Dark Energy from Mass Varying Neutrinos

TL;DR

The paper proposes mass varying neutrinos (MaVaNs) as a link between dark energy and neutrino physics, where a light acceleron field makes neutrino masses density-dependent. By formulating V(mν) = mν nν + V0(mν) and deriving w+1 = (mν nν)/V, it shows how a nearly flat V0 yields w ≈ −1 while keeping the neutrino contribution subdominant, naturally addressing the coincidence problem. A concrete microscopic realization with a sterile neutrino mass M(A) that depends on the acceleron field is analyzed, highlighting naturalness constraints that favor sub-eV cutoffs and potentially eV-scale sterile states detectable by experiments like MiniBooNE. The framework is explored across cosmology and astrophysics, including BBN, SN, solar neutrinos, baryogenesis, and high-energy cosmic rays, with specific predictions such as environment-dependent neutrino masses and possible acceleron-related effects that could be tested in upcoming observations. Overall, MaVaNs offer a testable, density-driven mechanism for dark energy with rich phenomenology across multiple scales and observables.

Abstract

We show that mass varying neutrinos (MaVaNs) can behave as a negative pressure fluid which could be the origin of the cosmic acceleration. We derive a model independent relation between the neutrino mass and the equation of state parameter of the neutrino dark energy, which is applicable for general theories of mass varying particles. The neutrino mass depends on the local neutrino density and the observed neutrino mass can exceed the cosmological bound on a constant neutrino mass. We discuss microscopic realizations of the MaVaN acceleration scenario, which involve a sterile neutrino. We consider naturalness constraints for mass varying particles, and find that both ev cutoffs and ev mass particles are needed to avoid fine-tuning. These considerations give a (current) mass of order an eV for the sterile neutrino in microscopic realizations, which could be detectable at MiniBooNE. Because the sterile neutrino was much heavier at earlier times, constraints from big bang nucleosynthesis on additional states are not problematic. We consider regions of high neutrino density and find that the most likely place today to find neutrino masses which are significantly different from the neutrino masses in our solar system is in a supernova. The possibility of different neutrino mass in different regions of the galaxy and the local group could be significant for Z-burst models of ultra-high energy cosmic rays. We also consider the cosmology of and the constraints on the ``acceleron'', the scalar field which is responsible for the varying neutrino mass, and briefly discuss neutrino density dependent variations in other constants, such as the fine structure constant.