Dennis B. Westra

De Sitter solutions in N = 4 matter coupled supergravity

We investigate the scalar potential of gauged N = 4 supergravity with matter. The extremum in the SU(1, 1)/U(1) scalars is obtained for an arbitrary number of matter multiplets. The constraints on the matter scalars are solved in terms of an explicit parametrisation of an SO(6, 6 + n) element. For the case of six matter multiplets we discuss both compact and noncompact gauge groups. In an example involving noncompact groups and four scalars we find a potential with an absolute minimum and a positive cosmological constant.

Potential and mass-matrix in gauged N = 4 supergravity

We discuss the potential and mass-matrix of gauged N = 4 matter coupled supergravity for the case of six matter multiplets, extending previous work by considering the dependence on all scalars. We consider all semi-simple gauge groups and analyse the potential and its first and second derivatives in the origin of the scalar manifold. Although we find in a number of cases an extremum with a positive cosmological constant, these are not stable under fluctuations of all scalar fields.

Gauging CSO groups in N=4 supergravity

We investigate a class of CSO-gaugings of = 4 supergravity coupled to 6 vector multiplets. Using the CSO-gaugings we do not find a vacuum that is stable against all scalar perturbations at the point where the matter fields are turned off. However, at this point we do find a stable cosmological scaling solution.

Scaling cosmologies of N=8 gauged supergravity

We construct exact cosmological scaling solutions in gauged supergravity. We restrict to solutions for which the scalar fields trace out geodesic curves on the scalar manifold. Under these restrictions it is shown that the axionic scalars are necessarily constant. The potential is then a sum of exponentials and has a very specific form that allows for scaling solutions. The scaling solutions describe eternal accelerating and decelerating power-law universes, which are unstable. An uplift of the solutions to 11-dimensional supergravity is carried out and the resulting time-dependent geometries are discussed. In the discussion we briefly comment on the fact that gauged supergravity allows accelerating stable scaling solutions.

Dynamics of generalized assisted inflation

We study the dynamics of multiple scalar fields and barotropic fluid in an FLRW-universe. The scalar potential is a sum of exponentials. All critical points are constructed and these include scaling and de Sitter solutions. A stability analysis of the critical points is performed for generalized assisted inflation, which is an extension of assisted inflation where the fields mutually interact. Effects in generalized assisted inflation which differ from assisted inflation are emphasized. One such difference is that an (inflationary) attractor can exist if some of the exponential terms in the potential are negative.

Group manifold reduction of dual N=1 d=10 supergravity

We perform a group manifold reduction of the dual version of N = 1 d = 10 supergravity to four dimensions. The effects of the 3- and 4-form gauge fields in the resulting gauged N = 4 d = 4 supergravity are studied in particular. The example of the group manifold SU(2) A— SU(2) is worked out in detail, and we compare for this case the four-dimensional scalar potential with gauged N = 4 supergravity.

Coset symmetries in dimensionally reduced heterotic supergravity

We investigate the coset structures which appear in the dimensional reduction of supergravity theories. Especially we investigate how to recognize the global symmetry groups if the coset is non-split. As an example we apply our analysis to the theories emanating from the dimensional reduction of Heterotic supergravity.