2D projection of the cosmic web as obtained from a supercomputer simulation. Credit: Dr. Ewald Puchwein and the Sherwood-Relics collaboration
Dark matter could consist of ultralight dark photons that have heated our universe: this is the new scenario proposed in a study recently published in Physical Review Letters. According to the authors, this hypothesis is in excellent agreement with observations made by the Cosmic Origin Spectrograph (COS) aboard the Hubble Space Telescope, which takes measurements of the “cosmic web”, the intricate and tenuous network of filaments that fills the space between galaxies.
Data collected by COS suggests that intergalactic cosmic filaments are hotter than predicted by hydrodynamic simulations of the Standard Model of structure formation.
“Since dark photons would be able to convert to low-frequency photons and heat up cosmic structures,” the scientists explain, “they might well explain experimental information. The study was carried out by SISSA researchers in collaboration with researchers from the universities of Tel Aviv, Nottingham and New York.
Dark photons are good candidates for dark matter
“Dark photons are hypothetical new particles that are the force carriers of a new force in the dark sector, much like the photon is the force carrier of electromagnetism,” explain authors James S. Bolton (University of Notitngham), Andrea Caputo (CERN and Tel Aviv University), Hongwan Liu (New York University) and Matteo Viel (SISSA).
“Unlike the photon, however, they can have mass. In particular, the ultralight dark photon – whose mass is twenty orders of magnitude less than that of the electron – is a good candidate for dark matter. »
Dark photons and ordinary photons are also expected to mix together like the different types of neutrinos, allowing dark matter from the ultralight dark photon to transform into low-frequency photons. These photons will heat 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 effective also in regions that are not very dense.
The missing element
Matteo Viel explains: “Usually cosmic filaments have been used to probe the fine-scale properties of dark matter, while in this case we used for the first time data from the low redshift intergalactic medium as a calorimeter, to check if all the heating processes known to us are sufficient to reproduce the data. We found that this is not the case: something is missing, which we model as a contribution produced by the dark photon”.
The work made it possible to identify the mass and the mixing of the dark photon with the photon of the standard model necessary to reconcile the divergence between the observations and the simulation. This effort could lead to further theoretical and observational research to explore the exciting possibility that the dark photon could constitute dark matter.