Supersymmetry joins the hunt for axions in a new electrodynamics blueprint

Axions have long been among the most tantalizing ghosts in particle physics: hypothetical, extremely light, electrically neutral particles that could make up dark matter and solve a stubborn puzzle about the strong nuclear force. Now a team of theoretical physicists has taken a step that could sharpen the search. In a study published in The European Physical Journal C, C. Roldán-Domínguez, H. Belich, W. Spalenza and colleagues present a supersymmetric extension of axionic electrodynamics, a framework that describes how axions couple to photons. By embedding the axion and the photon into the language of supersymmetry, the authors show that the theory acquires a richer cast of characters, including the axino, the saxion and the photino, and that familiar electromagnetic equations are quietly rewritten in surprising ways.

The starting point is the axion itself. In the 1970s, Roberto Peccei and Helen Quinn proposed a new symmetry to explain why the strong interactions, unlike the weak ones, show no violation of charge-parity symmetry. The spontaneous breaking of that symmetry would generate a pseudo-Nambu–Goldstone boson, the axion. Because axions are predicted to be extraordinarily light and carry no electric charge, they are notoriously hard to detect. The most promising handle is the axion–photon interaction, which allows axions to convert into photons in strong magnetic or electric fields. That conversion underlies a whole family of experiments hunting for galactic dark matter axions and axions streaming from the Sun, and it is the core of axionic electrodynamics, the effective theory the new work sets out to supersymmetrize.

Supersymmetry, or SUSY, is the hypothetical symmetry pairing every known boson with a fermionic partner and vice versa. The authors adopt a superspace and superfield approach, building an N=1 supersymmetric version of the effective axion–photon Lagrangian. In component fields, the resulting action describes the axion, the photon, and their superpartners: the axino, a fermion; the saxion, the scalar partner of the axion; and the photino, the fermionic partner of the photon. Supersymmetry forces new interactions into the theory, including fermionic self-interactions and a distinctive non-polynomial term linking the axino, the photino and the saxion. The authors stress that they are not building a full ultraviolet-complete axion model; the goal is to see how supersymmetry modifies the dynamical and propagating sectors of axion electrodynamics at the effective-field-theory level.

One of the study’s most striking results concerns Maxwell’s equations themselves. When the authors derive the field equations for the electromagnetic potential, fermionic bilinears built from the photino and axino appear on the scene. These bilinears can be interpreted as contributions to the polarization and magnetization of the vacuum, quantities that in ordinary electrodynamics belong to matter, not to empty space. In other words, the supersymmetric vacuum behaves like a polarized and magnetized medium, somewhat analogous to photons propagating through a plasma. The constitutive relations acquire fermionic corrections to both the permittivity and the permeability, an aspect the authors note is absent from the existing literature on anisotropic media and nonlinear post-Maxwellian extensions of electromagnetism.

The axion field also leaves its fingerprints on the constitutive relations. Because the effective electric displacement and magnetic field strength depend on both the electric and magnetic sectors, a magnetic field can induce polarization and an electric field can contribute to magnetization. The authors call this mixing bianisotropy, and point out that it is formally equivalent to the propagation of light in a magneto-electric medium, a behavior also familiar from axion electrodynamics in topological insulators. The saxion background, meanwhile, acts as a position-dependent effective permittivity and permeability factor. These are theoretical consequences of the model, not yet observations, but they suggest that supersymmetric axion backgrounds could mimic exotic optical media.

To probe how particles actually propagate, the team linearized the theory around a constant, homogeneous background magnetic field, a configuration common in astrophysics, where axion–photon conversion via the Primakoff effect takes place near magnetars and neutron stars. Solving the coupled wave equations for the photon, axion and saxion fluctuations, they derived dispersion relations for the mixed modes. The axion and saxion each mix with the photon but not with each other, since the propagating electric and magnetic perturbations are orthogonal. In the rest frame, the axion acquires an effective mass correction induced by the external magnetic field, extending a result previously known in the non-supersymmetric case to a supersymmetric setting.

The numbers involved are tiny but instructive. Using a magnetar-scale background field of 10^10 tesla, an axion–photon coupling of 10^-12 per GeV and an axion mass of 5×10^-7 eV, values consistent with astrophysical bounds reported by the Particle Data Group, the mass-squared correction depends on the supersymmetric self-interaction parameter f. For f much larger than the product of the coupling and the mass, the correction saturates at roughly 3×10^-35 GeV^2, negligible compared with the axion’s mass-squared of about 2.5×10^-13 eV^2. Only in a narrow window where f is comparable to that product, between roughly 10^-28 and 10^-26 in the units used, does the correction become noticeable, shifting the mass at the fourth decimal place. The authors emphasize these are model estimates, not measurements.

The fermionic sector delivers the study’s most conceptually interesting twist. When the dispersion relations of the axino and photino are computed in the same magnetic background, they no longer match those of the bosonic sector. The degeneracy between bosons and fermions is lifted, which signals a breaking of supersymmetry. Crucially, this breaking is not spontaneous, arising from the vacuum expectation value of some auxiliary field, nor is it communicated by soft breaking terms from a high scale. Instead, it emerges from the anisotropy introduced by the constant magnetic field itself, visible in the transformation law of the photino. The authors interpret this as a soft supersymmetry breaking triggered by the background, and note that the magnetic Primakoff effect in a supersymmetric context is thus accompanied by SUSY breaking. The background field also introduces a spatial anisotropy that, from the particle’s point of view, resembles a violation of Lorentz symmetry.

Beyond dispersion relations, the team used numerical methods to explore what happens when the axion interacts with a background magnetic field aligned with a radial electric field in a cylindrically symmetric setup, inspired by studies of cosmic strings. Solving the resulting nonlinear equations of motion, they identified classes of axionic and electromagnetic field configurations with nontrivial magnetic field profiles, including effective charge densities and transverse currents that could induce vortical structures. The authors are careful to frame this as a qualitative analysis in arbitrary units rather than a quantitative prediction for any specific physical system, but it illustrates how supersymmetric axion electrodynamics can generate structured electromagnetic configurations in strong-field environments.

The study closes with a list of open questions that could keep theorists busy. The quartic fermionic interactions in the action resemble a Nambu–Jona–Lasinio-type dynamics, hinting at a possible mechanism for generating the photino’s mass dynamically through fermion condensates. The axino–photino–photon coupling can be read as a supersymmetric analog of the Primakoff effect, in which axinos convert into photinos in an external electromagnetic field, and the authors outline how a production rate could eventually be computed once the effective masses are pinned down. They also speculate that neutral axinos and photinos could acquire magnetic moments through radiative corrections, potentially giving rise to an Aharonov–Casher-type effect in a background electric field. The effective structures generated by supersymmetry in this model, the authors suggest, may even offer clues for emergent electromagnetic phenomena in materials that behave as Weyl systems, where supersymmetry appears as an emergent property. All of this remains theoretical for now, but the framework provides additional interactions between candidate dark matter particles, and the authors expect that effects of this kind could be tested in high-energy astrophysical environments characterized by strong magnetic fields, such as neutron stars.

Subject of Research: A supersymmetric effective-field-theory extension of axion electrodynamics involving axions, photons and their superpartners

Article Title: A supersymmetric extension of axionic electrodynamics: from axions and photons to axinos and photinos

Article References: Roldán-Domínguez, C., Belich, H., Spalenza, W., Nogueira, A. L. M. A., Reetz, M., & Helayël-Neto, J. A. (2026). A supersymmetric extension of axionic electrodynamics: from axions and photons to axinos and photinos. The European Physical Journal C, 86(10), Article 1210. https://doi.org/10.1140/epjc/s10052-026-16468-4

Image Credits: AI Generated

DOI: 10.1140/epjc/s10052-026-16468-4

Keywords: axions, supersymmetry, axionic electrodynamics, axino, photino, saxion, dark matter, dispersion relations, Maxwell equations, Primakoff effect, magnetic field, theoretical physics