Search results for "PERTURBATION"
showing 10 items of 811 documents
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 $L_i^r$.
Combining heavy quark spin and local hidden gauge symmetries in the dynamical generation of hidden charm baryons
2013
We present a coupled channel unitary approach to obtain states dynamically generated from the meson-baryon interaction with hidden charm, using constraints of heavy quark spin symmetry. As a basis of states, we use (D) over barB, (D) over bar *B states, with B baryon charmed states belonging to the 20 representations of SU(4) with J(P) = 1/2(+), 3/2(+). In addition we also include the eta N-c and J/psi N states. The inclusion of these coupled channels is demanded by heavy quark spin symmetry, since in the large m(Q) limit the D and D* states are degenerate and are obtained from each other by means of a spin rotation, under which QCD is invariant. The novelty in the work is that we use dynam…
Kaon Physics: Theory Overview
2012
Kaon decays have played a key role in the construction of the Standard Model and continue to be an important testing ground of the electroweak flavour theory. They can provide new signals of CP-violation phenomena and, perhaps, a window into physics beyond the Standard Model. The interplay of long-distance QCD effects in strangeness-changing transitions can be analyzed, combining the short-distance Operator Product Expansion with Chiral Perturbation Theory techniques. A brief overview is presented, focusing on a few selected decay modes. A more detailed and comprehensive review can be found in arXiv:1107.6001.
K--pipi amplitudes from lattice QCD with a light charm quark.
2006
4 pages, 1 figure.-- PACS nrs.: 12.38.Gc, 13.25.Es, 11.30.Rd.-- ISI Article Identifier: 000244420700019.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0607220
Consistency between SU(3) and SU(2) covariant baryon chiral perturbation theory for the nucleon mass
2017
Abstract Treating the strange quark mass as a heavy scale compared to the light quark mass, we perform a matching of the nucleon mass in the SU(3) sector to the two-flavor case in covariant baryon chiral perturbation theory. The validity of the 19 low-energy constants appearing in the octet baryon masses up to next-to-next-to-next-to-leading order [1] is supported by comparing the effective parameters (the combinations of the 19 couplings) with the corresponding low-energy constants in the SU(2) sector [2] . In addition, it is shown that the dependence of the effective parameters and the pion-nucleon sigma term on the strange quark mass is relatively weak around its physical value, thus pro…
Probing the chiral regime of Nf=2 QCD with mixed actions
2011
17 páginas, 15 figuras, 9 tablas.-- El Pdf es la versión pre-print del artículo: arXiv:1008.1870v2
Finite Volume Scaling of Pseudo Nambu-Goldstone Bosons in QCD
2008
We consider chiral perturbation theory in a finite volume and in a mixed regime of quark masses. We take N_l light quarks near the chiral limit, in the so-called epsilon-regime, while the remaining N_h quarks are heavier and in the standard p-regime. We compute in this new mixed regime the finite-size scaling of the light meson correlators in the scalar, pseudoscalar, vector and axial vector channels.Using the replica method, we easily extend our results to the partially quenched theory. With the help of our results, lattice QCD simulations with 2+1 flavors can safely investigate pion physics with very light up and down quark masses even in the region where the pion's correlation length ove…
Lattice calculation of the pion transition form factor with Nf=2+1 Wilson quarks
2019
We present a lattice QCD calculation of the double-virtual neutral pion transition form factor, with the goal to cover the kinematic range relevant to hadronic light-by-light scattering in the muon $g\ensuremath{-}2$. Several improvements have been made compared to our previous work. First, we take into account the effects of the strange quark by using the ${N}_{f}=2+1$ coordinated lattice simulation gauge ensembles. Second, we have implemented the on-shell $\mathcal{O}(a)$ improvement of the vector current to reduce the discretization effects associated with Wilson quarks. Finally, in order to have access to a wider range of photon virtualities, we have computed the transition form factor …