A new study suggests that dark matter may be made of dark photons

A new study suggests that dark matter may be made of dark photons

2D projection of the cosmic web, obtained from a supercomputer simulation. Credit: Dr. Ewald Puchwein and the Sherwood-Relics collaboration

The new hypothetical particles could explain the observations made by the Cosmic Origins Spectrograph on[{” attribute=””>Hubble Space Telescope.

According to a new study published in Physical Review Letters, it is possible that dark matter is composed of ultralight dark photons that may have played a role in heating up the universe. This hypothesis is, according to the researchers, in excellent agreement with observations from the Cosmic Origin Spectrograph (COS) aboard the Hubble Space Telescope, which observes the intricate and diffuse network of filaments known as the “cosmic web” that exists between galaxies.

The data collected by COS suggest that the cosmic intergalactic filaments are hotter than predictions from hydrodynamical simulations of the standard model of structure formation.

“Since dark photons would be able to convert into low-frequency photons and heat up the cosmic structures,” the scientists explain “they could well explain the experimental information.”

The study has been carried out by SISSA researchers in collaboration with researchers at Tel Aviv, Nottingham, and New York Universities.

“Dark photons are a good candidate for dark matter”

“Dark photons are hypothetical new particles that are the force carriers for a new force in the dark sector, much like how the photon is the force carrier for electromagnetism” the authors James S. Bolton (University of Nottingham), Andrea Caputo (CERN and Tel Aviv University), Hongwan Liu (New York University), and Matteo Viel (SISSA) explain. “Unlike the photon, however, they can have mass. In particular, the ultralight dark photon—with a mass as small as twenty orders of magnitude less than that of the electron—is a good candidate for dark matter.”

Dark photons and regular photons are also expected to mix like the different types of neutrinos, allowing ultralight dark photon dark matter to convert into low-frequency photons. These photons will heat up the cosmic web but, unlike other heating mechanisms, based on astrophysical processes, such as star formation and galactic winds, this heating process is more diffuse and efficient also in regions that are not very dense.

The missing element

Matteo Viel explains: “Usually, cosmic filaments have been used to probe small scale properties of dark matter, while in this case we have used for the first time the low redshift intergalactic medium data as a calorimeter, to check whether all the heating processes we are aware of are sufficient to reproduce the data. We found that this is not the case: there is something missing, that we model as a contribution produced by the dark photon.”

The work identified the mass and mixing of the dark photon with the Standard Model photon required to reconcile the discrepancy between observations and simulation; this effort could drive further theoretical and observational investigations in order to explore the exciting possibility that the dark photon could constitute the dark matter.

Reference: “Comparison of Low-Redshift Lyman-α Forest Observations to Hydrodynamical Simulations with Dark Photon Dark Matter” by James S. Bolton, Andrea Caputo, Hongwan Liu and Matteo Viel, 18 November 2022, Physical Review Letters.
DOI: 10.1103/PhysRevLett.129.211102

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