127 research outputs found
Aspects of electrostatics in a weak gravitational field
Several features of electrostatics of point charged particles in a weak,
homogeneous, gravitational field are discussed using the Rindler metric to
model the gravitational field. Some previously known results are obtained by
simpler and more transparent procedures and are interpreted in an intuitive
manner. Specifically: (i) We show that the electrostatic potential of a charge
at rest in the Rindler frame is expressible as A_0=(q/l) where l is the affine
parameter distance along the null geodesic from the charge to the field point.
(ii) We obtain the sum of the electrostatic forces exerted by one charge on
another in the Rindler frame and discuss its interpretation. (iii) We show how
a purely electrostatic term in the Rindler frame appears as a radiation term in
the inertial frame. (In part, this arises because charges at rest in a weak
gravitational field possess additional weight due to their electrostatic
energy. This weight is proportional to the acceleration and falls inversely
with distance -- which are the usual characteristics of a radiation field.)
(iv) We also interpret the origin of the radiation reaction term by extending
our approach to include a slowly varying acceleration. Many of these results
might have possible extensions for the case of electrostatics in an arbitrary
static geometry. [Abridged Abstract]Comment: 26 pages; accepted for publication in Gen.Rel.Gra
Spacetime Information
In usual quantum theory, the information available about a quantum system is
defined in terms of the density matrix describing it on a spacelike surface.
This definition must be generalized for extensions of quantum theory which do
not have a notion of state on a spacelike surface. It must be generalized for
the generalized quantum theories appropriate when spacetime geometry fluctuates
quantum mechanically or when geometry is fixed but not foliable by spacelike
surfaces. This paper introduces a four-dimensional notion of the information
available about a quantum system's boundary conditions in the various sets of
decohering histories it may display. The idea of spacetime information is
applied in several contexts: When spacetime geometry is fixed the information
available through alternatives restricted to a spacetime region is defined. The
information available through histories of alternatives of general operators is
compared to that obtained from the more limited coarse- grainings of
sum-over-histories quantum mechanics. The definition of information is
considered in generalized quantum theories. We consider as specific examples
time-neutral quantum mechanics with initial and final conditions, quantum
theories with non-unitary evolution, and the generalized quantum frameworks
appropriate for quantum spacetime. In such theories complete information about
a quantum system is not necessarily available on any spacelike surface but must
be searched for throughout spacetime. The information loss commonly associated
with the ``evolution of pure states into mixed states'' in black hole
evaporation is thus not in conflict with the principles of generalized quantum
mechanics.Comment: 47pages, 2 figures, UCSBTH 94-0
Systems of Hess-Appel'rot type
We construct higher-dimensional generalizations of the classical
Hess-Appel'rot rigid body system. We give a Lax pair with a spectral parameter
leading to an algebro-geometric integration of this new class of systems, which
is closely related to the integration of the Lagrange bitop performed by us
recently and uses Mumford relation for theta divisors of double unramified
coverings. Based on the basic properties satisfied by such a class of systems
related to bi-Poisson structure, quasi-homogeneity, and conditions on the
Kowalevski exponents, we suggest an axiomatic approach leading to what we call
the "class of systems of Hess-Appel'rot type".Comment: 40 pages. Comm. Math. Phys. (to appear
Accelerating electromagnetic magic field from the C-metric
Various aspects of the C-metric representing two rotating charged black holes
accelerated in opposite directions are summarized and its limits are
considered. A particular attention is paid to the special-relativistic limit in
which the electromagnetic field becomes the "magic field" of two oppositely
accelerated rotating charged relativistic discs. When the acceleration vanishes
the usual electromagnetic magic field of the Kerr-Newman black hole with
gravitational constant set to zero arises. Properties of the accelerated discs
and the fields produced are studied and illustrated graphically. The charges at
the rim of the accelerated discs move along spiral trajectories with the speed
of light. If the magic field has some deeper connection with the field of the
Dirac electron, as is sometimes conjectured because of the same gyromagnetic
ratio, the "accelerating magic field" represents the electromagnetic field of a
uniformly accelerated spinning electron. It generalizes the classical Born's
solution for two uniformly accelerated monopole charges.Comment: 22 pages, 5 figure
Exact spectra, spin susceptibilities and order parameter of the quantum Heisenberg antiferromagnet on the triangular lattice
Exact spectra of periodic samples are computed up to .
Evidence of an extensive set of low lying levels, lower than the softest
magnons, is exhibited.
These low lying quantum states are degenerated in the thermodynamic limit;
their symmetries and dynamics as well as their finite-size scaling are strong
arguments in favor of N\'eel order.
It is shown that the N\'eel order parameter agrees with first-order spin-wave
calculations. A simple explanation of the low energy dynamics is given as well
as the numerical determinations of the energies, order parameter and spin
susceptibilities of the studied samples. It is shown how suitable boundary
conditions, which do not frustrate N\'eel order, allow the study of samples
with spins.
A thorough study of these situations is done in parallel with the more
conventional case .Comment: 36 pages, REVTeX 3.0, 13 figures available upon request, LPTL
preprin
Intrinsic and extrinsic properties of quantum systems
The paper attempts to convince that the orthodox interpretation of quantum
mechanics does not contradict philosophical realism by throwing light onto
certain properties of quantum systems that seem to have escaped attention as
yet. The exposition starts with the philosophical notions of realism. Then, the
quantum mechanics as it is usually taught is demoted to a mere part of the
theory called phenomenology of observations, and the common impression about
its contradiction to realism is explained. The main idea of the paper, the
physical notion of intrinsic properties, is introduced and many examples
thereof are given. It replaces the irritating dichotomy of quantum and
classical worlds by a much softer difference between intrinsic and extrinsic
properties, which concern equally microscopic and macroscopic systems. Finally,
the classicality and the quantum measurement are analyzed and found to present
some still unsolved problems. A possible way of dealing with the
Schr\"{o}dinger cat is suggested that is based on the intrinsic properties. A
simple quantum model of one classical property illustrates how our philosophy
may work.Comment: 20 pages, no figure. Comments are wellcom
The performance of the jet trigger for the ATLAS detector during 2011 data taking
The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided protonâproton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleonânucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction
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