4,206 research outputs found
A brief review of "little string theories"
This is a brief review of the current state of knowledge on "little string
theories", which are non-gravitational theories having several string-like
properties. We focus on the six dimensional maximally supersymmetric "little
string theories" and describe their definition, some of their simple
properties, the motivations for studying them, the DLCQ and holographic
constructions of these theories and their behaviour at finite energy density.
(Contribution to the proceedings of Strings '99 in Potsdam, Germany.)Comment: 11 pages, contribution to Strings '99 proceeding
On the theory of phase transition in muliferroics
In this paper we investigate peculiarities of phase transition high-symmetry
- incommensurate phase in inhomogeneous systems. We obtain the nonlinear
dispersion law and then present a renormalization group analysis of phase
transitions in multiferroics. We have determined the dependence of critical
indices on the nonextensivity parameter of the system
Percolation in high dimensions is not understood
The number of spanning clusters in four to nine dimensions does not fully
follow the expected size dependence for random percolation.Comment: 9-dimensional data and more points for large lattices added;
statistics improved, text expanded, table of exponents inserte
Noncommutative instantons revisited
We find a new gauge in which U(1) noncommutative instantons are explicitly
non-singular on the whole noncommutative R^4, thus resolving the previous
confusions of the author. We start with the pedagogical introduction to the
noncommutative gauge theories.Comment: 24pp. uses sprocl.st
Transport through molecular junctions with a nonequilibrium phonon population
The calculation of the nonlinear conductance of a single-molecule junction is
revisited. The self energy on the junction resulting from the electron-phonon
interaction has at low temperatures logarithmic singularities (in the real
part) and discontinuities (in the imaginary one) at the frequencies
corresponding to the opening of the inelastic channels. These singularities
generate discontinuities and logarithmic divergences (as a function of the bias
voltage) in the low-temperature differential conductance around the inelastic
thresholds. The self energy also depends on the population of the vibrational
modes. The case of a vibrating free junction (not coupled to a thermal bath),
where the phonon population is determined by the bias voltage is examined. We
compare the resulting zero-temperature differential conductance with the one
obtained for equilibrated phonons, and find that the difference is larger the
larger is the bare transmission of the junction and the product of the electron
dwell time on the junction with the phonon frequency.Comment: 4 page
Stable Non-Supersymmetric Supergravity Solutions from Deformations of the Maldacena-Nunez Background
We study a deformation of the type IIB Maldacena-Nunez background which
arises as the near-horizon limit of NS5 branes wrapped on a two-cycle. This
background is dual to a "little string theory" compactified on a two-sphere, a
theory which at low energies includes four-dimensional N = 1 super Yang-Mills
theory. The deformation we study corresponds to a mass term for some of the
scalar fields in this theory, and it breaks supersymmetry completely. In the
language of seven-dimensional SO(4) gauged supergravity the deformation
involves (at leading order) giving a VEV, depending only on the radial
coordinate, to a particular scalar field. We explicitly construct the
corresponding solution at leading order in the deformation, both in
seven-dimensional and in ten-dimensional supergravity, and we verify that it
completely breaks supersymmetry. Since the original background had a mass gap
and we are performing a small deformation, the deformed background is
guaranteed to be stable even though it is not supersymmetric.Comment: 1+31 pages, one figure. v2: minor clarifications, refs adde
Two-dimensional Site-Bond Percolation as an Example of Self-Averaging System
The Harris-Aharony criterion for a statistical model predicts, that if a
specific heat exponent , then this model does not exhibit
self-averaging. In two-dimensional percolation model the index .
It means that, in accordance with the Harris-Aharony criterion, the model can
exhibit self-averaging properties. We study numerically the relative variances
and for the probability of a site belongin to the
"infinite" (maximum) cluster and the mean finite cluster size . It was
shown, that two-dimensional site-bound percolation on the square lattice, where
the bonds play the role of impurity and the sites play the role of the
statistical ensemble, over which the averaging is performed, exhibits
self-averaging properties.Comment: 15 pages, 5 figure
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