622 research outputs found
Radiative decays of mesons in the NJL model
We revisit the theoretical predictions for anomalous radiative decays of
pseudoscalar and vector mesons. Our analysis is performed in the framework of
the Nambu-Jona-Lasinio model, introducing adequate parameters to account for
the breakdown of chiral symmetry. The results are comparable with those
obtained in previous approaches.Comment: 19 pages incl. 4 figure
Pion distribution amplitude and the pion-photon transition form factor in a nonlocal chiral quark model
We study the pion distribution amplitude (pi DA) in the context of a nonlocal chiral quark model. The corresponding Lagrangian reproduces the phenomenological values of the pion mass and decay constant, as well as the momentum dependence of the quark propagator obtained in lattice calculations. It is found that the obtained pi DA has two symmetric maxima, which arise from the new contributions generated by the nonlocal character of the interactions. This pi DA is applied to leading order and next-to-leading order calculations of the pion-photon transition form factor. Implications of the results are discussed
Right handed currents and FSI phases in B^0 --> \phi K^{*0}
We consider possible effects of New Physics (NP) on the angular distributions
of the decay B^0 --> \phi K^{*0}, showing how these effects depend on the
nature of nonstandard interactions. In a general framework based on
factorization, we show that triple products can be used to probe the chirality
of NP currents. In this analysis we take into account the presence of
non-vanishing strong phases, which is motivated by recent experimental
evidence. It is seen that the observability of right-handed NP is strongly
dependent on the relation between the relative magnitude of these phases and
the ratio of Standard Model and NP scales. As an application we estimate the
expected values of relevant observables in a particular Left Right Symmetric
Model.Comment: 16 pages, no figures. Comments and references added, conclusions
unchanged. Final version to appear in Phys. Rev.
Ordering phenomena in quasi one-dimensional organic conductors
Low-dimensional organic conductors could establish themselves as model
systems for the investigation of the physics in reduced dimensions. In the
metallic state of a one-dimensional solid, Fermi-liquid theory breaks down and
spin and charge degrees of freedom become separated. But the metallic phase is
not stable in one dimension: as the temperature is reduced, the electronic
charge and spin tend to arrange themselves in an ordered fashion due to strong
correlations. The competition of the different interactions is responsible for
which broken-symmetry ground state is eventually realized in a specific
compound and which drives the system towards an insulating state.
Here we review the various ordering phenomena and how they can be identified
by optic and magnetic measurements. While the final results might look very
similar in the case of a charge density wave and a charge-ordered metal, for
instance, the physical cause is completely different. When density waves form,
a gap opens in the density of states at the Fermi energy due to nesting of the
one-dimension Fermi surface sheets. When a one-dimensional metal becomes a
charge-ordered Mott insulator, on the other hand, the short-range Coulomb
repulsion localizes the charge on the lattice sites and even causes certain
charge patterns.
We try to point out the similarities and conceptional differences of these
phenomena and give an example for each of them. Particular emphasis will be put
on collective phenomena which are inherently present as soon as ordering breaks
the symmetry of the system.Comment: Review article Naturwissenschaften 200
Rare Kaon Decay K^+ --> \pi^+ \nu \bar{\nu} in SU(3)_C X SU(3)_L X U(1)_N Models
The rare kaon decay K^+ --> \pi^+ \nu \bar{\nu} is considered in the
framework of the models based on the SU(3)_C X SU(3)_L X U(1)_N (3 - 3 - 1)
gauge group. It is shown that a lower bound of the Z' mass in the 3 - 3 - 1
model with right-handed neutrinos at a value of 3 TeV is derived, while that in
the minimal version -- 1.7 TeV.Comment: 7 pages, 1 figure, late
Rare Kaon Decays
The current status of rare kaon decay experiments is reviewed. New limits in
the search for Lepton Flavor Violation are discussed, as are new measurements
of the CKM matrix.Comment: 8 pages, 3 figures, LaTeX, presented at the 3rd International
Conference on B Phyiscs and CP Violation, Taipei December 3-7, 199
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