Light scalar explanation for the 18 TeV GRB 221009A

The recent astrophysical transient Swift J1913.1 thorn 1946 may be associated with the ?-ray burst GRB 221009A. The redshift of this event is z ? 0.151. Very high-energy ? rays (up to 18 TeV) followed the transient and were observed by the Large High Altitude Air Shower Observatory (LHAASO); additionally, Carpet-2 detected a photonlike air shower of 251 TeV. Photons of such high energy are expected to readily annihilate with the diffuse extragalactic background light (EBL) before reaching Earth. If the ?-ray identification and redshift measurements are correct, new physics could be necessary to explain these measurements. This paper provides the first CP-even scalar explanation of the most energetic 18 TeV event reported by LHAASO. In this minimal scenario, the light scalar singlet S mixes with the Standard Model Higgs boson h. The highly boosted S particles are produced in the GRB and then undergo the radiative decay diphoton S ? ?? while propagating to Earth. The resulting photons may thus be produced at a remote region without being nullified by the EBL. Hence, the usual exponential reduction of ? rays is lifted due to an attenuation that is inverse in the optical depth, which becomes much larger due to the scalar carriers.

Automated summary

The recent astrophysical transient Swift J1913.1 at a redshift of z ≈ 0.151 may be associated with the γ-ray burst GRB 221009A. Very high-energy γ rays (up to 18 TeV) were observed following the transient, which is unexpected as photons of such high energy should annihilate with the diffuse extragalactic background light (EBL) before reaching Earth. This paper presents a CP-even scalar model to explain the 18 TeV event, proposing that highly boosted scalar particles are produced in the GRB and then undergo radiative decay while propagating to Earth, allowing the resulting photons to be produced without being nullified by the EBL.