We review recent developments and applications of the classification of the Weyl tensor in
higher dimensional Lorentzian geometries. First, we discuss the general setup, ie main …

A bstract We compute the entanglement entropy for some quantum field theories on de Sitter
space. We consider a superhorizon size spherical surface that divides the spatial slice into …

These notes are an expanded version of a review paper on closed string tachyon
condensation at the RTN workshop in Copenhagen in September 2003. We begin with a …

We construct smooth nonsupersymmetric soliton solutions with D1-brane, D5-brane, and
momentum charges in type IIB supergravity compactified on T 4× S 1, with the charges along …

We consider string theory in a time dependent orbifold with a null singularity. The singularity
separates a contracting universe from an expanding universe, thus constituting a big crunch …

We explore a classical instability of spacetimes of dimension D> 4. First, we consider static
solutions: generalized black holes and brane world metrics. The dangerous mode is a …

We continue and extend our earlier investigation``Strings in a Time-Dependent
Orbifold''(hep-th/0204168). We formulate conditions for an orbifold to be amenable to …

A bstract We study the evolution of holographic complexity in various AdS/CFT models
containing cosmological crunch singularities. We find that a notion of complexity measured …

We discuss a general iterative procedure for constructing time dependent solutions in open
string theory describing rolling of a generic tachyon field away from its maximum. These …

We propose a new cosmological scenario which resolves the conventional initial singularity
problem. The space–time geometry has an unconventional time-like singularity on a lower …