8 research outputs found
Electromagnetic form factors of charged and neutral kaons in an extended vector-meson-dominance model
A model is developed for electromagnetic form factors of the charged and
neutral K-mesons. The formalism is based on ChPT Lagrangians with vector
mesons. The form factors, calculated without fitting parameters, are in a good
agreement with experiment for space-like and time-like photon momenta.
Contribution of the two-kaon channels to the muon anomalous magnetic moment
a_\mu is calculated.Comment: 23 pages, 11 figures, accepted for publication in Eur. Phys. J.
Radiative decays with light scalar mesons and singlet-octet mixing in ChPT
We study different types of radiative decays involving f0(980) and a0(980)
mesons within a unified ChPT-based approach at one-loop level. Light scalar
resonances which are seen in pi pi, pi eta, K K-bar channels of phi(1020)
radiative decays and in J/psi decays are responsible for key questions of
low-energy dynamics in the strong interaction sector, and decays phi(1020) ->
gamma a0(980), phi(1020) -> gamma f0(980), a0(980) -> gamma gamma, f0(980) ->
gamma gamma are of interest for current experimental programs in Juelich,
Frascati and Novosibirsk. From theoretical point of view it is important to
verify whether light scalar mesons are members of some flavor octet or nonet.
We find a value of mixing angle dictated by consistency with experiment and
coupling structures of ChPT Lagrangian. Decay widths f0(980)/a0(980) -> gamma
rho(770)/omega(782), which are not studied experimentally yet, are predicted.
We also obtain several relations between widths, which hold independently of
coupling constants and represent a fingerprint of the model.Comment: 18 pages, 8 figures; misprints in text and tables corrected,
discussion extended, references added; version accepted for publication in
Eur.Phys.J.
Contribution of vector resonances to the {\bar B}_d^0 -> {\bar K}^{*0} mu^+ mu^- decay
The fully differential angular distribution for the rare flavor-changing
neutral current decay \bar{B}_d^0 -> \bar{K}^{*0} (-> K- pi+) mu+ mu- is
studied. The emphasis is placed on accurate treatment of the contribution from
the processes \bar{B}_d^0 -> \bar{K}^{*0} (-> K- pi+) V with intermediate
vector resonances V = rho(770), omega(782), phi(1020), J/psi, psi(2S), ...
decaying into the mu+ mu- pair. The dilepton invariant-mass dependence of the
branching ratio, longitudinal polarization fraction f_L of the \bar{K}^{*0}
meson, and forward-backward asymmetry A_{FB} is calculated and compared with
data from Belle, CDF and LHCb. It is shown that inclusion of the resonance
contribution may considerably modify the branching ratio, calculated in the SM
without resonances, even in the invariant-mass region far from the so-called
charmonia cuts applied in the experimental analyses. This conclusion crucially
depends on values of the unknown phases of the B^0 -> K^{*0} J/psi and B^0 ->
K^{*0} psi(2S) decay amplitudes with zero helicity.Comment: 12 pages, 4 figures, SVJour3 style; introduction and discussion
sections extended, references added; version accepted for publication in Eur.
Phys. J. C. arXiv admin note: substantial text overlap with arXiv:1111.409
P-wave excited baryons from pion- and photo-induced hyperon production
We report evidence for , , ,
, , and , and find
indications that might have a companion state at 1970\,MeV. The
controversial is not seen. The evidence is derived from a
study of data on pion- and photo-induced hyperon production, but other data are
included as well. Most of the resonances reported here were found in the
Karlsruhe-Helsinki (KH84) and the Carnegie-Mellon (CM) analyses but were
challenged recently by the Data Analysis Center at GWU. Our analysis is
constrained by the energy independent scattering amplitudes from either
KH84 or GWU. The two amplitudes from KH84 or GWU, respectively, lead to
slightly different branching ratios of contributing resonances but the
debated resonances are required in both series of fits.Comment: 22 pages, 28 figures. Some additional sets of data are adde
Soft electroweak bremsstrahlung:Theorems and astrophysical relevance
We analyze the structure of the amplitudes for electroweak bremsstrahlung in nucleon-nucleon collisions, for the charged (N+N-->N+N+e(-)+(ν) over bar (e)) and neutral (N+N-->N+N+nu(f)+(ν) over bar (f)) weak current. Theorems are derived for the matrix elements of the vector and axial-vector currents in the soft regime. A comparison is made with previous work, usually performed in the nonrelativistic limit and by using a one-pion exchange two-nucleon interaction in Born approximation. Such approaches are argued to be unrealistic. This is explicitly shown for the neutrino-pair emission process in neutron-neutron scattering. Our results are relevant for calculations of neutrino emissivities in supernovae and in cooling scenarios of neutron stars