Hints of Isocurvature Perturbations in the Cosmic Microwave Background?

Details Hints of Isocurvature Perturbations in the Cosmic Microwave Background? Hints of Isocurvature Perturbations in the Cosmic Microwave Background?

2006-11-30

arxiv.org/abs/astro-ph/0611917v4

JCAP0709:008,2007

Astronomy and Astrophysics

Astrophysics

v1&2: 4 pages, 2 figures. v4: 16 pages, 7 figures, iopart style. Revised the 'Other cosmological data' section, added a detail

Scientific paper

10.1088/1475-7516/2007/09/008

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.

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