Isospin Splitting in the Pion-Nucleon Couplings from QCD Sum Rules

We use QCD sum rules for the three point function of a pseudoscalar and two nucleonic currents in order to estimate the charge dependence of the pion nucleon coupling constant coming from isospin violation in the strong interaction. The effect can be attributed primarily to the difference of the quark condensates and . Assuming that the pi0 is a pure isostate we obtain for the splitting between the coupling of proton and neutron to the neutral pion an interval of [0.008 ; 0.023], the uncertainties coming mainly from the input parameters. In order to obtain the coupling to a physical pi0 we have to take pi - eta mixing into account leading to an interval of [0.012 ; 0.037]. The charged pion nucleon coupling is found to be the average of the two neutral ones. Electromagnetic effects are not included.Comment: contributed talk at CIPANP97 (Big Sky, Montana); 3 pages (aipproc.sty), no figure

Temperature-dependent "phason" elasticity in a random tiling quasicrystal

Both ``phason'' elastic constants have been measured from Monte Carlo simulations of a random-tiling icosahedral quasicrystal model with a Hamiltonian. The low-temperature limit approximates the ``canonical-cell'' tiling used to describe several real quasicrystals. The elastic constant K2 changes sign from positive to negative with decreasing temperature; in the ``canonical-cell'' limit, K2/K1 appears to approach -0.7, about the critical value for a phason-mode modulation instability. We compare to the experiments on i-AlPdMn and i-AlCuFe.Comment: 5 pages, 2 Postscript figures, LaTeX, uses revtex4, submitted to PR

Movement and Distribution of Esocids and Forage Fishes In A Power Plant Cooling Reservoir

One Muskellunge (Esox masquinongy) and 2 northern pike (E. Lucius) were surgically implanted with untrasonic transmitters and tracked in a South Dakota cooling reservoir from June 1979 to June 1980. The fishes inhabited the intake area of the reservoir during the summer (temperature range, 27.5 – 31.5˚ C) and the discharge area during the winter (temperature range, 4.5 – 31.5˚C). In the spring and fall, the fishes were located throughout the reservoir (temperature range, 12.0 – 28.5˚C). Highest rates of movement for the esocids were recorded during the spring (675 – 1,100 m/day). The lowest rates were recorded during late summer and fall (130-390 m/day). The muskellunge inhabited deeper water (4.5 m, average) than the northern pike (3.9 m, average) during the summer. Both esocid species inhabited the 0.5-3.0 m depth during the winter. Tracks made over a 24 hour period indicated greater distances moved by the muskellunge (2,063 m) than northern pike (487 m). Both the muskellunge and northern pike were most active during daylight periods, but they also moved at night. Echogram recordings indicated that forage fishes were distributed throughout the reservoir during the spring, summer, and fall, and were concentrated in the discharge area during winter

Global phase diagram of the spin-1 antiferromagnet with uniaxial anisotropy on the kagome lattice

The phase diagram of the XXZ spin-1 quantum magnet on the kagome lattice is studied for all cases where the $J_z$ coupling is antiferromagnetic. In the zero magnetic field case, the six previously introduced phases, found using various methods, are: the nondegenerate gapped photon phase which breaks no space symmetry or spin symmetry; the six-fold degenerate phase with plaquette order, which breaks both time reversal symmetry and translational symmetry; the "superfluid" (ferromagnetic) phase with an in-plane global U(1) symmetry broken, when $J_{xy} 0$; the nematic phase when $D < 0$ and large; and a phase with resonating dimers on each hexagon. We obtain all of these phases and partial information about their quantum phase transitions in a single framework by studying condensation of defects in the six-fold plaquette phases. The transition between nematic phase and the six-fold degenerate plaquette phase is potentially an unconventional second-order critical point. In the case of a nonzero magnetic field along $\hat{z}$, another ordered phase with translation symmetry broken is opened up in the nematic phase. Due to the breaking of time-reversal symmetry by the field, a supersolid phase emerges between the six-fold plaquette order and the superfluid phase. This phase diagram might be accessible in nickel compounds, BF$_4$ salts, or optical lattices of atoms with three degenerate states on every site.Comment: 17 pages, 16 figure

Delta s density in a proton and unpolarized lepton - polarized proton scatterings

It is shown that the parity--violating deep--inelastic scatterings of unpolarized charged leptons on polarized protons, $\ell^{\mp} + \vec P\to \stackrel{\scriptscriptstyle(-)}{\nu_{\ell}} + X$, could provide a sensitive test for the behavior and magnitude of the polarized strange--quark density in a proton. Below charm threshold these processes are also helpful to uniquely determine the magnitude of individual polarized parton distributions.Comment: LaTeX file, 12 pages+4 fiigures not included (available upon request

Finite temperature properties of quantum Lifshitz transitions between valence bond solid phases: An example of `local' quantum criticality

We study the finite temperature properties of quantum magnets close to a continuous quantum phase transition between two distinct valence bond solid phases in two spatial dimension. Previous work has shown that such a second order quantum `Lifshitz' transition is described by a free field theory and is hence tractable, but is nevertheless non-trivial. At $T>0$, we show that while correlation functions of certain operators exhibit $\omega/T$ scaling, they do not show analogous scaling in space. In particular, in the scaling limit, all such correlators are purely {\em local} in space, although the same correlators at T=0 decay as a power law. This provides a valuable microscopic example of a certain kind of `local' quantum criticality. The local form of the correlations arise from the large density of soft modes present near the transition that are excited by temperature. We calculate exactly the autocorrelation function for such operators in the scaling limit. Going beyond the scaling limit by including irrelevant operators leads to finite spatial correlations which are also obtained

Comments on differential cross section of phi-meson photoproduction at threshold

We show that the differential cross section d_sigma/d_t of gamma p --> \phi p reaction at the threshold is finite and its value is crucial to the mechanism of the phi meson photoproduction and for the models of phi-N interaction.Comment: 8 pages, 2 figure

Phonon-phason coupling in icosahedral quasicrystals

From relaxation simulations of decoration-based quasicrystal structure models using microscopically based interatomic pair potentials, we have calculated the (usually neglected) phonon-phason coupling constant. Its sign is opposite for the two alloys studied, i-AlMn and i-(Al,Cu)Li; a dimensionless measure of its magnitude relative to the phonon and phason elastic constants is of order 1/10, suggesting its effects are small but detectable. We also give a criterion for when phonon-phason effects are noticeable in diffuse tails of Bragg peaks.Comment: 7 pages, LaTeX, uses Europhys Lett macros (included

Non-relativistic Lee Model on two Dimensional Riemannian Manifolds

This work is a continuation of our previous work (JMP, Vol. 48, 12, pp. 122103-1-122103-20, 2007), where we constructed the non-relativistic Lee model in three dimensional Riemannian manifolds. Here we renormalize the two dimensional version by using the same methods and the results are shortly given since the calculations are basically the same as in the three dimensional model. We also show that the ground state energy is bounded from below due to the upper bound of the heat kernel for compact and Cartan-Hadamard manifolds. In contrast to the construction of the model and the proof of the lower bound of the ground state energy, the mean field approximation to the two dimensional model is not similar to the one in three dimensions and it requires a deeper analysis, which is the main result of this paper.Comment: 18 pages, no figure