We present a systematic analysis in perturbative quantum chromodynamics (@CD) of large-momentum-transfer exclusive processes. Predictions are given for the scaling behavior, angular dependence, helicity structure, and normalization of elastic and inelastic form factors and large-angle exclusive scattering amplitudes for hadrons and photons. We prove that these reactions are dominated by quark and gluon subprocesses at short distances, and thus that the dimensional-counting rules for the power-law falloff of these amplitudes with momentum transfer are rigorous predictions of @CD, modulo calculable logarithmic corrections from the behavior of the hadronic wave functions at short distances. These anomalous-dimension corrections are determined by evolution equations for process-independent meson and baryon "distribution amplitudes" Si(x, ,g) which control the valence-quark distributions in high-momentum-transfer exclusive reactions. The analysis can be carried out systematically in powers of a, (Q'), the QCD running coupling constant. Although the calculations are most conveniently carried out using light-cone perturbation theory and the light-cone gauge, we also present a gauge-independent analysis and relate the distribution amplitude to a gauge-invariant Bethe-Salpeter amplitude.

A rigorous QCD analysis of the inclusive annihilation decay rates of heavy quarkonium states is presented. The effective-field-theory framework of nonrelativistic QCD is used to separate the short-distance scale of annihilation, which is set by the heavy quark mass M , from the longer-distance scales asso- * On leave from Dept. of Physics and Astronomy, Northwestern University, Evanston, IL 60208. 1 ciated with quarkonium structure. The annihilation decay rates are expressed in terms of nonperturbative matrix elements of 4-fermion operators in nonrelativistic QCD, with coefficients that can be computed using perturbation theory in the coupling constant α s (M ). The matrix elements are organized into a hierarchy according to their scaling with v, the typical velocity of the heavy quark. An analogous factorization formalism is developed for the production cross sections of heavy quarkonium in processes involving momentum transfers of order M or larger. The factorization formulas are applied to the annihilation decay rates and production cross sections of S-wave states, up to corrections of relative order v 3 , and of P-wave states, up to corrections of relative order v 2 .

A rigorous QCD analysis of the inclusive annihilation decay rates of heavy quarkonium states is presented. The effective-field-theory framework of nonrelativistic QCD is used to separate the short-distance scale of annihilation, which is set by the heavy quark mass M , from the longer-distance scales asso- *

No abstract

In this paper we show that the apparent failure of QCD lattice perturbation theory to account for Monte Carlo measurements of perturbative quantities results from choosing the bare lattice coupling constant as the expansion parameter. Using instead LLrenormalized" coupling constants defined in terms of physical quantities, such as the heavy-quark potential, greatly enhances the predictive power of lattice perturbation theory. The quality of these predictions is further enhanced by a method for automatically determining the coupling-constant scale most appropriate to a particular quantity. We present a mean-field analysis that explains the large renormalizations relating lattice quantities, such as the coupling constant, to their continuum analogues. This suggests a new prescription for designing lattice operators that are more continuumlike than conventional operators. Finally, we provide evidence that the scaling of physical quantities can be asymptotic or perturbative already at (quenched) 0's as low as 5.7, provided the evolution from scale to scale is analyzed using renormalized perturbation theory. This result indicates that reliable simulations of QCD are possible at these same low O's.PACS number(s): 12.38. Gc, ll.lO.Gh, 12.38.B~

No abstract

We use perturbative Symanzik improvement to create a new staggered-quark action (HISQ) that has greatly reduced one-loop taste-exchange errors, no tree-level order a 2 errors, and no tree-level order (am) 4 errors to leading order in the quark's velocity v/c. We demonstrate with simulations that the resulting action has taste-exchange interactions that are at least 3-4 times smaller than the widely used ASQTAD action. We show how to estimate errors due to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate with simulations that such errors are no more than 1% when HISQ is used for light quarks at lattice spacings of 1/10 fm or less. The suppression of (am) 4 errors also makes HISQ the most accurate discretization currently available for simulating c quarks. We demonstrate this in a new analysis of the ψ − ηc mass splitting using the HISQ action on lattices where amc = 0.43 and 0.66, with full-QCD gluon configurations (from MILC). We obtain a result of 111(5) MeV which compares well with experiment. We discuss applications of this formalism to D physics and present our first high-precision results for Ds mesons.

Detailed leading-order quantum-chromodynamics (QCD) predictions are given for the scaling, angular, and helicity dependence of the reactions y y -~G (M =a, K, p, etc.) at large momentum transfer. In addition to providing a basic test of QCD at short distances, measurements can be used to determine the process-independent meson distribution amplitudes ~,+,(x,Q). Other related two-photon channels such as yy+yp, y*y-aO,qO,q', and vc+yy are also discussed. We also prove the existence of a fixed Regge singularity at J =O which couples to y p y p in the t channel but not to ya-yn-.