Scale-dependent CMB power asymmetry from primordial speed of sound and a generalized $\delta$N formalism

Abstract

We explore a plausible mechanism that the hemispherical power asymmetry in the CMB is produced by the spatial variation of the primordial sound speed parameter. We suggest that in a generalized approach of the $\delta N$ formalism the local e-folding number may depend on some other primordial parameters besides the initial values of inflaton. Here the $\delta N$ formalism is extended by considering the effects of a spatially varying sound speed parameter caused by a super-Hubble perturbation of a light field. Using this generalized $\delta N$ formalism, we systematically calculate the asymmetric primordial spectrum in the model of multi-speed inflation by taking into account the constraints of primordial non-Gaussianities. We further discuss specific model constraints, and the corresponding asymmetry amplitudes are found to be scale-dependent, which can accommodate current observations of the power asymmetry at different length scales.

14 pages, 2 figures, several references added, version published in JCAP

References in corpus (19)

• Observational Signatures and Non-Gaussianities of General Single Field Inflation
• Hemispherical power asymmetry in the three-year Wilkinson Microwave Anisotropy Probe sky maps
• Cosmic Microwave Background Quadrupole and Ellipsoidal Universe
• The Nature of Primordial Fluctuations from Anisotropic Inflation
• A Hemispherical Power Asymmetry from Inflation
• Superhorizon Perturbations and the Cosmic Microwave Background
• Constraints on cosmic hemispherical power anomalies from quasars
• A Scale-Dependent Power Asymmetry from Isocurvature Perturbations
• CMB Temperature Anisotropy from Broken Spatial Isotropy due to an Homogeneous Cosmological Magnetic Field
• N-flation from multiple DBI type actions
• Microwave Background Correlations from Dipole Anisotropy Modulation
• DBI-Curvaton
• Inflationary power asymmetry from primordial domain walls
• CMB Hemispherical Asymmetry: Long Mode Modulation and non-Gaussianity
• Hemispherical Power Asymmetry from a Space-Dependent Component of the Adiabatic Power Spectrum
• Large Nonlocal Non-Gaussianity from a Curvaton Brane
• A separate universe view of the asymmetric sky
• Generating $\fnl$ at $\ell\lsim 60$
• Scale-dependent hemispherical asymmetry from general initial state during inflation

Cited by in corpus (9)

• Challenges for $\Lambda$CDM: An update
• Dirac-Born-Infeld realization of sound speed resonance mechanism for primordial black holes
• Features from the non-attractor beginning of inflation
• Direction dependence of cosmological parameters due to cosmic hemispherical asymmetry
• Litmus Test for Cosmic Hemispherical Asymmetry in the Cosmic Microwave Background B-mode polarization
• Strongly scale-dependent CMB dipolar asymmetry from super-curvature fluctuations
• Testing the scale-dependent hemispherical asymmetry with the 21-cm power spectrum from the epoch of reionization
• Hemispherical Power Asymmetry of the Cosmic Microwave Background from a Remnant of a pre-Inflationary Topological Defect
• Cosmic Microwave Background Dipole Asymmetry could be explained by Axion Monodromy Cosmic Strings