Real-time Quantum evolution in the Classical approximation and beyond

With the goal in mind of deriving a method to compute quantum corrections for the real-time evolution in quantum field theory, we analyze the problem from the perspective of the Wigner function. We argue that this provides the most natural way to justify and extend the classical approximation. A simple proposal is presented that can allow to give systematic quantum corrections to the evolution of expectation values and/or an estimate of the errors committed when using the classical approximation. The method is applied to the case of a few degrees of freedom and compared with other methods and with the exact quantum results. An analysis of the dependence of the numerical effort involved as a function of the number of variables is given, which allow us to be optimistic about its applicability in a quantum field theoretical context.Comment: 32 pages, 6 figure

Cooperación y seguridad internacionales al comienzo del siglo XXI

Los procesos en los que se han consolidado estructuras más o menos institucionalizadas de seguridad, permiten comprender el alcance y las limitaciones de la teoría de la integración en una etapa de hegemonía imperfecta, regida por dinámicas diferentes a las que imperaron en décadas atrás. Desde el análisis científico, el marco de seguridad que proporciona o debe proporcionar estabilidad a los sistemas internacionales constituye uno de los temas centrales del neorrealismo

Una familia de elementos finitos clase C1, aplicación a flexión de placas de Kirchhoff

Se hace una pequeña introducción y después un estudio sobre las posibilidades y limitaciones en análisis de placas delgadas de elementos simples polinómicos de clase C1. Se expone una familia jerárquica de dichos elementos, que se aplica a varios casos particulares. En base a estos se deducen algunas conclusiones, especialmente en lo que se refiere a eficacia computacional. Al final se proponen trabajos a realizar a partir de los datos existentesPeer Reviewe

Generating Erler-Schnabl-type Solution for Tachyon Vacuum in Cubic Superstring Field Theory

We study a new set of identity-based solutions to analyze the problem of tachyon condensation in open bosonic string field theory and cubic superstring field theory. Even though these identity-based solutions seem to be trivial, it turns out that after performing a suitable gauge transformation, we are left with the known Erler-Schnabl-type solutions which correctly reproduce the value of the D-brane tension. This result shows explicitly that how a seemingly trivial solution can generate a non-trivial configuration which precisely represents to the tachyon vacuum.Comment: 22 pages, references added, appendix added, 2 subsections adde

Acute-on-chronic liver failure: A new syndrome that will re-classify cirrhosis.

Acute-on-chronic liver failure (ACLF) is a recently recognized syndrome characterized by acute decompensation (AD) of cirrhosis and organ/system failure(s) (organ failure: liver, kidney, brain, coagulation, circulation and/or respiration) and extremely poor survival (28-day mortality rate 30-40%). ACLF occurs in relatively young patients. It is especially frequent in alcoholic- and untreated hepatitis B associated-cirrhosis, in addition it is related to bacterial infections and active alcoholism, although in 40% of cases no precipitating event can be identified. It may develop at any time during the course of the disease in the patient (from compensated to long-standing cirrhosis). The development of ACLF occurs in the setting of a systemic inflammation, the severity of which correlates with the number of organ failures and mortality. Systemic inflammation may cause ACLF through complex mechanisms including an exaggerated inflammatory response and systemic oxidative stress to pathogen- or danger/damage-associated molecular patterns (immunopathology) and/or alteration of tissue homeostasis to inflammation caused either by the pathogen itself or through a dysfunction of tissue tolerance. A scoring system composed of three scores (CLIF-C OFs, CLIF-C AD, and CLIF-C ACLFs) specifically designed for patients with AD, with and without ACLF, allows a step-wise algorithm for a rational indication of therapy. The management of ACLF should be carried out in enhanced or intensive care units. Current therapeutic measures comprise the treatment for associated complications, organ failures support and liver transplantation

Comparison of |Q|=1 and |Q|=2 gauge-field configurations on the lattice four-torus

It is known that exactly self-dual gauge-field configurations with topological charge |Q|=1 cannot exist on the untwisted continuum 4-torus. We explore the manifestation of this remarkable fact on the lattice 4-torus for SU(3) using advanced techniques for controlling lattice discretization errors, extending earlier work of De Forcrand et. al. for SU(2). We identify three distinct signals for the instability of |Q|=1 configurations, and show that these manifest themselves early in the cooling process, long before the would-be instanton has shrunk to a size comparable to the lattice discretization threshold. These signals do not appear for our |Q|=2 configurations. This indicates that these signals reflect the truly global nature of the instability, rather than local discretization effects. Monte-Carlo generated SU(3) gauge field configurations are cooled to the self-dual limit using an O(a^4)-improved gauge action chosen to have small but positive O(a^6) errors. This choice prevents lattice discretization errors from destroying instantons provided their size exceeds the dislocation threshold of the cooling algorithm. Lattice discretization errors are evaluated by comparing the O(a^4)-improved gauge-field action with an O(a^4)-improved action constructed from the square of an O(a^4)-improved lattice field-strength tensor, thus having different O(a^6) discretization errors. The number of action-density peaks, the instanton size and the topological charge of configurations is monitored. We observe a fluctuation in the total topological charge of |Q|=1 configurations, and demonstrate that the onset of this unusual behavior corresponds with the disappearance of multiple-peaks in the action density. At the same time discretization errors are minimal.Comment: 12 pages, 9 figures, submitted to Phys. Rev.