A Scale-Dependent Power Asymmetry from Isocurvature Perturbations
arXiv:0907.0705 · doi:10.1103/PhysRevD.80.083507
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.
18 pages, 6 figures, submitted to PRD
References in corpus (22)
- Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
- Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results
- Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data
- High resolution CMB power spectrum from the complete ACBAR data set
- Hemispherical power asymmetry in the three-year Wilkinson Microwave Anisotropy Probe sky maps
- Detection of primordial non-Gaussianity (fNL) in the WMAP 3-year data at above 99.5% confidence
- Optimal limits on f_{NL}^{local} from WMAP 5-year data
- A Hemispherical Power Asymmetry from Inflation
- Reconstructed Density and Velocity Fields from the 2MASS Redshift Survey
- Non-Gaussianity, Spectral Index and Tensor Modes in Mixed Inflaton and Curvaton Models
- Superhorizon Perturbations and the Cosmic Microwave Background
- New Constraints on Oscillations in the Primordial Spectrum of Inflationary Perturbations
- Testable polarization predictions for models of CMB isotropy anomalies
- Correlated isocurvature perturbations from mixed inflaton-curvaton decay
- Non-isotropy in the CMB power spectrum in single field inflation
- Hints of Isocurvature Perturbations in the Cosmic Microwave Background?
- Gauging the cosmic microwave background
- Non-Gaussianity and Baryonic Isocurvature Fluctuations in the Curvaton Scenario
- Cold Dark Matter Isocurvature Perturbations: Constraints and Model Selection
- Neutralino Dark Matter and the Curvaton
- Real space tests of the statistical isotropy and Gaussianity of the WMAP CMB data
- Curvaton Decay into Baryons, anti-Baryons and Radiation