332 research outputs found
Stable diquark matter ?
Two-quark correlations ({\it diquarks}) may play an important role in
hadronic physics, particularly near the deconfinement point. This opens the
possibility of a net energy gain by means of a (non-perturbative) quark pairing
effect, perheps up to stabilize diquark droplets. We address in this work the
possibility of a self-bound, stable state of bulk diquark matter.Comment: 10p. PlainTeX, 2 Figures available upon request. IAG-USP Report No 3
Spin structure and longitudinal polarization of hyperon in e+e- annihilation at high energies
Longitudinal polarizations of different kinds of hyperons produced in e+e-
annihilation at LEP I and LEP II energies in different event samples are
calculated using two different pictures for the spin structure of hyperon: that
drawn from polarized deep inelastic lepton-nucleon scattering data or that
using SU(6) symmetric wave functions. The result shows that measurements of
such polarizations should provide useful information to the question of which
picture is more suitable in describing the spin effects in the fragmentation
processes.Comment: 26 pages with 10 figures. Submitted to Phys. Rev.
Second harmonic generation and birefringence of some ternary pnictide semiconductors
A first-principles study of the birefringence and the frequency dependent
second harmonic generation (SHG) coefficients of the ternary pnictide
semiconductors with formula ABC (A = Zn, Cd; B = Si, Ge; C = As, P) with
the chalcopyrite structures was carried out. We show that a simple empirical
observation that a smaller value of the gap is correlated with larger value of
SHG is qualitatively true. However, simple inverse power scaling laws between
gaps and SHG were not found. Instead, the real value of the nonlinear response
is a result of a very delicate balance between different intraband and
interband terms.Comment: 13 pages, 12 figure
How Could the Proton Transversity be Measured
The perspectives of two new nonstandard methods of transversal quark
polarization measurement are considered: the jet handedness and the so-called
"Collins effect" due to spin dependent T-odd fragmentation function responsible
for the left-right asymmetry in fragmenting of transversally polarized quarks.
Recent experimental indications in favor of these effects are observed: 1.The
correlation of the T-odd one-particle fragmentation functions found by DELPHI
in -jet decay. Integrated over the fraction of longitudinal and
transversal momenta, this correlation is of 1.6% order, which means order of
13% for the analyzing power. 2.A rather large () handedness
transversal to the production plane observed in the diffractive production of
() triples from nuclei by the --beam.
It shows a clear dynamic origin and resembles the single spin asymmetry
behavior.
All this makes us hope to use these effects in polarized DIS experiments for
transversity measurement. The first estimation of transversity was done by
using the azimuthal asymmetry in semi-inclusive DIS recently measured by HERMES
and SMC.Comment: 8 pages, Latex, czjphys2.sty. Talk at Int. Workshop "PRAHA-SPIN99",
Prague 6-11 Sept 1999. To appear in Czech.J.Phys Supp
Oscillatory behavior of closed isotropic models in second order gravity theory
Homogeneous and isotropic models are studied in the Jordan frame of the
second order gravity theory. The late time evolution of the models is analysed
with the methods of the dynamical systems. The normal form of the dynamical
system has periodic solutions for a large set of initial conditions. This
implies that an initially expanding closed isotropic universe may exhibit
oscillatory behaviour.Comment: 16 pages, 3 figures. With some minor improvements. To appear in
General Relativity and Gravitatio
A low-lying scalar meson nonet in a unitarized meson model
A unitarized nonrelativistic meson model which is successful for the
description of the heavy and light vector and pseudoscalar mesons yields, in
its extension to the scalar mesons but for the same model parameters, a
complete nonet below 1 GeV. In the unitarization scheme, real and virtual
meson-meson decay channels are coupled to the quark-antiquark confinement
channels. The flavor-dependent harmonic-oscillator confining potential itself
has bound states epsilon(1.3 GeV), S(1.5 GeV), delta(1.3 GeV), kappa(1.4 GeV),
similar to the results of other bound-state qqbar models. However, the full
coupled-channel equations show poles at epsilon(0.5 GeV), S(0.99 GeV),
delta(0.97 GeV), kappa(0.73 GeV). Not only can these pole positions be
calculated in our model, but also cross sections and phase shifts in the
meson-scattering channels, which are in reasonable agreement with the available
data for pion-pion, eta-pion and Kaon-pion in S-wave scattering.Comment: A slightly revised version of Zeitschrift fuer Physik C30, 615 (1986
The Detectability of Departures from the Inflationary Consistency Equation
We study the detectability, given CMB polarization maps, of departures from
the inflationary consistency equation, r \equiv T/S \simeq -5 n_T, where T and
S are the tensor and scalar contributions to the quadrupole variance,
respectively. The consistency equation holds if inflation is driven by a
slowly-rolling scalar field. Departures can be caused by: 1) higher-order terms
in the expansion in slow-roll parameters, 2) quantum loop corrections or 3)
multiple fields. Higher-order corrections in the first two slow-roll parameters
are undetectably small. Loop corrections are detectable if they are nearly
maximal and r \ga 0.1. Large departures (|\Delta n_T| \ga 0.1) can be seen if r
\ga 0.001. High angular resolution can be important for detecting non-zero
r+5n_T, even when not important for detecting non-zero r.Comment: 7 pages, 4 figures, submitted to PR
Search for a strongly decaying neutral charmed pentaquark
We present a search for a charmed pentaquark decaying strongly to
. Finding no evidence for such a state, we set limits on the cross
section times branching ratio relative to and under particular
assumptions about the production mechanism.Comment: To be published in Physics Letters
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