2,406 research outputs found
Dielectric function and plasmons in graphene
The electromagnetic response of graphene, expressed by the dielectric
function, and the spectrum of collective excitations are studied as a function
of wave vector and frequency. Our calculation is based on the full band
structure, calculated within the tight-binding approximation. As a result, we
find plasmons whose dispersion is similar to that obtained in the single-valley
approximation by Dirac fermions. In contrast to the latter, however, we find a
stronger damping of the plasmon modes due to inter-band absorption. Our
calculation also reveals effects due to deviations from the linear Dirac
spectrum as we increase the Fermi energy, indicating an anisotropic behavior
with respect to the wave vector of the external electromagnetic field
Evidence for Hydrodynamic Evolution in Proton-Proton Scattering at LHC Energies
In scattering at LHC energies, large numbers of elementary scatterings
will contribute significantly, and the corresponding high multiplicity events
will be of particular interest. Elementary scatterings are parton ladders,
identified with color flux-tubes. In high multiplicity events, many of these
flux tubes are produced in the same space region, creating high energy
densities. We argue that there are good reasons to employ the successful
procedure used for heavy ion collisions: matter is assumed to thermalizes
quickly, such that the energy from the flux-tubes can be taken as initial
condition for a hydrodynamic expansion. This scenario gets spectacular support
from very recent results on Bose-Einstein correlations in scattering at
900 GeV at LHC.Comment: 11 pages, 20 figure
Mutual synchronization and clustering in randomly coupled chaotic dynamical networks
We introduce and study systems of randomly coupled maps (RCM) where the
relevant parameter is the degree of connectivity in the system. Global
(almost-) synchronized states are found (equivalent to the synchronization
observed in globally coupled maps) until a certain critical threshold for the
connectivity is reached. We further show that not only the average
connectivity, but also the architecture of the couplings is responsible for the
cluster structure observed. We analyse the different phases of the system and
use various correlation measures in order to detect ordered non-synchronized
states. Finally, it is shown that the system displays a dynamical hierarchical
clustering which allows the definition of emerging graphs.Comment: 13 pages, to appear in Phys. Rev.
Ultimate photo-induced Kerr rotation achieved in semiconductor microcavities
Photoinduced Kerr rotation by more than radians is demonstrated in
planar quantum well microcavity in the strong coupling regime. This result is
close to the predicted theoretical maximum of . It is achieved by
engineering microcavity parameters such that the optical impedance matching
condition is reached at the smallest negative detuning between exciton
resonance and the cavity mode. This ensures the optimum combination of the
exciton induced optical non-linearity and the enhancement of the Kerr angle by
the cavity. Comprehensive analysis of the polarization state of the light in
this regime shows that both renormalization of the exciton energy and the
saturation of the excitonic resonance contribute to the observed optical
nonlinearities.Comment: Shortened version prepared to submit in Phys. Rev. Letter
Spiral Waves in Chaotic Systems
Spiral waves are investigated in chemical systems whose underlying
spatially-homogeneous dynamics is governed by a deterministic chaotic
attractor. We show how the local periodic behavior in the vicinity of a spiral
defect is transformed to chaotic dynamics far from the defect. The
transformation occurs by a type of period doubling as the distance from the
defect increases. The change in character of the dynamics is described in terms
of the phase space flow on closed curves surrounding the defect.Comment: latex file with three postscript figures to appear in Physical review
Letter
Gauge-invariant quark-antiquark nonlocal condensates in lattice QCD
We study, by numerical simulations on a lattice, the behaviour of the
gauge-invariant quark-antiquark nonlocal condensates in the QCD vacuum with
dynamical fermions. A determination is also done in the quenched approximation
and the results are compared with the full-QCD case. The fermionic correlation
length is extracted and compared with the analogous gluonic quantity.Comment: 14 pages, LaTeX file, + 6 PS figure
A multiloop improvement of non-singlet QCD evolution equations
An approach is elaborated for calculation of "all loop" contributions to the
non-singlet evolution kernels from the diagrams with renormalon chain
insertions. Closed expressions are obtained for sums of contributions to
kernels for the DGLAP equation and for the "nonforward" ER-BL
equation from these diagrams that dominate for a large value of , the
first -function coefficient. Calculations are performed in the covariant
-gauge in a MS-like scheme. It is established that a special choice of the
gauge parameter generalizes the standard "naive nonabelianization"
approximation. The solutions are obtained to the ER-BL evolution equation
(taken at the "all loop" improved kernel), which are in form similar to
one-loop solutions. A consequence for QCD descriptions of hard processes and
the benefits and incompleteness of the approach are briefly discussed.Comment: 13 pages, revtex, 2 figures are enclosed as eps-file, the text style
and figures are corrected following version, accepted for publication to
Phys. Rev.
The AdS(5)xS(5) Semi-Symmetric Space Sine-Gordon Theory
The generalized symmetric space sine-Gordon theories are a series of
1+1-integrable field theories that are classically equivalent to superstrings
on symmetric space spacetimes F/G. They are formulated in terms of a
semi-symmetric space as a gauged WZW model with fermions and a potential term
to deform it away from the conformal fixed point. We consider in particular the
case of PSU(2,2|4)/Sp(2,2)xSp(4) which corresponds to AdS(5)xS(5). We argue
that the infinite tower of conserved charges of these theories includes an
exotic N=(8,8) supersymmetry that is realized in a mildy non-local way at the
Lagrangian level. The supersymmetry is associated to a double central extension
of the superalgebra psu(2|2)+psu(2|2) and includes a non-trivial R symmetry
algebra corresponding to global gauge transformations, as well as 2-dimensional
spacetime translations. We then explicitly construct soliton solutions and show
that they carry an internal moduli superspace CP(2|1)xCP(2|1) with both bosonic
and Grassmann collective coordinates. We show how to semi-classical quantize
the solitons by writing an effective quantum mechanical system on the moduli
space which takes the form of a co-adjoint orbit of SU(2|2)xSU(2|2). The
spectrum consists of a tower of massive states in the short, or atypical,
symmetric representations, just as the giant magnon states of the string world
sheet theory, although here the tower is truncated.Comment: 39 pages, references adde
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