Hemispherical asymmetry from an isotropy violating stochastic gravitational wave background

Abstract

Measurement of Cosmic Microwave Background (CMB) temperature by Planck has resulted in extremely tight constraints on the $\Lambda$CDM model. However the data indicates a evidence of dipole modulated temperature fluctuations at large angular scale which is beyond the standard Statistically Isotropic (SI) $\Lambda$CDM model. The signal measured by Planck requires a scale dependent modulation amplitude that is beyond the scope of the phenomenological model considered by Planck. We propose a phenomenological model with mixed modulation field for scalar and tensor perturbations which affect the temperature fluctuations at large angular scales. Hence this model is a possible route to explain the scale dependent nature of the modulation field. The salient prediction of this model is the direction dependent tensor to scalar ratio which results in anisotropic Stochastic Gravitational Wave Background (SGWB). This feature is potentially measurable from the $B$-mode polarization map of Planck and BICEP-2 and leads to determination of the modulation strength. Measurability of SI violated polarization field due to this model is estimated for Planck and PRISM. Absence of the signal in the polarization field can restrict the viability of the model.

8 pages and 4 figures. Matches the published version

References in corpus (9)

• Hemispherical power asymmetry in the three-year Wilkinson Microwave Anisotropy Probe sky maps
• Power asymmetry in WMAP and Planck temperature sky maps as measured by a local variance estimator
• On the significance of power asymmetries in Planck CMB data at all scales
• Statistical Isotropy of CMB Polarization Maps
• The TT, TB, EB and BB correlations in anisotropic inflation
• Measuring Statistical Isotropy of CMB Anisotropy
• Linking the BICEP2 result and the hemispherical power asymmetry through spatial variation of $r$
• Scalar-tensor correlations and large-scale power suppression
• Scalar-Tensor Anti-Cross-Correlation does not Help to Reconcile the Tension between BICEP2 and Planck

Cited by in corpus (1)

• Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies