Do Baryons Trace Dark Matter in the Early Universe?
Baryon-density perturbations of large amplitude may exist if they are compensated by dark-matter perturbations such that the total density is unchanged. Primordial abundances and galaxy clusters allow these compensated isocurvature perturbations (CIPs) to have amplitudes as large as ∼10%. CIPs will modulate the power spectrum of cosmic microwave background (CMB) fluctuations—those due to the usual adiabatic perturbations—as a function of position on the sky. This leads to correlations between different spherical-harmonic coefficients of the temperature and/or polarization maps, and induces polarization B modes. Here, the magnitude of these effects is calculated and techniques to measure them are introduced. While a CIP of this amplitude can be probed on large scales with existing data, forthcoming CMB experiments should improve the sensitivity to CIPs by at least an order of magnitude
Additional Information© 2011 American Physical Society. Received 12 July 2011; revised 30 September 2011; published 22 December 2011. We thank G. Holder, T. L. Smith, M. LoVerde, C. Chiang, K. M. Smith, M. Zaldarriaga, and D. N. Spergel for stimulating conversations. We thank B. Jones and A. Fraisse for providing Spider parameters. D. G. was supported by NSF AST-0807044 and M. K. by DoE DE-FG03-92-ER40701 and NASA NNX10AD04G. Part of this research was carried out at the Jet Propulsion Laboratory, Caltech, under a contract with NASA.
Published - Grin2011p16897Phys_Rev_Lett.pdf