2,363 research outputs found
Dynamics of a lattice Universe
We find a solution to Einstein field equations for a regular toroidal lattice
of size L with equal masses M at the centre of each cell; this solution is
exact at order M/L. Such a solution is convenient to study the dynamics of an
assembly of galaxy-like objects. We find that the solution is expanding (or
contracting) in exactly the same way as the solution of a
Friedman-Lema\^itre-Robertson-Walker Universe with dust having the same average
density as our model. This points towards the absence of backreaction in a
Universe filled with an infinite number of objects, and this validates the
fluid approximation, as far as dynamics is concerned, and at the level of
approximation considered in this work.Comment: 14 pages. No figure. Accepted version for Classical and Quantum
Gravit
Exact Evolution of Discrete Relativistic Cosmological Models
22 pages, 16 figures22 pages, 16 figuresWe study the effects of inhomogeneities on the evolution of the Universe, by considering a range of cosmological models with discretized matter content. This is done using exact and fully relativistic methods that exploit the symmetries in and about submanifolds of spacetimes that themselves possess no continuous global symmetries. These methods allow us to follow the evolution of our models throughout their entire history, far beyond what has previously been possible. We find that while some space-like curves collapse to anisotropic singularities in finite time, others remain non-singular forever. The resulting picture is of a cosmological spacetime in which some behaviour remains close to Friedmann-like, while other behaviours deviate radically. In particular, we find that large-scale acceleration is possible without any violation of the energy conditions
Volume Weighted Measures of Eternal Inflation in the Bousso-Polchinski Landscape
We consider the cosmological dynamics associated with volume weighted
measures of eternal inflation, in the Bousso-Polchinski model of the string
theory landscape. We find that this measure predicts that observers are most
likely to find themselves in low energy vacua with one flux considerably larger
than the rest. Furthermore, it allows for a satisfactory anthropic explanation
of the cosmological constant problem by producing a smooth, and approximately
constant, distribution of potentially observable values of Lambda. The low
energy vacua selected by this measure are often short lived. If we require
anthropically acceptable vacua to have a minimum life-time of 10 billion years,
then for reasonable parameters a typical observer should expect their vacuum to
have a life-time of approximately 12 billion years. This prediction is model
dependent, but may point toward a solution to the coincidence problem of
cosmology.Comment: 35 pages, 8 figure
Greenberger-Horne-Zeilinger paradox for continuous variables
We show how to construct states for which a Greenberger-Horne-Zeilinger type
paradox occurs if each party measures either the position or momentum of his
particle. The paradox can be ascribed to the anticommutation of certain
translation operators in phase space. We then rephrase the paradox in terms of
modular and binary variables. The origin of the paradox is then due to the fact
that the associativity of addition of modular variables is true only for
c-numbers but does not hold for operators.Comment: 4 pages, no figure
Effects of Simple Carbohydrate vs. Carbohydrate-Protein Intake on Glucose Homeostasis Following Intense Exercise
Kluka, J., Baskerville, J., Clifton, K., Fisher, K., Marks, D., Weidner, C., Veerabhadrappa, P. and Braun, W.A. (FACSM), Shippensburg University, Shippensburg, PA.
Purpose: To test the effects of simple carbohydrate (CHO) and the combination of CHO and protein on blood glucose (BG) clearance following intense anaerobic exercise. Methods: Eight members (age = 18.8 ± 1.4 years) of the Shippensburg University Football team participated in the study. On separate test days, subjects were given either a placebo (PL) drink, a CHO drink (74 g CHO in 473 ml), or a carbohydrate-protein (C-PRO) drink (58 g CHO and 16 g PRO in 473 ml), upon completing the exercise bout. Before exercise, baseline measurements were taken for BG and heart rate. The subject then completed a 90-sec modified Wingate protocol (resistance set at 70% of the individual’s Wingate protocol resistance). BG was tested post-exercise, and every ten minutes after ingestion of the solution for 60 min. Results: Neither total revolutions completed (PL = 123.0±5.0; CHO = 126.9±3.9; C-PRO = 125.4±2.8) nor post-exercise BG (mg.dl-1) differed across treatments (PL = 88.6±6.5; CHO = 93.1±4.0; C-PRO = 101.1±4.7). However, CHO elicited the highest (p\u3c0.05) mean BG during recovery and the lowest BG was found in the PL. Conclusion: While matching post-exercise energy intake, C-PRO elicited a smaller BG area than CHO but tended to be larger than that of PL (p=0.052). C-PRO may be a better choice for post-exercise intake if aiming to maintain glucose homeostasis during recovery
Generic Bell correlation between arbitrary local algebras in quantum field theory
We prove that for any two commuting von Neumann algebras of infinite type,
the open set of Bell correlated states for the two algebras is norm dense. We
then apply this result to algebraic quantum field theory -- where all local
algebras are of infinite type -- in order to show that for any two spacelike
separated regions, there is an open dense set of field states that dictate Bell
correlations between the regions. We also show that any vector state cyclic for
one of a pair of commuting nonabelian von Neumann algebras is entangled (i.e.,
nonseparable) across the algebras -- from which it follows that every field
state with bounded energy is entangled across any two spacelike separated
regions.Comment: Third version; correction in the proof of Proposition
Can the Copernican principle be tested by cosmic neutrino background?
The Copernican principle, stating that we do not occupy any special place in
our universe, is usually taken for granted in modern cosmology. However recent
observational data of supernova indicate that we may live in the under-dense
center of our universe, which makes the Copernican principle challenged. It
thus becomes urgent and important to test the Copernican principle via
cosmological observations. Taking into account that unlike the cosmic photons,
the cosmic neutrinos of different energies come from the different places to us
along the different worldlines, we here propose cosmic neutrino background as a
test of the Copernican principle. It is shown that from the theoretical
perspective cosmic neutrino background can allow one to determine whether the
Copernican principle is valid or not, but to implement such an observation the
larger neutrino detectors are called for.Comment: JHEP style, 10 pages, 4 figures, version to appear in JCA
Anomalous scattering of highly dispersed pulsars
We report multifrequency measurements of scatter broadening times for nine
highly dispersed pulsars over a wide frequency range (0.6 -- 4.9 GHz). We find
the scatter broadening times to be larger than expected and to scale with
frequency with an average power-law index of , i.e. significantly
less than that expected from standard theories. Such possible discrepancies
have been predicted very recently by Cordes & Lazio.Comment: 7 pages, 4 figures, accepted for publication in ApJ Letter
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