A large portion of the universe is filled with invisible matter known as dark matter, and the dark photon is one of its leading theoretical candidates. As a hypothetical particle beyond the Standard Model, the dark photon exhibits electromagnetic-like interactions through kinetic mixing with the ordinary photon. Unlike photons, however, dark photons possess mass and interact much more weakly with charged particles.

Recently, Prof. GAO Zhifu from the Pulsar Research Group at the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences (CAS), in collaboration with Dr. Luiz Carlos Garcia de Andrade from the State University of Rio de Janeiro, Brazil, discovered a special effect induced by dark photons within the framework of the Einstein–Cartan–Holst theory for the first time. They also determined a key physical parameter—the BI parameter.

The study was published in The European Physical Journal C (2025, 85:433).

The Barbero-Immirzi (BI) parameter in Loop Quantum Gravity (LQG) theory may influence gravitational waves and their interactions with matter. Studying this parameter could reveal connections to dark matter and dark energy.

Moreover, Einstein-Cartan-Holst gravity, an extension of general relativity, introduces "torsion", which relates to the spacetime twisting and is linked to matter spin. This connection aids the study of matter-gravity interactions.

The research team uncovered a torsion - axion conversion mechanism, demonstrating that dark photons can induce the BI parameter through a special gravitational coupling. Based on theoretical analysis and simulations, the researchers investigated the magnetic helicity instability of dark photons, revealing how the axion oscillation frequency is regulated by the BI parameter. This discovery deepens our understanding of the early universe and supports searches for new - physics in high - energy experiments like the Large Hadron Collider ( LHC).

                                                                                                      The histogram for the BI parameter and the trace torsion mass in GeV