Absence of evidence for pentaquarks on the lattice

We study the question of whether or not QCD predicts a pentaquark state. We use the improved, fixed point lattice QCD action which has very little sensitivity to the lattice spacing and also allows us to reach light quark masses. The analysis was performed on a single volume of size $(1.8 {\rm fm})^3\times 3.6 {\rm fm}$ with lattice spacing of $a=0.102$ fm. We use the correlation matrix method to identify the ground and excited states in the isospin 0, negative parity channel. In the quenched approximation where dynamical quark effects are omitted, we do not find any evidence for a pentaquark resonance in QCD.Comment: 17 pages, 5 figures replaced with revised versio

On interlay between the magnetic susceptibilities of localized and itinerant electrons in hole-doped HTSCs

In the framework of the singlet-correlated motion of holes over oxygen sites in CuO 2 layers, a formula for the dynamic spin susceptibility has been derived taking into account the strong correlation between the magnetizations of the spins of the collective holes and localized moments on copper sites. The calculated behavior of the imaginary part of the susceptibility as a function of the frequency and wave vector is consistent with the available experimental data on the inelastic neutron scattering. The plot of the dispersion of the collective spin modes over the entire Brillouin zone is proposed. © Nauka/Interperiodica 2006

Dynamic spin susceptibility of hole-doped high-temperature superconductors in a singlet-correlated conduction band model

We have derived an expression for the dynamical spin susceptibility of a hole-doped high-temperature superconductor taking into account a strong correlation between the magnetization of spins of the localized and itinerant electrons. This formula has been used to calculate the imaginary part of the susceptibility as a function of the frequency and wave vector. The results are compared to experimental data on the inelastic neutron scattering in compounds of the YBa2Cu3O6+y type. A peak in the scattering intensity observed at an energy of about 40 meV in the region of wave vectors Q = (π, π) and an arc-shaped dispersion relief are interpreted as manifestations of the collective spin excitations in the system, the energy of which falls within a superconducting gap (spin exciton). The U-shaped divergent relief observed in the neutron scattering intensity is assigned to collective short-rage-order spin oscillations. © 2008 Pleiades Publishing, Ltd

Photoproduction of the Theta^+ and its vector and axial-vector structure

We present recent investigations on the vector and axial-vector transitions of the baryon antidecuplet within the framework of the self-consistent SU(3) chiral quark-soliton model, taking into account the 1/N_c rotational and linear m_s corrections. The main contribution to the electric-like transition form factor comes from the wave-function corrections. This is a consequence of the generalized Ademollo-Gatto theorem. It is also found that in general the leading-order contributions are almost canceled by the rotational 1/N_c corrections. The results are summarized as follows: the vector and tensor K^*-N-Theta coupling constants, g_{K^*-N-Theta}=0.74 - 0.87 and f_{K^*-N-Theta}=0.53 - 1.16, respectively, and Gamma_{Theta->KN}=0.71 MeV, based on the result of the K-N-Theta coupling constant g_{K-n-Theta}=0.83. We also show the differential cross sections and beam asymmetries, based on the present results. We also discuss the connection of present results with the original work by Diakonov, Petrov, and Polyakov.Comment: 9 pages, 6 figures, An invited talk given at the Workshop of Excited Nucleon - NSTAR2009 held in Beijing, April 19-22 200

Dielectric response function in t- J- V model

The dielectric response function ε{lunate} ( q, ω ) has been derived in the frame t - J - V model. In addition to the acoustic plasmon modes, a new collective charge excitation mode has been found. We have shown, that in layered cuprates the inverse dielectric function 1 / ε{lunate} ( q, ω ) may be negative in the area which partially overlaps the Fermi surface. Then, the interaction of quasiparticles via plasmon field causes the higher order harmonics in dx2 - y2-wave symmetry of the superconducting gap driven mainly by the superexchange interaction. © 2006 Elsevier B.V. All rights reserved

Positive parity pentaquark towers in large Nc QCD

We construct the complete set of positive parity pentaquarks, which correspond in the quark model to {\bar s} q^{Nc+1} states with one unit of orbital angular momentum L=1. In the large Nc limit they fall into the K=1/2 and K=3/2 irreps (towers) of the contracted SU(4)c symmetry. We derive predictions for the mass spectrum and the axial couplings of these states at leading order in 1/Nc. The strong decay width of the lowest-lying positive parity exotic state is of order O(1/Nc), such that this state is narrow in the large Nc limit. Replacing the antiquark with a heavy antiquark {\bar Q} q^{Nc+1}, the two towers become degenerate, split only by O(1/mQ) hyperfine interactions. We obtain predictions for the strong decay widths of heavy pentaquarks to ordinary baryons and heavy H(*)_{\bar Q} mesons at leading order in 1/Nc and 1/mQ.Comment: 21 pages, 2 figures, 5 table

Beyond CP violation: hadronic physics at BaBar

I report on recent studies of hadronic physics performed by the BaBar Collaboration. Emphasis is given to the measurement of the properties of newly discovered charmed hadrons and to the searches for light and heavy pentaquarks.Comment: 14 pages, 20 postscript figues, contributed to the Proceedings of the First APS Topical Group Meeting on Hadron Physics, Fermilab, Batavia, IL (October 24-26, 2004

Evolution of microstructure in advanced ferritic-martensitic steels under irradiation : the origin of low temperature radiation embrittlement

Advanced reduced activation ferritic/martensitic steels and oxide dispersion-strengthened steels exhibit significant radiation embrittlement under low temperature neutron irradiation. In this study we focused on atom probe tomography (APT) of Eurofer97 and ODS Eurofer steels irradiated with neutrons and heavy ions at low temperatures. Previous TEM studies revealed dislocation loops in the neutron-irradiated f\m steels. At the same time, our APT showed early stages of solid solution decomposition. High density (10$^{24}$ m$^{-3}$) of ∼3–5 nm clusters enriched in chromium, manganese, and silicon atoms were found in Eurofer 97 irradiated in BOR-60 reactor to 32 dpa at 332°C. In this steel irradiated with Fe ions up to the dose of 24 dpa, pair correlation functions calculated using APT data showed the presence of Cr-enriched pre-phases. APT study of ODS Eurofer found a significant change in the nanocluster composition after neutron irradiation to 32 dpa at 330 °C and an increase in cluster number density. APT of ODS steels irradiated with Fe ions at low temperatures revealed similar changes in nanoclusters. These results suggest that irradiation-induced nucleation and evolution of very small precipitates may be the origin of low temperature radiation embrittlement of f\m steels

Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production

We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The observed structure may be due to the interference between a strange (or anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L) photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log likelihood ratio of the resonant signal+background hypothesis and the phi-production based background only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1 table added, revise