Scalar Field with Robin Boundary Conditions in the Worldline Formalism

The worldline formalism has been widely used to compute physical quantities in quantum field theory. However, applications of this formalism to quantum fields in the presence of boundaries have been studied only recently. In this article we show how to compute in the worldline approach the heat kernel expansion for a scalar field with boundary conditions of Robin type. In order to describe how this mechanism works, we compute the contributions due to the boundary conditions to the coefficients A_1, A_{3/2} and A_2 of the heat kernel expansion of a scalar field on the positive real line.Comment: Presented at 8th Workshop on Quantum Field Theory Under the Influence of External Conditions (QFEXT 07), Leipzig, Germany, 16-21 Sep 200

First record of green crabs, Carcinus maenas (Linnaeus, 1758) in Golfo Nuevo, Chubut Argentina: a new northern limit of distribution in the Patagonian coast

El objetivo de esta nota es reportar la presencia del cangrejo verde europeo, Carcinus maenas en el Golfo Nuevo, en Chubut, Argentina. Este hallazgo extiende su rango de distribución 250 km al norte del primer reporte en el Golfo San Jorge, en las costas patagónicas. C. maenas es una de las especies invasoras acuáticas más exitosas del mundo, con poblaciones establecidas en todos los continentes. Es un depredador voraz, por lo que su presencia representa una amenaza para la integridad de los ecosistemas costeros del sur de Sudamérica y para las economías de las comunidades pesqueras de la región.This note was aimed at reporting the presence of the “European green crab” Carcinus maenas in the coast of Nuevo Gulf (Chubut, Argentina). This new record extends the actual distribution range of this species 250 km to the north of San Jorge Gulf, where it was previously reported. C. maenas is one of the most successful aquatic invaders in the world, with populations established on all continents, and represents a threat to the integrity of coastal ecosystems of southern South America, and also to the economies of fishing communities of South Atlantic.Fil: Torres, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; ArgentinaFil: Gonzalez Pisani, Ximena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Biología Subtropical. Universidad Nacional de Misiones. Instituto de Biología Subtropical; Argentin

Photon Scattering by an Electric Field in Noncommutative Spacetime

As is known, the existence of a small noncommutativity between coordinates would generate nonlocal self-interactions in the electromagnetic theory. To explore some consequences of this effect on the propagation of photons we consider Moyal space half-filled with a static and homogeneous electric field and analyze electromagnetic fluctuations on top of this step-like background. Both the localization of photons and the possibility of photon production by strong electric fields are addressed. Several aspects of the Klein paradox in this setup are discussed as well.Comment: 27 pages, 13 figure

Spectral functions of non-essentially self-adjoint operators

One of the many problems to which Dowker devoted his attention is the effect of a conical singularity in the base manifold on the behavior of the quantum fields. In particular, he studied the small-t asymptotic expansion of the heatkernel trace on a cone and its effects on physical quantities as the Casimir energy. In this paper, we review some peculiar results found in the last decade, regarding the appearance of non-standard powers of t, and even negative integer powers of log t, in this asymptotic expansion for the self-adjoint extensions of some symmetric operators with singular coefficients. Similarly, we show that the ζ-function associated with these self-adjoint extensions presents an unusual analytic structure.Instituto de Física La Plat

Affine Killing vector fields on homogeneous surfaces with torsion

Many  extensions  of  General  Relativity  are  based  on  considering  metric  and  affine  structures as independent properties of spacetime.  This leads to the possibility of introducing torsion as an independent degree of freedom.  In this article we examine the effects of torsion on the affine Killing vectors of two-dimensional manifolds.  We give a complete description of the Lie algebras of affine Killing vector fields on homogeneous surfaces.  This can be used in the search of non-metrizable surfaces of interest.Fil: D'ascanio, Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Gilkey, Peter. Mathematics Department, University Of Oregon; Estados UnidosFil: González Pisani, Pablo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Worldline approach to quantum field theories on flat manifolds with boundaries

We study a worldline approach to quantum field theories on flat manifolds with boundaries. We consider the concrete case of a scalar field propagating on + × D-1 which leads us to study the associated heat kernel through a one dimensional (worldline) path integral. To calculate the latter we map it onto an auxiliary path integral on the full D using an image charge. The main technical difficulty lies in the fact that a smooth potential on + × D-1 extends to a potential which generically fails to be smooth on D. This implies that standard perturbative methods fail and must be improved. We propose a method to deal with this situation. As a result we recover the known heat kernel coefficients on a flat manifold with geodesic boundary, and compute two additional ones, A 3 and A7/2. The calculation becomes sensibly harder as the perturbative order increases, and we are able to identify the complete A 7/2 with the help of a suitable toy model. Our findings show that the worldline approach is viable on manifolds with boundaries. Certainly, it would be desirable to improve our method of implementing the worldline approach to further simplify the perturbative calculations that arise in the presence of non-smooth potentials.Instituto de Física La Plat

Renormalization on noncommutative torus

We study a self-interacting scalar φ4 theory on the d-dimensional noncommutative torus. We determine, for the particular cases d= 2 and d= 4 , the counterterms required by one-loop renormalization. We discuss higher loops in two dimensions and two-loop contributions to the self-energy in four dimensions. Our analysis points toward the absence of any problems related to the ultraviolet/infrared mixing and thus to renormalizability of the theory. However, we find another potentially troubling phenomenon which is a wild behavior of the two-point amplitude as a function of the noncommutativity matrix θ.Instituto de Física La Plat

U(N) Yang-Mills in non-commutative space time

We present an approach to U c6 (N) Yang-Mills theory in non-commutative space based upon a novel phase-space analysis of the dynamical fields with additional auxiliary variables that generate Lorentz structure and colour degrees of freedom. To illustrate this formalism we compute the quadratic terms in the effective action focusing on the planar divergences so as to extract the \u3b2-function for the Yang-Mills coupling constant. Nonetheless the method presented is general and can be applied to calculate the effective action at arbitrary order of expansion in the coupling constant and is well suited to the computation of low energy one-loop scattering amplitudes

A new example of the effects of a singular background on the zeta function

Para motivar nuestra discusión, consideramos un campo escalar dimensional 1 + 1 que interactúa con un fondo estático de tipo Coulomb, de modo que el espectro de fluctuaciones cuánticas está dado por un operador diferencial de segundo orden en una sola coordenada r con un coeficiente singular proporcional a 1 / r . Encontramos que las funciones espectrales de este operador presentan un comportamiento interesante: la función ζ tiene múltiples polos en el plano complejo; en consecuencia, aparecen logaritmos del tiempo adecuado en la expansión de trazas de calor. Como consecuencia, la función ζ no proporciona una regularización finita de la acción efectiva. Este trabajo amplía resultados similares previamente derivados en el contexto de singularidades cónicas.Fil: Falomir, Horacio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Liniado, Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: González Pisani, Pablo Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin