Forward Compton Scattering with weak neutral current: constraints from sum rules

We generalize forward real Compton amplitude to the case of the interference of the electromagnetic and weak neutral current, formulate a low-energy theorem, relate the new amplitudes to the interference structure functions and obtain a new set of sum rules. We address a possible new sum rule that relates the product of the axial charge and magnetic moment of the nucleon to the 0th moment of the structure function $g_5(\nu,0)$. We apply the GDH and the finite energy sum rule for constraining the dispersive $\gamma Z$-box correction to the proton's weak charge.Comment: 6 pages, 2 figure

Can neutrino-induced photon production explain the low energy excess in MiniBooNE?

This report summarizes our study of Neutral Current (NC)-induced photon production in MiniBooNE, as motivated by the low energy excess in this experiment [A. A. Aquilar-Arevalo et al. (MiniBooNE Collaboration), Phys. Rev. Lett. 98, 231801 (2007); 103, 111801 (2009)]. It was proposed that NC photon production with two anomalous photon-$Z$ boson-vector meson couplings might explain the excess. However, our computed event numbers in both neutrino and antineutrino runs are consistent with the previous MiniBooNE estimate that is based on their pion production measurement. Various nuclear effects discussed in our previous works, including nucleon Fermi motion, Pauli blocking, and the $\Delta$ resonance broadening in the nucleus, are taken into account. Uncertainty due to the two anomalous terms and nuclear effects are studied in a conservative way.Comment: 7 pages, 4 figures, and 5 tables, typos corrected, references updated, version for publicatio

Electroweak Interactions in a Chiral Effective Lagrangian for Nuclei

We have studied electroweak (EW) interactions in quantum hadrodynamics (QHD) effective field theory (EFT). The Lorentz-covariant EFT contains nucleon, pion, $\Delta$, isoscalar scalar ($\sigma$) and vector ($\omega$) fields, and isovector vector ($\rho$) fields. The lagrangian exhibits a nonlinear realization of (approximate) $SU(2)_L \otimes SU(2)_R$ chiral symmetry and incorporates vector meson dominance. First, we discuss the EW interactions at the quark level. Then we include EW interactions in QHD EFT by using the background-field technique. The completed QHD EFT has a nonlinear realization of $SU(2)_L \otimes SU(2)_R \otimes U(1)_B$ (chiral symmetry and baryon number conservation), as well as realizations of other symmetries including Lorentz-invariance, $C$, $P$, and $T$. Meanwhile, as we know, chiral symmetry is manifestly broken due to the nonzero quark masses; the $P$ and $C$ symmetries are also broken because of weak interactions. These breaking patterns are parameterized in a general way in the EFT. Moreover, we have included the $\Delta$ resonance as manifest degrees of freedom in our QHD EFT, with a discussion of the irrelevance of the well-known pathologies involving high-spin fields from the modern EFT perspective. This enables us to discuss physics at the kinematics where the resonance becomes important. As a result, the effective theory uses hadronic degrees of freedom, satisfies the constraints due to QCD (symmetries and their breaking pattern), and is calibrated to strong-interaction phenomena. Applications to (anti)neutrino scattering are briefly discussed.Comment: 27 pages, 1 figure, intech.cls, submitted to "Quantum Field Theory", ISBN 979-953-307-392-6. (InTech, Rijeka, Croatia