
Seminars
Upcoming seminars
Joint seminars organized by the Theoretical Particle Physics Group of the VUB, the Service de Physique Théorique and the Service de Physique Théorique et Mathématique, both of the ULB, the High Energy Physics and Relativistic Field Theory group of the KUL, the Service de Mécanique et Gravitation of the UMons, and the International Solvay Institutes.
Talk requests or other comments can be addressed to the group leaders: Alexander Sevrin (VUB), Antoine Van Proeyen (KUL), Walter Troost (KUL) and Marc Henneaux (ULB).
This seminar series is supported by the IUAP/PAI V/27 and VI/11 Fundamental Interactions: at the Boundary of Theory, Phenomenology and Experiment, as well as by research projects of the three groups involved which are financed by the Fonds voor Wetenschappelijk Onderzoek  Vlaanderen and the Fonds National de la Recherche Scientifique.
Speakers are kindly invited to read the following Information for Speakers.
Academic year : September 2011  September 2012
 Unbalanced Holographic Superconductors and Spintronics
Francesco Bigazzi (University of Florence and INFN)
VUB/ULB – December 7, 2011
Superconductivity driven by the condensation of two fermionic species with different chemical potential is an interesting possibility relevant both in condensed matter and in finite density QCD setups.
The imbalance of spin populations in ferromagnetic materials is also a relevant ingredient of spintronics, the branch of electronics concerned with the study and applications of spin transport. While the behavior of unbalanced setups is well established at weak coupling, a precise theoretical model describing their physics in stronglycoupled unconventional systems (e.g. in quantum critical regions) is still lacking. With the aim of providing some toymodelbased insights on this issue, I will present the simplest holographic realization of strongly coupled unbalanced swave superconductors and forced ferromagnets in 2+1 dimensions. I will describe both equilibrium (phase diagram) and transport properties of these systems, with a focus on the conductivity matrix for charge, spin and heat currents.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 7, 2011 at 10:30
 Trivertices and SU(2)'s
Amihay Hanany (Imperial College London)
VUB/ULB  December 7, 2011
Given a graph with lines and 3valent vertices, one can construct, using a simple dictionary, a Lagrangian that has N=2 supersymmetry in 3+1 dimensions. This is a construction which generalizes the notion of a quiver. The vacuum moduli space of such a theory is well known to give moment map (F & D term) equations for a HyperKahler manifold. We will discuss the class of hyperkahler manifolds which arise due to such a construction and present their special properties. The Hilbert Series of these spaces can be computed and turns out to be a function of the number of external legs and loops in the graph but not on its detailed structure. The corresponding SCFT consequence of this property indicates a crucial universality of many Lagrangians, all of which have the same dynamics. The talk is based on http://arXiv.org/pdf/1012.2119
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 7, 2011 at 13:00
 Momentum space entanglement and renormalization in quantum field theory
Vijay Balasubramanian (University of Pennsylvania)
VUB/ULB – December 14, 2011
The degrees of freedom of any interacting quantum field theory are entangled in momentum space. Thus, in the vacuum state, the infrared degrees of freedom are described by a density matrix with an entanglement entropy. We derive a relation between this density matrix and the conventional Wilsonian effective action. We argue that the entanglement entropy of and mutual information between subsets of field theoretic degrees of freedom at different momentum scales are natural observables in quantum field theory and demonstrate how to compute these in perturbation theory. The results may be understood heuristically based on the scaledependence of the coupling strength and number of degrees of freedom. We measure the rate at which entanglement between degrees of freedom declines as their scales separate and suggest that this decay is related to the property of decoupling in quantum field theory.
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 14, 2011 at 10:30
 Jan Zaanen (Leiden)
VUB/ULB – December 14, 2011
Place: VUB/ULB, Campus Plaine, building NO, 5th floor, Salle Solvay
Time: Wednesday, December 14, 2011 at 13:00
Past seminars
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