The presence of fields with negative mass–squared typically leads to some form of instability in standard field theories. The observation that, at least in the light–cone gauge, strings propagating… (More)

We propose a model with a U(1)A×U(1)B gauge symmetry which contains topological strings carrying magnetic flux under each of the U(1)s. By calculating the tension of the first few low energy strings… (More)

We analyze supersymmetric solutions of M-theory based an a seven-dimensional internal space with SU(3) structure and a four-dimensional maximally symmetric space. The most general supersymmetry… (More)

We comment on the recent papers by Costa et al and Emparan, which show how one might generate supergravity solutions describing certain dielectric branes in ten dimensions. The “basic” such solutions… (More)

We consider the effect that gravity has when one tries to set up a constant background form field. We find that in analogy with the Melvin solution, where magnetic field lines self-gravitate to form… (More)

We study four-dimensional low energy effective actions for conifold transitions of Calabi-Yau spaces in the context of IIB supergravity. The actions are constucted by examining the mass of D3-branes… (More)

We demonstrate how Sen’s singular kink solution of the Born-Infeld tachyon action can be constructed by taking the appropriate limit of initially regular profiles. It is shown that the order in which… (More)

In many inflationary models, a large amount of energy is transferred rapidly to the long-wavelength matter fields during a period of preheating after inflation. We study how this changes the dynamics… (More)

In this paper we consider cosmological scaling solutions in general relativity coupled to scalar fields with a non-trivial moduli space metric. We discover that the scaling property of the cosmology… (More)

We investigate the nature of resonant tunneling in standard scalar Quantum Field Theory. Following the pioneering work of Banks, Bender and Wu we describe the quantum field theory in terms of… (More)