Abstract
This paper analyzes the supersymmetric solutions to five and six-dimensional minimal (un)gauged supergravities for which the bilinear Killing vector constructed from the Killing spinor is null. We focus on the spacetimes which admit an additional SO(1,1) boost symmetry. Upon the toroidal dimensional reduction along the Killing vector corresponding to the boost, we show that the solution in the ungauged case describes a charged, nonextremal black hole in a Friedmann–Lemaître–Robertson–Walker (FLRW) universe with an expansion driven by a massless scalar field. For the gauged case, the solution corresponds to a charged, nonextremal black hole embedded conformally into a Kantowski–Sachs universe. It turns out that these dimensional reductions break supersymmetry since the bilinear Killing vector and the Killing vector corresponding to the boost fail to commute. This represents a new mechanism of supersymmetry breaking that has not been considered in the literature before.
Highlights
Over the last two decades, many developments of superstring theory have been triggered by supersymmetric solutions in supergravities
The supersymmetric solutions are divided into two categories, according to the causal character of the vector field constructed from the Killing spinor, i.e., timelike and null classes
We pointed out that the null family of supersymmetric solutions ingauged supergravities admits an interesting class of dynamical spacetimes that describe black holes in an expanding universe upon dimensional reduction
Summary
Over the last two decades, many developments of superstring theory have been triggered by supersymmetric solutions in supergravities. It follows that supersymmetric black holes belonging to the timelike class are timeindependent with degenerate horizons and allow for a superposition principle, as inferred from the MajumdarPapapetrou solution. This represents a situation in which gravitational and electromagnetic fields are in mechanical equilibrium. The black hole is time-dependent and admits nondegenerate horizons, both of these properties counter to those for supersymmetric black holes in the timelike class This is possible because our supersymmetric solutions belong to the null family. We show that the five-dimensional null BPS family in minimal (un)gauged supergravity admits solutions describing (after a KK reduction) a black hole in equilibrium in an expanding universe.
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