Ulf H. Danielsson

The world next door: Results in landscape topography

Recently, it has become clear that neighboring multiple vacua might have interesting consequences for the physics of the early universe. In this paper we investigate the topography of the string landscape corresponding to complex structure moduli of flux compactified type IIB string theory. We find that series of continuously connected vacua are common. The properties of these series are described, and we relate the existence of infinite series of minima to certain unresolved mathematical problems in group theory. Numerical studies of the mirror quintic serve as illustrating examples.

A Note on inflation and transPlanckian physics

In this paper we consider the influence of trans-Planckian physics on the CMBR anisotropies produced by inflation. We consider a simple toy model that allows for analytic calculations and argue on general grounds, based on ambiguities in the choice of vacuum, that effects are expected with a magnitude of the order of

Black holes in asymptotically Lifshitz spacetime

H/\ensuremath{\Lambda},

The moduli space and monodromies of N = 2 supersymmetric SO(2r + 1) Yang-Mills theory

where H is the Hubble constant during inflation and \ensuremath{\Lambda} the scale for new physics, e.g., the Planck scale.

D-PARTICLE DYNAMICS AND BOUND STATES

A model of 3+1 dimensional gravity with negative cosmological constant coupled to abelian gauge fields has been proposed as a gravity dual for Lifshitz like critical phenomena in 2+1 dimensions. The finite temperature behavior is described by black holes that are asymptotic to the Lifshitz fixed point geometry. There is a one-parameter family of charged black holes, where the magnitude of the charge is uniquely determined by the black hole area. These black holes are thermodynamically stable and become extremal in the limit of vanishing size. The theory also has a discrete spectrum of localized objects described by non-singular spacetime geometries. The finite temperature behavior of Wilson loops is reminiscent of strongly coupled gauge theories in 3+1 dimensions, including screening at large distances.

Towards classical de Sitter solutions in string theory

Abstract We write down the weak-coupling limit of N = 2 supersymmetric Yang-Mills theory with arbitrary gauge group G . We find the weak-coupling monodromies represented in terms of Sp(2r, Z ) matrices depending on paths closed up to Weyl transformations in the Cartan space of complex dimension r , the rank of the group. There is a one to one relation between Weyl orbits of these paths and elements of a generalized braid group defined from G . We check that these weak-coupling monodromies behave correctly in limits of the moduli space corresponding to restrictions to subgroups. In the case of SO(2 r + 1) we write down the complex curve representing the solution of the theory. We show that the curve has the correct monodromies.

Transplanckian energy production and slow roll inflation

We study the low energy effective theory describing the dynamics of D-particles. This corresponds to the quantum-mechanical system obtained by dimensional reduction of (9+1)-dimensional supersymmetric Yang-Mills theory to 0+1 dimensions and can be interpreted as the nonrelativistic limit of the Born-Infeld action. We study the system of two like-charged D-particles and find evidence for the existence of non-BPS states whose mass grows like λ1/3 over the BPS mass. We give a string interpretation of this phenomenon in terms of a linear potential generated by strings stretching from the two D-particles. Some comments on the possible relations to black hole entropy and elevendimensional supergravity are also given.

Holographic superconductors with Lifshitz scaling

We investigate the type II string effective potential at tree-level for de Sitter critical points. We derive necessary ingredients for having de Sitter solutions in orientifold models with fluxes. Furthermore, we examine some explicit O6 compactifications in IIA theory on manifolds with SU(3)-structure in the limit where the orientifold sources are smeared. In particular, we use a simple ten-dimensional Ansatz for four-dimensional de Sitter solutions and find the explicit criteria in terms of the torsion classes such that these de Sitter solutions solve the equations of motion. We have verified these torsion conditions for the cosets and the Iwasawa manifold and it turns out that the conditions cannot be fulfilled for these spaces. However this investigation allows us to find new non-supersymmetric AdS solutions for some cosets. It remains an open question whether there exist SU(3)-structure manifolds that satisfy the conditions on the torsion classes for the simple de Sitter solutions to exist.

Creation of fundamental strings by crossing Dirichlet branes

In this paper we investigate how the energy density due to a nonstandard choice of initial vacuum affects the expansion of the universe during inflation. To do this we introduce source terms in the Friedmann equations making sure that we respect the relation between gravity and thermodynamics. We find that the energy production automatically implies a slow rolling cosmological constant. Hence we also conclude that there is no well defined value for the cosmological constant in the presence of sources. We speculate that a nonstandard vacuum can provide slow roll inflation on its own.

Spherically collapsing matter in AdS, holography, and shellons

Black holes in asymptotically Lifshitz spacetime provide a window onto finite temperature effects in strongly coupled Lifshitz models. We add a Maxwell gauge field and charged matter to a recently proposed gravity dual of (2+1)-dimensional Lifshitz theory. This gives rise to charged black holes with scalar hair, which correspond to the superconducting phase of holographic superconductors with z > 1 Lifshitz scaling. Along the way we analyze the global geometry of static, asymptotically Lifshitz black holes at the arbitrary critical exponent z > 1. In all known exact solutions there is a null curvature singularity in the black hole region, and, by a general argument, the same applies to generic Lifshitz black holes.