32,959 research outputs found
Structure Functions and Pair Correlations of the Quark-Gluon Plasma
Recent experiments at RHIC and theoretical considerations indicate that the
quark-gluon plasma, present in the fireball of relativistic heavy-ion
collisions, might be in a liquid phase. The liquid state can be identified by
characteristic correlation and structure functions. Here definitions of the
structure functions and pair correlations of the quark-gluon plasma are
presented as well as perturbative results. These definitions might be useful
for verifying the quark-gluon-plasma liquid in QCD lattice calculations.Comment: 9 pages, 1 figure, revised version (new remark on the coupling
parameter on page 2), to be published in Phys. Rev.
Quantum scissors: teleportation of single-mode optical states by means of a nonlocal single photon
We employ the quantum state of a single photon entangled with the vacuum
(|1,0>-|0,1>), generated by a photon incident upon a symmetric beam splitter,
to teleport single-mode quantum states of light by means of the Bennett
protocol. Teleportation of coherent states results in truncation of their Fock
expansion to the first two terms. We analyze the teleported ensembles by means
of homodyne tomography and obtain fidelities of up to 99 per cent for low
source state amplitudes. This work is an experimental realization of the
quantum scissors device proposed by Pegg, Phillips and Barnett (Phys. Rev.
Lett. 81, 1604 (1998)
Percolation-to-hopping crossover in conductor-insulator composites
Here, we show that the conductivity of conductor-insulator composites in
which electrons can tunnel from each conducting particle to all others may
display both percolation and tunneling (i.e. hopping) regimes depending on few
characteristics of the composite. Specifically, we find that the relevant
parameters that give rise to one regime or the other are (where is
the size of the conducting particles and is the tunneling length) and the
specific composite microstructure. For large values of , percolation
arises when the composite microstructure can be modeled as a regular lattice
that is fractionally occupied by conducting particle, while the tunneling
regime is always obtained for equilibrium distributions of conducting particles
in a continuum insulating matrix. As decreases the percolating behavior
of the conductivity of lattice-like composites gradually crosses over to the
tunneling-like regime characterizing particle dispersions in the continuum. For
values lower than the conductivity has tunneling-like
behavior independent of the specific microstructure of the composite.Comment: 8 pages, 5 figure
Current saturation and Coulomb interactions in organic single-crystal transistors
Electronic transport through rubrene single-crystal field effect transistors
(FETs) is investigated experimentally in the high carrier density regime (n ~
0.1 carrier/molecule). In this regime, we find that the current does not
increase linearly with the density of charge carriers, and tends to saturate.
At the same time, the activation energy for transport unexpectedly increases
with increasing n. We perform a theoretical analysis in terms of a well-defined
microscopic model for interacting Frohlich polarons, that quantitatively
accounts for our experimental observations. This work is particularly
significant for our understanding of electronic transport through organic FETs.Comment: Extended version with 1 additional figure and an appendix explaining
the consistency of the theoretical calculatio
Evaluation of a ln tan integral arising in quantum field theory
We analytically evaluate a dilogarithmic integral that is prototypical of
volumes of ideal tetrahedra in hyperbolic geometry. We additionally obtain new
representations of the Clausen function Cl_2 and the Catalan constant
G=Cl_2(\pi/2), as well as new relations between sine and Clausen function
values.Comment: 24 pages, no figure
Responses of the Brans-Dicke field due to gravitational collapses
We study responses of the Brans-Dicke field due to gravitational collapses of
scalar field pulses using numerical simulations. Double-null formalism is
employed to implement the numerical simulations. If we supply a scalar field
pulse, it will asymptotically form a black hole via dynamical interactions of
the Brans-Dicke field. Hence, we can observe the responses of the Brans-Dicke
field by two different regions. First, we observe the late time behaviors after
the gravitational collapse, which include formations of a singularity and an
apparent horizon. Second, we observe the fully dynamical behaviors during the
gravitational collapse and view the energy-momentum tensor components. For the
late time behaviors, if the Brans-Dicke coupling is greater (or smaller) than
-1.5, the Brans-Dicke field decreases (or increases) during the gravitational
collapse. Since the Brans-Dicke field should be relaxed to the asymptotic value
with the elapse of time, the final apparent horizon becomes time-like (or
space-like). For the dynamical behaviors, we observed the energy-momentum
tensors around ~ -1.5. If the Brans-Dicke coupling is greater than
-1.5, the component can be negative at the outside of the black hole.
This can allow an instantaneous inflating region during the gravitational
collapse. If the Brans-Dicke coupling is less than -1.5, the oscillation of the
component allows the apparent horizon to shrink. This allows a
combination that violates weak cosmic censorship. Finally, we discuss the
implications of the violation of the null energy condition and weak cosmic
censorship.Comment: 28 pages, 14 figure
Scaling Behavior of Quasi-One-Dimensional Vortex Avalanches in Superconducting Films
Scaling behaviour of dynamically driven vortex avalanches in superconducting
YBaCuO films deposited on tilted crystalline
substrates has been observed using quantitative magneto-optical imaging. Two
films with different tilt angles are characterized by the probability
distributions of avalanche size in terms of the number of moving vortices. It
is found in both samples that these distributions follow power-laws over up to
three decades, and have exponents ranging between 1.0 and 1.4. The
distributions also show clear finite-size scaling, when the system size is
defined by the depth of the flux penetration front -- a signature of
self-organized criticality. A scaling relation between the avalanche size
exponent and the fractal dimension, previously derived theoretically from
conservation of the number of magnetic vortices in the stationary state and
shown in numerical simulations, is here shown to be satisfied also
experimentally.Comment: 7 pages, 5 figure
- …