1,079,875 research outputs found
On avoiding cosmological oscillating behavior for S-brane solutions with diagonal metrics
In certain string inspired higher dimensional cosmological models it has been
conjectured that there is generic, chaotic oscillating behavior near the
initial singularity -- the Kasner parameters which characterize the asymptotic
form of the metric "jump" between different, locally constant values and
exhibit a never-ending oscillation as one approaches the singularity. In this
paper we investigate a class of cosmological solutions with form fields and
diagonal metrics which have a "maximal" number of composite electric S-branes.
We look at two explicit examples in D=4 and D=5 dimensions that do not have
chaotic oscillating behavior near the singularity. When the composite branes
are replaced by non-composite branes chaotic oscillatingComment: Corrected typos, published in Phys. Rev. D72, 103511 (2005
On the cancellation of 4-derivative terms in the Volkov-Akulov action
Recently Kuzenko and McCarty observed the cancellation of 4-derivative terms
in the Volkov-Akulov supersymmetric action for the fermionic
Nambu-Goldstone field. Here is presented a simple algebraic proof of the
cancellation based on using the Majorana bispinors and Fiertz identities. The
cancellation shows a difference between the Volkov-Akulov action and the
effective superfield action recently studied by Komargodski and Seiberg and
containing one 4-derivative term. We find out that the cancellation effect
takes place in coupling of the Nambu-Goldstone fermion with the Dirac field.
Equivalence between the KS and the VA Lagrangians is proved up to the first
order in the interaction constant of the NG fermions.Comment: 18 pages; the version accepted for publication in Phys. Rev. D; new
section regarding the proof of the equivalence between the
Komargodski-Seiberg and the Volkov-Akulov actions is added: some comments and
new references are include
Anisotropic glass-like properties in tetragonal disordered crystals
The low temperature acoustic and thermal properties of amorphous, glassy
materials are remarkably similar. All these properties are described
theoretically with reasonable quantitative accuracy by assuming that the
amorphous solid contains dynamical defects that can be described at low
temperatures as an ensemble of two-level systems (TLS), but the deep nature of
these TLSs is not clarified yet. Moreover, glassy properties were found also in
disordered crystals, quasicrystals, and even perfect crystals with a large
number of atoms in the unit cell. In crystals, the glassy properties are not
universal, like in amorphous materials, and also exhibit anisotropy. Recently
it was proposed a model for the interaction of two-level systems with arbitrary
strain fields (Phys. Rev. B 75, 64202, 2007), which was used to calculate the
thermal properties of nanoscopic membranes at low temperatures. The model is
also suitable for the description of anisotropic crystals. We describe here the
results of the calculation of anisotropic glass-like properties in crystals of
various lattice symmetries, emphasizing the tetragonal symmetry.Comment: 5 pages, no figure
An infinitesimally nonrigid polyhedron with nonstationary volume in the Lobachevsky 3-space
We give an example of an infinitesimally nonrigid polyhedron in the
Lobachevsky 3-space and construct an infinitesimal flex of that polyhedron such
that the volume of the polyhedron isn't stationary under the flex.Comment: 10 pages, 2 Postscript figure
Resonating-valence-bond structure of Gutzwiller-projected superconducting wave functions
Gutzwiller-projected (GP) wave functions have been widely used for describing
spin-liquid physics in frustrated magnets and in high-temperature
superconductors. Such wave functions are known to represent states of the
resonating-valence-bond (RVB) type. In the present work I discuss the RVB
structure of a GP singlet superconducting state with nodes in the spectrum. The
resulting state for the undoped spin system may be described in terms of the
"path integral" over loop coverings of the lattice, thus extending the known
construction for RVB states. The problem of the topological order in GP states
may be reformulated in terms of the statistical behavior of loops. The simple
example of the projected d-wave state on the square lattice demonstrates that
the statistical behavior of loops is renormalized in a nontrivial manner by the
projection.Comment: 6 pages, 4 figures, some numerical data adde
Hyperbolic Kac-Moody Algebra from Intersecting p-branes
A subclass of recently discovered class of solutions in multidimensional
gravity with intersecting p-branes related to Lie algebras and governed by a
set of harmonic functions is considered. This subclass in case of three
Euclidean p-branes (one electric and two magnetic) contains a cosmological-type
solution (in 11-dimensional model with two 4-forms) related to hyperbolic
Kac-Moody algebra (of rank 3). This solution describes the
non-Kasner power-law inflation.Comment: 15 pages, Latex. A talk presented at the Second Winter School on
Branes, Fields and Math. Phys. (Seoul, Korea). Corrected version. Journ.
ref.: J. Math. Phys., 40, (1999) 4072-4083; Corrigenda to appea
Intrinsic bistability and dual-core dark solitons and vortices in exciton polariton condensates
We investigate a new kind of dark solitons and vortices that can exist in the
exciton-polariton condensates. These structures have discontinuity in the
excitonic part of the polaritonic field and exist due to an intrinsic
multiplicity of the solutions for the exciton density in the given optical
field. Reported solutions are characterized by two very distinct localization
scales, and hence are coined as dual-core dark solitons and vortices
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