Ref HAL: hal-01071271_v1
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Résumé:

I propose to consider a new function on the moduli space of N=2 supersymmetruic gauge theories in 4 dimensions. It encodes the BPS spectrum of the theory and possesses many intersting properties which make it unique and one of the most natural objects to be studied.

Ref HAL: hal-01099930_v1
Ref Arxiv: 1412.8182
DOI: 10.1007/JHEP02(2015)176
WoS: 000350695900001
Ref. & Cit.: NASA ADS
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13 Citations
Résumé:

We use the twistorial construction of D-instantons in Calabi-Yau compactifications of type II string theory to compute an explicit expression for the metric on the hypermultiplet moduli space affected by these non-perturbative corrections. In this way we obtain an exact quaternion-Kahler metric which is a non-trivial deformation of the local c-map. In the four-dimensional case corresponding to the universal hypermultiplet, our metric fits the Tod ansatz and provides an exact solution of the continuous Toda equation. We also analyze the fate of the curvature singularity of the perturbative metric by deriving an S-duality invariant equation which determines the singularity hypersurface after inclusion of the D(-1)-instanton effects.

Commentaires: 20+12+4 pages

Ref HAL: hal-01059619_v1
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Résumé:

The low-energy effective action of Type II string theory compactified on a Calabi-Yau threefold is determined by the metric on the vector and hypermultiplet moduli spaces. The latter is known to receive instanton corrections coming from D-branes and NS5-branes wrapping cycles on the Calabi-Yau. I'll show how all of them can be nicely incorporated using twistorial techniques. In particular, fivebrane instantons are derived using S-duality of the type IIB formulation. I'll present also a conjecture for the Witten index of 4d N=2 gauge theories inspired by the twistorial description of the hypermultiplet moduli space.

Ref HAL: hal-01057398_v1
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Résumé:

I present an overview of the recent results and open problems in finding the non-perturbative effective action for compactifications of type II string theory on Calabi-Yau manifolds.

Ref HAL: hal-01052742_v1
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After a brief review of unusual features of the light front canonical formulations of field theories, I present the analysis of the canonical structure of the first order formulation of general relativity on a lightlike foliation. It appears to be quite different from the usual spacelike case leading, for instance, to the presence of tertiary constraints. Besides, I discuss the issue of the zero modes and argue that there might be some hidden correspondence with two-dimensional theories.

Ref HAL: hal-01006533_v1
Ref Arxiv: 1405.4792
DOI: 10.1007/JHEP08(2014)092
WoS: 000340505800005
Ref. & Cit.: NASA ADS
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6 Citations
Résumé:

Heterotic string compactifications on a $K3$ surface $\mathfrak{S}$ depend on a choice of hyperkähler metric, anti-self-dual gauge connection and Kalb-Ramond flux, parametrized by hypermultiplet scalars. The metric on hypermultiplet moduli space is in principle computable within the $(0,2)$ superconformal field theory on the heterotic string worldsheet, although little is known about it in practice. Using duality with type II strings compactified on a Calabi-Yau threefold, we predict the form of the quaternion-Kähler metric on hypermultiplet moduli space when $\mathfrak{S}$ is elliptically fibered, in the limit of a large fiber and even larger base. The result is in general agreement with expectations from Kaluza-Klein reduction, in particular the metric has a two-stage fibration structure, where the $B$-field moduli are fibered over bundle and metric moduli, while bundle moduli are themselves fibered over metric moduli. A more precise match must await a detailed analysis of $R^2$-corrected ten-dimensional supergravity.

Commentaires: 20 pages

Ref HAL: hal-00992829_v1
Ref Arxiv: 1405.0291
DOI: 10.1007/jhep11(2014)040
WoS: 000344749600003
Ref. & Cit.: NASA ADS
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7 Citations
Résumé:

We derive the fivebrane instanton corrections to the hypermultiplet moduli space $M_H$ of Calabi-Yau string vacua using S-duality symmetry of the type IIB formulation. The result is given in terms of a set of holomorphic functions on the twistor space of $M_H$. It contains not only all orders of the instanton expansion, but also takes into account the presence of D1-D(-1)-brane instantons. Furthermore, we provide a thorough study of the group of discrete isometries of $M_H$ and show that its closure requires a modification of certain symmetry transformations. After this modification, the fivebrane instantons are proven to be consistent with the full duality group.

Commentaires: 40 pages, 3 figures