Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published October 2009 | Published
Journal Article Open

A scale-dependent power asymmetry from isocurvature perturbations


If the hemispherical power asymmetry observed in the cosmic microwave background (CMB) on large angular scales is attributable to a superhorizon curvaton fluctuation, then the simplest model predicts that the primordial density fluctuations should be similarly asymmetric on all smaller scales. The distribution of high-redshift quasars was recently used to constrain the power asymmetry on scales k ≃ 1.5h Mpc^(-1), and the upper bound on the amplitude of the asymmetry was found to be a factor of 6 smaller than the amplitude of the asymmetry in the CMB. We show that it is not possible to generate an asymmetry with this scale dependence by changing the relative contributions of the inflaton and curvaton to the adiabatic power spectrum. Instead, we consider curvaton scenarios in which the curvaton decays after dark matter freezes out, thus generating isocurvature perturbations. If there is a superhorizon fluctuation in the curvaton field, then the rms amplitude of these perturbations will be asymmetric, and the asymmetry will be most apparent on large angular scales in the CMB. We find that it is only possible to generate the observed asymmetry in the CMB while satisfying the quasar constraint if the curvaton's contribution to the total dark matter density is small, but nonzero. The model also requires that the majority of the primordial power comes from fluctuations in the inflaton field. Future observations and analyses of the CMB will test this model because the power asymmetry generated by this model has a specific spectrum, and the model requires that the current upper bounds on isocurvature power are nearly saturated.

Additional Information

© 2009 American Physical Society. Received 3 July 2009; published 7 October 2009. We thank H. K. Eriksen for helpful correspondence. A. E. and M. K. are supported by DoE Contract No. DEFG03-92-ER40701 and the Gordon and Betty Moore Foundation. C. H. is supported by DoE Contract No. DEFG03-02-ER40701, the National Science Foundation under Contract No. AST-0807337, and the Alfred P. Sloan Foundation.

Attached Files

Published - Erickcek2009p6335Phys_Rev_D.pdf


Files (495.2 kB)
Name Size Download all
495.2 kB Preview Download

Additional details

August 19, 2023
October 19, 2023