Analysis of the Y(4140) and related molecular states with QCD sum rules

In this article, we assume that there exist scalar ${D}^\ast {\bar {D}}^\ast$, ${D}_s^\ast {\bar {D}}_s^\ast$, ${B}^\ast {\bar {B}}^\ast$ and ${B}_s^\ast {\bar {B}}_s^\ast$ molecular states, and study their masses using the QCD sum rules. The numerical results indicate that the masses are about $(250-500) \rm{MeV}$ above the corresponding ${D}^\ast -{\bar {D}}^\ast$, ${D}_s^\ast -{\bar {D}}_s^\ast$, ${B}^\ast -{\bar {B}}^\ast$ and ${B}_s^\ast -{\bar {B}}_s^\ast$ thresholds, the Y(4140) is unlikely a scalar ${D}_s^\ast {\bar {D}}_s^\ast$ molecular state. The scalar $D^\ast {\bar D}^\ast$, $D_s^\ast {\bar D}_s^\ast$, $B^\ast {\bar B}^\ast$ and $B_s^\ast {\bar B}_s^\ast$ molecular states maybe not exist, while the scalar ${D'}^\ast {\bar {D'}}^\ast$, ${D'}_s^\ast {\bar {D'}}_s^\ast$, ${B'}^\ast {\bar {B'}}^\ast$ and ${B'}_s^\ast {\bar {B'}}_s^\ast$ molecular states maybe exist.Comment: 19 pages, 36 figures, slight revisio

Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments

The strange properties of the nucleon are investigated within the framework of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying the symmetry conserving SU(3) quantization. We present the form factors $G^0_{E,M}(Q^2)$, $G^Z_M(Q^2)$ and the electric and magnetic strange form factors $G^s_{E,M}(Q^2)$ incorporating pion and kaon asymptotics. The results show a fairly good agreement with the recent experimental data from the SAMPLE and HAPPEX collaborations. We also present predictions for future measurements including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed. Accepted for publication in Phys.Rev.

Future Directions in Parity Violation: From Quarks to the Cosmos

I discuss the prospects for future studies of parity-violating (PV) interactions at low energies and the insights they might provide about open questions in the Standard Model as well as physics that lies beyond it. I cover four types of parity-violating observables: PV electron scattering; PV hadronic interactions; PV correlations in weak decays; and searches for the permanent electric dipole moments of quantum systems.Comment: Talk given at PAVI 06 workshop on parity-violating interactions, Milos, Greece (May, 2006); 10 page

Strange nucleon form factors in the perturbative chiral quark model

We apply the perturbative chiral quark model at one loop to calculate the strange form factors of the nucleon. A detailed numerical analysis of the strange magnetic moments and radii of the nucleon, and also the momentum dependence of the form factors is presented.Comment: 18 pages, 6 figure

K* nucleon hyperon form factors and nucleon strangeness

A crucial input for recent meson hyperon cloud model estimates of the nucleon matrix element of the strangeness current are the nucleon-hyperon-K* (NYK*) form factors which regularize some of the arising loops. Prompted by new and forthcoming information on these form factors from hyperon-nucleon potential models, we analyze the dependence of the loop model results for the strange-quark observables on the NYK* form factors and couplings. We find, in particular, that the now generally favored soft N-Lambda-K* form factors can reduce the magnitude of the K* contributions in such models by more than an order of magnitude, compared to previous results with hard form factors. We also discuss some general implications of our results for hadronic loop models.Comment: 9 pages, 8 figures, new co-author, discussion extended to the momentum dependence of the strange vector form factor

Subthreshold dynamics of the neural membrane potential driven by stochastic synaptic input

In the cerebral cortex, neurons are subject to a continuous bombardment of synaptic inputs originating from the network's background activity. This leads to ongoing, mostly subthreshold membrane dynamics that depends on the statistics of the background activity and of the synapses made on a neuron. Subthreshold membrane polarization is, in turn, a potent modulator of neural responses. The present paper analyzes the subthreshold dynamics of the neural membrane potential driven by synaptic inputs of stationary statistics. Synaptic inputs are considered in linear interaction. The analysis identifies regimes of input statistics which give rise to stationary, fluctuating, oscillatory, and unstable dynamics. In particular, I show that (i) mere noise inputs can drive the membrane potential into sustained, quasiperiodic oscillations (noise-driven oscillations), in the absence of a stimulus-derived, intraneural, or network pacemaker; (ii) adding hyperpolarizing to depolarizing synaptic input can increase neural activity (hyperpolarization-induced activity), in the absence of hyperpolarization-activated currents

Octet magnetic moments and the Coleman-Glashow sum rule violation in the chiral quark model

Baryon octet magnetic moments when calculated within the chiral quark model, incorporating the orbital angular momentum as well as the quark sea contribution through the Cheng-Li mechanism, not only show improvement over the non relativistic quark model results but also gives a non zero value for the right hand side of Coleman-Glashow sum rule. When effects due to spin-spin forces between constituent quarks as well as `mass adjustments' due to confinement are added, it leads to an excellent fit for the case of p, \Sigma^+, \Xi^o and violation of Coleman-Glashow sum rule, whereas in almost all the other cases the results are within 5% of the data.Comment: 5 RevTeX pages, accepted for publication in PRD(Rapid Communication

Parity violating target asymmetry in electron - proton scattering

We analyze the parity-violating (PV) components of the analyzing power in elastic electron-proton scattering and discuss their sensitivity to the strange quark contributions to the proton weak form factors. We point out that the component of the analyzing power along the momentum transfer is independent of the electric weak form factor and thus compares favorably with the PV beam asymmetry for a determination of the strangeness magnetic moment. We also show that the transverse component could be used for constraining the strangeness radius. Finally, we argue that a measurement of both components could give experimental information on the strangeness axial charge.Comment: 24 pages, Latex, 5 eps figures, submitted to Phys.Rev.

Z^* Resonances: Phenomenology and Models

We explore the phenomenology of, and models for, the Z^* resonances, the lowest of which is now well established, and called the Theta. We provide an overview of three models which have been proposed to explain its existence and/or its small width, and point out other relevant predictions, and potential problems, for each. The relation to what is known about KN scattering, including possible resonance signals in other channels, is also discussed.Comment: 29 pages, uses RevTeX4; expanded version (published form

Deuteron Electroweak Disintegration

We study the deuteron electrodisintegration with inclusion of the neutral currents focusing on the helicity asymmetry of the exclusive cross section in coplanar geometry. We stress that a measurement of this asymmetry in the quasi elastic region is of interest for an experimental determination of the weak form factors of the nucleon, allowing one to obtain the parity violating electron neutron asymmetry. Numerically, we consider the reaction at low momentum transfer and discuss the sensitivity of the helicity asymmetry to the strangeness radius and magnetic moment. The problems coming from the finite angular acceptance of the spectrometers are also considered.Comment: 30 pages, Latex, 7 eps figures, submitted to Phys.Rev.C e-mail: [email protected] , [email protected]