Year: 2025
Type: article
Abstract: We theoretically analyze the dipole anisotropy observed in the quasar distribution from the CatWISE2020 catalog. The catalog data shows a peak around $z\ensuremath{\approx}1$, suggesting the presence of a large-scale dipole component. We explore the possibility that this dipole could be driven by primordial density fluctuations from modes that were superhorizon at the time of cosmic microwave background (CMB) decoupling but have since entered the horizon and become subhorizon. In particular, we consider the impact of adiabatic modes with wave numbers $k$ in the range $({10}^{\ensuremath{-}4}\ensuremath{-}4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3})\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$, corresponding to wavelength scales of several Gpc. Such modes can create large-scale density variations, likely causing anisotropies in the distribution of matter and, as a result, affecting the number density of observed quasars. We find that these can lead to a significant contribution to the dipole for sources up to redshifts of about 1, but are unable to explain the observed dipole. We also demonstrate that a superhorizon curvature perturbations mode, with a comoving wave number $k\ensuremath{\lesssim}0.3{H}_{0}$ can lead to a significant enhancement in the locally inferred Hubble constant. This effect offers a viable explanation for the observed discrepancy between local and CMB inferred measurements of ${H}_{0}$.
DOI: 10.1103/ftk4-6zmz
Authors: Gopal Kashyap, Naveen K. Singh, Pankaj Jain
Institution: Vellore Institute of Technology University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: VIT University
Award: G2148626373
OpenAlex ID: W4415155703