Dark Energy and Neutrino Flavor from the Weak Axion
Abstract
Dynamical dark energy offers an alternative to a cosmological constant with distinct observational signatures. However, the small energy density scale, Hubble-sized mass, and Planckian excursions make simple models fine-tuned and unnatural. In this work, we show that a weak version of the axion, identified with the phase field of the anomalous U(1)B+L of the Standard Model, can generate the scale hierarchies expected for dark energy. The axion potential is controlled by sources of explicit baryon and lepton number violation and is radiatively stable. We show that the leading contribution comes from two inequivalent Weinberg operators, one B+L-conserving and one B+L-violating, which generate the axion potential. We propose a flavor selection rule in the lepton sector that simultaneously removes the quadratic divergence and dominant temperature-dependent contributions to the effective potential. The resulting potential first appears at quartic order in the axion-dependent neutrino masses and, depending on the flavor model and PMNS parameters, its amplitude is parametrically close to the dark-energy density. Since the scale of dark energy is sensitive to changes in the neutrino parameters, improved measurements of mββ, the sum of neutrino masses, δCP and θ23 can favor certain models. Cosmologically, the field behaves as thawing quintessence, stays frozen by Hubble friction until late times and never enters the adiabatic regime.
Related
- Resonant neutrino flavor conversion within dark matter spikes
- Quasi-steady flavor configuration of multi-energy neutrino ensembles
- Natural Saturation Of The Sterile Neutrino Dark Matter Resonant Production By a High Lepton Flavor Asymmetry In Primordial Plasma
- A Natural Dark Matter-Dark Energy Interaction from Axion-Monopole Dynamics
- Stability Analysis of Axion Dark Energy Model
BibTeX
@misc{bittar2026dark,
title = {{Dark Energy and Neutrino Flavor from the Weak Axion}},
author = {Pedro Bittar and Carlos E. M. Wagner},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.13128},
eprint = {2607.13128},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.13128},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Dark Energy and Neutrino Flavor from the Weak Axion
AU - Pedro Bittar
AU - Carlos E. M. Wagner
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2607.13128
UR - https://arxiv.org/abs/2607.13128
AB - Dynamical dark energy offers an alternative to a cosmological constant with distinct observational signatures. However, the small energy density scale, Hubble-sized mass, and Planckian excursions make simple models fine-tuned and unnatural. In this work, we show that a weak version of the axion, identified with the phase field of the anomalous U(1)_B+L of the Standard Model, can generate the scale hierarchies expected for dark energy. The axion potential is controlled by sources of explicit baryon and lepton number violation and is radiatively stable. We show that the leading contribution comes from two inequivalent Weinberg operators, one B+L-conserving and one B+L-violating, which generate the axion potential. We propose a flavor selection rule in the lepton sector that simultaneously removes the quadratic divergence and dominant temperature-dependent contributions to the effective potential. The resulting potential first appears at quartic order in the axion-dependent neutrino masses and, depending on the flavor model and PMNS parameters, its amplitude is parametrically close to the dark-energy density. Since the scale of dark energy is sensitive to changes in the neutrino parameters, improved measurements of m_ββ, the sum of neutrino masses, δ_CP and θ_23 can favor certain models. Cosmologically, the field behaves as thawing quintessence, stays frozen by Hubble friction until late times and never enters the adiabatic regime.
ER -