Abstract
JHEP 9906:014,1999 Recently, a number of authors have challenged the conventional assumption
that the string scale, Planck mass, and unification scale are roughly
comparable. It has been suggested that the string scale could be as low as a
TeV. In this note, we explore constraints on these scenarios. We argue that the
most plausible cases have a fundamental scale of at least 10 TeV and five
dimensions of inverse size 10 MeV. We show that a radial dilaton mass in the
range of proposed millimeter scale gravitational arises naturally in these
scenarios. Most other scenarios require huge values of flux and may not be
realizable in M Theory. Existing precision experiments put a conservative lower
bound of 6-10 TeV on the fundamental energy scale. We note that large
dimensions with bulk supersymmetry might be a natural framework for
quintessence, and make some other tentative remarks about cosmology.