26,639 research outputs found
Gravothermal Catastrophe, an Example
This work discusses gravothermal catastrophe in astrophysical systems and
provides an analytic collapse solution which exhibits many of the catastrophe
properties. The system collapses into a trapped surface with outgoing energy
radiated to a future boundary, and provides an example of catastrophic
collapse.Comment: To appear in Phys. Rev.
Re-examination of the possible tidal stream in front of the LMC
It has recently been suggested that the stars in a vertical extension of the
red clump feature seen in LMC color-magnitude diagrams could belong to a tidal
stream of material located in front of that galaxy. If this claim is correct,
this foreground concentration of stars could contribute significantly to the
rate of gravitational microlensing events observed in the LMC microlensing
experiments. Here we present radial velocity measurements of stars in this
so-called ``vertical red clump'' (VRC) population. The observed stellar sample,
it transpires, has typical LMC kinematics. It is shown that it is improbable
that an intervening tidal stream should have the same distribution of radial
velocities as the LMC, which is consistent with an earlier study that showed
that the VRC feature is more likely a young stellar population in the main body
of that galaxy. However, the kinematic data do not discriminate against the
possibility that the VRC is an LMC halo population.Comment: 10 pages, 3 figures, 1 table. Accepted for publication in ApJ
The Bell Theorem as a Special Case of a Theorem of Bass
The theorem of Bell states that certain results of quantum mechanics violate
inequalities that are valid for objective local random variables. We show that
the inequalities of Bell are special cases of theorems found ten years earlier
by Bass and stated in full generality by Vorob'ev. This fact implies precise
necessary and sufficient mathematical conditions for the validity of the Bell
inequalities. We show that these precise conditions differ significantly from
the definition of objective local variable spaces and as an application that
the Bell inequalities may be violated even for objective local random
variables.Comment: 15 pages, 2 figure
A Dirac sea pilot-wave model for quantum field theory
We present a pilot-wave model for quantum field theory in which the Dirac sea
is taken seriously. The model ascribes particle trajectories to all the
fermions, including the fermions filling the Dirac sea. The model is
deterministic and applies to the regime in which fermion number is
superselected. This work is a further elaboration of work by Colin, in which a
Dirac sea pilot-wave model is presented for quantum electrodynamics. We extend
his work to non-electromagnetic interactions, we discuss a cut-off
regularization of the pilot-wave model and study how it reproduces the standard
quantum predictions. The Dirac sea pilot-wave model can be seen as a possible
continuum generalization of a lattice model by Bell. It can also be seen as a
development and generalization of the ideas by Bohm, Hiley and Kaloyerou, who
also suggested the use of the Dirac sea for the development of a pilot-wave
model for quantum electrodynamics.Comment: 41 pages, no figures, LaTex, v2 minor improvements and addition
Finite-dimensional states and entanglement generation for a nonlinear coupler
We discuss a system comprising two nonlinear (Kerr-like) oscillators coupled
mutually by a nonlinear interaction. The system is excited by an external
coherent field that is resonant to the frequency of one of the oscillators. We
show that the coupler evolution can be closed within a finite set of -photon
states, analogously as in the \textit{nonlinear quantum scissors} model.
Moreover, for this type of evolution our system can be treated as a
\textit{Bell-like states} generator. Thanks to the nonlinear nature of both:
oscillators and their internal coupling, these states can be generated even if
the system exhibits its energy dissipating nature, contrary to systems with
linear couplings.Comment: Accepted for publication in Physical Review
The no-signaling condition and quantum dynamics
We show that the basic dynamical rules of quantum physics can be derived from
its static properties and the condition that superluminal communication is
forbidden. More precisely, the fact that the dynamics has to be described by
linear completely positive maps on density matrices is derived from the
following assumptions: (1) physical states are described by rays in a Hilbert
space, (2) probabilities for measurement outcomes at any given time are
calculated according to the usual trace rule, (3) superluminal communication is
excluded. This result also constrains possible non-linear modifications of
quantum physics.Comment: 4 page
From Einstein's Theorem to Bell's Theorem: A History of Quantum Nonlocality
In this Einstein Year of Physics it seems appropriate to look at an important
aspect of Einstein's work that is often down-played: his contribution to the
debate on the interpretation of quantum mechanics. Contrary to popular opinion,
Bohr had no defence against Einstein's 1935 attack (the EPR paper) on the
claimed completeness of orthodox quantum mechanics. I suggest that Einstein's
argument, as stated most clearly in 1946, could justly be called Einstein's
reality-locality-completeness theorem, since it proves that one of these three
must be false. Einstein's instinct was that completeness of orthodox quantum
mechanics was the falsehood, but he failed in his quest to find a more complete
theory that respected reality and locality. Einstein's theorem, and possibly
Einstein's failure, inspired John Bell in 1964 to prove his reality-locality
theorem. This strengthened Einstein's theorem (but showed the futility of his
quest) by demonstrating that either reality or locality is a falsehood. This
revealed the full nonlocality of the quantum world for the first time.Comment: 18 pages. To be published in Contemporary Physics. (Minor changes;
references and author info added
Local Realism of Macroscopic Correlations
We show that for macroscopic measurements which cannot reveal full
information about microscopic states of the system, the monogamy of Bell
inequality violations present in quantum mechanics implies that practically all
correlations between macroscopic measurements can be described by local
realistic models. Our results hold for sharp measurement and arbitrary closed
quantum systems.Comment: 9 pages incl. one Appendix, 2 figure
Tracing the Mass-Assembly History of Galaxies with Deep Surveys
We use the optical and near-infrared galaxy samples from the Munich
Near-Infrared Cluster Survey (MUNICS), the FORS Deep Field (FDF) and GOODS-S to
probe the stellar mass assembly history of field galaxies out to z ~ 5.
Combining information on the galaxies' stellar mass with their star-formation
rate and the age of the stellar population, we can draw important conclusions
on the assembly of the most massive galaxies in the universe: These objects
contain the oldest stellar populations at all redshifts probed. Furthermore, we
show that with increasing redshift the contribution of star-formation to the
mass assembly for massive galaxies increases dramatically, reaching the era of
their formation at z ~ 2 and beyond. These findings can be interpreted as
evidence for an early epoch of star formation in the most massive galaxies in
the universe.Comment: 3 pages, 2 figures; published in B. Aschenbach, V. Burwitz, G.
Hasinger, B. Leibundgut (eds.): "Relativistic Astrophysics and Cosmology -
Einstein's Legacy. Proceedings of the Conference held in Munich, 2006", ESO
Astrophysics Symposia, Springer Verlag, 2007, p. 310. Replaced to match final
published versio
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