Discussion Overview
The discussion revolves around the helicity of photons, the relationship between circular polarization and spin, the spin of gravitons, and the implications of local quantum field theories on the spins of elementary particles. It encompasses theoretical aspects, empirical findings, and the nature of higher spin fields in quantum field theory.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- Some participants question why the helicity of a photon is 1 and not 3 or higher, suggesting a connection to circular polarization and spin.
- One participant states that the spin of the graviton is 2 because it is represented by a symmetric tensor of order 2.
- There is a discussion about the implications of vector and tensor representations on the spins of fields, with some arguing that higher spins lead to redundant degrees of freedom.
- Some participants propose that local quantum field theory restricts elementary fermions to a spin of 1/2, while others mention theoretical models that allow for spin 3/2 in certain contexts.
- Several participants reference literature, including Weinberg's work, to support their claims about field theories and the treatment of higher spin fields.
- There is a debate about the existence of non-renormalizable field theories for spins greater than 3/2 and the challenges they present in terms of irreducible representations of the Poincare algebra.
- One participant raises a question about how to demonstrate that non-renormalizable theories do not provide irreducible representations, leading to further technical discussion.
Areas of Agreement / Disagreement
Participants express a range of views on the helicity of photons, the nature of spin in local field theories, and the treatment of higher spin fields. There is no consensus on several points, particularly regarding the implications of local quantum field theory on particle spins and the existence of field theories for higher spins.
Contextual Notes
Some participants note that discussions often overlook no-go theorems and focus instead on useful constructions, indicating a limitation in the literature regarding higher spin fields. Additionally, the treatment of unphysical degrees of freedom in higher spin theories remains a complex and unresolved issue.