TITLE:
A Scale-Dependent Power Asymmetry from Isocurvature Perturbations.
AUTHOR(S):
Adrienne Erickcek, Christopher Hirata, Marc Kamionkowski (Caltech).
DATE:
2009 Jul 04 (arXiv, posted, v1);
2009 Jul 04 (PRD, submitted);
2009 Aug 17 (PRD, accepted).
AVAILABILITY:
arXiv 0907.0705 (free);
APS (requires subscription).
PUBLICATION INFORMATION:
Phys. Rev. D, 80, 083507, 2009.
ABSTRACT:
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, and the upper bound on the amplitude of the asymmetry was found to be
a factor of six 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.
ADS BIBLIOGRAPHIC CODE: 2009PhRvD..80h3507E
COMMENTS: N/A.