Found 7 result(s)
Regular Seminar Andy au:O'Bannon'><span class='hl'>Andy</span> O'Bannon (University of Southampton)
at: 13:15 room S2.49  abstract: Mtheory is currently our best candidate for a theory of everything, but remains mysterious. We know Mtheory has M2 and M5branes. The lowenergy theory on a stack of coincident M2branes is wellunderstood: it is maximally supersymmetric ChernSimonsmatter theory. However, the lowenergy theory on a stack of coincident M5branes remains poorlyunderstood: it is a maximally supersymmetric theory of selfdual strings with zero tension. In this talk I will discuss one type of probe of the M5brane theory, namely selfdual strings with infinite tension. These play a role analogous to Wilson lines in gauge theories, but are twodimensional surfaces rather than lines, and hence are called Wilson surfaces. I will describe holographic calculations of entanglement entropy associated with these infinitetension selfdual strings, from which we extract a key parameter characterizing them, their central charge. This provides a count of the number of massless degrees of freedom living on them, and thus may shed light on some of the fundamental degrees of freedom of Mtheory. 
Regular Seminar Andy au:O'Bannon'><span class='hl'>Andy</span> O'Bannon (Southampton)
at: 14:00 room G.O. Jones 610  abstract: I will present a proof for a monotonicity theorem, or ctheorem, for a threedimensional Conformal Field Theory (CFT) on a space with a boundary, and for a higherdimensional CFT with a twodimensional defect. The proof is applicable only to renormalization group flows that preserve locality, reflection positivity, and Euclidean invariance along the boundary or defect, and that are localized at the boundary or defect, such that the bulk theory remains conformal along the flow. The method of proof is a generalization of Komargodskiâ€™s proof of Zamolodchikovâ€™s ctheorem. The key ingredient is an external â€œdilatonâ€ field introduced to match Weyl anomalies between the ultraviolet (UV) and infrared (IR) fixed points. Reflection positivity in the dilatonâ€™s effective action guarantees that a certain coefficient in the boundary/defect Weyl anomaly must take a value in the UV that is larger than (or equal to) the value in the IR. This boundary/defect ctheorem may have important implications for many theoretical and experimental systems, ranging from graphene to branes in string theory and Mtheory. 
Regular Seminar Andy au:Royston'><span class='hl'>Andy</span> Royston (Texas U.)
at: 14:00 room G.O. Jones 610  abstract: In this talk we consider BPS states in 4D, N=2 gauge theory in the presence of defects. We give a semiclassical description of these `framed BPS states' in terms of kernels of Dirac operators on moduli spaces of singular monopoles. For both framed and ordinary BPS states we present a conjectural map between the data of the semiclassical construction and the data of the lowenergy, quantumexact SeibergWitten description. This map incorporates both perturbative and nonperturbative field theory corrections to the supersymmetric quantum mechanics of the monopole collective coordinates. We use it to translate recent developments in the study of N=2 theories, including wallcrossing formulae and the noexotics theorem, into geometric statements about the Dirac kernels. The noexotics theorem implies a broad generalization of Sen's conjecture concerning the existence of L^2 harmonic forms on monopole moduli space. This talk is based on work done in collaboration with Greg Moore and Dieter Van den Bleeken. 
Regular Seminar Andy au:Royston'><span class='hl'>Andy</span> Royston (Texas AM)
at: 14:00 room H503  abstract: In this talk we consider BPS states in 4D, N=2 gauge theory in the presence of defects. We give a semiclassical description of these `framed BPS states' in terms of kernels of Dirac operators on moduli spaces of singular monopoles. For both framed and ordinary BPS states we present a conjectural map between the data of the semiclassical construction and the data of the lowenergy, quantumexact SeibergWitten description. This map incorporates both perturbative and nonperturbative field theory corrections to the supersymmetric quantum mechanics of the monopole collective coordinates. We use it to translate recent developments in the study of N=2 theories, including wallcrossing formulae and the noexotics theorem, into geometric statements about the Dirac kernels. The noexotics theorem implies a broad generalization of Sen's conjecture concerning the existence of L^2 harmonic forms on monopole moduli space. This talk is based on work done in collaboration with Greg Moore and Dieter Van den Bleeken. 
Regular Seminar Andy au:O'Bannon'><span class='hl'>Andy</span> O'Bannon (Oxford)
at: 14:00 room H503  abstract: The Kondo effect occurs in metals doped with magnetic impurities: in the ground state the electrons form a screening cloud around each impurity, leading to dramatic changes in the thermodynamic and transport properties of the metal. Although the singleimpurity Kondo effect is considered a solved problem, many questions remain, especially about the fate of the Kondo effect in the presence of multiple impurities. In particular, for a sufficiently dense concentration of impurities, a competition between the Kondo effect and interimpurity interactions can lead to quantum criticality and nonFermi liquid behavior, which remains poorly understood. In this talk I will present a model of the singleimpurity Kondo effect based on holography, also known as gaugegravity duality or the AdS/CFT correspondence, which may serve as a foundation for a new approach to the multipleimpurity system. 
Regular Seminar Andy au:O'Bannon'><span class='hl'>Andy</span> O'Bannon (MPI Munich)
at: 14:00 room 423  abstract: Gaugegravity duality is an extremely useful tool for studying stronglycoupled gauge theories, and has many applications to realworld systems, such as the quarkgluon plasma and quantum critical points. Most gaugegravity dualities involve a gauge theory with fields only in the adjoint representation of the gauge group. In many stronglycoupled systems, however, such as the quarkgluon plamsa, fields in the fundamental representation of the gauge group, 'flavor fields', are crucially important. For (3+1)dimensional gauge theories with gravity duals (AdS5/CFT4), the supergravity description of flavor fields is wellunderstood: flavor fields appear in supergravity as probe Dbranes in AdS5. The story for (2+1)dimensional gauge theories (AdS4/CFT3) is much less developed. Indeed, for supergravity on AdS4 x S7, the dual (2+1)dimensional field theory (without flavor) was only recently discovered. In this talk I will describe how to add flavor to this theory. In particular, I will present a general recipe to determine the field theory, and in particular the couplings of the flavor fields, given a probe Dbrane in AdS4. 
Regular Seminar andyopadhyay'>Pratul B<span class='hl'>andy</span>opadhyay (Indian Statistical Institute, Calcutta)
at: 14:00 room H503  abstract:
