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A reported 300 TeV photon-like event from the direction of gamma-ray burst GRB 221009A presents a puzzle: if it really came from the burst, conventional physics says background light should have absorbed it on the way to Earth. Two theoretical proposals offer possible ways around that problem—one based on Lorentz-invariance violation (LIV), and another combining axion-like particles with LIV. Neither establishes that new physics has been discovered.
What was reported about the 300 TeV event?
The Carpet-3 air-shower array reported a photon-like event with an estimated energy of 300 teraelectronvolts (TeV), arriving from the direction of GRB 221009A about 4,536 seconds after the Fermi Gamma-ray Burst Monitor (Fermi-GBM) trigger. Dmitry D. Ofengeim and Tsvi Piran describe the event in a paper published in Physical Review D on 27 October 2025. They make their explanation conditional: “If the association with this gamma-ray burst is real, then it poses two puzzles.” Physical Review D paper.
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The direction and timing motivate a possible connection to the burst, but do not by themselves prove the event came from it. The distinction matters: the propagation puzzle arises if the association is genuine, not simply because a 300 TeV event was reported.
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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteWhy should a 300 TeV gamma ray have been absorbed?
In the conventional picture, a high-energy gamma-ray photon can collide with lower-energy background light during its journey. The collision can create an electron and a positron, removing the original photon from the gamma-ray beam. This process, called gamma-gamma pair production, makes the universe increasingly opaque to sufficiently energetic gamma rays over long distances.
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So if the candidate photon traveled from a cosmological burst, its apparent survival is difficult to reconcile with ordinary expectations for propagation through background radiation. That is a conditional puzzle, not direct proof that the photon crossed the entire distance unimpeded: both its association with GRB 221009A and the interpretation of its journey matter.
How could Lorentz-invariance violation change the result?
Lorentz invariance is a core symmetry of relativity: the laws of physics take the same form for observers moving at constant velocities relative to one another. Ofengeim and Piran examine a theoretical possibility in which that symmetry is modified at high energies. In their LIV-only analysis, the modification can affect both the threshold for gamma-gamma pair production and the speed of photons as a function of energy.
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Higher interaction thresholds could reduce opacity
If LIV shifts the conditions required for pair production, a 300 TeV photon might be less likely to trigger the absorption process during its journey. In this model, the universe could therefore be more transparent to the photon than conventional physics predicts.
Energy-dependent speed could affect arrival time
The same broad kind of modification can also make photon travel time depend on energy. Ofengeim and Piran use this possibility to address the event’s late arrival relative to the burst’s trigger. Both effects are theoretical consequences of their chosen model; the reported timing does not independently demonstrate that photon speeds vary with energy.
The paper says first-order LIV appears incompatible with constraints from the burst’s TeV afterglow, while viable solutions emerge for higher-order versions of the model. Its proposed explanation therefore depends on the form of LIV assumed and on how the candidate event relates to the burst’s afterglow. Read the paper abstract at Physical Review D.
How does the axion-like-particle proposal differ?
A separate proposal by Giorgio Galanti and Marco Roncadelli combines two ingredients rather than relying on LIV alone. A Physics World report published on 30 September 2026 describes their framework as using photon–axion-like-particle (ALP) mixing in magnetic fields to help with propagation at lower energies, then invoking LIV for the 300 TeV event. Physics World report.
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ALPs are hypothetical particles that can mix with photons in magnetic fields. In the report’s account, conversion between photons and ALPs could help radiation avoid absorption along parts of its route, with conversion back to photons possible later. The report says ALPs alone do not explain the 300 TeV event in the parameter range considered, which is why LIV is part of the combined proposal.
This is distinct from Ofengeim and Piran’s LIV-only analysis. The Galanti–Roncadelli explanation is a theoretical framework summarized in the news report; the report’s account should not be mistaken for independent confirmation of either mechanism.
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What does the reported LIV parameter interval mean?
For a second-order, subluminal LIV model, Ofengeim and Piran report a scale of 1.30 with a −0.35/+0.56 interval, in units of 10−7 Planck energies, at 95.4% credibility. This is a model-dependent parameter interval from their analysis—not a direct measurement of a departure from relativity, and not a probability that new physics has been discovered. The authors’ paper.
Has the event proved that relativity is wrong?
No. The reported event is a candidate with a conditional association to GRB 221009A, and the proposed explanations rely on theoretical assumptions. A chance association or another explanation remains possible. Neither the LIV-only analysis nor the ALP-plus-LIV scenario turns one event into proof that Lorentz symmetry is violated.
Further observations could test whether high-energy photons show repeatable energy-dependent propagation signatures. Such observations would help distinguish among explanations; they are not guaranteed to confirm either proposal.
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