42339487
B spectroscopy from NRQCD with dynamical fermions.
We present a lattice investigation, partially including the effects of dynamical quarks, of the heavy-light mesons using NRQCD for the heavy quark and the Wilson action for the light quark. We perform an extensive calculation of the spectrum employing a multistate, multiexponential fitting analysis which enables us to extract the 2{ital S}-1{ital S} splitting as well as the {sup 1}{ital P}{sub 1}-{ital {bar S}} and hyperfine splittings. The Wilson action introduces a large systematic error into the calculation, and within this uncertainty we obtain agreement with experiment. We perform a comprehensive calculation of the heavy-light meson mass, investigating three methods and their range of validity. The agreement found between these methods confirms that Lorentz invariance can be restored at this order in NRQCD by a constant shift to all masses. We calculated spectroscopic quantities over a wide range in heavy quark mass and are able to perform a detailed investigation of heavy quark symmetry around the {ital b} quark mass. In particular, we extract the nonperturbative coefficients of terms in the heavy quark expansion of the meson binding energy. We demonstrate the importance of using tadpole-improved operators in such a calculation. {copyright} {ital 1996 The American Physical Society.}
119542063
Study of chiral symmetry in quenched QCD using the overlap Dirac operator
We compute fermionic observables relevant to the study of chiral symmetry in quenched QCD using the overlap Dirac operator for a wide range of fermion mass. We use analytical results to disentangle the contribution from exact zero modes and simplify our numerical computations. Details concerning the numerical implementation of the overlap Dirac operator are presented. {copyright} {ital 1999} {ital The American Physical Society}
119548610
Biased Metropolis-heat-bath algorithm for fundamental-adjoint SU(2) lattice gauge theory
For SU(2) lattice gauge theory with the fundamental-adjoint action an efficient heat-bath algorithm is not known so that one had to rely on Metropolis simulations supplemented by overrelaxation. Implementing a novel biased Metropolis-heat-bath algorithm for this model, we find improvement factors in the range 1.45 to 2.06 over conventionally optimized Metropolis simulations. If one optimizes further with respect to additional overrelaxation sweeps, the improvement factors are found in the range 1.3 to 1.8.
15338965
Infrared and ultraviolet properties of the Landau gauge quark propagator
Abstract We present a current summary of a program to study the quark propagator using lattice QCD. We use the Overlap and “Asqtad” quark actions on a number of lattice ensembles. to assess systematic errors. We comment on the place of this work amongst studies of QCD Green's functions in other formulations. A preliminary calculation of the running quark mass is presented.
121063312
Search for symmetry restoration in the fundamental SU(2) Higgs model
Abstract The phase structure of the fundamental SU(2) Higgs model at finite temperature is investigated close to the zero-temperature Higgs transition by Monte Carlo methods. In the confined phase at zero temperature we find a crossover from a confined to a deconfined region that remains quite sharp on lattices of temporal extent NT = 4 even close to the Higgs transition. On asymmetric lattices the Higgs transition shifts slightly compared to the zero-temperature, symmetric lattice, giving indirect evidence for symmetry restoration at high temperature.
14897456
Divergent chiral condensate in the quenched Schwinger model
We calculate numerically the eigenvalue distribution of the overlap Dirac operator in the quenched Schwinger model on a lattice. The distribution does not fit any of the three universality classes of spontaneous chiral-symmetry breaking, and its strong volume dependence indicates that the chiral condensate in the quenched theory is an ill-defined and divergent quantity. When we reweight configurations with the Dirac determinant to study the theory with N{sub f}=1, we obtain a distribution of eigenvalues that is well-behaved and consistent with the theory of explicit symmetry breaking due to the anomaly.
6958720
Precise measurement of the Xi - magnetic moment.
With 4.36{times}10{sup 6} events, spin precession in a magnetic field has been used to measure the magnetic moment of the {Xi}{sup {minus}} hyperon as {minus}0.6505{plus minus}0.0025 nuclear magnetons.
13473472
Decay distribution of high-transverse-momentum rho mesons.
20204600
Dynamics of multidimensional generalization of Bianchi type-IX cosmological models.
We investigate the dynamics of an 11-dimensional homogeneous cosmological model. We assume that the t = const hypersurfaces are products of a 3-dimensional Bianchi type-IX space and a 7-dimensional torus. Most results of our investigation hold when the 7-dimensional torus is replaced by an m-dimensional torus T/sup m/. We show that for a large class of vacuum solutions the physical space expands while the microspace contracts providing a natural mechanism of dimensional reduction. Matter satisfying a simple barotropic equation of state always breaks the process of dynamical dimensional reduction. With special attention we study the behavior of our model close to the initial singularity. In contrast with the 4-dimensional Bianchi type-IX cosmological model the Kasner solution always describes an approach to the initial singularity. We study the transition from the Kasner regime to the oscillatory regime. We show that matter does not significantly change this property. We have found some exact solutions; they describe isotropic physical space, and axially symmetric physical space. We also investigate high-temperature quantum effects and their effects on the dynamics of our model. We show that the high-temperature quantum corrections do not depend on the geometrical properties of space, provided it is compact. The high-temperature quantummore » corrections can be described by a macroscopic equation of state satisfied by radiation.« less
12748479
Evidence for time and directional enhancements of multimuon cosmic-ray events.
We have observed 1.05 x 10/sup 6/ single-muon and 6869 multimuon events deep underground with the Soudan 1 nucleon-decay detector. The single-muon flux is consistent with isotropy and with results of previous experiments. We have found indications of bursts of multimuon events, particularly from a direction near Cygnus X-3. These bursts arrive from an extended angular region of 30/sup 0/ x 30/sup 0/. The size of the angular region and the lack of a corresponding effect in the single-muon events are difficult to understand. In addition, there is weaker evidence for an excess in the time-integrated multimuon flux near the north galactic pole. We have evaluated the possibility that these effects are caused by random or systematic errors.
37501749
Search for direct CP violation in nonleptonic decays of charged Xi and lambda hyperons
A search for direct CP violation in the nonleptonic decays of hyperons has been performed. In comparing the product of the decay parameters, alpha(Xi)alpha(Lambda), in terms of an asymmetry parameter, A(XiLambda), between hyperons and antihyperons in the charged Xi-->Lambdapi and Lambda-->ppi decay sequence, we found no evidence of direct CP violation. The parameter A(XiLambda) was measured to be 0.012+/-0.014.