  We investigate the possibility that a heavy scalar field, whose mass exceeds
the Hubble scale during inflation, could leave non-negligible signatures in the
Cosmic Microwave Background (CMB) temperature anisotropy power spectrum through
the parametric resonance between its background oscillations and the inflaton
fluctuations. By assuming the heavy scalar field couples with the inflaton
derivatively, we show that the resonance can be efficient without spoiling the
slow-roll inflation. The primordial power spectrum modulated by the resonance
has a sharp peak at a specific scale and could be an origin of the anomalies
observed in the angular power spectrum of the CMB. In some values of
parameters, the modulated spectrum can fit the observed data better than the
simple power-law power spectrum, though the resultant improvement of the fit is
not large enough and hence other observations such as non-Gaussianity are
necessary to confirm that the CMB anomalies are originated from the resonant
effect of the heavy scalar field. The resonant signatures can provide an
opportunity to observe heavy degrees of freedom during inflation and improve
our understanding of physics behind inflation.
