Neutrino masses, matter-antimatter asymmetry, dark matter, and supermassive black hole formation explained with Majorons

TL;DR

The work proposes a two-Higgs-doublet Majoron model with a global U$(1)_L$ symmetry that is spontaneously broken, yielding a Majoron $J$ and heavy right-handed neutrinos to generate light neutrino masses via the seesaw and baryon asymmetry via leptogenesis. By introducing an enhanced electromagnetic anomaly $E$, the Majoron decays to photons with rate $\Gamma_J \propto E^2 m_J^3/F_J^2$, enabling infrared/optical/UV signals in current telescopes, and an eV-scale Majoron is produced through misalignment with relic density $\Omega_J h^2 \simeq 0.12\left(\frac{m_J}{25 \mathrm{eV}}\right)^{1/2}\left(\frac{F_J \theta_i}{2.7\times10^{11}\mathrm{GeV}}\right)^2$. The same decay generates a Lyman-Werner background that can trigger direct-collapse black hole formation in pristine halos, providing heavy seeds for high-redshift SMBHs, studied via a one-zone model that tracks the in-situ radiation and self-shielding. Constraints from JWST, MUSE, DESI, and HST are applied to the Majoron-photon coupling $g_{J\gamma\gamma}=\frac{\alpha_{em}}{\pi}\frac{E}{F_J}$, with current data already probing $E=18$, and the parameter space including $E=12$ and $E=18$ found to accommodate both DM and early SMBH formation, offering a testable, interconnected framework across particle physics and high-redshift astrophysics.

Abstract

The spontaneous breaking of a global lepton number symmetry can result in a (pseudo) Nambu-Goldstone boson known as the Majoron. We study a singlet Majoron model that couples to two Higgs doublets in which the lepton number current develops an electromagnetic anomaly, allowing the decay of Majorons into photons. We focus on Majorons at the eV scale with an enhanced anomaly and show that it serves as a dark matter candidate whose decay signals can be probed by space telescope observations. Furthermore, if the decay produces Lyman-Werner photons, heavy black hole seeds can be generated via the direct collapse mechanism and evolve into the active galactic nuclei we observe at high redshifts. Our framework thus simultaneously addresses the origin of neutrino masses, the baryon asymmetry of the Universe, the nature of dark matter, and the formation of high redshift supermassive black holes.

Figures (1)

• Figure 1: Parameter space and constraints for eV scale Majoron DM. Majoron models with different electromagnetic anomalies $E$ are plotted in solid lines, where we fix the Majoron abundance $\Omega_J h^2 = 0.12$ and choose $\theta_i = 3$. The dashed and dashdotted lines mark the region for direct collapse black holes formation. Current astrophysics constraints are shown in the color filled regions, while the projected end-of-mission reach of JWST is shown with the dotted line. The JWST projection is calculated using the smoothed version of the current constraint.