# String Seminars

This series consists of talks in the area of Superstring Theory.

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

## Background Independent Holographic Description : From Matrix Field Theory to Quantum Gravity

Tuesday May 22, 2012
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A local renormalization group procedure is proposed where length scale is changed in spacetime dependent manner. Combining this scheme with an earlier observation that high energy modes in renormalization group play the role of dynamical sources for low energy modes at each scale, we provide a prescription to derive background independent holographic duals for field theories.

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## On-shell Recursion Relation for String Tree-level Amplitude

Tuesday May 08, 2012
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It is well known that on-shell recursion relation can be applied to tree-level amplitude in string theory. One technical issue of the application is the sum of infinite middle on-shell states. We discuss how we can do the sum exactly to reproduce the known result.

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## Simple Scattering Amplitudes in Higher Dimensions

Tuesday Apr 17, 2012
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TBA

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## K3 Modular Parametrization and Calabi-Yau Threefold Moduli

Tuesday Mar 27, 2012
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A series of generalizations of the Weierstrass normal
form for elliptic curves to the case of K3 surfaces will be presented.  These have already been applied to better
understand F-theory/Heterotic string duality.
We will see how they also resolve a long-standing question of which
"mirror-compatible" variations of Hodge structure over the
thrice-punctured sphere can arise from families of Calabi-Yau threefolds.

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## Instanton - A Window into Physics of M5-branes

Friday Mar 23, 2012
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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.

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## Lifshitz Solutions in String Theory

Tuesday Mar 20, 2012
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I'll discuss solutions with Lifshitz scaling within
string supergravity for an arbitrary scaling component z. After showing how to
get exact Lifshitz spacetimes, I'll then look at more general solutions,
including black holes and flows between Lifshitz and adS spacetimes.

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## The MSSM Spectrum from Deforming the Heterotic Standard Embedding

Friday Mar 16, 2012
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## Quantum Integrability for Three-Point Functions

Friday Mar 02, 2012
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Quantum corrections to three-point functions of scalar single trace operators in planar ${\cal N}=4$ Super-Yang-Mills theory are studied using integrability. At one loop, we find  new algebraic structures that not only govern all two loop corrections to the mixing of the operators but also automatically incorporate all one loop diagrams correcting the tree level Wick contractions. Speculations about possible extensions of our construction to all loop orders are given. We also match our results with the strong coupling predictions in the classical (Frolov-Tseytlin) limit.

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## SUSY Gauge Theories on Squashed 3-spheres

Tuesday Feb 28, 2012
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I will explain some recent exact developments in N=2 SUSY gauge theories on 3-sphere and its deformations. I will begin by the analysis of Killing spinors and their generalization which are necessary to construct SUSY theories on curved spaces. Then I will sketch the exact computation of partition function using SUSY localization and present a general formula. Some applications to the physics of M5-branes will also be discussed.

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## Instanton Corrections to Hypermultiplet Moduli Spaces

Tuesday Feb 21, 2012
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Finding the exact, quantum corrected metric on the hypermultiplet moduli space in Type II string compactifications on Calabi-Yau threefolds is still an open problem. We address this issue by relating the quaternionic-Kähler metric on the hypermultiplet moduli space to the complex contact geometry on its twistor space. In this framework, Euclidean D-brane instantons are captured by contact transformations between different patches.

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## RECENT PUBLIC LECTURE

### Niels Bohr: Life Behind the Physics

Speaker: Vilhelm Bohr