Planck residuals anomaly as a fingerprint of alternative scenarios to
  inflation
  Planck's residuals of the CMB temperature power spectrum present a curious
oscillatory shape that resembles an extra smoothing effect of lensing and is
the source of the lensing anomaly. The smoothing effect of lensing to the CMB
temperature power spectrum is, to some extent, degenerate with oscillatory
modulations of the primordial power spectrum, in particular if the frequency is
close to that of the acoustic peaks. We consider the possibility that the
lensing anomaly reported by the latest Planck 2018 results may be hinting at an
oscillatory modulation generated by a massive scalar field during an
alternative scenario to inflation or by a sharp feature during inflation. We
use the full TTTEEE+low E CMB likelihood from Planck to derive constraints on
these two types of models. We obtain that in both cases the $A_L$ anomaly is
mildly reduced to slightly less than $2\sigma$, to be compared with the
$2.8\sigma$ deviation from $A_L=1$ in $\Lambda$CDM. Although the oscillatory
features are not able to satisfactorily ease the lensing anomaly, we find that
the oscillatory modulation generated during an alternative scenario alone, i.e.
with $A_L=1$, presents the lowest value of $\chi^2$, with $\Delta\chi^2=-13$
compared to $\Lambda$CDM. Furthermore, the Akaike Information Criterion
suggests that such an oscillation constitutes an attractive candidate since it
has a value $\Delta{\rm AIC}=-5$ with respect to $\Lambda$CDM, comparable to
the $A_L$ parameter. We also obtain that the equation of state parameter in the
alternative scenario is given at $1\sigma$ by $w=0.13\pm0.17$. Interestingly,
the matter bounce and radiation bounce scenarios are compatible with our
results. We discuss how these models of oscillatory features can be tested with
future observations.
