6,099 research outputs found
Tuning High-Harmonic Generation by Controlled Deposition of Ultrathin Ionic Layers on Metal Surfaces
High harmonic generation (HHG) from semiconductors and insulators has become
a very active area of research due to its great potential for developing
compact HHG devices. Here we show that by growing monolayers (ML) of insulators
on single-crystal metal surfaces, one can tune the harmonic spectrum by just
varying the thickness of the ultrathin layer, not the laser properties. This is
shown from numerical solutions of the time-dependent Schr\"odinger equation for
ML NaCl/Cu(111) systems () based on realistic potentials available
in the literature. Remarkably, the harmonic cutoff increases linearly with
and as much as an order of magnitude when going from 1 to 30, while
keeping the laser intensity low and the wavelength in the near-infrared range.
Furthermore, the degree of control that can be achieved in this way is much
higher than by varying the laser intensity. The origin of this behavior is the
reduction of electronic "friction" when moving from the essentially discrete
energy spectrum associated with a few-ML system to the continuous energy
spectrum (bands) inherent to an extended periodic system.Comment: 6 pages, 4 figure
Thin-shell wormholes with charge in F(R) gravity
In this article, we construct a class of constant curvature and spherically
symmetric thin-shell Lorentzian wormholes in F(R) theories of gravity and we
analyze their stability under perturbations preserving the symmetry. We find
that the junction conditions determine the equation of state of the matter at
the throat. As a particular case, we consider configurations with mass and
charge. We obtain that stable static solutions are possible for suitable values
of the parameters of the model.Comment: 10 pages, 2 figures; v2: minor changes, 1 new reference adde
Thin-shell wormholes with a double layer in quadratic F(R) gravity
We present a family of spherically symmetric Lorentzian wormholes in
quadratic F(R) gravity, with a thin shell of matter corresponding to the
throat. At each side of the shell the geometry has a different constant value
of the curvature scalar R. The junction conditions determine the equation of
state between the pressure and energy density at the throat, where a double
layer is also located. We analyze the stability of the configurations under
perturbations preserving the spherical symmetry. In particular, we study
thin-shell wormholes with mass and charge. We find that there exist values of
the parameters for which stable static solutions are possible.Comment: 12 pages, 2 figures; v3: improved version, 1 new reference adde
Runaway dilatonic domain walls
We explore the stability of domain wall and bubble solutions in theories with
compact extra dimensions. The energy density stored inside of the wall can
destabilize the volume modulus of a compactification, leading to solutions
containing either a timelike singularity or a region where space
decompactifies, depending on the metric ansatz. We determine the structure of
such solutions both analytically and using numerical simulations, and analyze
how they arise in compactifications of Einstein--Maxwell theory and Type IIB
string theory. The existence of instabilities has important implications for
the formation of networks of topological defects and the population of vacua
during eternal inflation.Comment: 29 pages with 19 figures. Replaced to match published versio
Grassmanian and Bosonic Thirring Models with Jump Defects
In this paper we discuss the Lax formulation of the Grassmanian and Bosonic
Thirring models in the presence of jump defects. For the Grassmanian case, the
defect is described by B\"acklund transformation which is responsible for
preserving the integrability of the model.
We then propose an extension of the B\"acklund transformation for the Bosonic
Thirring model which is verified by some B\"acklund transitions like
Vacuum-One soliton, One soliton - One soliton, One soliton - Two solitons and
Two solitons - Two solitons. The Lax formulation within the space split by the
defect leads to the integrability of Bosonic Thirring model.Comment: Latex 21 page
Type-II super-Backlund transformation and integrable defects for the N=1 super sinh-Gordon model
A new super-Backlund transformation for the N=1 supersymmetric sinh-Gordon
equation is constructed. Based on this construction we propose a type-II
integrable defect for the supersymmetric sinh-Gordon model consistent with this
new transformation through the Lagrangian formalism. Explicit expressions for
the modified conserved energy, momentum and supercharges are also computed. In
addition, we show for the model that the type-II defect can also been regarded
as a pair of fused defects of a previously introduced type. The explicit
derivation of the associated defect matrices is also presented as a necessary
condition for the integrability of the model.Comment: Latex 31 pages. Version accepted for publicatio
Thirring Model with Jump Defect
The purpose of our work is to extend the formulation of classical affine Toda
Models in the presence of jump defects to pure fermionic Thirring model. As a
first attempt we construct the Lagrangian of the Grassmanian Thirring model
with jump defect (of Backlund type) and present its conserved modified momentum
and energy expressions giving a first indication of its integrability.Comment: Poster contribution to the 5th International School on Field Theory
and Gravitation, Cuiaba, MT, Brazil, 20-24 Apr 2009. to be published in PoS
ISFTG(2009
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