Optimal CMB estimators for bispectra from excited states
  We propose optimal estimators for bispectra from excited states. Two common
properties of such bispectra are the enhancement in the collinear limit, and
the prediction of oscillating features. We review the physics behind excited
states and some of the choices made in the literature. We show that the
enfolded template is a good template in the collinear limit, but does poorly
elsewhere, establishing a strong case for an improved estimator. Although the
detailed scale dependence of the bispectra differs depending on various
assumptions, generally the predicted bispectra are either effectively 1 or
2-dimensional and a simple Fourier basis suffices for accurate reconstruction.
For an optimal CMB data analysis, combining all n-point functions, the choice
for the excited state needs to be the same when computing power spectrum,
bispectrum and higher order correlation functions. This has not always been the
case, which could lead to wrong conclusions. We calculate the bispectrum for
different choices previously discussed for the power spectrum, setting up a
consistent framework to search for evidence of excited states in the CMB data.
