Search results for "PERTURBATION"
showing 10 items of 811 documents
SU(3) Chiral approach to meson and baryon dynamics
1999
We report on recent progress on the chiral unitary approach, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV and meson baryon interaction up to the first baryonic resonances. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented, concretely the K^- p\to\Lambda(1405)\gamma reaction and the N^\ast (1535)N^\ast(1535)\pi and \eta couplings.
A non-perturbative chiral approach for meson-meson interactions
2000
A non-perturbative method which combines constraints from chiral symmetry breaking and coupled channel unitarity is used to describe meson-meson interactions up to \sqrt{s}\lesssim 1.2 GeV, extending in this way the range of applicability of the information contained in Chiral Perturbation Theory (\chi PT), since this perturbative series is typically restricted to \sqrt{s}\lesssim 500 MeV. The approach uses the O(p^2) and O(p^4) \chiPT Lagrangians. The seven free parameters resulting from the O(p^4) Lagrangian are fitted to the experimental data. The approach makes use of the expansion of T^{-1} instead of the amplitude itself as done in \chiPT. The former expansion is suggested by analogy …
Kaon weak matrix elements with Wilson fermions
2002
We present results of several numerical studies with Wilson fermions relevant for kaon physics. We compute the B_K parameter by using two different methods and extrapolate to the continuum limit. Our preliminary result is B_K(2 GeV)=0.66(7). Delta I=3/2 K->pi pi matrix elements are obtained by using the next-to-leading order expressions derived in chiral perturbation theory in which the low energy constants are determined by the lattice results computed at unphysical kinematics. From the simulation at beta=6.0 our (preliminary) results read: _{I=2}=0.14(1)(1) GeV^3 and _{I=2}=0.69(6)(6) GeV^3.
The scalar pion form factor in two-flavor lattice QCD
2013
We calculate the scalar form factor of the pion using two dynamical flavors of non-perturbatively $\mathcal{O}(a)$-improved Wilson fermions, including both the connected and the disconnected contribution to the relevant correlation functions. We employ the calculation of all-to-all propagators using stochastic sources and a generalized hopping parameter expansion. From the form factor data at vanishing momentum transfer, $Q^2=0$, and two non-vanishing $Q^2$ we obtain an estimate for the scalar radius $\left^\pi_{_{\rm S}}$ of the pion at one value of the lattice spacing and for five different pion masses. Using Chiral Perturbation Theory at next-to-leading order, we find $\left^\pi_{_{\rm S…
First observation of the KS → π0γ γ decay
2004
Using the NA48 detector at the CERN SPS, 31 KS → π 0γγ candidates with an estimated background of 13.7 ± 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS → π0γγ) z>0.2 = (4.9 ± 1.6stat ± 0.9 syst) × 10-8 in agreement with Chiral Perturbation Theory predictions. © 2003 Elsevier B.V. All rights reserved.
Charm mass dependence of the weak Hamiltonian in chiral perturbation theory
2004
Suppose that the weak interaction Hamiltonian of four-flavour SU(4) chiral effective theory is known, for a small charm quark mass m_c. We study how the weak Hamiltonian changes as the charm quark mass increases, by integrating it out within chiral perturbation theory to obtain a three-flavour SU(3) chiral theory. We find that the ratio of the SU(3) low-energy constants which mediate Delta I=1/2 and Delta I=3/2 transitions, increases rather rapidly with m_c, as \sim m_c ln (1/m_c). The logarithmic effect originates from "penguin-type" charm loops, and could represent one of the reasons for the Delta I=1/2 rule.
Hyperon forward spin polarizability gamma0 in baryon chiral perturbation theory
2015
We present the calculation of the hyperon forward spin polarizability gamma0 using manifestly Lorentz covariant baryon chiral perturbation theory including the intermediate contribution of the spin 3/2 states. As at the considered order the extraction of gamma0 is a pure prediction of chiral perturbation theory, the obtained values are a good test for this theory. After including explicitly the decuplet states, our SU(2) results have a very good agreement with the experimental data and we extend our framework to SU(3) to give predictions to the hyperons' gamma0 values. Prominent are the Sigma^- and Xi^- baryons as their photon transition to the decuplet is forbidden in SU(3) symmetry and th…
Electromagnetic decays of heavy baryons
1999
9 páginas, 3 figuras, 7 tablas.-- PACS number(s): 12.39.Fe, 12.39.Hg, 13.40.Hq, 14.20.Lq
EFFECTIVE FIELD THEORY OF THE SINGLE-NUCLEON SECTOR
2008
We address the issue of a consistent power counting scheme in manifestly Lorentz-invariant baryon chiral perturbation theory. We discuss the inclusion of vector mesons in the calculation of the nucleon electromagnetic form factors. We comment on the chiral expansion of the nucleon mass to order O(q**6).
Chiral dynamics and the reactions pp↦dK+ and pp↦dπ+η
2001
We perform a study of the final-state interactions of the K+\(\) and the \(\)d systems in the reactions pp↦dK+\(\) and pp↦dπ+η. Since the two-meson system couples strongly to the a0(980) resonance, these reactions are expected to be an additional source of information about the controversial scalar sector. We also show that these reactions present peculiar features which can shed additional light on the much debated meson-baryon scalar sector with strangeness -1. We deduce the general structure of the amplitudes close to the dK+\(\) threshold, allowing for primary K+\(\) as well as π+η production with the two mesons in relative S- or P-wave. The interactions of the mesons are accounted for …