A Proposal for Constraining Initial Vacuum by CMB
  We propose a theoretical framework that can possibly constrain the initial
vacuum by Cosmic Microwave Background (CMB) observations. With a generic vacuum
without any particular choice a priori, thereby keeping both the Bogolyubov
coefficients in the analysis, we compute observable parameters from two- and
three-point correlation functions. We are thus left with constraining four
model parameters from the two complex Bogolyubov coefficients. We also
demonstrate a method of finding out the constraint relations between the
Bogolyubov coefficients using the theoretical normalization condition and
observational data of power spectrum and bispectrum from CMB. Finally, we
discuss the possible pros and cons of the analysis.
