Hints of Isocurvature Perturbations in the Cosmic Microwave Background?
  The improved data on the cosmic microwave background (CMB) anisotropy allow a better determination of the adiabaticity of the primordial perturbation. Interestingly, we find that recent CMB data seem to favor a contribution of a primordial isocurvature mode where the entropy perturbation is positively correlated with the primordial curvature perturbation and has a large spectral index (niso ~ 3). With 4 additional parameters we obtain a better fit to the CMB data by Delta chi^2 = 9.7 compared to an adiabatic model. For this best-fit model the nonadiabatic contribution to the CMB temperature variance is 4%. According to a Markov Chain Monte Carlo analysis the nonadiabatic contribution is positive at more than 95% C.L. The exact C.L. depends somewhat on the choice of priors, and we discuss the effect of different priors as well as additional cosmological data. 
Reijo Keskitalo (HIP and Helsinki U.), Hannu Kurki-Suonio (Helsinki   U.), Vesa Muhonen (HIP and Helsinki U.) and Jussi Vali...