391 research outputs found
J/psi dissociation by light mesons in an extended Nambu Jona-Lasinio model
An alternative model for the dissociation of the J/psi is proposed. Chiral
symmetry is properly implemented. Abnormal parity interactions and mesonic form
factors naturally arise from the underlying quark sub-structure. Analytic
confinement for the light quarks is generated by appropriately chosen the quark
interaction kernels. Dissociation cross sections of the J/psi by either a pion
or a rho meson are then evaluated and discussed.Comment: 24 pages, 13 figures, final versio
Gauge invariance in two-particle scattering
It is shown how gauge invariance is obtained for the coupling of a photon to
a two-body state described by the solution of the Bethe-Salpeter equation. This
is illustrated both for a complex scalar field theory and for interaction
kernels derived from chiral effective Lagrangians.Comment: 16 pages, 2 figures, references added and commented o
Electromagnetic Vacuum of Complex Media: Dipole Emission vs. Light Propagation, Vacuum Energy, and Local Field Factors
We offer a unified approach to several phenomena related to the
electromagnetic vacuum of a complex medium made of point electric dipoles. To
this aim, we apply the linear response theory to the computation of the
polarization field propagator and study the spectrum of vacuum fluctuations.
The physical distinction among the local density of states which enter the
spectra of light propagation, total dipole emission, coherent emission, total
vacuum energy and Schwinger-bulk energy is made clear. Analytical expressions
for the spectrum of dipole emission and for the vacuum energy are derived.
Their respective relations with the spectrum of external light and with the
Schwinger-bulk energy are found. The light spectrum and the Schwinger-bulk
energy are determined by the Dyson propagator. The emission spectrum and the
total vacuum energy are determined by the polarization propagator. An exact
relationship of proportionality between both propagators is found in terms of
local field factors. A study of the nature of stimulated emission from a single
dipole is carried out. Regarding coherent emission, it contains two components.
A direct one which is transferred radiatively and directly from the emitter
into the medium and whose spectrum is that of external light. And an indirect
one which is radiated by induced dipoles. The induction is mediated by one (and
only one) local field factor. Regarding the vacuum energy, we find that in
addition to the Schwinger-bulk energy the vacuum energy of an effective medium
contains local field contributions proportional to the resonant frequency and
to the spectral line-width.Comment: Typos fixed, journal ref. adde
Multi-Scaling of Correlation Functions in Single Species Reaction-Diffusion Systems
We derive the multi-fractal scaling of probability distributions of
multi-particle configurations for the binary reaction-diffusion system in and for the ternary system in
. For the binary reaction we find that the probability of finding particles in a fixed volume element at time
decays in the limit of large time as for and
t^{-Nd/2}t^{-\frac{N(N-1)\epsilon}{4}+\mathcal{O}(\ep^2)} for . Here
\ep=2-d. For the ternary reaction in one dimension we find that
. The principal tool of our study is the dynamical
renormalization group. We compare predictions of \ep-expansions for
for binary reaction in one dimension against exact known
results. We conclude that the \ep-corrections of order two and higher are
absent in the above answer for for .
Furthermore we conjecture the absence of \ep^2-corrections for all values of
.Comment: 10 pages, 6 figure
Transport properties of a periodically driven superconducting single electron transistor
We discuss coherent transport of Cooper pairs through a Cooper pair shuttle.
We analyze both the DC and AC Josephson effect in the two limiting cases where
the charging energy is either much larger or much smaller than the
Josephson coupling . In the limit we present the detailed
behavior of the critical current as a function of the damping rates and the
dynamical phases. The AC effect in this regime is very sensitive to all
dynamical scales present in the problem. The effect of fluctuations of the
external periodic driving is discussed as well. In the opposite regime the
system can be mapped onto the quantum kicked rotator, a classically chaotic
system. We investigate the transport properties also in this regime showing
that the underlying classical chaotic dynamics emerges as an incoherent
transfer of Cooper pairs through the shuttle. For an appropriate choice of the
parameters the Cooper pair shuttle can exhibit the phenomenon of dynamical
localization. We discuss in details the properties of the localized regime as a
function of the phase difference between the superconducting electrodes and the
decoherence due to gate voltage fluctuations. Finally we point how dynamical
localization is reflected in the noise properties of the shuttle.Comment: 22 pages, 7 figures; v3 (published version): added references,
improved readabilit
Effects of technicolor on standard model running couplings
We discuss the running couplings in the standard model, SU(3SU(2U(1, when the Higgs sector is replaced by SU(
technicolor. Particular attention is given to the running of the couplings at
momentum scales where technicolor is nonperturbative, and in this region we
apply a relativistic constituent technifermion model. This model has been
tested against the known running of the QED coupling due to nonperturbative
QCD. An understanding of this low momentum running allows the calculation of
the couplings at a higher scale, , where technicolor becomes
perturbative. We provide numerical values for the changes in the three standard
model couplings between and due to technicolor, assuming
separately ``one doublet'' and ``one family'' technicolor models. The
distinction between a running and walking technicolor coupling is also
considered.Comment: 14 pages of LaTeX, UTPT-94-
New Physics and the Landau Pole
In scalar field theories the Landau pole is an ultraviolet singularity in the
running coupling constant that indicates a mass scale at which the theory
breaks down and new physics must intervene. However, new physics at the pole
will in general affect the running of the low energy coupling constant, which
will in turn affect the location of the pole and the related upper limit
(``triviality'' bound) on the low energy coupling constant. If the new physics
is strongly coupled to the scalar fields these effects can be significant even
though they are power suppressed. We explore the possible range of such effects
by deriving the one loop renormalization group equations for an effective
scalar field theory with a dimension 6 operator representing the low energy
effects of the new physics. As an independent check we also consider a
renormalizable model of the high-scale physics constructed so that its low
energy limit coincides with the effective theory.Comment: 26 pages, 5 figure
Exact steady-state velocity of ratchets driven by random sequential adsorption
We solve the problem of discrete translocation of a polymer through a pore,
driven by the irreversible, random sequential adsorption of particles on one
side of the pore. Although the kinetics of the wall motion and the deposition
are coupled, we find the exact steady-state distribution for the gap between
the wall and the nearest deposited particle. This result enables us to
construct the mean translocation velocity demonstrating that translocation is
faster when the adsorbing particles are smaller. Monte-Carlo simulations also
show that smaller particles gives less dispersion in the ratcheted motion. We
also define and compare the relative efficiencies of ratcheting by deposition
of particles with different sizes and we describe an associated
"zone-refinement" process.Comment: 11 pages, 4 figures New asymptotic result for low chaperone density
added. Exact translocation velocity is proportional to (chaperone
density)^(1/3
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