17,583 research outputs found
Integrability of generalized (matrix) Ernst equations in string theory
The integrability structures of the matrix generalizations of the Ernst
equation for Hermitian or complex symmetric -matrix Ernst potentials
are elucidated. These equations arise in the string theory as the equations of
motion for a truncated bosonic parts of the low-energy effective action
respectively for a dilaton and - matrix of moduli fields or for a
string gravity model with a scalar (dilaton) field, U(1) gauge vector field and
an antisymmetric 3-form field, all depending on two space-time coordinates
only. We construct the corresponding spectral problems based on the
overdetermined -linear systems with a spectral parameter and the
universal (i.e. solution independent) structures of the canonical Jordan forms
of their matrix coefficients. The additionally imposed conditions of existence
for each of these systems of two matrix integrals with appropriate symmetries
provide a specific (coset) structures of the related matrix variables. An
equivalence of these spectral problems to the original field equations is
proved and some approach for construction of multiparametric families of their
solutions is envisaged.Comment: 15 pages, no figures, LaTeX; based on the talk given at the Workshop
``Nonlinear Physics: Theory and Experiment. III'', 24 June - 3 July 2004,
Gallipoli (Lecce), Italy. Minor typos, language and references corrections.
To be published in the proceedings in Theor. Math. Phy
Parallel density matrix propagation in spin dynamics simulations
Several methods for density matrix propagation in distributed computing
environments, such as clusters and graphics processing units, are proposed and
evaluated. It is demonstrated that the large communication overhead associated
with each propagation step (two-sided multiplication of the density matrix by
an exponential propagator and its conjugate) may be avoided and the simulation
recast in a form that requires virtually no inter-thread communication. Good
scaling is demonstrated on a 128-core (16 nodes, 8 cores each) cluster.Comment: Submitted for publicatio
Process studies in the hydro- and geosphere of the tropical/subtropical North Atlantic Cruise No. 04 December 03, – April 03, 2006/2007, Fort de France (Martinique) – Las Palmas (Spain)
MEXIT: Maximal un-coupling times for stochastic processes
Classical coupling constructions arrange for copies of the \emph{same} Markov
process started at two \emph{different} initial states to become equal as soon
as possible. In this paper, we consider an alternative coupling framework in
which one seeks to arrange for two \emph{different} Markov (or other
stochastic) processes to remain equal for as long as possible, when started in
the \emph{same} state. We refer to this "un-coupling" or "maximal agreement"
construction as \emph{MEXIT}, standing for "maximal exit". After highlighting
the importance of un-coupling arguments in a few key statistical and
probabilistic settings, we develop an explicit \MEXIT construction for
stochastic processes in discrete time with countable state-space. This
construction is generalized to random processes on general state-space running
in continuous time, and then exemplified by discussion of \MEXIT for Brownian
motions with two different constant drifts.Comment: 28 page
The Post-Newtonian Approximation of the Rigidly Rotating Disc of Dust to Arbitrary Order
Using the analytic, global solution for the rigidly rotating disc of dust as
a starting point, an iteration scheme is presented for the calculation of an
arbitrary coefficient in the post-Newtonian (PN) approximation of this
solution. The coefficients were explicitly calculated up to the 12th PN level
and are listed in this paper up to the 4th PN level. The convergence of the
series is discussed and the approximation is found to be reliable even in
highly relativistic cases. Finally, the ergospheres are calculated at
increasing orders of the approximation and for increasingly relativistic
situations.Comment: 19 pages, 2 tables, 4 figures Accepted for publication in Phys. Rev.
The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
For extrasolar planets discovered using the radial velocity method, the
spectral characterization of the host star leads to a mass-estimate of the star
and subsequently of the orbiting planet. In contrast, if also the orbital
velocity of the planet would be known, the masses of both star and planet could
be determined directly using Newton's law of gravity, just as in the case of
stellar double-line eclipsing binaries. Here we report on the detection of the
orbital velocity of extrasolar planet HD209458b. High dispersion ground-based
spectroscopy during a transit of this planet reveals absorption lines from
carbon monoxide produced in the planet atmosphere, which shift significantly in
wavelength due to the change in the radial component of the planet orbital
velocity. These observations result in a mass determination of the star and
planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec
blueshift of the carbon monoxide signal with respect to the systemic velocity
of the host star suggests the presence of a strong wind flowing from the
irradiated dayside to the non-irradiated nightside of the planet within the
0.01-0.1 mbar atmospheric pressure range probed by these observations. The
strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3
in this planet's upper atmosphere.Comment: 11 Pages main article and 6 pages suppl. information: A final, edited
version appears in the 24 May 2010 issue of Natur
Dynamics of Dissipative Quantum Hall Edges
We examine the influence of the edge electronic density profile and of
dissipation on edge magnetoplasmons in the quantum Hall regime, in a
semiclassical calculation. The equilibrium electron density on the edge,
obtained using a Thomas-Fermi approach, has incompressible stripes produced by
energy gaps responsible for the quantum Hall effect. We find that these stripes
have an unobservably small effect on the edge magnetoplasmons. But dissipation,
included phenomenologically in the local conductivity, proves to produce
significant oscillations in the strength and speed of edge magnetoplasmons in
the quantum Hall regime.Comment: 23 pages including 10 figure
Proof of a generalized Geroch conjecture for the hyperbolic Ernst equation
We enunciate and prove here a generalization of Geroch's famous conjecture
concerning analytic solutions of the elliptic Ernst equation. Our
generalization is stated for solutions of the hyperbolic Ernst equation that
are not necessarily analytic, although it can be formulated also for solutions
of the elliptic Ernst equation that are nowhere axis-accessible.Comment: 75 pages (plus optional table of contents). Sign errors in elliptic
case equations (1A.13), (1A.15) and (1A.25) are corrected. Not relevant to
proof contained in pape
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