Ruben Minasian

Generalized structures of N=1 vacua

We characterize = 1 vacua of type-II theories in terms of generalized complex structure on the internal manifold M. The structure group of T(M)⊕T*(M) being SU(3) × SU(3) implies the existence of two pure spinors Φ1 and Φ2. The conditions for preserving = 1 supersymmetry turn out to be simple generalizations of equations that have appeared in the context of = 2 and topological strings. They are (d+H∧)Φ1 = 0 and (d+H∧)Φ2 = FRR. The equation for the first pure spinor implies that the internal space is a twisted generalized Calabi-Yau manifold of a hybrid complex-symplectic type, while the RR-fields serve as an integrability defect for the second.

Supersymmetric backgrounds from generalized Calabi-Yau manifolds

We show that the supersymmetry transformations for type II string theories on six-manifolds can be written as differential conditions on a pair of pure spinors, the exponentiated Kahler form eiJ and the holomorphic form Ω. The equations are explicitly symmetric under exchange of the two pure spinors and a choice of even or odd-rank RR field. This is mirror symmetry for manifolds with torsion. Moreover, RR fluxes affect only one of the two equations: eiJ is closed under the action of the twisted exterior derivative in IIA theory, and similarly Ω is closed in IIB. Modulo a different action of the B–field, this means that supersymmetric SU(3)-structure manifolds are all generalized Calabi-Yau manifolds, as defined by Hitchin. An equivalent, and somewhat more conventional, description is given as a set of relations between the components of intrinsic torsions modified by the NS flux and the Clifford products of RR fluxes with pure spinors, allowing for a classification of type II supersymmetric vacua on six-manifolds. We find in particular that supersymmetric six-manifolds are always complex for IIB backgrounds while they are twisted symplectic for IIA.

The baryonic branch of Klebanov-Strassler solution: a supersymmetric family of SU(3) structure backgrounds

We exhibit a one-parameter family of regular supersymmetric solutions of type IIB theory that describes the baryonic branch of the Klebanov-Strassler (KS) theory. The solution is obtained by applying the supersymmetry conditions for SU(3)-structure manifolds to an interpolating ansatz proposed by Papadopoulos and Tseytlin. Other than at the KS point, the family does not have a conformally-Ricci-flat metric, neither it has self-dual three-form flux. By varying also the string coupling, our solution smoothly interpolates between Klebanov-Strassler and Maldacena-Nu?ez (MN). The asymptotic IR and UV are that of KS throughout the interpolating flow, except for the extremal value of the parameter where the UV solution drastically changes to MN.

Generalized complex manifolds and supersymmetry

We find a worldsheet realization of generalized complex geometry, a notion introduced recently by Hitchin which interpolates between complex and symplectic manifolds. The two–dimensional model we construct is a supersymmetric relative of the Poisson sigma model used in the context of deformation quantization.

String Loop Corrections to the Universal Hypermultiplet

We study loop corrections to the universal dilaton supermultiplet for type IIA strings compactified on Calabi-Yau threefolds. We show that the corresponding quaternionic kinetic terms receive non-trivial one-loop contributions proportional to the Euler number of the Calabi-Yau manifold, while the higher-loop corrections can be absorbed by field ��

Mirror Symmetric SU(3)-Structure Manifolds with NS Fluxes

When string theory is compactified on a six-dimensional manifold with a nontrivial NS flux turned on, mirror symmetry exchanges the flux with a purely geometrical composite NS form associated with lack of integrability of the complex structure on the mirror side. Considering a general class of T3-fibered geometries admitting SU(3) structure, we find an exchange of pure spinors (eiJ and Ω) in dual geometries under fiberwise T–duality, and study the transformations of the NS flux and the components of intrinsic torsion. A complementary study of action of twisted covariant derivatives on invariant spinors allows to extend our results to generic geometries and formulate a proposal for mirror symmetry in compactifications with NS flux.

Supersymmetric M-theory compactifications with fluxes on seven-manifolds and G-structures

We consider Minkowski compactifications of M-theory on generic seven-dimensional manifolds. After analyzing the conditions on the four-form flux, we establish a set of relations between the components of the intrinsic torsion of the internal manifold and the components of the four-form flux needed for preserving supersymmetry. The existence of two nowhere vanishing vectors on any seven-manifold with G2 structure plays a crucial role in our analysis, leading to the possibility of four-dimensional compactifications with = 1 and = 2 supersymmetry.

Kaluza-Klein bundles and manifolds of exceptional holonomy

We show how in the presence of RR two-form field strength the conditions for preserving supersymmetry on six- and seven-dimensional manifolds lead to certain generalizations of monopole equations. For six dimensions the string frame metric is Kahler with the complex structure that descends from the octonions if in addition we assume F(1,1) = 0. The susy generator is a gauge covariantly constant spinor. For seven dimensions the string frame metric is conformal to a G2 metric if in addition we assume the field strength to obey a self-duality constraint. Solutions to these equations lift to geometries of G2 and Spin(7) holonomy respectively.

Non-compact Calabi–Yau manifolds and localized gravity

Abstract We study localization of gravity in flat space in superstring theory. We find that an induced Einstein–Hilbert term can be generated only in four dimensions, when the bulk is a non-compact Calabi–Yau threefold with non-vanishing Euler number. The origin of this term is traced to R4 couplings in ten dimensions. Moreover, its size can be made much larger than the ten-dimensional gravitational Planck scale by tuning the string coupling to be very small or the Euler number to be very large. We also study the width of the localization and discuss the problems for constructing realistic string models with no compact extra dimensions.

Nontrivial RR two‐form field strength and SU(3)‐structure

We discuss how in the presence of a nontrivial RR two-form field strength and nontrivial dilaton the conditions of preserving supersymmetry on six-dimensional manifolds lead to generalized monopole and Killing spinor equations. We construct an SU(3)-structure on these manifolds and give the explicit expression of its intrinsic torsion in terms of the RR two-form field strength and dilaton. We show that the manifold is Kahler if F(1,1) = 0.