Search results for " Perturbation theory"
showing 10 items of 358 documents
Effective field theory description of the pion form factor
1997
7 páginas, 2 figuras.-- PACS: 14.40.Aq; 13.40.Gp; 13.6O.Fz; 12.39.Fe.-- arXiv:hep-ph/9707347v1
Kaon Decays in the Standard Model
2011
A comprehensive overview of kaon decays is presented. The Standard Model predictions are discussed in detail, covering both the underlying short-distance electroweak dynamics and the important interplay of QCD at long distances. Chiral perturbation theory provides a universal framework for treating leptonic, semileptonic and nonleptonic decays including rare and radiative modes. All allowed decay modes with branching ratios of at least 10^(-11) are analyzed. Some decays with even smaller rates are also included. Decays that are strictly forbidden in the Standard Model are not considered in this review. The present experimental status and the prospects for future improvements are reviewed.
5 QCD on the Lattice
2008
Since Wilson’s seminal papers of the mid-1970s, the lattice approach to Quantum Chromodynamics has become increasingly important for the study of the strong interaction at low energies, and has now turned into a mature and established technique. In spite of the fact that the lattice formulation of Quantum Field Theory has been applied to virtually all fundamental interactions, it is appropriate to discuss this topic in a chapter devoted to QCD, since by far the largest part of activity is focused on the strong interaction. Lattice QCD is, in fact, the only known method which allows ab initio investigations of hadronic properties, starting from the QCD Lagrangian formulated in terms of quark…
Bounds on rare decays of η and η′ mesons from the neutron EDM
2019
We provide model-independent bounds on the rates of rare decays $\ensuremath{\eta}({\ensuremath{\eta}}^{\ensuremath{'}})\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$ based on experimental limits on the neutron electric dipole moment (nEDM). Starting from phenomenological $\ensuremath{\eta}({\ensuremath{\eta}}^{\ensuremath{'}})\ensuremath{\pi}\ensuremath{\pi}$ couplings, the nEDM arises at the two-loop level. The leading-order relativistic chiral perturbation theory calculation with the minimal photon coupling to charged pions and a proton inside the loops leads to a finite, counterterm-free result. This is an improvement upon previous estimates which used approximations in evalu…
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…
Corrections to the SU(3) × SU(3) Gell-Mann-Oakes-Renner relation and chiral couplings $ L_8^r $ and $ H_2^r $
2012
Next to leading order corrections to the SU(3) × SU(3) Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two types of integration kernels in the FESR are used to suppress the contribution of the kaon radial excitations to the hadronic spectral function, one with local and the other with global constraints. The result for the pseudoscalar current correlator at zero momentum is ψ 5(0) = (2.8 ± 0.3) ×10-3 GeV4, leading to the chiral corrections to GMOR: δ K = (55 ± 5)%. The resulting uncertainties are mostly due to variations in the upper limit of integration in the FESR, within the stability reg…
$\eta$-$\eta\prime$ mixing in Large-Nc ChPT: discussion, phenomenology, and prospects
2016
A systematic study of the η-η ′ mixing in Large-Nc chiral perturbation theory is presented [1] with special emphasis on the role of the next-to-next-to-leading-order contributions in the combined momentum, quark-mass, and 1/Nc expansions. At this order, loop corrections as well as OZIrule-violating pieces need to be included. Mixing angles as well as pseudoscalar decay constants are discussed within this framework. The results are compared with recent phenomenological approaches.
The spectrum of bosonized QCD2 in the chiral limit
1991
Abstract By studying an equivalent non-abelian bosonic theory we resolve the spectrum of Quantum Chromodynamics in one space-one time dimensions for massless quarks. The emphasis is placed in the non chiral sector described by colored meson fields. Two and four point functions of these fields are explicitly calculated in the large N limit. Some of the relevant issues: chiral symmetry realization, phases, baryon spectrum, topology etc …, are revisited.
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.
Hadron structure at lowQ2
2007
This review deals with the structure of hadrons, strongly interacting many-body systems consisting of quarks and gluons. These systems have a size of about 1 fm, which shows up in scattering experiments at low momentum transfers $Q$ in the GeV region. At this scale the running coupling constant of Quantum Chromodynamics (QCD), the established theory of the strong interactions, becomes divergent. It is therefore highly intriguing to explore this theory in the realm of its strong interaction regime. However, the quarks and gluons can not be resolved at the GeV scale but have to be studied through their manifestations in the bound many-body systems, for instance pions, nucleons and their reson…