Visible Branes with Negative Tension in Heterotic M-Theory

Abstract

It is shown that there exist large classes of BPS vacua in heterotic M-theory which have negative tension on the visible orbifold plane, positive tension on the hidden plane and positive tension, physical five-branes in the bulk space. Explicit examples of such vacua are presented. Furthermore, it is demonstrated that the ratio, beta/|alpha|, of the bulk five-brane tension to the visible plane tension can, for several large classes of such vacua, be made arbitrarily small. Hence, it is straightforward to find vacua with the properties required in the examples of the Ekpyrotic theory of cosmology - a visible brane with negative tension and beta/|alpha| small. This contradicts recent claims in the literature.