Feynman Diagrams


richard feynman

Richard Feynman, born in 1918, was an American theoretical physicist, who played a major role in the field of quantum electrodynamics(QED) with a significant contribution.

He made a great contribution in promoting particle physics as well, using his other famous skill, in addition to being a brilliant scientist - ability to teach and share his knowledge in such a way that an audience could effortlessly understands it - and enjoy it too in equal measure.

Feynman's great contribution to the QED made him a recipient to share the Nobel prize for physics in 1965.The diagrams, which he came up with to explain the interaction between the sub atomic particles, came to be known as Feynman Diagrams, left an indelible mark in his illustrious legacy for years to come.

Richard Feynman died in 1988.


Feynman Diagrams

There are four fundamental forces in nature. They are:

  1. Electromagnetic Force
  2. Gravitational Attraction
  3. Strong Interaction
  4. Weak Interaction

Richard Feynman came up with a graphical representation of interactions, while taking into account the exchange particle or force carrier particle that plays the crucial role in them.

Feynman diagrams use a series of lines and vertices to illustrate the particle interactions. In addition, a wiggly line is used to represent the exchange particle. At each vertex, the following must be conserved:

  1. Charge
  2. Lepton Number
  3. Baryon Number
  4. Momentum
  5. Energy

Now, let's look at a simple Feynman diagram. It shows the electromagnetic force of repulsion between two electrons:

force of repulsion -feynman diagram


  • The vertical axis represents time and the horizontal axis represents space.
  • The total charge at both vertices remains -2.
  • The first electron releases a photon to be received by the second electron, which in turn creates the force of repulsion.
  • The momentum and energy are conserved. So are the baryon number and lepton numbers.

Electron Capture

Election Capture takes place when a proton from a proton-rich nucleus interact with an electron in an inner shell of the atom, just outside the nucleus.

W+ boson, the exchange particle, turns the electron into a neutrino.

electron capture -feynman diagram


Beta Decay

When a neutron or proton in an unstable nucleus emits a beta particle, the process is called beta decay. In both cases, the exchange particle is a W boson.

β- Decay

electron capture -feynman diagram


In this case, W-, released by the neutron, turns into an anti-neutrino and an electron - β- particle.


β+ Decay

electron capture -feynman diagram


In this case, W+, released by the proton, turns into an neutrino and an positron - β+ particle.


Neutron-neutrino Interaction


neutron-neutrino interaction -feynman diagram


When a neutron interacts with a neutrino, a W- boson is released as the exchange particle, which in turn interacts with the neutrino to form the β- particle.


Proton-antineutrino Interaction


proton-antineutrino interaction -feynman diagram


When a proton interacts with an antineutrino, a W+ boson is released as the exchange particle, which in turn interacts with the antineutrino to form the β+ particle.


Photons and W-bosons

Both photons and W-bosons are exchange particles or force carrier particles. Bosons, however, are different from photons, because,

  1. Bosons have non-zero rest mass.
  2. The range of bosons is less than 0.001 fm.
  3. Bosons are positively or negatively charged.





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