Researchers investigate direct detection of dark photons using radio telescopes

Overcoming technical challenges with innovative solutions

When exploring the use of radio telescopes to look for electromagnetic signals connected to dark photons, the study team encountered a huge technical obstacle. The shape of the reflector in dish telescopes had to be spherical with the receiver positioned in the center due to the non-relativistic nature of dark matter. 

Existing dished radio telescopes, like the FAST in China, have parabolic-shaped dishes made for detecting distant radio signals, making them inappropriate for focusing electromagnetic signals brought on by dark photons onto the receiver.

But when one of the researchers, Haipeng An, went to the UFITS summer cosmology program held at the FAST site, something new happened. He discovered that the receiver positioned above the dish could be rotated around to observe radio waves coming from various angles while learning the specifics of how the FAST telescope works. 

Based on this finding, An came up with the hypothesis that, even though dark photon-induced electromagnetic waves wouldn't concentrate at the receiver, they might create a theoretically calculable distribution on top of the dish.

An's Theoretical Predictions

According to An's theoretical predictions, radio telescopes' mobile receivers might gather electromagnetic signals from various areas. The sensitivity of the telescopes to dark photon-induced signals could be improved by comparing the acquired signals with the projected distributions. 

Surprisingly, the team discovered that even without taking the distribution into account, the FAST telescope's exceptional sensitivity already exceeded the cosmic microwave background constraint, potentially opening the door to the detection of dark matter if it is made up of dark photons and falls within the right mass range.

The scientists also showed that dark photon dark matter might create electric signals on dipole antennas by analyzing observation data gathered by the FAST radio observatory. They estimated the possibility of other radio telescopes, like LOFAR and the upcoming SKA observatory, in discovering dark photon dark matter by utilizing interferometry technology to increase sensitivity.

Study abstract: 

Dark photons can be the ultralight dark matter candidate, interacting with Standard Model particles via kinetic mixing. We propose to search for ultralight dark photon dark matter (DPDM) through the local absorption at different radio telescopes. The local DPDM can induce harmonic oscillations of electrons inside the antenna of radio telescopes. It leads to a monochromatic radio signal and can be recorded by telescope receivers. Using the observation data from the FAST telescope, the upper limit on the kinetic mixing can already reach 10-12 for DPDM oscillation frequencies at 1–1.5 GHz, which is stronger than the cosmic microwave background constraint by about one order of magnitude. Furthermore, large-scale interferometric arrays like LOFAR and SKA1 telescopes can achieve extraordinary sensitivities for direct DPDM search from 10 MHz to 10 GHz.