516 research outputs found

### Brane-Induced Gravity's Shocks

We construct exact gravitational field solutions for a relativistic particle
localized on a tensional brane in brane-induced gravity. They are a
generalization of gravitational shock waves in 4D de Sitter space. We provide
the metrics for both the normal branch and the self-inflating branch DGP
braneworlds, and compare them to the 4D Einstein gravity solution and to the
case when gravity resides only in the 5D bulk, without any brane-localized
curvature terms. At short distances the wave profile looks the same as in four
dimensions. The corrections appear only far from the source, where they differ
from the long distance corrections in 4D de Sitter space. We also discover a
new non-perturbative channel for energy emission into the bulk from the
self-inflating branch, when gravity is modified at the de Sitter radius.Comment: 4 pages, revtex4; v4: a sign error corrected; the correction
tantamount to swapping normal and self-inflating branch solutions; the only
significant change is that the spectacular new instability is on the
self-inflating branch in the limit of vanishing brane tension; more details
available in hep-th/050203

### Electronic structure and optical properties of quantum confined lead-salt nanowires

In the framework of four-band envelope-function formalism, developed earlier
for spherical semiconductor nanocrystals, we study the electronic structure and
optical properties of quantum-confined lead-salt (PbSe and PbS) nanowires (NWs)
with a strong coupling between the conduction and the valence bands. We derive
spatial quantization equations, and calculate numerically energy levels of
spatially quantized states of a transverse electron motion in the plane
perpendicular to the NW axis, and electronic subbands developed due to a free
longitudinal motion along the NW axis. Using explicit expressions for
eigenfunctions of the electronic states, we also derive analytical expressions
for matrix elements of optical transitions and study selection rules for
interband absorption.
Next we study a two-particle problem with a conventional long-range Coulomb
interaction and an interparticle coupling via medium polarization. The obtained
results show that due to a large magnitude of the high-frequency dielectric
permittivity of PbSe material, and hence, a high dielectric NW/vacuum contrast,
the effective coupling via medium polarization significantly exceeds the
effective direct Coulomb coupling at all interparticle separations along the NW
axis. Furthermore, the strong coupling via medium polarization results in a
bound state of the longitudinal motion of the lowest-energy electron-hole pair
(a longitudinal exciton), while fast transverse motions of charge carriers
remain independent of each other.Comment: Some misprints and mistakes are correcte

### The Biedenharn Approach to Relativistic Coulomb-type Problems

The approach developped by Biedeharn in the sixties for the relativistic
Coulomb problem is reviewed and applied to various physical problems.Comment: 16 pages, 4 figure

### Excitonic gap, phase transition, and quantum Hall effect in graphene

We suggest that physics underlying the recently observed removal of
sublattice and spin degeneracies in graphene in a strong magnetic field
describes a phase transition connected with the generation of an excitonic gap.
The experimental form of the Hall conductivity is reproduced and the main
characteristics of the dynamics are described. Predictions of the behavior of
the gap as a function of temperature and a gate voltage are made.Comment: Revtex4, 10 pages, 4 figures, text essentially extended, one figure
and references added; v3: to match PRB versio

### Energy flow of moving dissipative topological solitons

We study the energy flow due to the motion of topological solitons in
nonlinear extended systems in the presence of damping and driving. The total
field momentum contribution to the energy flux, which reduces the soliton
motion to that of a point particle, is insufficient. We identify an additional
exchange energy flux channel mediated by the spatial and temporal inhomogeneity
of the system state. In the well-known case of a DC external force the
corresponding exchange current is shown to be small but non-zero. For the case
of AC driving forces, which lead to a soliton ratchet, the exchange energy flux
mediates the complete energy flow of the system. We also consider the case of
combination of AC and DC external forces, as well as spatial discretization
effects.Comment: 24 pages, 5 figures, submitted to Chao

### Magnetopolaronic effects in electron transport through a single-level vibrating quantum dot

Magneto-polaronic effects are considered in electron transport through a
single-level vibrating quantum dot subjected to a transverse (to the current
flow) magnetic field. It is shown that the effects are most pronounced in the
regime of sequential electron tunneling, where a polaronic blockade of the
current at low temperatures and an anomalous temperature dependence of the
magnetoconductance are predicted. In contrast, for resonant tunneling of
polarons the peak conductance is not affected by the magnetic field.Comment: 7 pages, 2 figure

### The Fate of the Initial State Fluctuations in Heavy Ion Collisions. III The Second Act of Hydrodynamics

Hydrodynamical description of the "Little Bang" in heavy ion collisions is
surprisingly successful, mostly due to the very small viscosity of the
Quark-Gluon plasma. In this paper we systematically study the propagation of
small perturbations, also treated hydrodynamically. We start with a number of
known techniques allowing for analytic calculation of the propagation of small
perturbations on top of the expanding fireball. The simplest approximation is
the "geometric acoustics", which substitutes the wave equation by mechanical
equations for the propagating "phonons". Next we turn to the case in which
variables can be separated, in which case one can obtain not only the eikonal
phases but also amplitudes of the perturbation. Finally, we focus on the so
called Gubser flow, a particular conformal analytic solution for the fireball
expansion, on top of which one can derive closed equations for small
perturbations. Perfect hydrodynamics allows all variables to be separated and
all equations to be solved in terms of known special functions. We can thus
collect the analytical expression for all the harmonics and reconstruct the
complete Green function of the problem. In the viscous case the equations still
allow for variable separation, but one of the equations has to be solved
numerically. We still can collect all the harmonics and show real-time
perturbation evolution, observing viscosity-induced changes in the spectra and
the correlation functions of secondaries. We end up by comparing the calculated
angular shape of the correlation function to the STAR experimental data, and
find, for sufficiently large viscosity, a surprisingly good agreement.Comment: The paper was changed after PRC referee report. It was resubmitted in
this for

### Electric excitation of spin resonance in antiferromagnetic conductors

Antiferromagnetism couples electron spin to its orbital motion, thus allowing
excitation of electron-spin transitions by an ac electric rather than magnetic
field - with absorption, exceeding that of common electron spin resonance at
least by four orders of magnitude. In addition to potential applications in
spin electronics, this phenomenon may be used as a spectroscopy to study
antiferromagnetic materials of interest - from chromium to borocarbides,
cuprates, iron pnictides, and organic and heavy fermion conductors.Comment: the journal print versio

### Normal ground state of dense relativistic matter in a magnetic field

The properties of the ground state of relativistic matter in a magnetic field
are examined within the framework of a Nambu-Jona-Lasinio model. The main
emphasis of this study is the normal ground state, which is realized at
sufficiently high temperatures and/or sufficiently large chemical potentials.
In contrast to the vacuum state, which is characterized by the magnetic
catalysis of chiral symmetry breaking, the normal state is accompanied by the
dynamical generation of the chiral shift parameter $\Delta$. In the chiral
limit, the value of $\Delta$ determines a relative shift of the longitudinal
momenta (along the direction of the magnetic field) in the dispersion relations
of opposite chirality fermions. We argue that the chirality remains a good
approximate quantum number even for massive fermions in the vicinity of the
Fermi surface and, therefore, the chiral shift is expected to play an important
role in many types of cold dense relativistic matter, relevant for applications
in compact stars. The qualitative implications of the revealed structure of the
normal ground state on the physics of protoneutron stars are discussed. A
noticeable feature of the $\Delta$ parameter is that it is insensitive to
temperature when $T \ll \mu_0$, where $\mu_0$ is the chemical potential, and
{\it increases} with temperature for $T > \mu_0$. The latter implies that the
chiral shift parameter is also generated in the regime relevant for heavy ion
collisions.Comment: 28 pages, 6 figures; v2: title changed in journa

### Non-Perturbative One-Loop Effective Action for Electrodynamics in Curved Spacetime

In this paper we explicitly evaluate the one-loop effective action in four
dimensions for scalar and spinor fields under the influence of a strong,
covariantly constant, magnetic field in curved spacetime. In the framework of
zeta function regularization, we find the one-loop effective action to all
orders in the magnetic field up to linear terms in the Riemannian curvature. As
a particular case, we also obtain the one-loop effective action for massless
scalar and spinor fields. In this setting, we found that the vacuum energy of
charged spinors with small mass becomes very large due entirely by the
gravitational correction.Comment: LaTeX, 23 page

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