536 research outputs found
Sequential vector and axial-vector meson exchange and chiral loops in radiative phi decay
We study the radiative decay into and taking into account mechanisms in which there are two sequential
vector-vector-pseudoscalar or axial-vector--vector--pseudoscalar steps followed
by the coupling of a vector meson to the photon, considering the final state
interaction of the two mesons. There are other mechanisms in which two kaons
are produced through the same sequential mechanisms or from decay into
two kaons and then undergo final state interaction leading to the final pair of
pions or , this latter mechanism being the leading one. The results
of the parameter free theory, together with the theoretical uncertainties, are
compared with the latest experimental results of KLOE at Frascati.Comment: 28 pages, 20 figure
Endophenotypes of executive functions in obsessive compulsive disorder? A meta-analysis in unaffected relatives.
Endophenotypes are mediator traits between genetic influences and clinical phenotypes. Meta-analyses have consistently shown modest impairments of executive functioning in obsessive compulsive disorder (OCD) patients compared to healthy controls. Similar deficits have also been reported in unaffected relatives of OCD patients, but have not been quantified. We conducted the first meta-analysis combining all studies investigating executive functioning in unaffected relatives of individuals with OCD to quantify any deficits. A search of Pubmed, Medline and PsychInfo databases identified 21 suitable papers comprising 707 unaffected relatives of OCD patients and 842 healthy controls. Effect sizes were calculated using random effects models. Unaffected relatives displayed a significant impairment in global executive functioning. Analyses of specific executive functioning subdomains revealed impairments in: planning, visuospatial working memory and verbal fluency. Deficits in executive functioning are promising endophenotypes for OCD. To identify further biomarkers of disease risk/resilience in OCD, we suggest examining specific executive functioning domains
Corrections to Fermi's Golden Rule in Decays
We analyze the decays utilizing a formulation of
transition rates which explicitly exhibits corrections to Fermi's Golden Rule.
These corrections arise in systems in which the phase space and/or matrix
element varies rapidly with energy, as happens in , which is
just above threshold. We show that the theoretical corrections resolve a
puzzling discrepancy between theory and experiment for the branching
ratio
Unitary chiral dynamics in J/Psi to VPP decays and the role of scalar mesons
We make a theoretical study of the J/Psi decays into \omega\pi\pi,
\phi\pi\pi, \omega K \bar{K} and \phi K\bar{K} using the techniques of the
chiral unitary approach stressing the important role of the scalar resonances
dynamically generated through the final state interaction of the two
pseudoscalar mesons. We also discuss the importance of new mechanisms with
intermediate exchange of vector and axial-vector mesons and the role played by
the OZI rule in the J/\Psi\phi\pi\pi vertex, quantifying its effects. The
results nicely reproduce the experimental data for the invariant mass
distributions in all the channels considered.Comment: 29 pages, 10 figure
The interference in the reaction and the search for the decay
We describe the interference between amplitudes and ,
where meson is considered in the frameworks of the four-quark model and
the model of the scalar molecule. The general expressions for the
differential cross section with the radiative corrections and two angle cuts
are given. The interference patterns are obtained in the spectrum of the
differential cross section by the energy of the photon and in the full cross
section by the energy of the beams.Comment: 21 pages, revtex, 8 ps files of figure
Pseudoscalar Meson Mixing in Effective Field Theory
We show that for any effective field theory of colorless meson fields, the
mixing schemes of particle states and decay constants are not only related but
also determined exclusively by the kinetic and mass Lagrangian densities. In
the general case, these are bilinear in terms of the intrinsic fields and
involve non-diagonal kinetic and mass matrices. By applying three consecutive
steps this Lagrangian can be reduced into the standard quadratic form in terms
of the physical fields. These steps are : (i) the diagonalization of the
kinetic matrix, (ii) rescaling of the fields, and (iii) the diagonalization of
the mass matrix. In case, where the dimensions of the non-diagonal kinetic and
mass sub-matrices are respectively, and , this procedure
leads to mixing schemes which involve angles and
field rescaling parameters. This observation holds true irrespective with the
type of particle interactions presumed. The commonly used mixing schemes,
correspond to a proper choice of the kinetic and mass matrices, and are derived
as special cases. In particular, - mixing, requires one angle, if
and only if, the kinetic term with the intrinsic fields has a quadratic form.Comment: REVTeX, 6 page
Quark Mass Ratios in ChPT with the Difference of Quark Condensates Considered
The chiral effective Lagrangian for pseudoscalar nonet is constructed in
consideration of isospin breaking. And the difference of quark condensates is
taken accounted. The SU(3) singlet eta0 is not taken as Goldstone-boson. The
mixing with and without isospin symmetry is considered. The quark mass ratios
are obtained through solving the mass equations of mesons. We estimate the
change of quark mass ratios according to the change of the masses of pion+ and
kaon+ to see how the electromagnetic corrections affect our results. It turn
out that massless up quark is possible. The upper limit for mu/md is around
0.39. 2ms/(mu+md)=24.23~25.12. The values for quark condensate ratios and other
constants are limited in narrow ranges.Comment: 10 page
Radiative decay of rho^0 and phi mesons in a chiral unitary approach
We study the rho^0 and phi decays into pi^+ pi^- gamma, pi^0 pi^0 gamma and
phi into pi^0 eta gamma using a chiral unitary approach to deal with the final
state interaction of the M M system. The final state interaction modifies only
moderately the large momenta tail of the photon spectrum of the rho^0 --> pi^+
pi^- gamma decay. In the case of phi decay the contribution to pi^+ pi^- gamma
and pi^0 pi^0 gamma decay proceeds via kaonic loops and gives a distribution of
pi pi invariant masses in which the f_0(980) resonance shows up with a very
distinct peak. The spectrum found for phi --> pi^0 pi^0 gamma decay agrees with
the recent experimental results obtained at Novosibirsk. The branching ratio
for phi --> pi^0 eta gamma, dominated by the a_0(980), is also in agreement
with recent Novosibirsk results.Comment: 14 pages, 3 figures. Revised version using an antisymmetric tensor
notation for the vector mesons. To appear in Physics Letters
Radiative decays of light vector mesons in a quark level linear sigma model
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma
decays in the framework of a U(3)xU(3) linear sigma model which includes
constituent quarks. For the first two decays this approach improves results
based on the anomalous Wess-Zumino term, with contributions due to SU(3)
symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays
are dominated by resonant eta' exchange . Our calculation for the later decays
improves and update similar calculations in the -closely related- framework of
vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x10^{-5} and
BR(phi to omega gamma gamma)=2.8x10^{-6} within the scope of the
high-luminosity phi factories.Comment: 8 pages, submitted to Phys. Rev.
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