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Register a new userEffective Chiral Theory for Radiative Decays of Mesons
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An extended $U(3)_Lbigotimes U(3)_R$ chiral theory which includes pseudoscalar and vector meson nonets as dynamic degrees of freedom is presented. We combine a hidden symmetry approach with a general procedure of including the $eta$ meson into chiral theory. The $U(3)_Lbigotimes U(3)_R$ and the SU(3) symmetries are broken by the mechanism based on quark mass matrix. Meson radiative decay widths are parameterized in terms of a single and real $eta-eta$ mixing angle $theta_P$, a U(3)_V symmetry breaking scale parameter c_W, and the radiative decay constants $F_pi, F_K, F_eta, F_{eta}$, for the $pi, eta$, K, $eta $ mesons, respectively. Taking $F_pi = 93 MeV$, a global fit to decay width data yields F_K/F_pi = 1.16 pm 0.11, F_eta/F_pi = 1.14pm 0.04, F_{eta}/F_pi = 1.09 pm 0.04, c_W = -0.19 pm0.03, theta_P =-(15.4 pm 1.8)^o.
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En effective chiral theory of large N_C QCD of pseudoscalar, vector, and axial-vector mesons is reviewed.
Since the pioneering work of Weinberg, Chiral Effective Field Theory ($chi$EFT) has been widely and successfully utilized in nuclear physics to study many-nucleon interactions and associated electroweak currents. Nuclear $chi$EFT has now developed into an intense field of research and is applied to study light to medium mass nuclei. In this contribution, we focus on the development of electroweak currents from $chi$EFT and present applications to selected nuclear electroweak observables.
The new data on $rho,omega,phi$ radiative decays into $pi^0gamma,etagamma,etagamma$ from SND experiment at VEPP-2M $e^+e^-$ collider are presented.
We evaluate the Fermi and Gamow-Teller (GT) matrix elements in tritium $beta$-decay by including in the charge-changing weak current the corrections up to one loop recently derived in nuclear chiral effective field theory ($chi$ EFT). The trinucleon wave functions are obtained from hyperspherical-harmonics solutions of the Schru007fodinger equation with two- and three-nucleon potentials corresponding to either $chi$ EFT (the N3LO/N2LO combination) or meson-exchange phenomenology (the AV18/UIX combination). We find that contributions due to loop corrections in the axial current are, in relative terms, as large as (and in some cases, dominate) those from one-pion exchange, which nominally occur at lower order in the power counting. We also provide values for the low-energy constants multiplying the contact axial current and three-nucleon potential, required to reproduce the experimental GT matrix element and trinucleon binding energies in the N3LO/N2LO and AV18/UIX calculations.
Two-nucleon axial charge and current operators are derived in chiral effective field theory up to one loop. The derivation is based on time-ordered perturbation theory, and accounts for cancellations between the contributions of irreducible diagrams and the contributions due to non-static corrections from energy denominators of reducible diagrams. Ultraviolet divergencies associated with the loop corrections are isolated in dimensional regularization. The resulting axial current is finite and conserved in the chiral limit, while the axial charge requires renormalization. A complete set of contact terms for the axial charge up to the relevant order in the power counting is constructed.
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