62,252 research outputs found
Composite electric S-brane solutions with maximal number of branes
In this paper we consider (n+1)-dimensional cosmological model with scalar
field and antisymmetric (p+2)-form. Using an electric composite Sp-brane ansatz
the field equations for the original system reduce to the equations for a
Toda-like system with n(n-1)/2 quadratic constraints on the charge densities.
For certain odd dimensions (D = 4m+1 = 5, 9, 13, ...) and (p+2)-forms (p = 2m-1
= 1, 3, 5, ...) these algebraic constraints can be satisfied with the maximal
number of charged branes ({\it i.e.} all the branes have non-zero charge
densities). These solutions are characterized by self-dual or anti-self-dual
charge density forms Q (of rank 2m). For these algebraic solutions with the
particular D, p, Q and non-exceptional dilatonic coupling constant \lambda we
obtain general cosmological solutions to the field equations and some
properties of these solutions are highlighted (e.g. Kasner-like behavior, the
existence of attractor solutions). We prove the absence of maximal
configurations for p =1 and even D (e.g. for D =10 supergravity models and
those of superstring origin).Comment: 19 pages JHEP format, references adde
Anomalous scaling of passively advected magnetic field in the presence of strong anisotropy
Inertial-range scaling behavior of high-order (up to order N=51) structure
functions of a passively advected vector field has been analyzed in the
framework of the rapid-change model with strong small-scale anisotropy with the
aid of the renormalization group and the operator-product expansion. It has
been shown that in inertial range the leading terms of the structure functions
are coordinate independent, but powerlike corrections appear with the same
anomalous scaling exponents as for the passively advected scalar field. These
exponents depend on anisotropy parameters in such a way that a specific
hierarchy related to the degree of anisotropy is observed. Deviations from
power-law behavior like oscillations or logarithmic behavior in the corrections
to structure functions have not been found.Comment: 15 pages, 18 figure
A study of positive energy condition in Bianchi V spacetimes via Noether symmetries
In this paper we use Noether symmetries of the geodesic Lagrangian in Bianchi
V spacetimes to study various cosmological solutions of Einstein's field
equations. Our first result is the identification of the subalgebras of Noether
symmetries of the equations of motions in such spacetimes with dimension 4, 5,
6, 7, 9 or 10 of the maximal algebra of Lie point symmetries of dimension 13.
Secondly we give physical interpretation of new cosmological solutions which
satisfy positive energy condition and yield critical bounds on the expansion
coefficient , in which the underlying non-flat spacetimes carry
interesting physical properties. Specifically the energy density behaves in one
of the following ways. (i) It is positive and constant for all time. (ii) It
varies with time and attains a global maximum after some time and then
asymptotically converges to zero. (iii) It increases for all time and attains a
maximum value at the asymptotic limit . In particular a
non-flat spacetime is obtained that mimics the expansion in a flat FRW universe
dominated by vacuum energy such that the expansion factor has the same form in
both. However, the energy density is dynamical in the former.Comment: Some typos are corrected. Some considerations into f(R) gravity is
also carried out in the light of obtained results. Accepted for publication
in EPJ
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