A phenomenological dipole anisotropy in primordial perturbations induces dipolar and quadrupolar anisotropies in SIGW energy density spectra, producing frequency-dependent PTA overlap reduction functions that depend on pulsar sky distribution, but NANOGrav 15-year data yields no significant evidence
Relating the inhomogeneous power spectrum to the CMB hemispherical anisotropy
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abstract
We relate the observed hemispherical anisotropy in the cosmic microwave radiation data to an inhomogeneous power spectrum model. The hemispherical anisotropy can be parameterized in terms of the dipole modulation model. This model leads to correlations between spherical harmonic coefficients corresponding to multipoles, l and l+1. We extract the $l$ dependence of the dipole modulation amplitude, A, by making a fit to the WMAP and PLANCK CMBR data. We propose an inhomogeneous power spectrum model and show that it also leads to correlations between multipoles, l and l+1. The model parameters are determined by making a fit to the data. The spectral index of the inhomogeneous power spectrum is found to be consistent with zero.
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Forecasts show that future 21 cm surveys can deliver moderate constraints on the scale-dependent growth index and HI bias in viable f(R) models.
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Exploring the statistical anisotropy of primordial curvature perturbations with pulsar timing arrays
A phenomenological dipole anisotropy in primordial perturbations induces dipolar and quadrupolar anisotropies in SIGW energy density spectra, producing frequency-dependent PTA overlap reduction functions that depend on pulsar sky distribution, but NANOGrav 15-year data yields no significant evidence
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Constraining Scale-Dependent Growth in $f(R)$ Gravity with Future 21 cm Surveys
Forecasts show that future 21 cm surveys can deliver moderate constraints on the scale-dependent growth index and HI bias in viable f(R) models.