An Observational Test of Two-field Inflation
  We study adiabatic and isocurvature perturbation spectra produced by a period of cosmological inflation driven by two scalar fields. We show that there exists a model-independent consistency condition for all two-field models of slow-roll inflation, despite allowing for model-dependent linear processing of curvature and isocurvature perturbations during and after inflation on super-horizon scales. The scale-dependence of all spectra are determined solely in terms of slow-roll parameters during inflation and the dimensionless cross-correlation between curvature and isocurvature perturbations. We present additional model-dependent consistency relations that may be derived in specific two-field models, such as the curvaton scenario. 
David Wands (1), Nicola Bartolo (2,3), Sabino Matarrese (2) and   Antonio Riotto (2) ((1) Portsmouth, (2) Padova, (3) Sussex)