Lorentz Violation Explains High-Energy Photon from Gamma-Ray Burst GRB 221009A

The extraordinary burst of gamma rays known as GRB 221009A has yielded a surprising discovery, prompting physicists to reconsider fundamental laws of nature, as Dmitry Ofengeim and Tsvi Piran, both from the Racah Institute of Physics at The Hebrew University, alongside their colleagues, report evidence of an exceptionally high-energy photon. Detecting a 300 teraelectronvolt photon originating from this distant event presents two significant challenges to current understanding, as such energetic particles should have been absorbed by background light during their journey to Earth, and its late arrival, long after the initial burst, is difficult to explain through conventional astrophysics. This research proposes that violations of Lorentz invariance, a cornerstone of Einstein’s theory of relativity, may resolve these puzzles by altering how particles interact with light and by subtly changing the speed of photons based on their energy, allowing the high-energy photon to reach Earth and explaining the observed delay. By analysing this single photon, the team establishes new limits on the energy scale at which these fundamental symmetries might break down, suggesting that higher-order violations of Lorentz invariance offer a viable explanation for the observed phenomena.

Is the observed high-energy photon a signal of new physics? Its arrival from a cosmological distance challenges the Standard Model, requiring explanations for how it traversed such vast distances without significant attenuation. Furthermore, the detection of this photon is puzzling given that the very-high-energy afterglow observed by LHAASO has already faded, necessitating a novel astrophysical mechanism to account for this temporal delay. This work demonstrates that Lorentz invariance violation (LIV), emerging as a low-energy limit of certain quantum gravity theories, offers a potential solution to both these puzzles. LIV alters thresholds of particle interaction, modifies the opacity of the extragalactic background, and induces energy-dependent variations in photon velocity, ultimately affecting the photon time of flight. The research investigates the implications of the LIV parameter for understanding these observed phenomena
TeV Photon Detection from GRB 221009A

The detection of a photon with an energy of approximately 18. 9 TeV following the gamma-ray burst GRB 221009A represents a significant breakthrough in gamma-ray astronomy, exceeding previous records. GRB 221009A was already notable for its intensity, making this detection even more remarkable. The detection relied on combined data from the Large High Altitude Air Shower Observatory (LHAASO) and the Carpet-3 array. LHAASO is sensitive to very high-energy gamma rays and cosmic rays, while Carpet-3 is a ground-based array designed to detect extensive air showers.

The detection involved reconstructing the energy and direction of the primary photon from the extensive air shower it created when interacting with the Earth’s atmosphere. The very high energy of the photon places strong constraints on the possible emission mechanisms within the GRB. Standard models struggle to explain such high-energy emission. The paper explores external inverse Compton scattering (EIC) and synchrotron self-Compton (SSC) as potential mechanisms, but both require specific conditions to reach such high energies. The high-energy photon must have travelled through the GRB emission region and the intergalactic medium without being absorbed by pair production, placing constraints on the density of photons and the magnetic field strength.

This detection opens a new energy frontier in gamma-ray astronomy, demonstrating that GRBs can produce photons with energies far beyond what was previously thought possible. It provides a unique opportunity to test fundamental physics, such as Lorentz invariance and the nature of spacetime at very high energies, and will help to refine and constrain models of GRB emission. Future observations with more sensitive instruments are needed to search for similar high-energy photons from other GRBs, and combining gamma-ray observations with observations at other wavelengths, such as X-rays, optical, and radio, and with neutrino observations will provide a more complete picture of GRBs and their environments.

Delayed TeV Photon Challenges Cosmic Distance Limits

Recent observations of the exceptionally bright gamma-ray burst GRB 221009A have presented a significant challenge to our understanding of high-energy particle physics and astrophysics. Researchers detected a very high-energy photon, with an energy of 300 TeV, arriving over an hour after the initial burst and the peak of the observed TeV afterglow. This presents two puzzles: how the photon traversed vast cosmic distances without being absorbed by background light, and why it arrived so much later than other detected particles. Standard physics predicts this photon should have been absorbed, and its delayed arrival is difficult to explain through conventional astrophysical mechanisms.

To resolve these puzzles, scientists investigated the possibility of Lorentz invariance violation (LIV), a concept suggesting that the speed of light may not be constant for all energies. This idea, arising from certain theoretical frameworks, could alter how photons interact with background light and affect their travel time. The team explored whether LIV could simultaneously explain both the photon’s survival and its delayed arrival, finding that a simple, linear form of LIV is insufficient, requiring more complex models. The research demonstrates that higher-order LIV models, specifically those involving a quadratic relationship between energy and the speed of light, can successfully explain the observations, predicting that higher-energy photons experience greater delays and can modify the interaction thresholds with background light, allowing the 300 TeV photon to reach Earth.

Furthermore, the analysis of the observed light curve from the LHAASO telescope revealed that the probability of observing a photon with such a significant delay is low unless LIV is invoked. The team calculated the likelihood of the delayed photon arising from the same emission process as the earlier TeV photons, and found that LIV provides a compelling explanation for the observed timing. This work not only offers a potential solution to the puzzles presented by GRB 221009A, but also provides valuable constraints on theories that attempt to extend the Standard Model of particle physics.

Lorentz Violation Explains High-Energy Photon Arrival

The detection of a 300 TeV photon by the Carpet-3 array, potentially associated with the gamma-ray burst GRB 221009A, presents two challenges for current astrophysical understanding. Firstly, the photon’s high energy suggests it should have been absorbed while travelling from its source due to interactions with the extragalactic background light. Secondly, its late arrival, long after the peak of lower-energy emissions detected by LHAASO, is difficult to explain with standard astrophysical models. This research investigates whether violations of Lorentz invariance, a cornerstone of modern physics, could simultaneously resolve both these puzzles.

The team demonstrates that incorporating Lorentz invariance violation into models of photon propagation can shift the energy threshold for particle interaction, allowing the high-energy photon to reach Earth without being absorbed. Furthermore, the same mechanism predicts a delay in the arrival time of higher-energy photons, potentially explaining the observed time difference between the Carpet-3 detection and the LHAASO observations. By analysing the likelihood of obtaining such a solution, the researchers identify viable parameter ranges for the degree of Lorentz invariance violation, particularly favouring models where the effect increases with photon energy. Specifically, they find that a quadratic Lorentz invariance violation is consistent with the observations.