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P. Smyth

Publications and source records attributed to P. Smyth.

2 recordsLinked to original sources

On certain Kähler quotients of quaternionic Kähler manifolds

We prove that, given a certain isometric action of a two-dimensional Abelian group A on a quaternionic Kähler manifold M which preserves a submanifold N\subset M, the quotient M'=N/A has a natural Kähler structure. We verify that the assumptions on the group action and on the submanifold N\subset M are satisfied for a large class of examples obtained from the supergravity c-map. In particular, we find that all quaternionic Kähler manifolds M in the image of the c-map admit an integrable complex structure compatible with the quaternionic structure, such that N\subset M is a complex submanifold. Finally, we discuss how the existence of the Kähler structure on M' is required by the consistency of spontaneous {\cal N}=2 to {\cal N}=1 supersymmetry breaking.

math.DG

Stability of Horava-Witten Spacetimes

Horava-Witten spacetimes necessarily include two branes of opposite tension. If these branes are BPS we are led to a puzzle: a negative tension brane should be unstable as it can loose energy by expanding, whereas a BPS brane should be stable as it resides at a minimum of the energy. We provide a detailed analysis of the energy of such braneworld spacetimes in 5 dimensions. This allows us to show by a non-perturbative positive energy theorem that Horava-Witten spacetimes are stable, essentially because the dynamics of the branes is entirely accounted for by the behaviour of the bulk fields. We also perform an ADM perturbative Hamiltonian analysis at quadratic order in order to illustrate the stability properties more explicitly.

hep-th