Covariant Effective Field Theory for Nuclear Structure and Nuclear Currents

Recent progress in Lorentz-covariant quantum field theories of the nuclear many-body problem (quantum hadrodynamics or QHD) is discussed. The effective field theory studied here contains nucleons, pions, isoscalar scalar (\sigma) and vector (\omega) fields, and isovector vector (\rho) fields. The theory exhibits a nonlinear realization of spontaneously broken SU(2)_L \times SU(2)_R chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the nuclear currents and the strong-interaction dynamics, it satisfies the symmetries of the underlying theory of QCD, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. Moreover, it has recently been verified that for normal nuclear systems, it is possible to expand the effective Lagrangian systematically in powers of the meson fields (and their derivatives) and to truncate the expansion reliably after the first few orders. Using a mean-field version of the energy functional, accurate quantitative results are obtained for the bulk and single-particle properties of medium- and heavy-mass nuclei. The importance of modern perspectives in effective field theory and density functional theory for understanding these successes of QHD is emphasized. The inclusion of hadronic electromagnetic structure and of nonanalytic terms in the energy functional is also considered briefly. As a further application, weak-interaction currents are studied in the QHD framework. The axial-vector current, evaluated through the leading order in the field expansion, satisfies both PCAC and the Goldberger--Treiman relation, and the corresponding vector and axial-vector charges satisfy the familiar chiral charge algebra to all orders in the pion field.Comment: 32 pages, 9 figures, LaTeX2e with svmult.cls and svmultphys.clo; invited lecture at 307. WE-Heraeus-Seminar, "Relativistic Structure Models for the Physics of Radioactive Nuclear Beams," 5/12-16/2003, Bad Honnef, Germany. Reference list put into correct order; four typos fixe

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

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

Recent Progress in Quantum Hadrodynamics

Quantum hadrodynamics (QHD) is a framework for describing the nuclear many-body problem as a relativistic system of baryons and mesons. Motivation is given for the utility of such an approach and for the importance of basing it on a local, Lorentz-invariant lagrangian density. Calculations of nuclear matter and finite nuclei in both renormalizable and nonrenormalizable, effective QHD models are discussed. Connections are made between the effective and renormalizable models, as well as between relativistic mean-field theory and more sophisticated treatments. Recent work in QHD involving nuclear structure, electroweak interactions in nuclei, relativistic transport theory, nuclear matter under extreme conditions, and the evaluation of loop diagrams is reviewed.Comment: 115 pages, REVTeX 3.0 with epsf.sty, ijmpe1.sty, srev.sty, symbols.sty, plus 10 figure

Effective Field Theory in Nuclear Many-Body Physics

Recent progress in Lorentz-covariant quantum field theories of the nuclear many-body problem (quantum hadrodynamics, or QHD) is discussed. The importance of modern perspectives in effective field theory and density functional theory for understanding the successes of QHD is emphasized. To appear in: 150 Years of Quantum Many-Body Theory: A conference in honour of the 65th birthdays of John W. Clark, Alpo J. Kallio, Manfred L. Ristig, and Sergio Rosati.Comment: 10 pages, REVTeX 3.0 with epsf.sty, plus 2 figure