Search results for "PERTURBATION"
showing 10 items of 811 documents
Perturbative chiral violations for domain-wall QCD with improved gauge actions
2006
We investigate, in the framework of perturbation theory at finite $N_s$, the effectiveness of improved gauge actions in suppressing the chiral violations of domain-wall fermions. Our calculations show substantial reductions of the residual mass when it is compared at the same value of the gauge coupling, the largest suppression being obtained when the DBW2 action is used. Similar effects can also be observed for a power-divergent mixing coefficient which is chirally suppressed. No significant reduction instead can be seen in the case of the difference between the vector and axial-vector renormalization constants when improved gauge actions are used in place of the plaquette action. We also …
Nucleon andΔ(1232)form factors at low momentum transfer and small pion masses
2012
An expansion of the electromagnetic form factors of the nucleon and $\ensuremath{\Delta}(1232)$ in small momentum transfer and pion mass is performed in a manifestly covariant EFT framework consistent with chiral symmetry and analyticity. We present the expressions for the nucleon and $\ensuremath{\Delta}(1232)$ electromagnetic form factors, charge radii, and electromagnetic moments in the framework of $SU(2)$ baryon chiral perturbation theory, with nucleon and $\ensuremath{\Delta}$-isobar degrees of freedom, to next-to-leading order. Motivated by the results for the proton electric radius obtained from the muonic-hydrogen atom and electron-scattering process, we extract values for the seco…
Chiral sum rules and vacuum condensates from tau-lepton decay data
2015
QCD finite energy sum rules, together with the latest updated ALEPH data on hadronic decays of the tau-lepton are used in order to determine the vacuum condensates of dimension $d=2$ and $d=4$. These data are also used to check the validity of the Weinberg sum rules, and to determine the chiral condensates of dimension $d=6$ and $d=8$, as well as the chiral correlator at zero momentum, proportional to the counter term of the ${\cal{O}}(p^4)$ Lagrangian of chiral perturbation theory, $\bar{L}_{10}$. Suitable (pinched) integration kernels are introduced in the sum rules in order to suppress potential quark-hadron duality violations. We find no compelling indications of duality violations in t…
From Hadronic τ Decays to the Chiral Couplings and
2009
A sum rule analysis of the hadronic τ -decay data can be used to determine the low-energy constants L 10 r ( μ ) and C 87 r ( μ ) . These constants are QCD chiral-order parameters, which appear at order p 4 and p 6 , respectively, in the chiral perturbation theory expansion of the V − A correlator. At order p 4 we obtain L 10 r ( M ρ ) = − ( 5.22 ± 0.06 ) ⋅ 10 − 3 . Including in the analysis the order p 6 contributions, we get L 10 r ( M ρ ) = − ( 4.06 ± 0.39 ) ⋅ 10 − 3 and C 87 r ( M ρ ) = ( 4.89 ± 0.19 ) ⋅ 10 − 3 GeV − 2 .
SU(3)-breaking corrections to the hyperon vector couplingf1(0)in covariant baryon chiral perturbation theory
2009
This work was partially supported by the MEC Grant No. FIS2006-03438 and the European Community- Research Infrastructure Integrating Activity Study of Strongly Interacting Matter (Hadron-Physics2, Grant Agreement 227431) under the Seventh Framework Programme of EU. L. S. G. acknowledges support from the MICINN in the Program ‘‘Juan de la Cierva.’’ J. M. C. acknowledges the same institution for an FPU grant.
The A5 and the pion field
2005
In this talk, an SU(Nf)xSU(Nf)Yang-Mills model with a compact extra-dimension is used to describe the spin-1 mesons and pions of massless QCD in the large-Nc. The right 4D symmetry and symmetry-breaking pattern is produced by imposing appropriate boundary conditions. The Goldstone boson fields are constructed using a Wilson line. We derive the low-energy limit (chiral lagrangian), discuss rho-meson dominance, sum rules between resonance couplings and the relation with the QCD high-energy behavior. Finally, we provide an analytic expression for the two-point function of vector and axial currents.
N/Ddescription of two meson amplitudes and chiral symmetry
1998
The most general structure of an elastic partial wave amplitude when the unphysical cuts are neglected is deduced in terms of the N/D method. This result is then matched to lowest order, ${\mathcal{O}}(p^2)$, Chiral Perturbation Theory($\chi$PT) and to the exchange (consistent with chiral symmetry) of resonances in the s-channel. The extension of the method to coupled channels is also given. Making use of the former formalism, the $\pi\pi$ and $K\pi$(I=1/2) P-wave scattering amplitudes are described without free parameters when taking into account relations coming from the 1/$N_c$ expansion and unitarity. Next, the scalar sector is studied and good agreement with experiment up to $\sqrt{s}=…
Two Meson Scattering Amplitudes and their Resonances from Chiral Symmetry and the N/D Method
1999
We study the vector and scalar meson-meson amplitudes up to \sqrt{s}\lesssim 1.4 GeV and their associated spectroscopy. The study has been done considering jointly the N/D method, Chiral Symmetry and implications from large N_c QCD. The N/D method provides us with the way to unitarize the tree level amplitudes constructed in agreement with Chiral Symmetry and its breaking (explicit and spontaneous). These amplitudes are calculated making use of the lowest order Chiral Perturbation Theory (\chiPT) Lagrangians and the exchanges of resonances compatible with Chiral Symmetry as given in. On the other hand the large N_c considerations allow us to distinguish between elementary (as elementary as …
Vanishing chiral couplings in the large-Nc resonance theory
2007
5 pages, 2 figures.-- PACS nrs.: 12.39.Fe; 11.15.Pg; 12.38.-t.-- ISI Article Identifier: 000247625300022.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0611375
Charm and bottom quark masses from QCD moment sum rules
2002
In this work the charm and bottom quark masses are determined from QCD moment sum rules for the charmonium and upsilon systems. In our analysis we include both the results from non-relativistic QCD and perturbation theory at next-next-to-leading order. For the pole masses we obtain $M_c=1.75\pm 0.15$ GeV and $M_b=4.98\pm 0.125$ GeV. Using the potential-subtracted mass in intermediate steps of the calculation the MS-masses are determined to $m_c(m_c) = 1.19 \pm 0.11$ GeV and $m_b(m_b) = 4.24 \pm 0.10$ GeV.