Search results for "Chiral perturbation Theory"
showing 10 items of 294 documents
Form factors of radiative pion decays in nonlocal chiral quark models
2012
We study the radiative pion decay π +→e +ν eγ within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F V(q2) and the slope of the axial-vector form factor F A(q2) at threshold. Our results are compared with available experimental information and with the predictions given by the Nambu-Jona-Lasinio model. In addition we calculate the low energy constants δ 5 and δ 6, comparing our results with the values obtained in chiral perturbation theory.
Dynamical twisted mass fermions with light quarks: simulation and analysis details
2008
In a recent paper [hep-lat/0701012] we presented precise lattice QCD results of our European Twisted Mass Collaboration (ETMC). They were obtained by employing two mass-degenerate flavours of twisted mass fermions at maximal twist. In the present paper we give details on our simulations and the computation of physical observables. In particular, we discuss the problem of tuning to maximal twist, the techniques we have used to compute correlators and error estimates. In addition, we provide more information on the algorithm used, the autocorrelation times and scale determination, the evaluation of disconnected contributions and the description of our data by means of chiral perturbation theo…
Electromagnetic form factors of spin 1/2 doubly charmed baryons
2018
We study the electromagnetic form factors of the doubly charmed baryons, using covariant chiral perturbation theory within the extended on-mass-shell (EOMS) scheme. Vector-meson contributions are also taken into account. We present results for the baryon magnetic moments, charge and magnetic radii. While some of the chiral Lagrangian parameters could be set to values determined in previous works, the available lattice results for $\Xi_{cc}^+$ and $\Omega_{cc}^+$ only allow for robust constraints on the low-energy constant (LEC) combination, $c_{89}(=-\frac{1}{3}c_8+4c_9)$. The couplings of the doubly charmed baryons to the vector mesons have been estimated assuming the Okubo--Zweig--Iizuka …
Finite-size scaling of the quark condensate in quenched lattice QCD
1999
We confront the finite volume and small quark mass behaviour of the scalar condensate, determined numerically in quenched lattice QCD using Neuberger fermions, with predictions of quenched chiral perturbation theory. We find that quenched chiral perturbation theory describes the numerical data well, allowing us to extract the infinite volume, chiral limit scalar condensate, up to a multiplicative renormalization constant.
Isospin-breaking contributions to ε ′ / ε
2020
Abstract We present an updated analysis of isospin-violating corrections to ε ′/ε in the framework of chiral perturbation theory, taking advantage of the currently improved knowledge on quark masses and nonperturbative parameters. The role of the different ingredients entering into the analysis is carefully assessed. Our final result is Ω eff = 0.110 − 0.088 + 0.090 [1].
Finite-size scaling of vector and axial current correlators
2002
Using quenched chiral perturbation theory, we compute the long-distance behaviour of two-point functions of flavour non-singlet axial and vector currents in a finite volume, for small quark masses, and at a fixed gauge-field topology. We also present the corresponding predictions for the unquenched theory at fixed topology. These results can in principle be used to measure the low-energy constants of the chiral Lagrangian, from lattice simulations in volumes much smaller than one pion Compton wavelength. We show that quenching has a dramatic effect on the vector correlator, which is argued to vanish to all orders, while the axial correlator appears to be a robust observable only moderately …
Heavy Baryons and electromagnetic decays
2000
In this talk I review the theory of electromagnetic decays of the ground state baryon multiplets with oneheavy quark, calculated using Heavy Hadron Chiral Perturbation Theory. The M1 and E2 amplitudes for (S^{*}-> S gamma), (S^{*} -> T gamma) and (S -> T gamma)are separately analyzed. All M1 transitions are calculated up to O(1/��_��^2). The E2 amplitudes contribute at the same order for (S^{*}-> S gamma), while for (S^{*} -> T gamma) they first appear at O(1/(m_Q ��_��^2))and for (S -> T gamma) are completely negligible. Once the loop contributions is considered, relations among different decay amplitudes are derived. Furthermore, one can obtain an absolute prediction for…
Quantum loops in the resonance chiral theory: the vector form factor
2004
27 páginas, 7 figuras.-- arXiv:hep-ph/0407240v1
Magnetic moments of theΛ(1405)andΛ(1670)resonances
2002
By using techniques of unitarized chiral perturbation theory, where the $\ensuremath{\Lambda}(1405)$ and $\ensuremath{\Lambda}(1670)$ resonances are dynamically generated, we evaluate the magnetic moments of these resonances and their transition magnetic moment. The results obtained here differ appreciably from those obtained with existing quark models. The width for the $\ensuremath{\Lambda}(1670)\ensuremath{\rightarrow}\ensuremath{\Lambda}(1405)\ensuremath{\gamma}$ transition is also evaluated, leading to a branching ratio of the order of $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}.$
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 …