Breaking in Four Dimensional Lattice QCD

Virtual quark pair screening leads to breaking of the string between fundamental representation quarks in QCD. For unquenched four dimensional lattice QCD, this (so far elusive) phenomenon is studied using the recently developed truncated determinant algorithm (TDA). The dynamical configurations were generated on an Athlon 650 MHz PC. Quark eigenmodes up to 420 MeV are included exactly in these TDA studies performed at low quark mass on large coarse (but O($a^2$) improved) lattices. A study of Wilson line correlators in Coulomb gauge extracted from an ensemble of 1000 two-flavor dynamical configurations reveals evidence for flattening of the string tension at distances R $\geq$ approximately 1 fm.Comment: 16 pages, 5 figures, Latex (deleted extraneous eps figure file

Measuring AGN Feedback with the Sunyaev-Zel'dovich Effect

One of the most important and poorly-understood issues in structure formation is the role of outflows driven by active galactic nuclei (AGN). Using large-scale cosmological simulations, we compute the impact of such outflows on the small-scale distribution of the cosmic microwave background (CMB). Like gravitationally-heated structures, AGN outflows induce CMB distortions both through thermal motions and peculiar velocities, by processes known as the thermal and kinetic Sunyaev-Zel'dovich (SZ) effects, respectively. For AGN outflows the thermal SZ effect is dominant, doubling the angular power spectrum on arcminute scales. But the most distinct imprint of AGN feedback is a substantial increase in the thermal SZ distortions around elliptical galaxies, post-starburst ellipticals, and quasars, which is linearly proportional to the outflow energy. While point source subtraction is difficult for quasars, we show that by appropriately stacking microwave measurements around early-type galaxies, the new generation of small-scale microwave telescopes will be able to directly measure AGN feedback at the level important for current theoretical models.Comment: 12 pages, 12 figures, submitted to ApJ (comments welcome

Study of Charmonia near the deconfining transition on an anisotropic lattice with O(a) improved quark action

We study hadron properties near the deconfining transition in the quenched lattice QCD simulation. This paper focuses on the heavy quarkonium states, such as $J/\psi$ meson. In order to treat heavy quarks at $T>0$, we adopt the $O(a)$ improved Wilson action on anisotropic lattice. We discuss $c\bar{c}$ bound state observing the wave function and compare the meson correlators at above and below $T_c$. Although we find a large change of correlator near the $T_c$, the strong spatial correlation which is almost the same as confinement phase survives even $T\sim 1.5T_c$.Comment: 19 pages, 10 figure