Sourced Scalar Fluctuations in Bouncing Cosmology
  We calculate the scalar power spectrum generated by sourced fluctuations due
to coupling between the scalar field, which holds most of the energy density of
the universe, and a gauge field for a general FLRW metric. For this purpose we
calculate the curvature perturbation to second order in the presence of gauge
fields, and show that the gauge fields behave like an additional potential
term. We then apply the analysis to the case of slow-contraction. Due to the
interaction between the scalar field and gauge fields additional 'sourced'
tensor and scalar spectra are generated. The resulting spectra are chiral,
slightly blue and arbitrarily close to scale invariance. The only difference
between the tensor and scalar spectra is the coupling constant with an
${\mathcal O}(1)$ numerical coefficient, and some momentum space polarization
vectors. As a result the tilt of the spectra are the same. For the nearly scale
invariant case, the momentum integration gives the same leading contribution.
Hence, $r\simeq 1/9$ where the deviation from this value is controlled by the
deviation from scale invariance, and is not in agreement with CMB observations.
Deviating considerably from near scale invariance, and considering a bluer tilt
with $n_T>0.12$, the model cannot account for CMB observations, but can be
detected by LIGO and/or LISA in the future.
