Two-pion-exchange parity-violating potential and n⃗p→dγ\vec{n} p \to d \gamma

We calculate the parity-violating nucleon-nucleon potential in heavy-baryon chiral perturbation theory up to the next-to-next-to-leading order. The one-pion exchange comes in the leading order and the next-to-next-to-leading order consists of two-pion-exchange and the two-nucleon contact terms. In order to investigate the effect of the higher order contributions, we calculate the parity-violating asymmetry in $\vec{n} p \to d \gamma$ at the threshold. The one-pion dominates the physical observable and the two-pion contribution is about or less than 10% of the one-pion contribution.Comment: 3 pages, contribution to the workshop PAVI06 held in Milos island, Greece, May 16-20, 200

Renormalization Group Flow Equation at Finite Density

For the linear sigma model with quarks we derive renormalization group flow equations for finite temperature and finite baryon density using the heat kernel cutoff. At zero temperature we evolve the effective potential to the Fermi momentum and compare the solutions of the full evolution equation with those in the mean field approximation. We find a first order phase transition either from a massive constituent quark phase to a mixed phase, where both massive and massless quarks are present, or from a metastable constituent quark phase at low density to a stable massless quark phase at high density. In the latter solution, the formation of droplets of massless quarks is realized even at low density.Comment: 30 pages, 9 figures; typos corrected, section 3 revised, one reference added, two references updated, submitted to Phys. Rev.

Relativistic Attosecond Electron Bunches from Laser-Illuminated Droplets

The generation of relativistic attosecond electron bunches is observed in three-dimensional, relativistic particle-in-cell simulations of the interaction of intense laser light with droplets. The electron bunches are emitted under certain angles which depend on the ratios of droplet radius to wavelength and plasma frequency to laser frequency. The mechanism behind the multi-MeV attosecond electron bunch generation is investigated using Mie theory. It is shown that the angular distribution and the high electron energies are due to a parameter-sensitive, time-dependent local field enhancement at the droplet surface.Comment: 4 pages, 5 figures, REVTeX-styl

Transverse Lattice

The transverse lattice approach to non-perturbative light-front hamiltonian QCD is described. Preliminary results on the pi-rho system are presented, at fixed DLCQ and Tamm-Dancoff cut-offs. A renormalised, approximately Lorentz covariant light-front hamiltonian is found to leading order of the colour-dielectric expansion, compatible with a massless pion. The pi light-front wavefunction is compared with experiment. Exclusive processes agree reasonably well, given the approximations, but inclusive processes, sensitive to higher Fock state structure, still exhibit large cut-off artifacts.Comment: 11 pages, Invited talk at Xth International Light-Cone Meeting on Non-Perturbative QCD and Hadron Phenomenology, Heidelberg 12-17 June 200

Glueball calculations in large-N_c gauge theory

We use the light-front Hamiltonian of transverse lattice gauge theory to compute from first principles the glueball spectrum and light-front wavefunctions in the leading order of the 1/N_c colour expansion. We find 0^{++}, 2^{++}, and 1^{+-} glueballs having masses consistent with N_c=3 data available from Euclidean lattice path integral methods. The wavefunctions exhibit a light-front constituent gluon structure.Comment: 4 pages, 2 figures, uses macro boxedeps.tex, minor corrections in revised versio

Model-independent view on the low-mass proton-antiproton enhancement

We present a simple interpretation of the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.Comment: 10 pages, 2 figure

Classical pion fields in the presence of source

Classical pion field similar to Disoriented Chiral Condensate (DCC) is considered in the presence of the external source. This field is similar to DCC in the sense that its isotopic orientation is specified with a single vector at the whole space. We study the classical field solutions in the nonlinear sigma-model both in the chiral limit with massless pion and for the finite pion mass. In both cases the field resembles the Coulomb field of charged particle however the nonlinear pion interactions lead to the existence of several solutions. In the massless case and for the very small size of the source there is the lot of classical solutions with finite discrete energies. In the more realistic situation of large nucleus (heavy ion) there are no stable solutions of the above type, but there is the possibility for the formation of the quasistationary states. They can live for a long time slowly decaying through the emission of very soft pions. The structure and the energies of these solutions is investigated numerically.Comment: 10 pages, LaTeX, 1 figure, epsfig.sty, corrected typos, added reference

Transverse Lattice Approach to Light-Front Hamiltonian QCD

We describe a non-perturbative procedure for solving from first principles the light-front Hamiltonian problem of SU(N) pure gauge theory in D spacetime dimensions (D>2), based on enforcing Lorentz covariance of observables. A transverse lattice regulator and colour-dielectric link fields are employed, together with an associated effective potential. We argue that the light-front vacuum is necessarily trivial for large enough lattice spacing, and clarify why this leads to an Eguchi-Kawai dimensional reduction of observables to 1+1-dimensions in the infinite N limit. The procedure is then tested by explicit calculations for 2+1-dimensional SU(infinity) gauge theory, within a first approximation to the lattice effective potential. We identify a scaling trajectory which produces Lorentz covariant behaviour for the lightest glueballs. The predicted masses, in units of the measured string tension, are in agreement with recent results from conventional Euclidean lattice simulations. In addition, we obtain the potential between heavy sources and the structure of the glueballs from their light-front wavefunctions. Finally, we briefly discuss the extension of these calculations to 3+1-dimensions.Comment: 55 pages, uses macro boxedeps.tex, minor corrections in revised versio