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This equation suggests a path integral, of a Lagrangian that contains terms for both general relativity and the Standard Model in highly abbreviated form. Compressing it all into one line is a stunt, of course, rather than an actually useful equation. :) It glosses over many technical issues (for instance that we don't actually know how to do quantum ...


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Because you are looking only at the so-called global part, i.e. the part of the gauge transformation which resembles a group action. Recall that the vector bosons transform as $$ A_\mu \to g A_\mu g^{-1} - (\partial_\mu g) g^{-1}$$ where the first part is the global part of the gauge transformation, which tells you that $A_\mu$ transform in the Adjoint ...


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Inflation, separation of gravity from other forces, separation of strong from electroweak force, and electroweak symmetry breaking, are all different events. It's easiest to start by describing the different sorts of fields involved. Quantum fields get classified by their "spin", which describes the angular momentum states that field quanta (particles) can ...


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We use gauge theories because they - as an experimental fact - describe the world correctly. Asking why that which we use to describe the world describes the world is not a meaningful physics question. Since hitherto gauge theories have been amazingly successful in describing fundamental interactions, we would of course look for a gauge description of a new ...


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First off the Standard Model (SM) is chrial, so left and right handed fermions are in different representations of the gauge group. The rep of $SU(3)$ is determined by the color charge. Gluons are in the adjoint of $SU(3)$, which is the 8 of $SU(3)$. Both left and right handed quarks are in the fundamental rep, which is a $3$ (or a $\bar{3}$) (for example, ...



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