Neutron electric polarizability from unquenched lattice QCD using the background field approach

A calculational scheme for obtaining the electric polarizability of the neutron in lattice QCD with dynamical quarks is developed, using the background field approach. The scheme differs substantially from methods previously used in the quenched approximation, the physical reason being that the QCD ensemble is no longer independent of the external electromagnetic field in the dynamical quark case. One is led to compute (certain integrals over) four-point functions. Particular emphasis is also placed on the physical role of constant external gauge fields on a finite lattice; the presence of these fields complicates the extraction of polarizabilities, since it gives rise to an additional shift of the neutron mass unrelated to polarizability effects. The method is tested on a SU(3) flavor-symmetric ensemble furnished by the MILC Collaboration, corresponding to a pion mass of m_pi = 759 MeV. Disconnected diagrams are evaluated using stochastic estimation. A small negative electric polarizability of alpha =(-2.0 +/- 0.9) 10^(-4) fm^3 is found for the neutron at this rather large pion mass; this result does not seem implausible in view of the qualitative behavior of alpha as a function of m_pi suggested by Chiral Effective Theory.Comment: 36 pages, 11 figures. Note added concerning analytic continuation in the external electric field; some notation made more precis

Finite volume study of electric polarizabilities from lattice QCD

Knowledge of the electric polarizability is crucial to understanding the interactions of hadrons with electromagnetic fields. The neutron polarizability is very sensitive to the quark mass and is expected to diverge in the chiral limit. Here we present results for the electric polarizability of the neutron, neutral pion, and neutral kaon on eight ensembles with nHYP-smeared clover dynamical fermions with two different pion masses (227 and 306 MeV). These are currently the lightest pion masses used in polarizability studies. For each pion mass we compute the polarizability at four different volumes and perform an infinite volume extrapolation for the three hadrons. Along with the infinite volume extrapolation we conduct a chiral extrapolation for the kaon polarizability to the physical point. We compare our results for the neutron polarizability to predictions from chiral perturbation theory.Comment: 7 pages, 11 figure

Phenomenology of the Baryon Resonance 70-plet at Large N_c

We examine the multiplet structure and decay channels of baryon resonances in the large N_c QCD generalization of the N_c = 3 SU(6) spin-flavor 70. We show that this ``70'', while a construct of large N_c quark models, actually consists of five model-independent irreducible spin-flavor multiplets in the large N_c limit. The preferred decay modes for these resonances fundamentally depend upon which of the five multiplets to which the resonance belongs. For example, there exists an SU(3) ``8'' of resonances that is eta-philic and pi-phobic, and an ``8'' that is the reverse. Moreover, resonances with a strong SU(3) ``1'' component prefer to decay via a K-bar rather than via a pi. Remarkably, available data appears to bear out these conclusions.Comment: 26 pages, ReVTe

Chiral Properties of Pseudoscalar Mesons on a Quenched 20420^4 Lattice with Overlap Fermions

The chiral properties of the pseudoscalar mesons are studied numerically on a quenched $20^4$ lattice with the overlap fermion. We elucidate the role of the zero modes in the meson propagators, particularly that of the pseudoscalar meson. The non-perturbative renormalization constant $Z_A$ is determined from the axial Ward identity and is found to be almost independent of the quark mass for the range of quark masses we study; this implies that the $O(a^2)$ error is small. The pion decay constant, $f_{\pi}$, is calculated from which we determine the lattice spacing to be 0.148 fm. We look for quenched chiral log in the pseudoscalar decay constants and the pseudoscalar masses and we find clear evidence for its presence. The chiral log parameter $\delta$ is determined to be in the range 0.15 -- 0.4 which is consistent with that predicted from quenched chiral perturbation theory.Comment: Version accepted for publication by PRD. A few minor typographical errors have been corrected. 24 pages, 11 figure

Magnetic moments of vector, axial, and tensor mesons in lattice QCD

We present a calculation of magnetic moments for selected spin-1 mesons using the techniques of lattice QCD. This is carried out by introducing progressively small static magnetic field on the lattice and measuring the linear response of a hadron's mass shift. The calculations are done on $24^4$ quenched lattices using standard Wilson actions, with $\beta$=6.0 and pion mass down to 500 MeV. The results are compared to those from the form factor method where available.Comment: 8 pages, 11 figure

Pion Decay Constant, ZAZ_A and Chiral Log from Overlap Fermions

We report our calculation of the pion decay constant $f_\pi$, the axial renormalization constant $Z_A$, and the quenched chiral logarithms from the overlap fermions. The calculation is done on a quenched $20^4$ lattice at $a=0.148$ fm using tree level tadpole improved gauge action. The smallest pion mass we reach is about 280 MeV. The lattice size is about 4 times the Compton wavelength of the lowest mass pion.Comment: Lattice2001(Hadronic Matrix Elements), 3pages, 5figure

Coulomb Driven New Bound States at the Integer Quantum Hall States in GaAs/Al(0.3)Ga(0.7)As Single Heterojunctions

Coulomb driven, magneto-optically induced electron and hole bound states from a series of heavily doped GaAs/Al(0.3)Ga(0.7)As single heterojunctions (SHJ) are revealed in high magnetic fields. At low magnetic fields (nu > 2), the photoluminescence spectra display Shubnikov de-Haas type oscillations associated with the empty second subband transition. In the regime of the Landau filling factor nu < 1 and 1 < nu <2, we found strong bound states due to Mott type localizations. Since a SHJ has an open valence band structure, these bound states are a unique property of the dynamic movement of the valence holes in strong magnetic fields