Showing papers by "Center for Theoretical Physics published in 2014"

Backreaction and continuum limit in a closed universe filled with black holes

Abstract: We discuss the continuum limit of the initial data for a vacuum, closed cosmological model with black holes as the only sources of the gravitational field. The model we consider is an exact solution of the constraint equations and represents a vacuum universe with a number of black holes placed on a spatial slice of S3 topology considered at the moment of its largest expansion when the black holes are momentary at rest. We explain how and under what conditions the Friedmann–Lemaitre–Robertson–Walker (FLRW) metric arises as the continuum limit when the number of black holes contained in the model goes to infinity. We also discuss the relation between the effective cosmological parameters of the model, inferred from the large scale geometry of the spacetime, and the masses of individual black holes. In particular, we prove an estimate for the difference between the total effective mass of the system and the sum of the masses of all black holes, thus quantifying the effects of the inhomogeneities in the matter distribution or the cosmological backreaction.

Nucleosynthesis of elements in gamma ray bursts engines

Abstract: We consider the gamma ray burst (GRB) central engine that is powered by the collapse of a massive rotating star or compact binary merger. The engine is a hot and dense accretion disk, which is composed of free nucleons, electron-positron pairs, and helium, and cooled by neutrino emission. A significant number density of neutrons in the inner disk body provide conditions for neutron rich plasma in the GRB outflows or jets. Helium is synthesized in the inner disk if the accretion rate is large, and heavy nuclei are also formed in the outer disk at distances above 150-250 $r_{g}$ from the black hole. We study the process of nucleosynthesis in the GRB engine, depending on its physical properties. The GRB central engine is hydrodynamically modeled in the frame of a dense and hot disk which accretes with a high rate (up to 1 Solar mass per second) onto a maximally spinning, stellar mass black hole. The synthesis of heavy nuclei up to germanium and gallium is then followed by the nuclear reaction network. The accretion at high rate onto a Kerr black hole feeds the engine activity and establishes conditions for efficient synthesis of heavy nuclei in the disk. These processes may have important observational implications for the jet deceleration process and heavy elements observed in the spectra of GRB afterglows.

Fraction of isospectral states exhibiting quantum correlations

Abstract: For several types of correlations: mixed-state entanglement in systems of distinguishable particles, particle entanglement in systems of indistinguishable bosons and fermions and non-Gaussian correlations in fermionic systems we estimate the fraction of non-correlated states among the density matrices with the same spectra. We prove that for the purity exceeding some critical value (depending on the considered problem) fraction of non-correlated states tends to zero exponentially fast with the dimension of the relevant Hilbert space. As a consequence a state randomly chosen from the set of density matrices possessing the same spectra is asymptotically a correlated one. To prove this we developed a systematic framework for detection of correlations via nonlinear witnesses.

Effect of one-, two-, and three-body atom loss processes on superpositions of phase states in Bose-Josephson junctions

Abstract: In a two-mode Bose-Josephson junction formed by a binary mixture of ultracold atoms, macroscopic superpositions of phase states are produced during the time evolution after a sudden quench to zero of the coupling amplitude. Using quantum trajectories and an exact diagonalization of the master equation, we study the effect of one-, two-, and three-body atom losses on the superpositions by analyzing separately the amount of quantum correlations in each subspace with fixed atom number. The quantum correlations useful for atom interferometry are estimated using the quantum Fisher information. We identify the choice of parameters leading to the largest Fisher information, thereby showing that, for all kinds of loss processes, quantum correlations can be partially protected from decoherence when the losses are strongly asymmetric in the two modes.

The global robotic telescopes intelligent array for e-science (gloria)

Abstract: GLORIA is a collaborative web-2.0 project based on a network of robotic teles copes, which has become the first free-access network opened to the world for public outreach and specially for e-Science projects.

Pi of the Sky full system and the new telescope

Abstract: Resumen es: El Pi of the Sky es un sistema de telescopios de campo amplio, que buscan fen omenos astrof isicos de escala t e m p o r a l c o r t a , e n e s p e c ...

Photometric Analysis of Pi of the Sky Data

Abstract: Pi of the Sky is a system of two wide field of view robotic telescopes, which search for short timescale astrophysical phenomena, especially for prompt optical GRB emissions. The system was designed for autonomous operation, monitoring a large fraction of the sky with 12m–13m range and time resolution of the order of 1–10 seconds. Two fully automatic Pi of the Sky detectors located in Spain (INTA — INTA El Arenosillo Test Centre in Mazagon, near Huelva.) and Chile (SPDA — San Pedro de Atacama Observatory.) have been observing the sky almost every night in search of rare optical phenomena. They also collect a lot of useful observations which include e.g. many kinds of variable stars. To be able to draw proper conclusions from the data received, adequate quality of the data is very important. Pi of the Sky data is subject to systematic errors caused by various factors, such as cloud cover, seen as significant fluctuations in the number of stars observed by the detector, problems with conducting mounting, a strong background of the moon or the passing of a bright object, e.g., a planet, near the observed star. Some of these adverse effects have already been detected during the cataloging of individual measurements, but the quality of our data was still not satisfactory for us. In order to improve the quality of our data, we have developed two new procedures based on two different approaches. In this article we will report on these procedures, give some examples, and we will show how these procedures improve the quality of our data.

Effect of one-, two-, and three-body atom loss processes on superpositions of phase states in Bose-Josephson junctions

Abstract: In a two-mode Bose-Josephson junction formed by a binary mixture of ultracold atoms, macroscopic superpositions of phase states are produced during the time evolution after a sudden quench to zero of the coupling amplitude. Using quantum trajectories and an exact diagonalization of the master equation, we study the effect of one-, two-, and three-body atom losses on the superpositions by analyzing separately the amount of quantum correlations in each subspace with fixed atom number. The quantum correlations useful for atom interferometry are estimated using the quantum Fisher information. We identify the choice of parameters leading to the largest Fisher information, thereby showing that, for all kinds of loss processes, quantum correlations can be partially protected from decoherence when the losses are strongly asymmetric in the two modes.