String Theory Seminar
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Mon, 23/04/2012 12:00 |
Carlos Nunez (Swansea University) |
String Theory Seminar  |
L3 |
| I will discuss some recent progress connecting different quiver gauge theories and some applications of these results. | |||
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Mon, 30/04/2012 12:00 |
Andrew Hodges (Oxford) |
String Theory Seminar |
L3 |
A simple formula is given for the  -field tree-level MHV gravitational
amplitude, based on soft limit factors. It expresses the full  symmetry
naturally, as a determinant of elements of a symmetric ( ) matrix. |
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Mon, 07/05/2012 12:00 |
Noppadol Mekareeya (Max Planck Institut fuer Physik) |
String Theory Seminar |
L3 |
| In this talk, I will focus on an infinite class of 3d N=4 gauge theories which can be constructed from a certain set of ordered pairs of integer partitions. These theories can be elegantly realised on brane intervals in string theory. I will give an elementary review on such brane constructions and introduce to the audience a symmetry, known as mirror symmetry, which exchanges two different phases (namely the Higgs and Coulomb phases) of such theories. Using mirror symmetry as a tool, I will discuss a certain geometrical aspect of the vacuum moduli spaces of such theories in the Coulomb phase. It turns out that there are certain infinite subclasses of such spaces which are special and rather simple to study; they are complete intersections. I will mention some details and many interesting features of these spaces. | |||
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Mon, 14/05/2012 12:00 |
Yang-Hui He (City University London) |
String Theory Seminar |
L3 |
| We establish a correspondence between generalized quiver gauge theories in four dimensions and congruence subgroups of the modular group, hinging upon the trivalent graphs which arise in both. The gauge theories and the graphs are enumerated and their numbers are compared. The correspondence is particularly striking for genus zero torsion-free congruence subgroups as exemplified by those which arise in Moonshine. We analyze in detail the case of index 24, where modular elliptic K3 surfaces emerge: here, the elliptic j-invariants can be recast as dessins d'enfant which dictate the Seiberg-Witten curves. | |||
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Mon, 21/05/2012 12:00 |
Chris Hull (Imperial College London) |
String Theory Seminar |
L3 |
| String theory on a torus requires the introduction of dual coordinates conjugate to string winding number. This leads to physics and novel geometry in a doubled space. This will be compared to generalized geometry, which doubles the tangent space but not the manifold. For a d-torus, string theory can be formulated in terms of an infinite tower of fields depending on both the d torus coordinates and the d dual coordinates. This talk focuses on a finite subsector consisting of a metric and B-field (both d x d matrices) and a dilaton all depending on the 2d doubled torus coordinates. The double field theory is constructed and found to have a novel symmetry that reduces to diffeomorphisms and anti-symmetric tensor gauge transformations in certain circumstances. It also has manifest T-duality symmetry which provides a generalisation of the usual Buscher rules to backgrounds without isometries. The theory has a real dependence on the full doubled geometry: the dual dimensions are not auxiliary. It is concluded that the doubled geometry is physical and dynamical. | |||
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Mon, 28/05/2012 12:00 |
Sungjay Lee (University of Cambridge) |
String Theory Seminar |
L3 |
| Instantons and W-bosons in 5d N=2 Yang-Mills theory arise from a circle compactification of the 6d (2,0) theory as Kaluza-Klein modes and winding self-dual strings, respectively. We study an index which counts BPS instantons with electric charges in Coulomb and symmetric phases. We first prove the existence of unique threshold bound state of U(1) instantons for any instanton number. By studying SU(N) self-dual strings in the Coulomb phase, we find novel momentum-carrying degrees on the worldsheet. The total number of these degrees equals the anomaly coefficient of SU(N) (2,0) theory. We finally propose that our index can be used to study the symmetric phase of this theory, and provide an interpretation as the superconformal index of the sigma model on instanton moduli space. | |||
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Mon, 11/06/2012 12:00 |
David Shih (Rutgers University) |
String Theory Seminar |
L3 |
