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I saw this equation on a coffee mug, and I am wondering what it means. I am not far enough along in physics to understand it. Does it actually mean anything or is it gibberish?

enter image description here

I can't embed the image because I am a new user.

(But I can, L.M.)

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Answer to the embedded question : I don't understand why you chose such an ugly angled typeface to write this question . –  Frédéric Grosshans May 20 '11 at 10:05
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2 Answers 2

up vote 7 down vote accepted

Dear Ganesh, it's a totally valid and legitimate interaction Lagrangian of the electron field as it interacts via the electroweak interactions.

Note that this is just a part of the overall Lagrangian and only includes the electron - and its neutrino - as it interacts by exchanging photons, W-boson, and Z-bosons. Note that the "parts" of the electron that are spinning differently, the left-handed $\psi_{eL}$ and right-handed $\psi_{eR}$ electron, are treated differently. In this fundamental way of writing it, the gauge fields responsible for all the forces are the fields $\vec A_\mu$ for the $SU(2)$ group and $B_\mu$ for the $U(1)$ factor. Other particles and kinetic terms for electrons, the gauge bosons, and other particles have to be added.

Particle physicists would probably not write the explicit $\hbar$ factors because whoever studies the electroweak theory usually uses units in which $\hbar=1$. Also, the claim that the interaction Lagrangian is legit doesn't imply that the creator of the mug understands particle physics. It's more likely that he copied it from somewhere - or, more likely, asked a physicist to give him the text.

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Thank you very much! –  Ganesh May 19 '11 at 17:19
It was a pleasure. –  Luboš Motl May 19 '11 at 17:42
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It's the electroweak Lagrangian. In laymen's terms, it describes how photons, electrons and neutrinos interact with one another. Each term represents a possible interaction. See this wiki page for more info. You will see a similar, equivalent Lagrangian expression there with some more detailed explanations, should you want it.

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