Dark Photons: Closer to Dark Matter

Physicists propose a new path for understanding the relationship between dark matter and mysterious dark photons. Scientists suggest that these particles could have nearly identical masses.

Unraveling the Invisible Universe

Researchers have explored a novel way particles in a "dark" sector could interact with the particles we know. They aimed to determine if a special kind of mixing could explain the existence of dark photons. These dark photons are theorized to be like faint echoes of regular light, imperceptible to our direct senses.

The team investigated a theoretical group of dark particles, essentially a hidden family of subatomic components. This family includes:

Dark "gauge fields": Fundamental force carriers in the dark sector.
"Dark Higgs doublet": Particles responsible for giving mass to others within the dark sector.

The dark Higgs plays a role analogous to the familiar Higgs boson in our universe, endowing mass to dark particles.

Cosmic Connections

The study focused on a phenomenon called "non-abelian kinetic mixing." This complex interaction causes certain dark forces to link with the forces of our universe. Through this mixing, one dark force particle could transform into a dark photon, while others would remain as dark matter.

The researchers calculated the behavior of these hidden particles, particularly how they acquire mass. This mixing is facilitated by other "scalar" particles, which are fundamental particles without spin, acting as a bridge between the dark world and ours.

The key finding revealed that the dark photon, referred to as $A'$ , would be only slightly heavier than its dark matter counterparts, the charged dark gauge bosons ( $X^\pm_\mu$ ). The mass difference, expressed as $m^2_{A'} - m^2_{X^\pm}$ , is very small, approximately $m^2_X(\epsilon^2_Z + \epsilon^2_A)$ . This indicates they are almost the same weight. These charged dark particles are theorized to remain stable and could constitute the universe's cosmic dark matter.

Testing the Shadows

"The dark photon and dark matter particle can have a nearly degenerate mass spectrum due to the non-abelian kinetic mixing," the authors state. This implies that future experiments spotting both a dark photon and a dark matter particle would lend support to this theoretical model.

However, this model has specific requirements:

It necessitates some "crossing scalars" (the bridging particles) to be quite heavy to avoid conflicts with current observational data.
A "dark Higgs boson" (the dark sector's equivalent of the Higgs) is crucial for the dark matter particles to interact and achieve the correct abundance in the universe.

Future studies will aim to explore methods for detecting these nearly-identical particles.

This new concept offers a fresh avenue for understanding the mysterious cosmic dance between dark matter and its fleeting dark light.

Reference:

Zhou, H. (2022). Quasi-degenerate dark photon and dark matter. arXiv preprint arXiv:2209.08843.