141 research outputs found
Two-pion-exchange parity-violating potential and
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 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
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
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.
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
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