Search results for "quantum chromodynamics"
showing 10 items of 1027 documents
A solution to the strong CP problem transforming the theta angle to the KM CP-violating phase
2010
It is shown that in the scheme with a rotating fermion mass matrix (i.e. one with a scale-dependent orientation in generation space) suggested earlier for explaining fermion mixing and mass hierarchy, the theta angle term in the QCD action of topological origin can be eliminated by chiral transformations, while giving still nonzero masses to all quarks. Instead, the effects of such transformations get transmitted by the rotation to the CKM matrix as the KM phase giving, for theta of order unity, a Jarlskog invariant typically of order 10(-5), as experimentally observed. Strong and weak CP violations appear then as just two facets of the same phenomenon.
Probing the chiral weak Hamiltonian at finite volumes
2006
Non-leptonic kaon decays are often described through an effective chiral weak Hamiltonian, whose couplings ("low-energy constants") encode all non-perturbative QCD physics. It has recently been suggested that these low-energy constants could be determined at finite volumes by matching the non-perturbatively measured three-point correlation functions between the weak Hamiltonian and two left-handed flavour currents, to analytic predictions following from chiral perturbation theory. Here we complete the analytic side in two respects: by inspecting how small ("epsilon-regime") and intermediate or large ("p-regime") quark masses connect to each other, and by including in the discussion the two …
Abelian dominance and the dual Meissner effect in local unitary gauges in SU(2) gluodynamics
2007
Performing highly precise Monte-Carlo simulations of SU(2) gluodynamics, we observe for the first time Abelian dominance in the confining part of the static potential in local unitary gauges such as the F12 gauge. We also study the flux-tube profile between the quark and antiquark in these local unitary gauges and find a clear signal of the dual Meissner effect. The Abelian electric field is found to be squeezed into a flux tube by the monopole supercurrent. This feature is the same as that observed in the non-local maximally Abelian gauge. These results suggest that the Abelian confinement scenario is gauge independent. Observing the important role of space-like monopoles in the Polyakov g…
Magnetic moments of heavy baryons in the relativistic three-quark model
2006
The magnetic moments of ground state single, double and triple heavy baryons containing charm or bottom quarks are calculated in a relativistic three-quark model, which, in the heavy quark limit, is consistent with Heavy Quark Effective Theory and Heavy Hadron Chiral Perturbation Theory. The internal quark structure of baryons is modeled by baryonic three-quark currents with a spin-flavor structure patterned according to standard covariant baryonic wave functions and currents used in QCD sum rule calculations.
Large-NCproperties of theρandf0(600)mesons from unitary resonance chiral dynamics
2011
We construct $\ensuremath{\pi}\ensuremath{\pi}$ amplitudes that fulfill exact elastic unitarity, account for one-loop chiral perturbation theory contributions and include all $1/{N}_{C}$ leading terms, with the only limitation of considering just the lowest-lying nonet of exchanged resonances. Within such a scheme, the ${N}_{C}$ dependence of $\ensuremath{\sigma}$ and $\ensuremath{\rho}$ masses and widths is discussed. Robust conclusions are drawn in the case of the $\ensuremath{\rho}$ resonance, confirming that it is a stable meson in the limit of a large number of QCD colors, ${N}_{C}$. Less definitive conclusions are reached in the scalar-isoscalar sector. With the present quality of dat…
QCD isospin breaking in meson masses, decay constants and quark mass ratios
2001
The procedure to calculate masses and matrix-elements in the presence of mixing of the basis states is explained in detail. We then apply this procedure to the two-loop calculation in Chiral Perturbation Theory of pseudoscalar masses and decay constants including quark mass isospin breaking. These results are used to update our analysis of $K_{\ell4}$ done previously and obtain a value of $m_u/m_d$ in addition to values for the low-energy-constants $L_i^r$.
Nucleon and delta masses in QCD
1992
Using the positivity of the path integral measure of $QCD$ and defining a structure for the quark propagator in a background field according to the fluxon scenario for confinement, we calculate and compare the correlators for nucleon and delta. From their shape we elucidate about the origin of their mass difference, which in our simplified scenario is due to the tensor structure in the propagator. This term arises due to a dynamical mechanism which is responsible simultaneously for confinement and spontaneous chiral symmetry breaking. Finally we discuss, by comparing the calculated correlators with the Lehmann representation, the possibility that a strong CP and/or P violation occurs as a c…
Δ-baryon electromagnetic form factors in lattice QCD
2008
We develop techniques to calculate the four Delta electromagnetic form factors using lattice QCD, with particular emphasis on the sub-dominant electric quadrupole form factor that probes deformation of the Delta. Results are presented for pion masses down to approximately 350 MeV for three cases: quenched QCD, two flavors of dynamical Wilson quarks, and three flavors of quarks described by a mixed action combining domain wall valence quarks and dynamical staggered sea quarks. The magnetic moment of the Delta is chirally extrapolated to the physical point and the Delta charge density distributions are discussed.
Semileptonic decays of theBcmeson
2001
We study the semileptonic transitions ${B}_{c}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c},$ $J/\ensuremath{\psi},$ D, ${D}^{*},$ B, ${B}^{*},$ ${B}_{s},$ ${B}_{s}^{*}$ in the framework of a relativistic constituent quark model. We use experimental data on leptonic $J/\ensuremath{\psi}$ decay, lattice and QCD sum rule results on leptonic ${B}_{c}$ decay, and experimental data on radiative ${\ensuremath{\eta}}_{c}$ transitions to adjust the quark model parameters. We compute all form factors of the above semileptonic ${B}_{c}$ transitions and give predictions for various semileptonic ${B}_{c}$ decay modes including their $\ensuremath{\tau}$ modes when they are kinematically accessible. Th…
Quark degrees of freedom in hadronic systems
2000
Quantum Chromodynamics (QCD) is the theory of the strong interactions. We review descriptions of hadronic systems motivated by QCD, analyzing the recent controversy between gluonic and bosonic degrees of freedom under the prism of the Cheshire Cat Principle. Our analysis leads to an optimal scheme to study hadronic properties. We proceed to extend this low energy descriptions to the deep inelastic regime.