6,430 research outputs found
Generalized Chaplygin Gas Models tested with SNIa
The so called Generalized Chaplygin Gas (GCG) with the equation of state was recently proposed as a candidate for dark
energy in the Universe. In this paper we confront the GCG with SNIa data.
Specifically we have tested the GCG cosmology in three different classes of
models with (1) , ; (2) ,
and (3) , , as well as the
model withouth any assumption on . The best fitted models are
obtained by minimalizing the function and levels in the
plane. We supplemented our analysis with confidence intervals
in the plane, as well as one-dimensional probability
distribution functions for models parameter. The general conclusion is that
SNIa data strongly support the Chaplygin gas (with ). Extending our
analysisby relaxing the flat prior lead to the result that even though the best
fitted values of are formally non-zero, still they are close to flat
case. It should be viewed as an advantage of the GCG model since in similar
analysisof CDM model high negative value of were found to
be bestfitted to the data and independent inspiration from CMBR and
extragalactic astronomy has been invoked to fix the curvature problem. Our
results show clearly that in Generalized Chaplygin Gas cosmology distant
supernovae should be brighter than in CDM model.This prediction seems
to be confirmed with new Riess high redshift SNIa sample. Moreover, we argue
that with the future SNAP data it would be possible to differentiate between
models with various value of parameter and/or discriminated between
GCG, Cardassian and CDM modelsComment: 54 pages 29 figures improved version analysis flat prior relaxed high
redshift Riess SNIa sample include
Quantum Field Theory on Spacetimes with a Compactly Generated Cauchy Horizon
We prove two theorems which concern difficulties in the formulation of the
quantum theory of a linear scalar field on a spacetime, (M,g_{ab}), with a
compactly generated Cauchy horizon. These theorems demonstrate the breakdown of
the theory at certain `base points' of the Cauchy horizon, which are defined as
`past terminal accumulation points' of the horizon generators. Thus, the
theorems may be interpreted as giving support to Hawking's `Chronology
Protection Conjecture', according to which the laws of physics prevent one from
manufacturing a `time machine'. Specifically, we prove: Theorem 1: There is no
extension to (M,g_{ab}) of the usual field algebra on the initial globally
hyperbolic region which satisfies the condition of F-locality at any base
point. In other words, any extension of the field algebra must, in any globally
hyperbolic neighbourhood of any base point, differ from the algebra one would
define on that neighbourhood according to the rules for globally hyperbolic
spacetimes. Theorem 2: The two-point distribution for any Hadamard state
defined on the initial globally hyperbolic region must (when extended to a
distributional bisolution of the covariant Klein-Gordon equation on the full
spacetime) be singular at every base point x in the sense that the difference
between this two point distribution and a local Hadamard distribution cannot be
given by a bounded function in any neighbourhood (in MXM) of (x,x). Theorem 2
implies quantities such as the renormalized expectation value of \phi^2 or of
the stress-energy tensor are necessarily ill-defined or singular at any base
point. The proofs rely on the `Propagation of Singularities' theorems of
Duistermaat and H\"ormander.Comment: 37 pages, LaTeX, uses latexsym and amsbsy, no figures; updated
version now published in Commun. Math. Phys.; no major revisions from
original versio
Quantum fidelity in the thermodynamic limit
We study quantum fidelity, the overlap between two ground states of a
many-body system, focusing on the thermodynamic regime. We show how drop of
fidelity near a critical point encodes universal information about a quantum
phase transition. Our general scaling results are illustrated in the quantum
Ising chain for which a remarkably simple expression for fidelity is found.Comment: 4 pages, 4 figures, rearranged a bit to improve presentatio
Vacuum as a less hostile environment to entanglement
We derive sufficient conditions for infinite-dimensional systems whose
entanglement is not completely lost in a finite time during its decoherence by
a passive interaction with local vacuum environments. The sufficient conditions
allow us to clarify a class of bipartite entangled states which preserve their
entanglement or, in other words, are tolerant against decoherence in a vacuum.
We also discuss such a class for entangled qubits.Comment: Replaced by the published versio
Molecular dynamics of folding of secondary structures in Go-type models of proteins
We consider six different secondary structures of proteins and construct two
types of Go-type off-lattice models: with the steric constraints and without.
The basic aminoacid-aminoacid potential is Lennard Jones for the native
contacts and a soft repulsion for the non-native contacts. The interactions are
chosen to make the target secondary structure be the native state of the
system. We provide a thorough equilibrium and kinetic characterization of the
sequences through the molecular dynamics simulations with the Langevin noise.
Models with the steric constraints are found to be better folders and to be
more stable, especially in the case of the -structures. Phononic spectra
for vibrations around the native states have low frequency gaps that correlate
with the thermodynamic stability. Folding of the secondary structures proceeds
through a well defined sequence of events. For instance, -helices fold
from the ends first. The closer to the native state, the faster establishment
of the contacts. Increasing the system size deteriorates the folding
characteristics. We study the folding times as a function of viscous friction
and find a regime of moderate friction with the linear dependence. We also
consider folding when one end of a structure is pinned which imitates
instantaneous conditions when a protein is being synthesized. We find that,
under such circumstances, folding of helices is faster and of the
-sequences slower.Comment: REVTeX, 14 pages, EPS figures included, JCP in pres
Evolution of a Self-interacting Scalar Field in the spacetime of a Higher Dimensional Black Hole
In the spacetime of n-dimensional static charged black hole we examine the
mechanism by which the self-interacting scalar hair decay. It is turned out
that the intermediate asymptotic behaviour of the self-interacting scalar field
is determined by an oscilatory inverse power law. We confirm our results by
numerical calculations.Comment: RevTex, 6 pages, 8 figures, to be published in Phys.Rev.D1
Core-Collapse Supernovae: Modeling between Pragmatism and Perfectionism
We briefly summarize recent efforts in Garching for modeling stellar core
collapse and post-bounce evolution in one and two dimensions. The transport of
neutrinos of all flavors is treated by iteratively solving the coupled system
of frequency-dependent moment equations together with a model Boltzmann
equation which provides the closure. A variety of progenitor stars, different
nuclear equations of state, stellar rotation, and global asymmetries due to
large-mode hydrodynamic instabilities have been investigated to ascertain the
road to finally successful, convectively supported neutrino-driven explosions.Comment: 8 pages, contribution to Procs. 12th Workshop on Nuclear
Astrophysics, Ringberg Castle, March 22-27, 200
3C454.3 reveals the structure and physics of its 'blazar zone'
Recent multi-wavelength observations of 3C454.3, in particular during its
giant outburst in 2005, put severe constraints on the location of the 'blazar
zone', its dissipative nature, and high energy radiation mechanisms. As the
optical, X-ray, and millimeter light-curves indicate, significant fraction of
the jet energy must be released in the vicinity of the millimeter-photosphere,
i.e. at distances where, due to the lateral expansion, the jet becomes
transparent at millimeter wavelengths. We conclude that this region is located
at ~10 parsecs, the distance coinciding with the location of the hot dust
region. This location is consistent with the high amplitude variations observed
on ~10 day time scale, provided the Lorentz factor of a jet is ~20. We argue
that dissipation is driven by reconfinement shock and demonstrate that X-rays
and gamma-rays are likely to be produced via inverse Compton scattering of
near/mid IR photons emitted by the hot dust. We also infer that the largest
gamma-to-synchrotron luminosity ratio ever recorded in this object - having
taken place during its lowest luminosity states - can be simply due to weaker
magnetic fields carried by a less powerful jet.Comment: 19 pages, 3 figures, accepted for publication in Ap
N-particle nonclassicality without N-particle correlations
Most of known multipartite Bell inequalities involve correlation functions
for all subsystems. They are useless for entangled states without such
correlations. We give a method of derivation of families of Bell inequalities
for N parties, which involve, e.g., only (N-1)-partite correlations, but still
are able to detect proper N-partite entanglement. We present an inequality
which reveals five-partite entanglement despite only four-partite correlations.
Classes of inequalities introduced here can be put into a handy form of a
single non-linear inequality. An example is given of an N qubit state, which
strongly violates such an inequality, despite having no N-qubit correlations.
This surprising property might be of potential value for quantum information
tasks.Comment: 5 page
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