Search results for "Field Theory"
showing 10 items of 1188 documents
TheA 1-and the ϕ-meson in QCD
1993
Recently we used a method of stable analytic extrapolation to test whether strictly local duality between the asymptotic and the resonance region, which is believed to be valid in QCD, appears already at the present stage of QCD calculations. Probing the QCD ϱ-amplitude, we found a prominent bump structure in the resonance region, i.e. a rather direct evidence for the validity of local duality. In the present paper we confirm and extend this result by giving two further applications, theA1-meson and the ϕ-meson. While we do not meet theA1, as was to be expected since other sum rules can not separate it from the continuum, too, the extrapolation of the ϕ-amplitude leads to an enormous bump. …
Spectrum of SU(2) gauge theory with two fermions in the adjoint representation
2008
We present preliminary results of lattice simulations of SU(2) gauge theory with two Wilson fermions in the adjoint representation. This theory has recently attracted considerable attention because it might possess an infrared fixed point (or an almost-fixed-point), and hence be a candidate for a walking technicolor theory. In this work we study the particle spectrum of the theory, and compare it with more familiar spectrum of the theory with SU(2) gauge fields and two flavors of fundamental representation fermions.
Four-quark operators and non-leptonic weak transitions
1991
72 páginas, 12 figuras, 6 tablas.-- CERN-TH-5906-90 ; CPT-2393.
Testing chiral effective theory with quenched lattice QCD
2008
We investigate two-point correlation functions of left-handed currents computed in quenched lattice QCD with the Neuberger-Dirac operator. We consider two lattice spacings a ~ 0.09, 0.12 fm and two different lattice extents L ~ 1.5, 2.0 fm; quark masses span both the p- and the epsilon-regimes. We compare the results with the predictions of quenched chiral perturbation theory, with the purpose of testing to what extent the effective theory reproduces quenched QCD at low energy. In the p-regime we test volume and quark mass dependence of the pseudoscalar decay constant and mass; in the epsilon-regime, we investigate volume and topology dependence of the correlators. While the leading order b…
Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks inppcollisions ats=8 TeVwith the ATLAS detector
2016
This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb(-1) of pp collisions at a center-of-m ...
Bottomonium precision tests from full lattice QCD: Hyperfine splitting, ϒ leptonic width, and b quark contribution to e+e−→hadrons
2021
We calculate the mass difference between the $\mathrm{\ensuremath{\Upsilon}}$ and ${\ensuremath{\eta}}_{b}$ and the $\mathrm{\ensuremath{\Upsilon}}$ leptonic width from lattice QCD using the highly improved staggered quark formalism for the $b$ quark and including $u$, $d$, $s$ and $c$ quarks in the sea. We have results for lattices with lattice spacing as low as 0.03 fm and multiple heavy quark masses, enabling us to map out the heavy quark mass dependence and determine values at the $b$ quark mass. Our results are ${M}_{\mathrm{\ensuremath{\Upsilon}}}\ensuremath{-}{M}_{{\ensuremath{\eta}}_{b}}=57.5(2.3)(1.0)\text{ }\text{ }\mathrm{MeV}$ (where the second uncertainty comes from neglect of …
Generalized on-shell renormalization of heavy quarks
1992
A generalized on-shell (GOS) renormalization scheme of QCD is developed to evaluate the renormalization of heavy quark wave functions and currents. All large logarithms arising from the physical range of quark masses and momentum transferq 2 can be absorbed into wave function and vertex renormalization. Our results are more general than those of the heavy quark effective theory and agree with the latter only at zero recoil. The proposed GOS scheme is very suitable for the μ/m Q expansion. As an application we discuss the renormalization of the flavour changing currentsb-c, t-b andt-c.
Study ofB→πℓνandB→ρℓνdecays and determination of|Vub|
2005
We present an analysis of exclusive charmless semileptonic B-meson decays based on 83x10{sup 6} BB pairs recorded with the BABAR detector at the {upsilon}(4S) resonance. Using isospin symmetry, we measure branching fractions B(B{sup 0}{yields}{pi}{sup -}l{sup +}{nu})=(1.38{+-}0.10{+-}0.16{+-}0.08)x10{sup -4} and B(B{sup 0}{yields}{rho}{sup -}l{sup +}{nu})=(2.14{+-}0.21{+-}0.48{+-}0.28)x10{sup -4}, where the errors are statistical, experimental systematic, and due to form-factor shape uncertainties. We compare the measured distribution in q{sup 2}, the momentum-transfer squared, with theoretical predictions for the form factors from lattice QCD and light-cone sum rules, and extract the Cabib…
Two-flavour lattice QCD correlation functions in the deconfinement transition region
2013
We report on a lattice QCD calculation with two dynamical flavors of the isovector vector correlator in the high-temperature phase. We analyze the correlator in terms of the associated spectral function by performing a fit for the difference of the thermal and vacuum spectral functions, using also an exact sum rule that constrains this difference. Additonally we carry out a direct fit for the thermal spectral function, and obtain good agreement between the two analyses for frequencies below the two-pion threshold. Under the assumption that the spectral function is smooth in that region, we give an estimate of the electrical conductivity.
Heavy-baryon quark model picture from lattice QCD
2015
The ground state and excited spectra of baryons containing three identical heavy quarks, $b$ or $c$, have been recently calculated in nonperturbative lattice QCD. The energy of positive and negative parity excitations has been determined with high precision. Lattice results constitute a unique opportunity to learn about the quark-confinement mechanism as well as elucidating our knowledge about the nature of the strong force. We analyze the nonperturbative lattice QCD results by means of heavy-quark static potentials derived using SU(3) lattice QCD. We make use of different numerical techniques for the three-body problem.