Beyond the local Universe: Impacts of scalar field coupled to non-relativistic neutrinos on bulk flow

• Published in: Astroparticle physics Vol. 169; p. 103110
• Main Author: Yarahmadi, Muhammad
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2025
• Subjects: Bulk flow; Neutrinos; Bulk flow; Neutrinos
• ISSN: 0927-6505
• DOI: 10.1016/j.astropartphys.2025.103110

This study explores the role of neutrinos in the Universe’s expansion history, tracing their transition from a relativistic phase in the early Universe to non-relativistic massive particles at later epochs. Within the framework of neutrino coupling with a scalar field, we examine cosmic evolution from radiation domination to dark energy dominance. By analyzing combined datasets (Pantheon+, Cosmic Microwave Background, Baryon Acoustic Oscillations, Cosmic Chronometers, and CMB lensing), we constrain the total neutrino mass to ∑mν<0.105eV (95% CL). The transition redshifts znr range from 76 to 205, marking the onset of matter domination. The coupling parameter is constrained to α=5.64±1.1, consistent with growing neutrino quintessence, reinforcing the role of neutrinos despite their small mass. Late-time evolution analyses, comparing scenarios with and without neutrino coupling, reveal that non-relativistic neutrinos contribute to cosmic anisotropy. At low redshifts (0.001<z<0.1), the bulk flow direction aligns with the CMB dipole, while at higher redshifts, it correlates with the dark energy dipole. The evolution of neutrino density-to-redshift ratios suggests that a decreasing neutrino density weakens gravitational influence, leading to an increase in bulk velocity within 0.1<z<1 and a decline within 1<z<1.4. These findings highlight the role of non-relativistic neutrinos in shaping cosmic anisotropy and dark energy dynamics, offering new perspectives on the Universe’s large-scale evolution.