String Theory clues for the low-$\ell$ CMB ?
  "Brane Supersymmetry Breaking" is a peculiar string-scale mechanism that can
unpair Bose and Fermi excitations in orientifold models. It results from the
simultaneous presence, in the vacuum, of collections of D-branes and
orientifolds that are not mutually BPS, and is closely tied to the scale of
string excitations. It also leaves behind, for a mixing of dilaton and internal
breathing mode, an exponential potential that is just too steep for a scalar to
emerge from the initial singularity while descending it. As a result, in this
class of models the scalar can generically bounce off the exponential wall, and
this dynamics brings along, in the power spectrum, an infrared depression
typically followed by a pre-inflationary peak. We elaborate on a possible link
between this type of bounce and the low-$\ell$ end of the CMB angular power
spectrum. For the first 32 multipoles, one can reach a 50 % reduction in
$\chi^{\,2}$ with respect to the standard $\Lambda$CDM setting.
