Hint at new physics from the gamma ray burst GRB 221009A

by Marco Roncadelli (INFN Pavia & Brera Observatory)

Monday 20 Nov 2023, 12:00 → 13:30 Europe/Rome

Aula Rasetti (Dip. di Fisica - Edificio G. Marconi)

 On October 11, 2022 the LHAASO collaboration reported on a gamma-ray emission from the GRB 221009A at redshift 0.151, extending up to (13 — 18) TeV depending on the spectral analysis. According to conventional physics the extragalactic background light (EBL) — namely the infrared/optical light emitted by all stars during the cosmic evolution — prevents observations of the highest energy photons seen by LHAASO. Therefore, some new physics should reduce the opacity due to the EBL, as also claimed by LHAASO itself. We have shown that axion-like particles (ALPs) — naturally predicted by superstrings — do the job for a mass and a two-photon coupling which are observationally viable. The reason is due to photon-ALP oscillations in cosmic magnetic fields. Accordingly, during propagation photons acquire a “split personality”: when they behave as true photons are absorbed, but when they behave as ALPs no absorption occurs. Thus, the cosmic opacity gets drastically reduced, thereby allowing for the observability of GRB 221009A up to 18 TeV. This result adds up to two previous suggestions of an ALP with the same properties, so that we now have three consistent hints pointing towards the existence of a very specific ALP, which is also a good candidate for cold dark matter.