Search results for "electrodynamics"
showing 10 items of 820 documents
Pion cloud contribution to the s-wave repulsion in pionic atoms
1995
Abstract The nuclear pion cloud contribution to the pion self-energy for pionic atoms is evaluated and one finds large cancellations between terms involving the ππ amplitude and other terms originating from the chiral lagrangian partners. While the individual terms depend strongly on the off-shell extrapolation of the ππ amplitude, the sum is model independent within the Olson and Turner family of chiral lagrangians keeping ξ + 4 η constant, as previously found for the πN → ππN and pion double-charge exchange in nuclei, and vanishes in the limit of m π → 0. One finds a small net repulsion which is however too small to account for the “missing” s-wave repulsion. A revision of the present sta…
Spin-dependent potentials from lattice QCD
2006
The spin-dependent corrections to the static inter-quark potential are phenomenologically relevant to describing the fine and hyperfine spin splitting of the heavy quarkonium spectra. We investigate these corrections, which are represented as the field strength correlators on the quark-antiquark source, in SU(3) lattice gauge theory. We use the Polyakov loop correlation function as the quark-antiquark source, and by employing the multi-level algorithm, we obtain remarkably clean signals for these corrections up to intermediate distances of around 0.6 fm. Our observation suggests several new features of the corrections.
Generalized parton distributions of the pion in a Bethe Salpeter approach
2004
We calculate generalized parton distribution functions in a field theoretic formalism using a covariant Bethe-Salpeter approach for the determination of the bound-state wave function. We describe the procedure in an exact calculation in scalar Electrodynamics proving that the relevant corrections outside our scheme vanish. We extend the formalism to the Nambu--Jona-Lasinio model, a realistic theory of the pion. We go in both cases beyond all previous calculations and discover that all important features required by general physical considerations, like symmetry properties, sum rules and the polynomiality condition, are explicitly verified. We perform a numerical study of their behavior in t…
Color Anomaly and Flavor-Singlet Axial Charge of the Proton in the Chiral Bag: The Cheshire Cat Revisited
1997
Quantum effects inside the chiral bag induce a color anomaly which requires a compensating surface term to prevent breakdown of color gauge invariance. We show that the presence of this surface term first discovered several years ago allows one to derive in a gauge-invariant way a chiral-bag version of the Shore-Veneziano two-component formula for the flavor-singlet axial charge of the proton. This has relevance to what is referred to as the ``proton spin problem" on the one hand and to the Cheshire-Cat phenomenon in hadron structure on the other. We show that when calculated to the leading order in the color gauge coupling and for a specific color electric monopole configuration in the bag…
V P gamma radiative decay of resonances dynamically generated from the vector meson-vector meson interaction
2010
We evaluate the radiative decay into a vector, a pseudoscalar and a photon of several resonances dynamically generated from the vector-vector interaction. The process proceeds via the decay of one of the vector components into a pseudoscalar and a photon, which have an invariant mass distribution very different from phase space as a consequence of the two vector structure of the resonances. Experimental work along these lines should provide useful information on the nature of these resonances.
Dynamically generated resonances from the vector octet-baryon decuplet interaction and their radiative decays into γ-baryon decuplet
2009
The dynamically generated resonances from vector meson-baryon decuplet are studied using Lagrangians of the hidden gauge theory for vector interactions. One shows that some of the generated states can be associated with some known baryon resonances in the PDG data, while others are predictions for new states. Furthermore, we calculate the radiative decay widths of these resonances into a photon and a baryon decuplet.
Matrix elements of decays
2004
We present a numerical computation of matrix elements of ?I = 3/2 K ? ?? decays by using Wilson fermions. In order to extrapolate to the physical point we work at unphysical kinematics and we resort to Chiral Perturbation Theory at the next-to-leading order. In particular we explain the case of the electroweak penguins 07,8 which can contribute significantly in the theoretical prediction of sol|??/?. The study is done at ? = 6.0 on a 243 × 64 lattice.
Majoron effects in rare kaon decays
1989
Abstract We analyze, in the framework of the recently introduced doublet majoron model, the contribution from the emission of a pair of light scalars to the decay K + → π + + nothing . We find that, for reasonable choices of the parameters, the new scalar contribution may be as large as one additional neutrino-antineutrino mode and provide a substantial modification of the pion spectrum. The effect may be a few times larger in the triplet majoron model.
A modified born term model for π± Δ electroproduction
1974
An electric Born type model is used to describeπ±Δ electroproduction at high energies. The electric pion form factor is taken from VDM; the contact term form factor and theΔ form factor are set equal to the proton form factor (or equal to zero) which is left as an arbitrary parameter, and is determined by a fit of the model to the recentπ+δ0 andπ−Δ++ electroproduction data.
Fermion Regge poles and relations between phase shifts in the pion-nucleon scattering
1967
A Regge pole model is proposed. It is shown that simple relations between the smallπN phase shifts can be obtained without using any Regge pole parameters.