Calculating Non-adiabatic Pressure Perturbations during Multi-field
  Inflation
  Isocurvature perturbations naturally occur in models of inflation consisting
of more than one scalar field. In this paper we calculate the spectrum of
isocurvature perturbations generated at the end of inflation for three
different inflationary models consisting of two canonical scalar fields. The
amount of non-adiabatic pressure present at the end of inflation can have
observational consequences through the generation of vorticity and subsequently
the sourcing of B-mode polarisation. We compare two different definitions of
isocurvature perturbations and show how these quantities evolve in different
ways during inflation. Our results are calculated using the open source
Pyflation numerical package which is available to download.
