Past seminars, Department of Gravitation and Field Theory, ICN

EL FONDO COSMICO DE RADIACION: STATUS ACTUAL Y PERSPECTIVAS PARA EL FUTURO

por

Dra. Susana Landau

Universidad de Buenos Aires, Argentina

Resumen: Las mediciones de la anisotropía y polarización del Fondo Cósmico de Radiación (FCR) son una de las mejores herramientas para estudiar el universo temprano así como también para testear modelos alternativos al modelo estándar de Big Bang. En los ultimos años se han realizado gran cantidad de observaciones con globos y telescopios terrestres, culminando con el satélite WMAP. En esta charla, describimos el origen de las anisotropías primarias y secundarias del FCR. A su vez, presentaremos resultados recientes asi como también las estimaciones de parámetros cosmológicos como la densidad de bariones, de materia oscura, la constante de Hubble asi como los parámetros correspondientes a los modelos de inflación. Por ultimo, se discutirán los experimentos futuros y que tipo de información se espera obtener.

BACKREACTION: FROM LORENTZ-DIRAC TO DE SITTER STABILITY

by

Prof. E. Verdaguer

University of Barcelona

Abstract: We will begin with the well known backreaction problem in classical electrodynamics where the reaction to the radiation of a charged particle can be described by the Lorentz-Dirac equation. We will review the limits of validity of the equation, the spurious solutions and the ways to deal with them. A very similar problem appears in semiclassical gravity where the semiclassical Einstein equations describe the reaction of the gravitational field to quantum fields. In this context we study the stability of de Sitter spacetime under spatially homogeneous and isotropic perturbations due to non-conformal fields in a large variety of vacuum states and conclude that this spacetime is stable.

SUPERSYMMETRIC SOLITONS AND DYNAMICS OF NON-ABELIAN GAUGE THEORIES

by

Prof. A. Yung

University of Minnesota & NPI, St. Petersburg & ITEP, Moscow

Abstract: First we discuss non-Abelian flux tubes (strings) in supersymmetric gauge theories with gauge group U(N). They are supposed to be responsible for non-Abelian confinement. Their main feature is the presence of orientational zero modes which rotate the color flux inside the
non-Abelian subgroup. The effective low energy dynamics of these orientational moduli is described by two dimensional CP(N-1) sigma
models. Confined monopoles of the bulk theory are seen as kinks in the effective CP(N-1) model. Next we focus on field theory prototypes
of D-branes. We consider N=2 QED with domain walls and flux tubes. We show that U(1) gauge field can be localized in the domain wall
world volume. Moreover flux tubes can end on the domain wall and their end points play a role of electric charges in the effective 2+1 dimensional QED living on the wall.

RELATIVITY THEORY ON THE TEST BENCH

by

Dr. Ralf Lehnert

Max Planck Institut für Physik, Munich, Germany

Abstract: The largest gap in our understanding of Nature at the fundamental level is perhaps a unified description of quantum theory and gravity. Although there are a number of theoretical approaches to this issue, experimental research in this field is hampered by the expected Planck suppression of quantum-gravity effects. However, violations of spacetime symmetries have recently been identified as promising signatures: various models for underlying physics can accommodate minuscule Lorentz breakdown, and such effects are amenable to ultrahigh-precision tests. This talk will give an overview of the subject. Topics such as motivations, the SME test model, mechanisms for relativity violations, and experimental tests will be reviewed. Possible future research directions will be discussed briefly.

COLISION DE DOS AGUJEROS NEGROS

por

M. en C. Milton Ruiz

ICN -- UNAM

Resumen: En esta charla discutimos las principales técnicas empleadas en relatividad numérica para conseguir evoluciones estables de dos agujeros negros en órbita. Usando un ejemplo simple, discutimos los recientes resultados obtenidos tales como la energía radiada por el sistema en forma de ondas gravitacionales.

May 27, 2008 (Tuesday, 17:00, Marcos Moshinsky Auditorium)

NONPERTURBATIVE RESULTS IN NONCOMMUTATIVE FIELD THEORY

by

Dr. Wolgang Bietenholz

John von Neumann Institute for Computing (NIC), Zeuthen, Germany

Abstract: We present a non-perturbative study of the phi^4 model on a three dimensional non-commutative space, based on numerical simulations. A new phase occurs where translation symmetry is spontaneously broken, so that stripe patterns dominate. In this phase the dispersion relation is deformed in the IR sector, in agreement with the property of UV/IR mixing. Next we address non-commutative U(1) gauge theory, where general Wilson loops are complex. In d=2 small Wilson loops are real and follow an area law, whereas for large Wilson loops the complex phase rises linearly with the area, analogous to the Aharonov-Bohm effect. In d=4 we investigate the phase diagram and its extrapolation to the continuum and infinite volume by means of a double scaling limit. Due to another phase of broken translation symmetry the photon appears to be IR stable in non-commutative spaces, despite the perturbatively negative IR singularity. We evaluate the corresponding dispersion relation explicitly.

May 8, 2008

PATRONES DE BUSQUEDA EN HOMINIDOS

por

Dr. Octavio Miramontes

IF-UNAM

Resumen: Un tema que ha despertado mucho interes recientemente es el de la difusion anomala, donde los objetos en movimiento pueden ser superdifusivos o subdifusivos. El estudio de como los animales se desplazan cuando realizan busquedas de recursos en su medio ambiente, evidencia que se trata de procesos de difusión anomala relacionados con optimizacion. Los vuelos de Levy son un tipo de difusion anomala que caracteriza los desplazamientos de hominidos como los monos arania y los humanos prehistoricos y modernos. La caracterizacion de dichos desplazamientos sugiere una categoria de universalidad compartida con una gran variedad de procesos fisicos donde hay estadisticas que muestran colas largas.

April 30, 2008 (Wednesday, 17:00, auditorium Marcos Moshinsky, new building)

HIGH ENERGY COLLISIONS OF BLACK HOLES

by

Dr. Ulrich Sperhake

Friedrich-Schiller University, Jena

Abstract: We present numerical simulations of collisions of black holes with varying boost parameter. This study covers the range from vanishing initial boost to the regime where the total mass is dominated by the kinetic energy. These simulations represent the most dynamic and violent scenarios studied to date using numerical methods. The resulting gravitational wave emission is analyzed and compared with analytic predictions.
April 24, 2008

CARBON NANOTUBES AND THEIR APPLICATIONS

por

Dr. Vladimir Basiuk

ICN-UNAM

Resumen: Se dará una breve información sobre que son los nanotubos de carbono, sus diferentes tipos (dependiendo del número de paredes, quiralidad, terminaciones, etc.), sobre los métodos de su obtención, sus observaciones microscópicas, la historia de su descubrimiento, así como sus aplicaciones presentes y futuras.

April 24, 2008 (Thursday, 13:00, seminar room, new building)

GEOMETRY AND WILSON LOOPS IN (2+1)-DIMENSIONAL GRAVITY

by

Dr. Catherine Meusburger

Perimeter Institute, Waterloo

Abstract: Due to the absence of local gravitational degrees of freedom, Einstein's theory of gravity in (2+1) dimensions can be formulated as a Chern-Simons gauge theory. The Chern-Simons formulation of (2+1)-dimensional gravity provides an efficient parametrisation of phase space and Poisson structure, which serves as a starting point for quantisation, as well as a complete set of gauge invariant Wilson loop observables. Its drawback is that it obscures the underlying spacetime geometry and thereby complicates the physical interpretation of the theory.

In my talk I relate the geometrical and the Chern-Simons description of vacuum spacetimes of general genus and with general cosmological constant. I discuss how the geometry of the spacetime can be recovered from the variables parametrising the phase space in the Chern-Simons formalism and how changes of geometry manifest themselves as transformations on the phase space. I show that the two basic transformations which change the geometry of the spacetime, infinitesimal Dehn twists and grafting along a closed, simple geodesic, are generated via the Poisson bracket by the two associated canonical Wilson loop observables. By introducing a description in which the cosmological constant plays the role of a deformation parameter, I demonstrate that these two transformations are closely related and that grafting can be viewed as an infinitesimal Dehn twist (earthquake) with a formal parameter whose square is minus the cosmological constant.
April 17, 2008

ON A NONCOMMUTATIVE VERSION OF THE MOVING-FRAME FORMALISM OF ELI CARTAN AND ITS EVENTUAL USE IN CONSTRUCTING A NONCOMMUTATIVE EXTENSION OF THE SCHWARZSCHILD METRIC, AS WELL AS OF OTHER POPULAR METRICS, AND A DISCUSSION OF THE RELATION OF THE CONDITION THAT THERE BE NO JACOBI ANOMALY WITH THE CONDITION THAT THE METRIC BE RICCI FLAT.

by

Prof. John Madore

University of Paris, Orsay

Abstract: See title.

April 10, 2008

NONCOMMUTATIVE GRAVITY AND SCHWARZSCHILD SOLUTION

by

Prof. Peter Schupp

Jacobs University, Bremen

Abstract: Heuristic arguments suggest that the classical picture of smooth commutative spacetime should be replaced by some kind of quantum geometry at length scales and energies where quantum as well as gravitational effects are important. Motivated by this idea much research has been devoted to the study of quantum field theory on noncommutative spacetimes. More recently the focus has started to shift back to gravity in this context. We give an introductory overview to the formulation of general relativity in a noncommutative spacetime background and discuss the possibility of exact solutions.

April 3, 2008

GEOMETRY IN TRANSITION: A MODEL OF EMERGENT GEOMETRY

by

Prof. Denjoe O'Connor

Abstract: A possible scenario in which classsical geometry arises as an emergent concept is illustrated by discussing a simple 3 matrix model that exhibits the basic phenomenon.

THE DYNAMICS OF CLASSICAL SPINNING PARTICLES IN CURVED SPACETIME

by

Dr. Dinesh Singh

University of Regina, Canada

Abstract: Understanding the kinematic and dynamical properties of spinning astrophysical objects in strong gravitational fields is a longstanding topic of general relativity research. This involves a direct coupling of the object's spin angular momentum to the background gravitational field due to a black hole, gravitational wave, or any other mass-energy distribution. External forces and torques due to this coupling are then applied to the object that drive it away from geodesic motion in curved space-time. Considerable progress has occurred since the first contribution to the subject by Mathisson in the 1930s, most notably due to Papapetrou in the 1950s, and then by Dixon about twenty years thereafter. While competing models disagree with respect to higher order multipole moment effects, all approaches recover the leading order terms due to the mass monopole and spin dipole, which describe the Mathisson-Papapetrou-Dixon (MPD) equations of motion.

This presentation explores some applications of the MPD equations to describe the dynamics of a classical spinning particle in orbit around static and rotating black holes, with potential observational consequences for gravitational radiation detection in space by the Laser Interferometric Space Antenna (LISA) under development. Focus will be given to recent numerical work on orbital dynamics around a Schwarzschild black hole in the presence of infalling radiation, as described by the Vaidya metric. An analytic description of circular motion around a Kerr black hole, based on an approximated form of the MPD equations, will also be shown. This presentation will conclude with some very recent work outlining a more complete analytic treatment of the MPD equations, with the potential for impact on many research directions in general relativity today.

Resumen: En esta plática explicaremos cómo la transición confinamiento-deconfinamiento es descrita desde el punto de vista de la correspondencia Gauge-Gravitación. Inicialmente describiremos la transición de Hawking-Page entre un espacio-tiempo anti de Sitter y otro anti de Sitter con hoyo negro. Luego describiremos la solución de Klebanov-Strassler y y una solución con una asíntota similar en la frontera, pero con un hoyo negro en el origen. Daremos evidencias de una transición entre estas dos fases. Finalmente mostraremos cómo esta transición podría ocurrir (termo)-dinámicamente en el marco de la fase deconfinada.

Resumen: El estudio de la mecánica cuántica en el toro borroso es el estudio de la mecánica cuántica sobre el toro plano T^2, un plano con coordenadas $\chi$ y $\varphi$, donde los puntos $\chi=-\pi$, $\varphi=-\pi$ se identifican con los $\chi=\pi$, $\varphi=\pi$ respectivamente, "no conmutativo" (las comillas se explicarán). Se discutirá la mecánica cuántica ordinaria de una partícula moviendose en T^2, y después la mecánica cuántica en donde los operadores $\hat{\chi}$ y $\hat{\varphi}$ "no conmutan". Estudiando las funciones clásicas de Weyl asociadas con operadores sobre T^2 nos dará un "producto Moyal" distinto al usual.

Resumen: Nuestro planeta, como el único mundo habitado que conocemos, nos ha dado las primeras lecciones de lo compleja que resulta la interacción entre la biosfera y los procesos geológicos y atmosféricos. Este conocimiento se está usando para determinar que compuestos podrían indicar la presencia de vida en otros mundos. En este seminario se presentarán a las bioseñales y a los instrumentos que serán capaces de detectarlas.

JETS ASTROFISICOS DE FUENTES VARIABLES

por

Dr. Alejandro Raga

ICN-UNAM

Resumen: Objetos astrofisicos "compactos" (estrellas o agujeros negros) a veces eyectan pares de "jets" (= chorros) hipersonicos en direcciones opuestas. El mecanismo preferido (por nosotros los astronomos) para explicar la eyeccion es la presencia de un disco de acrecion alrededor del objeto compacto, el cual "pierde" material que pasa a formar los jets.
Los jets mismos tienen una dinamica interesante, con formacion de choques como resultado de una variabilidad en la eyeccion. Esta dinamica puede ser descrita analiticamente (con modelos de "ram pressure balance" o de "conservacion de momento"), o numericamente
(con simulaciones axisimetricas o 3D). De estos modelos se pueden hacer predicciones que se pueden comparar en forma directa con observaciones de jets astrofisicos.
Este juego entre modelos dinamicos y observaciones de jets astrofisicos ha permitido lograr un entendimiento sobre estos objetos practicamente no igualado en ningun campo de la astrofisica. Este exito se debe a que las observaciones resuelven tanto espacial como
temporalmente los flujos asociados con (al menos algunos) jets astrofisicos.