Per Berglund

Supergravity microstates for BPS black holes and black rings

We demonstrate a solution generating technique, modulo some constraints, for a large class of smooth supergravity solutions with the same asymptotic charges as a five dimensional 3-charge BPS black hole or black ring, dual to a D1/D5/P system. These solutions are characterized by a harmonic function with both positive and negative poles, which induces a geometric transition whereby singular sources have disappeared and all of the net charge at infinity is sourced by fluxes through two-cycles joining the poles of the harmonic function.

Stringy corrections to Kähler potentials, SUSY breaking, and the cosmological constant problem

The moduli of N = 1 compactifications of IIB string theory can be stabilized by a combination of fluxes (which freeze complex structure moduli and the dilaton) and nonperturbative superpotentials (which freeze Kahler moduli), typically leading to supersymmetric AdS vacua. We show that stringy corrections to the Kahler potential qualitatively alter the structure of the effective scalar potential even at large volume, and can give rise to non-supersymmetric vacua including metastable de Sitter spacetimes. Our results suggest an approach to solving the cosmological constant problem, so that the scale of the 1-loop corrected cosmological constant can be much smaller than the scale of supersymmetry breaking.

Non-perturbative superpotentials in F-theory and string duality

A bstractWe use open-closed string duality between F-theory on K3 × K3 and type II strings on CY manifolds without branes to study non-perturbative superpotentials in generalized flux compactifications. On the F-theory side we obtain the full flux potential including D3-instanton contributions and show that it leads to an explicit and simple realization of the three ingredients of the KKLT model for stringy dS vacua. The D3- instanton contribution is highly non-trivial, can be systematically computed including the determinant factors and demonstrates that a particular flux lifts very effectively zero modes on the instanton. On the closed string side, we describe a generalization of the Gukov- Vafa-Witten superpotential for type II strings on generalized CY manifolds, depending on all moduli multiplets.

New Higgs transitions between dual N = 2 string models

Abstract We describe a new kind of transition between topologically distinct N = 2 type II Calabi-Yau vacua through points with enhanced non-abelian gauge symmetries together with fundamental charged matter hyper multiplets. We connect the appearance of matter to the local geometry of the singularity and discuss the relation between the instanton numbers of the Calabi-Yau manifolds taking part in the transition. In a dual heterotic string theory on K 3 × T 2 the process corresponds to Higgsing a semi-classical gauge group or equivalently to a variation of the gauge bundle. In special cases the situation reduces to simple conifold transitions in the Coulomb phase of the non-abelian gauge symmetries.

Periods for Calabi-Yau and Landau-Ginzburg vacua☆

Abstract The complete structure of the moduli space of Calabi-Yau manifolds and the associated Landau-Ginzburg theories, and hence also of the corresponding low-energy effective theory that results from (2, 2) superstring compactification, may be determined in terms of certain holomorphic functions called periods. These periods are shown to be readily calculable for a great many such models. We illustrate this by computing the periods explicitly for a number of classes of Calabi-Yau manifolds. We also point out that it is possible to read off from the periods certain important information relating to the mirror manifolds.

On type IIB vacua with varying coupling constant

Abstract We describe type IIB compactifications with varying coupling constant in d = 6,7,8,9 dimensions, where part of the ten-dimensional SL (2,ℤ) symmetry is broken by a background with γ 1 ( n )orγ( n ) monodromy for n = 2,3,4. This extends the known class of F-theory vacua to theories which are dual to heterotic compactifications with reduced rank. On compactifying on a further torus, we obtain a description of the heterotic moduli space of G bundles over elliptically fibered manifolds without vector structure in terms of complex geometries.

Matter from G2 manifolds

Abstract We describe how chiral matter charged under SU ( N ) and SO (2 N ) gauge groups arises from codimension seven singularities in compactifications of M-theory on manifolds with G 2 holonomy. The geometry of these spaces is that of a cone over a six-dimensional Einstein space which can be constructed by (multiple) unfolding of hyper-Kahler quotient spaces. In type IIA the corresponding picture is given by stacks of intersecting D6-branes and chiral matter arises from open strings stretching between them. Usually one obtains (bi)fundamental representations but by including orientifold six-planes in the type IIA picture we find more exotic representations like the anti-symmetric, which is important for the study of SU (5) grand unification, and trifundamental representations. We also exhibit many cases where the G 2 metrics can be described explicitly, although in general the metrics on the spaces constructed via unfolding are not known.

ON ELEVATING FREE-FERMION Z2×Z2 ORBIFOLDS MODELS TO COMPACTIFICATIONS OF F THEORY

We study the elliptic fibrations of some Calabi–Yau threefolds, including the Z2×Z2 orbifold with (h1,1,h2,1)=(27, 3), which is equivalent to the common framework of realistic free-fermion models, as well as related orbifold models with (h1,1,h2,1)=(51, 3) and (31, 7). However, two related puzzles arise when one considers the (h1,1,h2,1)=(27, 3) model as an F theory compactification to six dimensions. The condition for the vanishing of the gravitational anomaly is not satisfied, suggesting that the F theory compactification does not make sense, and the elliptic fibration is well defined everywhere except at four singular points in the base. We speculate on the possible existence of N=1 tensor and hypermultiplets at these points which would cancel the gravitational anomaly in this case.

De Sitter spacetimes from warped compactifications of IIB string theory

Abstract We continue our study of codimension two solutions of warped spacetime varying compactifications of string theory. In this Letter we discuss a non-supersymmetric solution of the classical type IIB string theory with de Sitter gravity on a codimension two uncompactified part of spacetime. A non-zero positive value of the cosmological constant is induced by the presence of non-trivial stringy moduli, such as the axion–dilaton system for the type IIB string theory. Furthermore, the naked singularity of the codimension two solution is resolved by the presence of a small but non-zero cosmological constant.

Topology from cosmology

We show that cosmological observables can constrain the topology of the compact additional dimensions predicted by string theory. To do this, we develop a general strategy for relating cosmological observables to the microscopic parameters of the potentials and field-dependent kinetic terms of the multiple scalar fields that arise in the low-energy limit of string theory. We apply this formalism to the Large Volume Scenarios in Type IIB flux compactifications where analytical calculations are possible. Our methods generalize to other settings.