62 research outputs found
TIME-SYMMETRIC INITIAL DATA SETS IN 4--D DILATON GRAVITY
I study the time--symmetric initial--data problem in theories with a massless
scalar field (dilaton), free or coupled to a Maxwell field in the stringy way,
finding different initial--data sets describing an arbitrary number of black
holes with arbitrary masses, charges and asymptotic value of the dilaton. The
presence of the scalar field gives rise to a number of interesting effects. The
mass and charges of a single black hole are different in its two asymptotically
flat regions across the Einstein--Rosen bridge. The same happens to the value
of the dilaton at infinity. This forbids the identification of these asymptotic
regions in order to build (Misner) wormholes in the most naive way. Using
different techniques, I find regular initial data for stringy wormholes. The
price payed is the existence singularities in the dilaton field. The presence
of a single--valued scalar seems to constrain strongly the allowed topologies
of the initial space--like surface. Other kinds of scalar fields (taking values
on a circle or being defined up to an additive constant) are also briefly
considered.Comment: latex file, 38 pages
Gravitational Geons on the Brane
In this paper, we examine the possibility of static, spherically symmetric
gravitational geons on a 3 dimensional brane embedded in a 4+1 dimensional
space-time. We choose a specific g_tt for the brane-world space-time metric. We
then calculate g_rr analytically in the weak field limit and numerically for
stronger fields. We show that the induced field equations on the brane do admit
gravitational geon solutions.Comment: 14 pages with 9 figures. To appear in General Relativity and
Gravitatio
Ising model with periodic pinning of mobile defects
A two-dimensional Ising model with short-range interactions and mobile
defects describing the formation and thermal destruction of defect stripes is
studied. In particular, the effect of a local pinning of the defects at the
sites of straight equidistant lines is analysed using Monte Carlo simulations
and the transfer matrix method. The pinning leads to a long-range ordered
magnetic phase at low temperatures. The dependence of the phase transition
temperature, at which the defect stripes are destabilized, on the pinning
strength is determined. The transition seems to be of first order, with and
without pinning.Comment: 7 pages, 7 figure
A Dodecalogue of Basic Didactics from Applications of Abstract Differential Geometry to Quantum Gravity
We summarize the twelve most important in our view novel concepts that have
arisen, based on results that have been obtained, from various applications of
Abstract Differential Geometry (ADG) to Quantum Gravity (QG). The present
document may be used as a concise, yet informal, discursive and peripatetic
conceptual guide-cum-terminological glossary to the voluminous technical
research literature on the subject. In a bonus section at the end, we dwell on
the significance of introducing new conceptual terminology in future QG
research by means of `poetic language'Comment: 16 pages, preliminary versio
Energy Distribution in f(R) Gravity
The well-known energy problem is discussed in f(R) theory of gravity. We use
the generalized Landau-Lifshitz energy-momentum complex in the framework of
metric f(R) gravity to evaluate the energy density of plane symmetric solutions
for some general f(R) models. In particular, this quantity is found for some
popular choices of f(R) models. The constant scalar curvature condition and the
stability condition for these models are also discussed. Further, we
investigate the energy distribution of cosmic string spacetime.Comment: 15 pages, accepted for publication in Gen. Relativ. & Gra
Classical approach in quantum physics
The application of a classical approach to various quantum problems - the
secular perturbation approach to quantization of a hydrogen atom in external
fields and a helium atom, the adiabatic switching method for calculation of a
semiclassical spectrum of hydrogen atom in crossed electric and magnetic
fields, a spontaneous decay of excited states of a hydrogen atom, Gutzwiller's
approach to Stark problem, long-lived excited states of a helium atom recently
discovered with the help of Poincar section, inelastic
transitions in slow and fast electron-atom and ion-atom collisions - is
reviewed. Further, a classical representation in quantum theory is discussed.
In this representation the quantum states are treating as an ensemble of
classical states. This approach opens the way to an accurate description of the
initial and final states in classical trajectory Monte Carlo (CTMC) method and
a purely classical explanation of tunneling phenomenon. The general aspects of
the structure of the semiclassical series such as renormgroup symmetry,
criterion of accuracy and so on are reviewed as well. In conclusion, the
relation between quantum theory, classical physics and measurement is
discussed.Comment: This review paper was rejected from J.Phys.A with referee's comment
"The author has made many worthwhile contributions to semiclassical physics,
but this article does not meet the standard for a topical review"
Quantum mechanics, Furry's hypothesis and a measure of decoherence in the K^0 \bar{K}^0 system
We consider strangeness correlations of the EPR type in K^0 \bar{K}^0 pairs
created in a J^{PC} = 1^{--} state as a function of time under the hypothesis
that spontaneous decoherence takes place. We parameterize the degree of
decoherence by a factor (1-\zeta) which multiplies the quantum-mechanical
interference terms occurring in the amplitudes for like and unlike strangeness
events and discuss the dependence of this procedure on the basis chosen in the
K^0--\bar{K}^0 space to which the interference terms correspond. Consequently,
all statements about the ``decoherence parameter'' \zeta inferred from
experimental data are basis-dependent as well. We illustrate this point by
estimating the value of \zeta for the two bases {K_L, K_S} and {K^0, \bar{K}^0}
with the help of recent data of the CPLEAR experiment.Comment: 12 pages, 1 figure, revte
Entanglement, Bell Inequalities and Decoherence in Particle Physics
We demonstrate the relevance of entanglement, Bell inequalities and
decoherence in particle physics. In particular, we study in detail the features
of the ``strange'' system as an example of entangled
meson--antimeson systems. The analogies and differences to entangled spin--1/2
or photon systems are worked, the effects of a unitary time evolution of the
meson system is demonstrated explicitly. After an introduction we present
several types of Bell inequalities and show a remarkable connection to CP
violation. We investigate the stability of entangled quantum systems pursuing
the question how possible decoherence might arise due to the interaction of the
system with its ``environment''. The decoherence is strikingly connected to the
entanglement loss of common entanglement measures. Finally, some outlook of the
field is presented.Comment: Lectures given at Quantum Coherence in Matter: from Quarks to Solids,
42. Internationale Universit\"atswochen f\"ur Theoretische Physik,
Schladming, Austria, Feb. 28 -- March 6, 2004, submitted to Lecture Notes in
Physics, Springer Verlag, 45 page
Exact Theorems Concerning CP and CPT Violations in C=-1 Entangled State of Pseudoscalar Neutral Mesons
Neutral pseudoscalar mesons in an entangled or Einstein-Podolsky-Rosen state
are routinely produced in phi and B factories. Based on the peculiar properties
of an entangled state, we present some general exact theorems about parameters
characterizing CP and CPT violations, by using various asymmetries defined for
the correlated decays of the two entangled mesons, which are rigorously
calculated.Comment: 10 pages, published versio
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
- âŠ