Search results for "Chiral perturbation Theory"
showing 10 items of 294 documents
Integrating out strange quarks in ChPT
2007
We study three flavour chiral perturbation theory in a limit where the strange quark mass is much larger than the external momenta and the up and down quark masses, and where the external fields are those of two-flavour chiral perturbation theory. In this case, the theory reduces to the one of SU(2)_L x SU(2)_R. Through this reduction, one can work out the strange quark mass dependence of the LECs in the two-flavour case. We present the pertinent relations at two-loop order for F,B and l_i.
Determination of the ΔS=1 weak Hamiltonian of the SU(4) chiral limit through topological zero-mode wave functions
2008
38 pages, 9 figures.-- Published in: JHEP05(2008)043, available at: http://dx.doi.org/10.1088/1126-6708/2008/05/043 (open-acess).
Isospin breaking andf0(980)-a0(980)mixing in theη(1405)→π0f0(980)reaction
2012
We make a theoretical study of the eta(1405) -> pi(0)f(0)(980) and eta(1405) -> pi(0)a(0)(980) reactions with an aim to determine the isospin violation and the mixing of the f(0)(980) and a(0)(980) resonances. We make use of the chiral unitary approach where these two resonances appear as composite states of two mesons, dynamically generated by the meson-meson interaction provided by chiral Lagrangians. We obtain a very narrow shape for the f(0)(980) production in agreement with a BES experiment. As to the amount of isospin violation, or f(0)(980) and a(0)(980) mixing, assuming constant vertices for the primary eta(1405) -> pi K-0 (K) over bar and eta(1405) -> pi(0)pi(0)eta production, we f…
A test of chiral perturbation theory from the measurement of the decay KS → γγ
1995
Data from NA31 experiment at CERN have been used to measure the decay KS → γγ. From 69 candidate events of the type K0 → γγ, 52 events can be attributed to KL → γγ and one event is expected from background processes. The ratio of the relative decay widths R = Γ(KS → γγ)Γ(KL → γγ) is measured to be R = 2.2 ± 1.0(stat.) ± 0.3(syst.) ± 0.2(ext.) where the external systematic error is due to the experimental uncertainty in the branching ratio of the decay KL → γγ. This translates into a branching ratio of BR(KS → γγ) = (2.2 ± 1.1) × 10−6. If these data are combined with the published data from an earlier data taking period with the same experiment, the ratio R is determined to be R = 2.35 ± 0.7…
η′transition form factor from space- and timelike experimental data
2016
The ${\ensuremath{\eta}}^{\ensuremath{'}}$ transition form factor is reanalyzed in view of the recent first observation by BESIII of the Dalitz decay ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\gamma}{e}^{+}{e}^{\ensuremath{-}}$ in both space- and timelike regions at low and intermediate energies using the Pad\'e approximants method. The present analysis provides a suitable parametrization for reproducing the measured form factor in the whole energy region and allows one to extract the corresponding low-energy parameters together with a prediction of their values at the origin, related to ${\mathrm{\ensuremath{\Gamma}}}_{{\ensuremath{\eta}}^{\ensuremath{'}}\ens…
THE NUCLEON MASS AND PION-NUCLEON SIGMA TERM FROM A CHIRAL ANALYSIS OF Nf = 2 + 1 LATTICE QCD WORLD DATA
2014
Fits of the p4 covariant SU(2) baryon chiral perturbation theory to lattice QCD nucleon mass data from several collaborations for 2 and 2+1 flavors are presented. We consider contributions from explicit Δ(1232) degrees of freedom, finite volume and finite spacing corrections. We emphasize here on our Nf = 2 + 1 study. We obtain low-energy constants of natural size that are compatible with the rather linear pion-mass dependence of the nucleon mass observed in lattice QCD. We report a value of σπN = 41(5)(4) MeV in the 2 flavor case and σπN = 52(3)(8) MeV for 2+1 flavors.
Lattice QCD calculation of the electroweak box diagrams for the kaon semileptonic decays
2021
We present a lattice QCD calculation of the axial $\gamma W$-box diagrams relevant for the kaon semileptonic decays. We utilize a recently proposed method, which connects the electroweak radiative corrections in Sirlin's representation to that in chiral perturbation theory. It allows us to use the axial $\gamma W$-box correction in the SU(3) limit to obtain the low energy constants for chiral perturbation theory. From first principles our results confirm the previously used low energy constants provided by the minimal resonance model with a significant reduction in uncertainties.
Pion photoproduction off nucleons in covariant chiral perturbation theory
2019
Pion photoproduction off the nucleon close to threshold is studied in covariant baryon chiral perturbation theory at O($p^3$) in the extended-on-mass-shell scheme, with the explicit inclusion of the $\Delta(1232)$ resonance using the $\delta$ counting. The theory is compared to the available data of cross sections and polarization observables for all the charge channels. Most of the necessary low energy constants are well known from the analysis of other processes and the comparison with data strongly constrains some of the still unknown ones. The $\Delta(1232)$ contribution is significant in improving the agreement with data, even at the low energies considered.
Isospin Violation inϵ′
2003
On the basis of a next-to-leading-order calculation in chiral perturbation theory, the first complete analysis of isospin breaking for direct $CP$ violation in ${K}^{0}\ensuremath{\rightarrow}2\ensuremath{\pi}$ decays is performed. We find a destructive interference between three different sources of isospin violation in the $CP$ violation parameter ${ϵ}^{\ensuremath{'}}$. Within the uncertainties of large-${N}_{c}$ estimates for the low-energy constants, the isospin violating correction for ${ϵ}^{\ensuremath{'}}$ is below 15%.
Long-Distance Contributions to theKL→μ+μ−Decay Width
1998
The dispersive two-photon contribution to the ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay amplitude is analyzed, using chiral perturbation theory techniques and large- ${N}_{C}$ considerations. A consistent description of the decays ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$, $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, and ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ is obtained. As a by-product, one predicts $B(\ensuremath{\eta}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})\phantom{\rule{0ex}{0ex}…