Mikkel Nielsen

Manifestly supersymmetric M-theory

In this paper, the low-energy effective dynamics of M-theory, eleven-dimensional supergravity, is taken off-shell in a manifestly supersymmetric formulation. We show that a previously proposed relaxation of the superspace torsion constraints does indeed accommodate a current supermultiplet which lifts the equations of motion corresponding to the ordinary second order derivative supergravity lagrangian. We comment on the relation and application of this completely general formalism to higher-derivative (R4) corrections. Some details of the calculation are saved for a later publication.

The domain walls of gauged maximal supergravities and their M-theory origin

We consider gauged maximal supergravities with CSO(p,q,r) gauge groups and their relation to the branes of string and M-theory. The gauge groups are characterised by n mass parameters, where n is the transverse dimension of the brane. We give the scalar potentials and construct the corresponding domain wall solutions. In addition, we show the higher-dimensional origin of the domain walls in terms of (distributions of) branes. We put particular emphasis on the CSO(p,q,r) gauged supergravities in D = 9 and D = 8, which are related to the D7-brane and D6-brane, respectively. In these cases, twisted and group manifold reductions are shown to play a crucial role. We also discuss salient features of the corresponding brane distributions.

Scalar cosmology with multi-exponential potentials

We investigate cosmologies with an arbitrary number of scalars and the most general multi-exponential potential. By formulating the equations of motion in terms of autonomous systems, we complete the classification of power-law and de Sitter solutions as critical points, e.g. attractor and repeller solutions, in terms of the scalar couplings. Many of these solutions have been overlooked in the literature. We provide specific examples for double and triple exponential potentials with one and two scalars, where we find numerical solutions, which interpolate between the critical points. Some of these correspond to the reduction of new exotic S-brane solutions.

(p,q) 5-Branes in Non-Zero B-field

We consider type-IIB (p,q) 5-branes in constant non-zero background tensor potentials, or equivalently, with finite constant field strength on the brane. At linear level, zero-modes are introduced and the physical degrees of freedom are found to be parametrised by a real 2- or 4-form field strength on the brane. An exact, SL(2,)-covariant solution to the full non-linear supergravity equations is then constructed. The resulting metric space-times are analysed, with special emphasis on the limiting cases with maximal values of the tensor. The analysis provides an answer to how the various background tensor fields are related to Born-Infeld degrees of freedom and to non-commutativity parameters.

Non-commutative open (p,q)-string theories

In this paper we make an SL(2,Z)-covariant generalisation of the noncommutative theories, NCYM and NCOS on the D3-brane, and NCOS on the D5-brane in type IIB. Usually, the noncommutative theories are obtained by studying perturbative F-string theory, and the parameters governing the noncommutative theories are given by the open string data. The S-duality of NCYM and NCOS on the D3-brane has been seen by dualising the background, keeping the F-string under study fixed. We give an SL(2,Z)-covariant generalisation of the open string data relevant when one instead studies perturbative (p,q)-string theory. The S-duality of NCYM and NCOS on the D3-brane is reproduced by instead keeping the background fixed and studying different (p,q)-string theories. We also obtain new noncommutative open (p,q)-string theories on the D3-brane and the D5-brane which are S-dual to ordinary NCOS. The theories are studied using the supergravity duals of the D3-brane and the D5-brane, corresponding to a probe brane in the relevant background.

On the Equivalence of Bound State Solutions

In this paper we show the equivalence of various (nonthreshold) bound state solutions of branes, or equivalently branes in background potentials, in ten- and eleven-dimensional supergravity. We compare solutions obtained in two very different ways. One method uses a zero mode analysis to make an ansatz which makes it possible to solve the full nonlinear supergravity equations. The other method utilizes T duality techniques to turn on the fields on the brane. To be specific, in eleven dimensions we show the equivalence for the (M2,M5) bound state, or equivalently an M5-brane in a C(3) field, where we also consider the (MW,M2,M2′,M5) solution, which can be obtained from the (M2,M5) bound state by a boost. In ten dimensions we show the equivalence for the ((F,D1),D3) bound states as well as the bound states of (p,q) five-branes with lower dimensional branes in type IIB, corresponding to D3-branes in B(2) and C(2) fields and (p,q) five-branes in B(2), C(2) and C(4) fields. We also comment on the recently proposed V duality related to infinitesimally boosted solutions.

Domain walls and the creation of strings

The phenomenon of creation of strings, occurring when particles pass through a domain wall and related to the Hanany-Witten effect via dualities, is discussed in ten and nine dimensions. We consider both the particle actions in massive backgrounds and the 1/4-supersymmetric particle-string-domain-wall supergravity solutions and discuss their physical interpretation. In 10D we discuss the D0-F1-D8 system in massive IIA theory while in 9D the SL(2, R)-generalization is constructed. It consists of (p, q)-particles, (r, s)-strings and the double domain-wall solution of the three different 9D gauged supergravities where a subgroup of SL(2, R) is gauged.

Gauged supergravities from Bianchi's group manifolds

We construct maximal D = 8 gauged supergravities by the reduction of D = 11 supergravity over three-dimensional group manifolds. Such manifolds are classified into two classes, A and B, and eleven types. This Bianchi classification carries over to the gauged supergravities. The class A theories have 1/2 BPS domain wall solutions that uplift to purely gravitational solutions consisting of 7D Minkowski and a 4D Euclidean geometry. These geometries are generically singular. The two regular exceptions correspond to the nearhorizon limit of the single- or double-centre Kaluza–Klein monopole. In contrast, the class B supergravities are defined by a set of equations of motion that cannot be integrated to an action and allow for no 1/2 BPS domain walls.