Andreas S. Kronfeld

Monopole condensation and color confinement

Abstract Monopole condensation is responsible for confinement in U(1) lattice gauge theory. Using numerical simulations and the abelian projection, we demonstrate that this mechanism persists in SU(2) nonabelian gauge theories. Our results support the picture of the QCD vacuum as a dual superconductor.

Heavy quarkonium physics

This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.

Massive fermions in lattice gauge theory

This paper presents a formulation of lattice fermions applicable to all quark masses, large and small. We incorporate interactions from previous light-fermion and heavy-fermion methods, and thus ensure a smooth connection to these limiting cases. The couplings in improved actions are obtained for arbitrary fermion mass m{sub q}, without expansions around small- or large-mass limits. We treat both the action and external currents. By interpreting on-shell improvement criteria through the lattice theory{close_quote}s Hamiltonian, one finds that cutoff artifacts factorize into the form b{sub n}(m{sub q}a)[{bold p}a]{sup s{sub n}} where {bold p} is a momentum characteristic of the system under study, s{sub n} is related to the dimension of the nth interaction, and b{sub n}(m{sub q}a) is a bounded function, numerically always of order 1 or less. In heavy-quark systems {bold p} is typically rather smaller than the fermion mass m{sub q}. Therefore, artifacts of order (m{sub q}a){sup s} do not arise, even when m{sub q}a{approx_gt}1. An important by-product of our analysis is an interpretation of the Wilson and Sheikholeslami-Wohlert actions applied to nonrelativistic fermions. {copyright} {ital 1997} {ital The American Physical Society}

Topology and Dynamics of the Confinement Mechanism

Abstract We carry out the abelian projection of SU( N ) gauge theories, both in the continuum and on the lattice. Then the degrees of freedom are abelian gauge fields, gluons, quarks, and magnetic monopoles. No approximation is involved, just gauge fixing. We discuss the topology of the monopoles in detail and investigate their role in the confinement mechanism using numerical simulations.

QCD and strongly coupled gauge theories: challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

B- and D-meson decay constants from three-flavor lattice QCD

We calculate the leptonic decay constants ofB (s) andD (s) mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavy-light meson correlation functions on the MILC asqtad-improved staggered gauge congurations which include the eects of three light dynamical sea quarks. We simulate with several values of the light valence- and sea-quark masses (down to ms=10) and at three lattice spacings (a 0.15, 0.12, and 0.09 fm) and extrapolate to the physical up and down quark masses and the continuum using expressions derived in heavy-light meson staggered chiral perturbation theory. We renormalize the heavy-light axial current using a mostly nonperturbative method such that only a small correction to unity must be computed in lattice perturbation theory and higher-order terms are expected to be small. We obtain f B+ = 196:9(8:9) MeV, fBs = 242:0(9:5) MeV, f D+ = 218:9(11:3) MeV, fDs = 260:1(10:8) MeV, and the SU(3) avor-breaking ratios fBs =fB = 1:229(26) and fDs =fD = 1:188(25), where the numbers in parentheses are the total statistical and systematic uncertainties added in quadrature.

Semileptonic decays of d mesons in three-flavor lattice QCD.

We present the first three-flavor lattice QCD calculations for D-->pilnu and D-->Klnu semileptonic decays. Simulations are carried out using ensembles of unquenched gauge fields generated by the MILC Collaboration. With an improved staggered action for light quarks, we are able to simulate at light quark masses down to 1/8 of the strange mass. Consequently, the systematic error from the chiral extrapolation is much smaller than in previous calculations with Wilson-type light quarks. Our results for the form factors at q(2)=0 are f(D-->pi)(+)(0)=0.64(3)(6) and f(D-->K)(+)(0)=0.73(3)(7), where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the Cabibbo-Kobayashi-Maskawa matrix elements |V(cd)|=0.239(10)(24)(20) and |V(cs)|=0.969(39)(94)(24), where the last errors are from experimental uncertainties.

Semileptonic D→π/K and B→π/D decays in 2+1 flavor lattice QCD

We present results for form factors of semileptonic decays of D and B mesons in 2 + 1 flavor lattice QCD using the MILC gauge configurations. With an improved staggered action for light quarks, we successfully reduce the systematic error from the chiral extrapolation. The results for D decays are in agreement with experimental ones. The results for B decays are preliminary. Combining our results with experimental branching ratios, we then obtain the CKM matrix elements | V c d | , | V c s | , | V c b | and | v u b | . We also check CKM unitarity, for the first time, using only lattice QCD as the theoretical input.

Charmed-meson decay constants in three-flavor lattice QCD

We present the first lattice QCD calculation with realistic sea quark content of the D+-meson decay constant f(D+). We use the MILC Collaborations publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). We obtain f(D+)=201+/-3+/-17 MeV, where the errors are statistical and a combination of systematic errors. We also obtain f(Ds)=249+/-3+/-16 MeV for the Ds meson.

B→πlν semileptonic form factor from three-flavor lattice QCD: A model-independent determination of |Vub|

We calculate the form factor