Discussion Overview
The discussion revolves around the concept of Coulomb singularity in Quantum Chromodynamics (QCD), particularly in the context of quarkonium states involving two gluons in the final state. Participants seek clarification on the definition, expression, and implications of this singularity, as well as its relation to other theories like Quantum Electrodynamics (QED) and Non-Relativistic Quantum Chromodynamics (NRQCD).
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- One participant asks for a definition of Coulomb singularity in QCD and requests an example involving Feynman diagrams.
- Another participant inquires about the meaning of Coulomb singularity in QED, suggesting a potential comparison between the two theories.
- A participant explains that Coulomb singularity arises when a virtual gluon is exchanged between a quark pair in a meson, noting that the singularity occurs as the relative velocity of the quarks approaches zero, leading to an expression of the form ~1/v.
- This same participant expresses uncertainty about the origin of the ~1/v expression and suggests that Coulomb singularities may only exist in QCD, not in QED.
- Another participant questions the model being referenced, indicating they have not encountered the ~1/v expression in full QCD.
- A participant clarifies that they are specifically discussing Non-Relativistic Quantum Chromodynamics (NRQCD).
- A later post provides a reference to a paper that may contain relevant information on the topic.
Areas of Agreement / Disagreement
Participants do not appear to reach consensus on the definition and implications of Coulomb singularity in QCD, with multiple competing views and uncertainties expressed regarding its relationship to QED and the specific models being discussed.
Contextual Notes
There are limitations in the discussion regarding the assumptions behind the ~1/v expression and the applicability of different models (QCD vs. NRQCD). The discussion also reflects a lack of clarity on the derivation of certain terms and their relevance in the context of the theories mentioned.
Who May Find This Useful
Researchers and students interested in Quantum Chromodynamics, Non-Relativistic Quantum Chromodynamics, and the study of quarkonium states may find this discussion relevant.
And with this information, I think we have Coulomb singularities only in QCD, but not in QED. 