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Colin J. Morningstar

Publications and source records attributed to Colin J. Morningstar.

12 recordsLinked to original sources
arXiv2014

The finite volume spectrum of excited states from lattice QCD simulations

We present results for the spectrum of excited mesons obtained from temporal correlations of spatially-extended single-hadron and multi-hadron operators computed in lattice QCD. The stochastic LapH algorithm is implemented on anisotropic, dynamical lattices for isovectors for pions of mass $390$ MeV. A large correlation matrix with single-particle and two-particle probe operators is diagonalized to identify resonances. The masses of excited states in the $I=1, S=0, T_{1u}^+$ channel as well as the mixing of single and multi-particle probe operators are presented.

hep-lat↗
arXiv2013

Applications of the Stochastic LapH Method

Progress in computing the hadron spectrum in lattice QCD using stochastic LapH quark propaga- tors is described. The stochastic LapH algorithm is a particular quark smearing algorithm that also allows the computation of all-to-all quark propagators. All-to-all quark propagators are required in our approach of using a large set of spatially extended hadron operators and explicit multi- particle operators to access excited states. We report on the progress made in the various isospin channels on 2+1 dynamical, anisotropic lattices generated by the Hadron Spectrum Collaboration.

hep-lat↗
arXiv2010

Phase Shift with LapH Propagators

The pion-pion scattering phase shift is computed using LapH propagators. The LapH method for computing quark propagators is used to form two-particle correlation functions with a number of different operators. Excited state energies of two-particle states on 2+1 dynamical, anisotropic lattices (Mpi=390 MeV) are computed to determine the phase shift in the isospin-2 channel. The signal for t-to-t diagrams for the isospin-0 channel are also presented to demonstrate the efficacy of the stochastic LapH method which combines LapH with diluted Z4 noise sources.

hep-lat↗
arXiv1999

The glueball spectrum from an anisotropic lattice study

The spectrum of glueballs below 4 GeV in the SU(3) pure-gauge theory is investigated using Monte Carlo simulations of gluons on several anisotropic lattices with spatial grid separations ranging from 0.1 to 0.4 fm. Systematic errors from discretization and finite volume are studied, and the continuum spin quantum numbers are identified. Care is taken to distinguish single glueball states from two-glueball and torelon-pair states. Our determination of the spectrum significantly improves upon previous Wilson action calculations.

hep-lat↗
arXiv1998

Perturbative matching of lattice and continuum heavy-light currents with NRQCD heavy quarks

The temporal and spatial components of the heavy-light vector current and the spatial components of the axial current are expressed in terms of lattice-regulated operators suitable for simulations of B and D mesons. The currents are constructed by matching the appropriate scattering amplitudes in continuum QCD and a lattice model to one-loop order in perturbation theory. In the lattice theory, the heavy quarks are treated using the nonrelativistic (NRQCD) formulation and the light quarks are described by the tadpole-improved clover action. The light quarks are treated as massless. Our currents include relativistic and discretization corrections through O(alpha_s/M, a alpha_s), where M is the heavy-quark mass, a is the lattice spacing, and alpha_s is the QCD coupling. As in our previous construction of the temporal component of the heavy-light axial current, mixing between several lattice operators is encountered at one-loop order, and O(a alpha_s) dimension-four improvement terms are identified.

hep-lat↗
arXiv1998

One-loop matching of lattice and continuum heavy-light axial vector currents using NRQCD

The temporal component of the heavy-light axial vector current is constructed to one-loop order in perturbation theory and to order 1/M, where M is the heavy quark mass, in terms of operators suitable for use in lattice simulations of B and D mesons. The O(a)-improved clover action is used for the massless light quark, where a is the lattice spacing, and propagation of the heavy quark is described by a nonrelativistic lattice action.

hep-lat↗
arXiv1994

Core -- a New Computational Technique for Lattice Systems

The COntractor REnormalization group (CORE) method, a new approach to solving Hamiltonian lattice systems, is introduced. The method combines contraction and variational techniques with the real-space renormalization group approach. It applies to lattice systems of infinite extent and is ideal for studying phase structure and critical phenomena. The CORE approximation is systematically improvable and can treat systems with dynamical fermions. The method is tested using the 1+1-dimensional Ising model.

hep-lat↗
arXiv1994

Radiative Corrections to the Kinetic Couplings in Nonrelativistic Lattice QCD

The heavy-quark mass and wave function renormalizations, energy shift, and radiative corrections to two important couplings, the so-called kinetic couplings, in nonrelativistic lattice QCD are determined to leading order in tadpole-improved perturbation theory. The scales at which to evaluate the running QCD coupling for these quantities, except the wave function renormalization, are obtained using the Lepage-Mackenzie prescription. When the bare quark mass is greater than the inverse lattice spacing, the kinetic coupling corrections are roughly 10\% of the tree-level coupling strengths; these corrections grow quickly as the bare quark mass becomes small. A need for computing the two-loop corrections to the energy shift and mass renormalization is demonstrated.

hep-lat↗
arXiv1993

The Improvement Program in Nonrelativistic Lattice QCD

Progress in the improvement program in nonrelativistic lattice QCD is outlined. The leading radiative corrections to the heavy-quark mass renormalization, energy shift, and two important kinetic coupling coefficients are presented. The reliability of tadpole-improved perturbation theory in determining the energy shift and mass renormalization is demonstrated.

hep-lat↗
arXiv1993

The Heavy Quark Self-Energy in Nonrelativistic Lattice QCD

The heavy quark self-energy in nonrelativistic lattice QCD is calculated to $O(α_s)$ in perturbation theory. An action which includes all spin-independent relativistic corrections to order $v^2$, where $v$ is the typical heavy quark velocity, and all spin-dependent corrections to order $v^4$ is used. The standard Wilson action and an improved multi-plaquette action are used for the gluons. Results for the mass renormalization, wavefunction renormalization, and energy shift are given; tadpole contributions are found to be large. A tadpole improvement scheme in which all link variables are rescaled by a mean-field factor is also studied. The effectiveness of this scheme in offsetting the large tadpole contributions to the heavy quark renormalization parameters is demonstrated.

hep-lat↗