357,830 research outputs found
Analogs of noninteger powers in general analytic QCD
In contrast to the coupling parameter in the usual perturbative QCD (pQCD),
the coupling parameter in the analytic QCD models has cuts only on the negative
semiaxis of the Q^2-plane (where q^2 = -Q^2 is the momentum squared), thus
reflecting correctly the analytic structure of the spacelike observables. The
Minimal Analytic model (MA, named also APT) of Shirkov and Solovtsov removes
the nonphysical cut (at positive Q^2) of the usual pQCD coupling and keeps the
pQCD cut discontinuity of the coupling at negative Q^2 unchanged. In order to
evaluate in MA the physical QCD quantities whose perturbation expansion
involves noninteger powers of the pQCD coupling, a specific method of
construction of MA analogs of noninteger pQCD powers was developed by Bakulev,
Mikhailov and Stefanis (BMS). We present a construction, applicable now in any
analytic QCD model, of analytic analogs of noninteger pQCD powers; this method
generalizes the BMS approach obtained in the framework of MA. We need to know
only the discontinuity function of the analytic coupling (the analog of the
pQCD coupling) along its cut in order to obtain the analytic analogs of the
noninteger powers of the pQCD coupling, as well as their timelike (Minkowskian)
counterparts. As an illustration, we apply the method to the evaluation of the
width for the Higgs decay into b+(bar b) pair.Comment: 29 pages, 5 figures; sections II and III extended, appendix B is ne
Single Cut Integration
We present an analytic technique for evaluating single cuts for one-loop
integrands, where exactly one propagator is taken to be on shell. Our method
extends the double-cut integration formalism of one-loop amplitudes to the
single-cut case. We argue that single cuts give meaningful information about
amplitudes when taken at the integrand level. We discuss applications to the
computation of tadpole coefficients.Comment: v2: corrected typo in abstrac
Infinite temperature limit of meson spectral functions calculated on the lattice
We analyze the cut-off dependence of mesonic spectral functions calculated at
finite temperature on Euclidean lattices with finite temporal extent. In the
infinite temperature limit we present analytic results for lattice spectral
functions calculated with standard Wilson fermions as well as a truncated
perfect action. We explicitly determine the influence of `Wilson doublers' on
the high momentum structure of the mesonic spectral functions and show that
this cut-off effect is strongly suppressed when using an improved fermion
action.Comment: 25 pages, 8 figure
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