Search results for "electrodynamics"
showing 10 items of 820 documents
Effect of higher orbital angular momenta in the baryon spectrum
2001
We have performed a Faddeev calculation of the baryon spectrum for the chiral constituent quark model including higher orbital angular momentum states. We have found that the effect of these states is important, although a description of the baryon spectrum of the same quality as the one given by including only the lowest-order configurations can be obtained. We have studied the effect of the pseudoscalar quark-quark interaction on the relative position of the positive- and negative-parity excitations of the nucleon as well as the effect of varying the strength of the color-magnetic interaction.
Photon-pion charge asymmetry in e+e− reactions: A laboratory for perturbative QCD phases
1987
Abstract The charge asymmetry in the production of a photon and a meson in e + e - annihilation is studied in perturbative QCD. This quantity measures the interference of amplitudes governed by different momentum scales. It is thus a powerful tool to probe strong interaction phases at high energy and in the context of Sudakov exponentiation and the chromo Coulomb phase. We find a null result at the lowest non-trivial order off α s in the entire kinematic region described by perturbative QCD.
Hyperon forward spin polarizability gamma0 in baryon chiral perturbation theory
2015
We present the calculation of the hyperon forward spin polarizability gamma0 using manifestly Lorentz covariant baryon chiral perturbation theory including the intermediate contribution of the spin 3/2 states. As at the considered order the extraction of gamma0 is a pure prediction of chiral perturbation theory, the obtained values are a good test for this theory. After including explicitly the decuplet states, our SU(2) results have a very good agreement with the experimental data and we extend our framework to SU(3) to give predictions to the hyperons' gamma0 values. Prominent are the Sigma^- and Xi^- baryons as their photon transition to the decuplet is forbidden in SU(3) symmetry and th…
Quantum loops in radiative decays of the a1 and b1 axial-vector mesons
2007
A previous model where the low-lying axial-vector mesons are dynamically generated, implementing unitarity in coupled channels in the vector-pseudoscalar (V P) meson interaction, is applied to evaluate the decay widths of the a1(1260) and b1(1235) axial-vector mesons into �. Unlike the case of the a1, the b1 radiative decay is systematically underestimated at tree level. In this work we evaluate for the first time the loop contribution coming from an initial V P vertex. Despite the large superficial divergence of the loops, the convergence of the relevant loops can be established by using arguments of gauge invariance. The partial decay widths obtained agree with the experimental values wit…
Gauge fields, hidden local symmetries, and meson exchange currents
1997
Abstract The model dependence of the electromagnetic isovector meson exchange current (MEC) operator at higher momentums transfer is studied. For this purpose, the MEC operator constructed from a Lagrangian of the πϱa 1 system obtained within the framework of the hidden local symmetries (HLS) approach is compared with the analogous operator derived earlier from a minimal Yang-Mills (YM) Lagrangian. Numerical results for the deuteron disintegration near threshold show that the model dependent part of the exchange current modifies the tail of the cross section sensibly and that the presence of the a 1 meson both in the MEC and in the nuclear interaction provides a consistent description of th…
CP violation and electric-dipole-moment at low energy tau-pair production
2004
CP violation at low energy is investigated at the tau electromagnetic vertex. High statistics at B factories, and on top of the Upsilon resonances, allows a detailed investigation of CP-odd observables related to the tau-pair production. The contribution of the tau electric dipole moment is considered in detail. We perform an analysis independent from the high energy data by means of correlation and linear spin observables at low energy. We show that different CP-odd asymmetries, associated to the normal-transverse and normal-longitudinal correlation terms can be measured at low energy accelerators, both at resonant and non resonant energies. These observables allow to put stringent and ind…
Radial and elliptic flow at RHIC: further predictions
2001
Using a hydrodynamic model, we predict the transverse momentum dependence of the spectra and the elliptic flow for different hadrons in Au+Au collisions at sqrt(s) = 130 A GeV. The dependence of the differential and p_t-integrated elliptic flow on the hadron mass, equation of state and freeze-out temperature is studied both numerically and analytically.
Tau weak dipole moments from azumthal asymmetries
1999
We show that transverse and normal single-$tau$ polarization of $tau$ pairs produced at $e^+$ $e^-$ unpolarized collisions, at the $Z$ peak, are sensitive to weak (magnetic and electric) dipole moments of the $tau$. We also show how these components of the $\tau$ polarization are accessible by measuring appropriate azimuthal asymmetries in the angular distribution of its decay products. Sensitivities of the order of $10^{-18}$ $e\cdot cm$, for the weak-electric dipole moment, and $10^{-4}$ ($10^{-3}$), for the real (imaginary) part of the weak-magnetic dipole moment of $\tau$, may be achieved. Compatible bounds are also presented from spin-spin correlated asymmetries.
Description of rotating N=Z nuclei in terms of isovector pairing
2004
A systematic investigation of the rotating $N=Z$ even-even nuclei in the mass $A=58-80$ region has been performed within the frameworks of the Cranked Relativistic Mean field, Cranked Relativistic Hartree Bogoliubov theories and cranked Nilsson-Strutinsky approach. Most of the experimental data is well accounted for in the calculations. The present study suggests that there is strong isovector $np$-pair field at low spin, the strength of which is defined by the isospin symmetry. At high spin, the isovector pair field is destroyed and the data are well described by the calculations assuming zero pairing. No clear evidence for the existence of the isoscalar $t=0$ $np$-pairing has been obtaine…
Two-loop gluino contributions to the neutron electric dipole moment in theCP-violating minimal supersymmetric standard model
2005
We analyze two-loop gluino corrections to the neutron electric dipole moment (EDM) in the minimal supersymmetry extension of the standard model (MSSM). The dependence of two-loop corrections on the relevant CP violating phases differs from that of the one-loop contributions, and there is a region in the parameter space where the two-loop contributions are comparable with the one-loop contributions. Our numerical results show that the two-loop corrections can be as large as 30% of the one-loop results.