  With the recent publication of the measurements of the radiation angular
power spectrum from the BOOMERanG Antarctic flight (de Bernardis et al. 2000),
it has become apparent that the currently favoured spatially-flat cold dark
matter model (matter density parameter $\Omega_{\rm m}=0.3$, flatness being
restored by a cosmological constant $\Omega_{\Lambda}=0.7$, Hubble parameter
$h=0.65$, baryon density parameter $\Omega_{\rm b}h^2=0.02$) no longer provides
a good fit to the data. We describe a phenomenological approach to resurrecting
this paradigm. We consider a primordial power spectrum which incorporates a
bump, arbitrarily placed at $k_{\rm b}$, and characterized by a Gaussian in log
$k$ of standard deviation $\sigma_{\rm b}$ and amplitude ${\rm A}_{\rm b}$,
that is superimposed onto a scale-invariant power spectrum. We generate a range
of theoretical models that include a bump at scales consistent with cosmic
microwave background and large-scale structure observations, and perform a
simple $\chi^2$ test to compare our models with the $COBE$ DMR data and the
recently published BOOMERanG and MAXIMA data. Unlike models that include a high
baryon content, our models predict a low third acoustic peak. We find that low
$\ell$ observations (20 $< \ell <$ 200) are a critical discriminant of the
bumps because the transfer function has a sharp cutoff on the high $\ell$ side
of the first acoustic peak...
