Photon-pair threshold, opacity and cascades
Research context
research method · conditional · As of 2026-10-10
Two photons can produce an electron–positron pair only above an angle-dependent invariant threshold.
Key knowledge
Two photons can produce an electron–positron pair only above an angle-dependent invariant threshold. Opacity integrates the target spectrum, angles and path; produced pairs can reprocess energy, so a spectral cutoff is not automatically a unique intrinsic acceleration limit.
Values and equations
ε1 ε2(1-cos θ) ≥ 2 m_e^2 c^4
- ε1,ε2
- Photon energies in the same frame J
- θ
- Collision angle rad
- m_e
- Electron mass kg
- c
- Speed of light m s^-1
Conditions and scope
- Threshold is in one inertial frame; parallel photons cannot meet it at finite energy.
- Pair cascades require transport, cooling and geometry beyond a single optical-depth estimate.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
High energy astrophysics: photon-photon pair production: Two-photon threshold, opacity and cascade limitations (selected source body inspected).
2026-10-10 · Bounded source check of the recorded statement and conditions. This does not certify a unique physical model, reproduce the cited study or replace independent branch review.
Entry details
Permanent link to this entry ↗- Record identity
- research-earth-gamma-pair-opacity
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference