13,533 research outputs found
Bouncing of gravitons emitted from the brane to the bulk back to the brane
Solutions of geodesic equations describing propagation of gravitons in the
bulk are studied in a cosmological model with one extra dimension. Brane with
matter is embedded in the bulk. It is shown that in the period of early
cosmology gravitons emitted from the brane to the bulk under certain conditions
can return back to the brane. The model is discussed in two alternative
approaches: (i) brane with static metric moving in the AdS space, and (ii)
brane located at a fixed position in extra dimension with non-static metric.
Transformation of coordinates from the one picture to another is performed. In
both approaches conditions for gravitons emitted to the bulk to come back to
the brane are found.Comment: LaTeX2e, 12 pages. Refs. added. arXiv admin note: text overlap with
arXiv:1204.235
Relaxation to magnetohydrodynamics equilibria via collision brackets
Metriplectic dynamics is applied to compute equilibria of fluid dynamical
systems. The result is a relaxation method in which Hamiltonian dynamics
(symplectic structure) is combined with dissipative mechanisms (metric
structure) that relaxes the system to the desired equilibrium point. The
specific metric operator, which is considered in this work, is formally
analogous to the Landau collision operator. These ideas are illustrated by
means of case studies. The considered physical models are the Euler equations
in vorticity form, the Grad-Shafranov equation, and force-free MHD equilibria.Comment: Conference Proceeding (Theory of Fusions Plasmas, 2018), 9 pages, 8
figure
Generalized Massive Gravity and Galilean Conformal Algebra in two dimensions
Galilean conformal algebra (GCA) in two dimensions arises as contraction of
two copies of the centrally extended Virasoro algebra ( with ). The central charges of
GCA can be expressed in term of Virasoro central charges. For finite and
non-zero GCA central charges, the Virasoro central charges must behave as
asymmetric form . We propose that, the bulk
description for 2d GCA with asymmetric central charges is given by general
massive gravity (GMG) in three dimensions. It can be seen that, if the
gravitational Chern-Simons coupling behaves as of order
O() or (), the central charges
of GMG have the above dependence. So, in non-relativistic scaling
limit , we calculated GCA parameters and finite
entropy in term of gravity parameters mass and angular momentum of GMG.Comment: 9 page
Particle production in p-p collisions at sqrt(s) = 17 GeV within the statistical model
A thermal-model analysis of particle production of p-p collisions at sqrt(s)
= 17 GeV using the latest available data is presented. The sensitivity of model
parameters on data selections and model assumptions is studied. The system-size
dependence of thermal parameters and recent differences in the statistical
model analysis of p-p collisions at the super proton synchrotron (SPS) are
discussed. It is shown that the temperature and strangeness undersaturation
factor depend strongly on kaon yields which at present are still not well known
experimentally. It is conclude, that within the presently available data at the
SPS it is rather unlikely that the temperature in p-p collisions exceeds
significantly that expected in central collisions of heavy ions at the same
energy.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
Consistent Truncation to Three Dimensional (Super-)gravity
For a general three dimensional theory of (super-)gravity coupled to
arbitrary matter fields with arbitrary set of higher derivative terms in the
effective action, we give an algorithm for consistently truncating the theory
to a theory of pure (super-)gravity with the gravitational sector containing
only Einstein-Hilbert, cosmological constant and Chern-Simons terms. We also
outline the procedure for finding the parameters of the truncated theory. As an
example we consider dimensional reduction on S^2 of the 5-dimensional minimal
supergravity with curvature squared terms and obtain the truncated theory
without any curvature squared terms. This truncated theory reproduces correctly
the exact central charge of the boundary CFT.Comment: LaTeX file, 22 page
Ancilla-assisted sequential approximation of nonlocal unitary operations
We consider the recently proposed "no-go" theorem of Lamata et al [Phys. Rev.
Lett. 101, 180506 (2008)] on the impossibility of sequential implementation of
global unitary operations with the aid of an itinerant ancillary system and
view the claim within the language of Kraus representation. By virtue of an
extremely useful tool for analyzing entanglement properties of quantum
operations, namely, operator-Schmidt decomposition, we provide alternative
proof to the "no-go" theorem and also study the role of initial correlations
between the qubits and ancilla in sequential preparation of unitary entanglers.
Despite the negative response from the "no-go" theorem, we demonstrate
explicitly how the matrix-product operator(MPO) formalism provides a flexible
structure to develop protocols for sequential implementation of such entanglers
with an optimal fidelity. The proposed numerical technique, that we call
variational matrix-product operator (VMPO), offers a computationally efficient
tool for characterizing the "globalness" and entangling capabilities of
nonlocal unitary operations.Comment: Slightly improved version as published in Phys. Rev.
Back Reaction of Hawking Radiation on Black Hole Geometry
We propose a model for the geometry of a dynamical spherical shell in which
the metric is asymptotically Schwarzschild, but deviates from Ricci-flatness in
a finite neighbourhood of the shell. Hence, the geometry corresponds to a
`hairy' black hole, with the hair originating on the shell. The metric is
regular for an infalling shell, but it bifurcates, leading to two disconnected
Schwarzschild-like spacetime geometries. The shell is interpreted as either
collapsing matter or as Hawking radiation, depending on whether or not the
shell is infalling or outgoing. In this model, the Hawking radiation results
from tunnelling between the two geometries. Using this model, the back reaction
correction from Hawking radiation is calculated.Comment: Latex file, 15 pages, 4 figures enclosed, uses eps
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