Why do we know that an elementary particle is a point particle?

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SUMMARY

The discussion centers on the nature of elementary particles, particularly their classification as point particles within Quantum Field Theory (QFT). Participants clarify that while particles like electrons are often described as point-like, they are fundamentally states in a Hilbert space defined by irreducible representations of the Poincaré group. The conversation highlights that protons and neutrons, being composite particles, exhibit size due to their internal structure, unlike elementary particles such as electrons and neutrinos, which are treated as point particles in experimental contexts. The complexities of scattering theory in curved spacetime and the implications of wave-packet behavior during measurements are also discussed.

PREREQUISITES
  • Quantum Field Theory (QFT) fundamentals
  • Poincaré group and its role in particle physics
  • Understanding of wave-packet theory
  • Basic principles of scattering theory
NEXT STEPS
  • Study the implications of the Poincaré group in Quantum Field Theory
  • Explore the concept of wave-packets in quantum mechanics
  • Research scattering theory in both flat and curved spacetimes
  • Examine the Dirac equation and its application to elementary particles
USEFUL FOR

Physicists, particularly those specializing in particle physics, quantum mechanics, and theoretical physics, will benefit from this discussion. It is also relevant for students and researchers interested in the foundational aspects of Quantum Field Theory and the nature of elementary particles.

  • #31
A. Neumaier said:
It is a stable infraparticle, which means that it has an additional mass degree of freedom, which behaves like an additional momentum dof.
Here is more on infraparticles. For more on the branch point of the electron propagator, see, e.g., section II of
 
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