A groundbreaking study has revealed a novel effect caused by dark photons—hypothetical particles thought to make up a portion of the universe's elusive dark matter. This discovery, made within the framework of Einstein–Cartan–Holst gravity, provides new insights into the fundamental interactions between matter and gravity.

The study was conducted by Prof. GAO Zhifu from the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences, in collaboration with Dr. Luiz Carlos Garcia de Andrade from the State University of Rio de Janeiro, Brazil. Their findings, which include the first identification of a key physical quantity known as the Barbero–Immirzi (BI) parameter induced by dark photons, were published in The European Physical Journal C.

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.

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 researchers 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, they investigated the magnetic helicity instability of dark photons, revealing how the axion oscillation frequency is regulated by the BI parameter. 

These findings provide a deeper theoretical framework for understanding the early universe and offer new avenues for testing beyond-Standard-Model physics in high-energy experiments, such as those conducted at the Large Hadron Collider (LHC).

The histogram for the BI parameter and the trace torsion mass in GeV (Image by XAO)