91̽»¨

Abstract:

We present the first examples of cosmological solutions to four-dimensional heterotic models which include an evolving bundle modulus. The particular bundle modulus we consider corresponds to the width of a gauge five brane. As such our solutions can be used to describe the evolution in one of these models after a small instanton transition. We find that certain properties are generic to these solutions, regardless of initial conditions. This enables us to make some definite statements about the dynamics subsequent to a small instanton transition despite the fact that we cannot microscopically describe the process itself. We also show that an effective description of the small instanton transition by a continuous matching of fields and their first derivatives is precluded by the form of the respective low-energy theories before and after the transition. © 2004 The American Physical Society.

Abstract:

We present a Kähler potential for four-dimensional heterotic M-theory which includes moduli describing a gauge five-brane living on one of the orbifold fixed planes. This result can also be thought of as describing compactifications of either of the weakly coupled heterotic strings in the presence of a gauge five-brane. This is the first example of a Kähler potential in these theories which includes moduli describing background gauge field configurations. Our results are valid when the solitons width is much smaller than the size scale of the Calabi-Yau threefold and can be used to provide a more complete description of some moving brane scenarios. We point out that, in general, it is not consistent to truncate away the gauge five-brane moduli in a simple manner. © 2004 The American Physical Society.

Abstract:

In a two-dimensional toy model, motivated from five-dimensional heterotic M theory, we study the collision of scalar field kinks with boundaries. By numerical simulation of the full two-dimensional theory, we find that the kink is always inelastically reflected with a model-independent fraction of its kinetic energy converted into radiation. We show that the reflection can be analytically understood as a fluctuation around the scalar field vacuum. This picture suggests the possibility of spontaneous emission of kinks from the boundary due to small perturbations in the bulk. We verify this picture numerically by showing that the radiation emitted from the collision of an initial single kink eventually leads to a bulk populated by many kinks. Consequently, processes changing the boundary charges are practically unavoidable in this system. We speculate that the system has a universal final state consisting of a stack of kinks, their number being determined by the initial energy. © 2004 The American Physical Society.

Abstract:

We compute the moduli Kähler potential for M theory on a compact manifold of [Formula Presented] holonomy in a large radius approximation. Our method relies on an explicit [Formula Presented] structure with small torsion, its periods and the calculation of the approximate volume of the manifold. As a verification of our result, some of the components of the Kähler metric are computed directly by integration over harmonic forms. We also discuss the modification of our result in the presence of codimension-four singularities and derive the gauge-kinetic functions for the massless gauge fields that arise in this case. © 2004 The American Physical Society.

Abstract:

We study the time evolution of freely rolling moduli in the context of M-theory on a G2 manifold. This free evolution approximates the correct dynamics of the system at sufficiently large values of the moduli when effects from non-perturbative potentials and flux are negligible. Moduli fall into two classes, namely bulk moduli and blow-up moduli. We obtain a number of non-trivial solutions for the time-evolution of these moduli. As a generic feature, we find the blow-up moduli always expand asymptotically at early and late time. © SISSA/ISAS 2004.