It is shown that a change in the signature of the space-time metric together with compactification of internal dimensions could occur in a six-dimensional cosmological model. We also show that this is due to interaction with Maxwell fields having support in the internal part of the space-time. PACS: 0.420.Gz,0.4.50+h

This paper represents a continuation of our programme [16, 13] of extending various concepts of general topology from the setting of Hausdorff (or, at most, 7̂ ) spaces, in which they are usually embedded, to the larger classes of spaces we need to consider in the theory of computation. The topic of compactification poses an obvious challenge to this programme, since only a Tychonoff space can h...

It is shown – using a FRW model with S 3 × S 6 as spatial sections and a positive cosmological constant – that classical signature change implies a new compactification mechanism. The internal scale factor is of the order Λ −1/2 , and the solutions are stable against small perturbatons. In the case of compactified S 6 , it is shown that the effective four-dimensional space-time metric has Loren...

Following a recent suggestion by Randall and Sundrum, we consider string compactification scenarios in which a compact slice of AdS-space arises as a subspace of the compactification manifold. A specific example is provided by the type II orientifold equivalent to type I theory on (orbifolds of) T , upon taking into account the gravitational backreaction of the D3-branes localized inside the T ...

The duality symmetry group of the cosets SU(n, 1) SU(n)⊗ U(1) , which describe the moduli space of a two-dimensional subspace of an orbifold model with (n − 1) complex Wilson lines moduli, is discussed. The full duality group and its explicit action on the moduli fields are derived. ∗ e-mail: [email protected]. 1 The derivation of a field theoretic low-energy effective action from string ...

We discuss various dual pairs of M-theory compactifications. Each pair consists of a compactification in which the two-brane plays the central role in relation to a string theory and a compactification in which the five-brane takes center stage. We show that in many examples such dual pairs are interchanged by the same duality transformation in each case.

We derive the noncommutative torus compactification of M(atrix) theory directly from the string theory by imposing mixed boundary conditions on the membranes. The relation of various dualities in string theory and M(atrix) theory compactification on the noncommutative torus are studied.

We study the T 5/Z2 orbifold compactification of the M-theory matrix model. This model was originally studied by Dasgupta, Mukhi, and Witten. It was found that one had to add 16 5-branes to the system to make the compactification consistent. We demonstrate how this is mimicked in the matrix model. E-mail: [email protected] E-mail: [email protected] A recent proposal by Banks, Fischler, Shenker and Suss...

For a T3.s-ordered space, certain families of maps are designated as "defining families." For each such defining family we construct the smallest T=-ordered compactification such that each member of the family can be extended to the compactification space. Each defining family also generates a quasi-uniformity on the space whose bicompletion produces the same T=-ordered

We construct the Hilbert compactification of the universal moduli space of semistable vector bundles over smooth curves. The Hilbert compactification is the GIT quotient of some open part of an appropriate Hilbert scheme of curves in a Graßmannian. It has all the properties asked for by Teixidor.