11,240 research outputs found
Shear and Vorticity in a Combined Einstein-Cartan-Brans-Dicke Inflationary Lambda-Universe
A combined BCDE (Brans-Dicke and Einstein-Cartan) theory with lambda-term is
developed through Raychaudhuri's equation, for inflationary scenario. It
involves a variable cosmological constant, which decreases with time, jointly
with energy density, cosmic pressure, shear, vorticity, and Hubble's parameter,
while the scale factor, total spin and scalar field increase exponentially. The
post-inflationary fluid resembles a perfect one, though total spin grows, but
the angular speed does not (Berman, 2007d). Keywords: Cosmology; Einstein;
Brans-Dicke; Cosmological term; Shear; Spin; Vorticity; Inflation;
Einstein-Cartan; Torsion. PACS: 04.20.-q ; 98.80.-k ; 98.80.Bp ; 98.80.JkComment: 8 pages including front one. Published versio
A General Relativistic Rotating Evolutionary Universe
We show that when we work with coordinate cosmic time, which is not proper
time, Robertson-Walker's metric, includes a possible rotational state of the
Universe. An exact formula for the angular speed and the temporal metric
coefficient, is found.Comment: 5 pages including front cover. Publishe
Number Partitioning on a Quantum Computer
We present an algorithm to compute the number of solutions of the
(constrained) number partitioning problem. A concrete implementation of the
algorithm on an Ising-type quantum computer is given.Comment: 5 pages, 1 figure, see also
http://rugth30.phys.rug.nl/compphys/qce.ht
Duality orbits of non-geometric fluxes
Compactifications in duality covariant constructions such as generalised
geometry and double field theory have proven to be suitable frameworks to
reproduce gauged supergravities containing non-geometric fluxes. However, it is
a priori unclear whether these approaches only provide a reformulation of old
results, or also contain new physics. To address this question, we classify the
T- and U-duality orbits of gaugings of (half-)maximal supergravities in
dimensions seven and higher. It turns out that all orbits have a geometric
supergravity origin in the maximal case, while there are non-geometric orbits
in the half-maximal case. We show how the latter are obtained from
compactifications of double field theory.Comment: 39 pages, 1 figure, 6 tables; v2: refs added, published versio
On the residual dependence index of elliptical distributions
The residual dependence index of bivariate Gaussian distributions is
determined by the correlation coefficient. This tail index is of certain
statistical importance when extremes and related rare events of bivariate
samples with asymptotic independent components are being modeled. In this paper
we calculate the partial residual dependence indices of a multivariate
elliptical random vector assuming that the associated random radius is in the
Gumbel max-domain of attraction. Furthermore, we discuss the estimation of
these indices when the associated random radius possesses a Weibull-tail
distribution.Comment: 11 pages, case \theta=1 now include
AKSZ constructions for topological membranes on -manifolds
We consider AKSZ constructions of BV actions for closed topological
membranes, and their dimensional reductions to topological string sigma-models.
Two inequivalent AKSZ constructions for topological membranes on
-manifolds are proposed, in each of which the two existing topological
membrane theories appear as different gauge fixed versions. Their dimensional
reductions give new AKSZ constructions for the topological A-model, which on
further dimensional reduction gives an AKSZ formulation of supersymmetric
quantum mechanics. We show that the two AKSZ membrane models originate through
worldvolume dimensional reduction of a single AKSZ threebrane theory, which
gives the standard 2-Courant bracket as the underlying derived bracket. Double
dimensional reduction of the twisted topological threebrane theory on a circle
yields the standard Courant sigma-model for string theory with NS-NS flux.Comment: 36 pages; Final version to be published in Fortschritte der Physi
Quantum breaking time near classical equilibrium points
By using numerical and semiclassical methods, we evaluate the quantum
breaking, or Ehrenfest time for a wave packet localized around classical
equilibrium points of autonomous one-dimensional systems with polynomial
potentials. We find that the Ehrenfest time diverges logarithmically with the
inverse of the Planck constant whenever the equilibrium point is exponentially
unstable. For stable equilibrium points, we have a power law divergence with
exponent determined by the degree of the potential near the equilibrium point.Comment: 4 pages, 5 figure
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