Collinear Approximation of Photon Interactions in a Consistent Lorentz-Violating Extension
Funding: Croatian Science Foundation (HRZZ), call PDIP-2026
Project number: PDIP-2026-1575
PI: Maykoll A. Reyes
Host institution: University of Rijeka
Duration: 14. 09. 2026. – 13. 09. 2028. (24 months)
Funds: 42.550,00 EUR
Summary
Lorentz Invariance Violation (LIV) is a key phenomenological probe for Quantum Gravity. However, current gamma-ray LIV studies face two major limitations. First, phenomenological bounds are typically derived using isolated effects, ignoring concurrent processes that may already exclude the explored parameter space. Second, calculations of dynamical effects within the Standard Model Extension (SME) rely heavily on approximations that break down near interaction thresholds (the asymptotic approximation) and can produce a misinterpretation of astrophysical data. This project resolves these limitations by establishing a consistent, threshold-accurate dynamical framework for gamma-ray LIV phenomenology. This will be achieved through three core objectives. First (O1) I will combine existing observational bounds for concurrent phenomenological effects of the same LIV model to isolate the parameter space fully compatible with current gamma-ray observations. Second (O2), within the viable parameter space, I will employ the collinear approximation to compute interaction rates beyond the asymptotic limit for the processes relevant for the universe transparency and atmospheric showers (vacuum Cherenkov, photon decay, Breit-Wheeler pair production, Bethe-Heitler, and Bremsstrahlung). Finally (O3), I will numerically evaluate these threshold-accurate analytical rates and compile the results into HDF5 libraries formatted for direct integration into astroparticle propagation simulation programs (e.g., LIVCorsika, LIVPropa). These threshold-accurate interaction rates will provide the exact theoretical inputs needed by LIV researchers within experimental collaborations (e.g., MAGIC, CTAO, LST) and developers of astrophysical simulation codes. This open-access dataset will be readily available to the broader scientific community, enabling rapid applications such as direct integration into LIVCorsika.
Objectives
- O1: Synthesize current multi-process observational bounds to isolate the phenomenological parameter space strictly compatible with existing gamma-ray observations.
- O2: Analytically derive modified interaction matrix elements beyond the massless limit for key gamma-ray processes (vacuum Cherenkov, photon decay, Breit-Wheeler, Bethe-Heitler, and Bremsstrahlung).
- O3: Numerically integrate these threshold-accurate analytical expressions and package the results into HDF5 libraries, ready for future integration into simulation programs (e.g. LIVCorsika, LIVPropa).
Team
- Maykoll A. Reyes (University of Rijeka) – principal investigator.
- Tomislav Terzić (University of Rijeka) – senior collaborator.
- Filip Reščić (University of Rijeka) – PhD student.
- José Manuel Carmona (University of Zaragoza) – senior collaborator.
- José Luis Cortés (University of Zaragoza) – senior collaborator.
- Ardit Gkioni (University of Zaragoza) – PhD student.