Past String Theory Seminar

1 December 2014
12:00
Dmytro Volin
Abstract

The planar N=4 SYM is believed to be integrable. Following this thoroughly justified belief, its exact spectrum had been encoded recently into a quantum spectral curve (QSC). We can explicitly solve the QSC in various regimes; in particular, one can perform a highly-efficient weak coupling expansion.

I will explain how QSC looks like for the harmonic oscillator and then, using this analogy, introduce the QSC equations for the SYM spectrum. We will use these equations to compute a particular 6-loop conformal dimension in real time and then discuss explicit results (found up to 10-loop orders) as well as some general statements about the answer at any loop-order.

  • String Theory Seminar
24 November 2014
12:00
Mario Garcia Fernandez
Abstract

I will give an overview of ongoing joint work with R. Rubio and C. Tipler, in which we study the moduli problem for the Strominger system of equations. Building on the work of De la Ossa and Svanes and, independently, of Anderson, Gray and Sharpe, we construct an elliptic complex whose first cohomology group is the space of infinitesimal deformations of a solution of the strominger system. I will also discuss an intriguing link between this moduli problem and a moduli problem for holomorphic Courant algebroids over Calabi-Yau threefolds. Finally, we will see how the problem for the Strominger system embeds naturally in generalized geometry, and discuss some perspectives of this approach.

  • String Theory Seminar
17 November 2014
12:00
Paul Richmond
Abstract

I will describe the computation of the supersymmetric Renyi entropy across an entangling 3-sphere for five-dimensional superconformal field theories. For a class of USp(2N) gauge theories I’ll also construct a holographic dual 1/2 BPS black hole solution of Euclidean Romans F(4) supergravity. The large N limit of the gauge theory results will be shown to agree perfectly with the supergravity computations.

  • String Theory Seminar
10 November 2014
12:00
Tomasz Lukowski
Abstract
In this talk I will discuss how to construct all solutions consistent with crossing symmetry in the limit of large central charge $c ~ N^2$, starting from the four-point correlator of the stress tensor multiplet in N=4 SYM. Unitarity forces the introduction of a scale $\Delta_{gap}$ and these solutions organize as a double expansion in 1/c and $1/\Delta_{gap}$. These solutions are valid to leading order in 1/c and to all orders in $1/\Delta_{gap}$ and reproduce, in particular, instanton corrections previously found. Comparison with such instanton computations allows to fix $\Delta_{gap}$. Using this gap scale one can explain the upper bounds for the scaling dimension of unprotected operators observed in the numerical superconformal bootstrap at large central charge. Furthermore, I will present connections between such upper bounds and positivity constraints arising from causality in flat space and I will discuss how certain relations derived from causality constraints for scattering in AdS follow from crossing symmetry.
 
  • String Theory Seminar
3 November 2014
12:00
Abstract
I will begin by introducing different surface defects in 4d N=2 supersymmetric gauge theories, and discuss how the 4d supersymmetry breaking effect can descend into the 2d world volume theories of the surface defects.
I will then discuss how certain surface defects can naturally appear as saddle point solutions in 4d N=1 and N=2 superconformal indices, also confirm this with explicit 2d elliptic genus calculations. I will wrap up the talk by discussing their roles in different field theoretic dualities.
  • String Theory Seminar
27 October 2014
12:00
Sven Krippendorf
Abstract

I will discuss the implementation of explicit stabilisation of all closed string moduli in fluxed type IIB Calabi-Yau compactifications with chiral matter.  Using toric geometry we construct Calabi-Yau manifolds with del Pezzo singularities. D-branes located at such singularities can support the Standard Model gauge group and matter content. We consider Calabi-Yau manifolds with a discrete symmetry that reduces the effective number of complex structure moduli, which allows us to calculate the corresponding periods and find explicit flux vacua. We compute the values of the flux superpotential and the string coupling at these vacua. Starting from these explicit complex structure solutions, we obtain AdS and dS minima where the Kaehler moduli are stabilised by a mixture of D-terms, non-perturbative and perturbative alpha'-corrections as in the LARGE Volume Scenario.

  • String Theory Seminar
20 October 2014
12:00
Andreas Braun
Abstract

I will discuss several recent developments regarding the construction of fluxes for F-theory on Calabi-Yau fourfolds. Of particular importance to the effective physics is the structure of the middle (co)homology groups, on which new results are presented. Fluxes dynamically drive the fourfold to Noether-Lefschetz loci in moduli space. While the structure of such loci is generally unknown for Calabi-Yau fourfolds, this problem can be answered in terms of arithmetic for K3 x K3 and a classification is possible.

  • String Theory Seminar
16 June 2014
12:00
Abstract
<em>I will discuss the validity of the claims that eternal inflation populates the landscape and show the reasons for the mathematical inconsistency between the two. Within the formalism of quantum cosmology, solutions for the wavefunction of the universe to the landscape are Anderson localized. The latter can give rise to observational tests of the landscape, some of which are already supported from Planck's findings of anomalies at large scales.</em>
  • String Theory Seminar
9 June 2014
12:00
Igor Buchberger
Abstract
<em>I will discuss four-dimensional minimally supersymmetric toroidal orientifold models with D-branes and worldvolume flux. With flux but no orbifold projection, these models are well understood. They have been used extensively in various phenomenological contexts, and are T-dual to D-branes at angles. With orbifold, supersymmetry is reduced also in the closed string sector, and T-duality relations are not always straightforward. I will discuss work in progress on aspects of the one-loop string effective actions of these more general models.</em>
  • String Theory Seminar

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