A String-Inspired Model for the Low-$\ell$ CMB
  We present a semi--analytic exploration of some low--$\ell$ angular power
spectra inspired by "Brane Supersymmetry Breaking". This mechanism splits Bose
and Fermi excitations in String Theory, leaving behind an exponential potential
that is just too steep for the inflaton to emerge from the initial singularity
while descending it. As a result, the scalar generically bounces against the
exponential wall, which typically introduces an infrared depression and a
pre--inflationary peak in the power spectrum of scalar perturbations. We
elaborate on a possible link between this phenomenon and the low--$\ell$ CMB.
For the first 32 multipoles, combining the hard exponential with a milder one
leading to $n_s\simeq 0.96$ and with a small gaussian bump we have attained a
reduction of $\chi^{\,2}$ to about 46% of the standard $\Lambda$CDM setting,
with both WMAP9 and PLANCK 2013 data. This result corresponds to a
$\chi^{\,2}/DOF$ of about 0.45, to be compared with a $\Lambda$CDM value of
about 0.85. The preferred choices combine naturally quadrupole depression, a
first peak around $\ell=5$ and a wide minimum around $\ell=20$. We have also
gathered some evidence that similar spectra emerge if the hard exponential is
combined with more realistic models of inflation. A problem of the preferred
examples is their slow convergence to an almost scale--invariant profile.
