I'm just reading Srednicki's QFT book, where the author gave an exercise on this axion. He posed the Lagrangian as (\partial_\mu a)^2+(\theta+a/f)F\tilde{F}, then he said we can use the shifting symmetry of a to kill the theta term.
But even if we do that, we're left with the term...
Consider the usual phi^4 theory, when we derive the Lehmann-Kallen representation of the propagator, by inserting a complete set we know that the propagator has a branch cut starting from 4m^2, where the m is the physical mass.
My question is: what's the construction of these...
When people discuss the Schwinger model, sometimes they still call the electron field spin-1/2 and the EM field spin-1. I wonder if there's some justification for these calling, since there's no rotations at all in 1+1 spacetime. I know for SO(n) with n>=2, one can always have well-defined spins.
Consider the simplest \phi^4 with Z_2 breaking. Before the shift, \langle\phi\rangle=0 by symmetry. After the shift, the vev of the shifted field is zero, which means \langle\phi\rangle\neq0, which in turn means we have picked the corresponding vacuum out of two possibilities. However, through...
I had read it. It doesn't address my question. For example, the equation (34.19) in the online version of that book shows that a field carries two symmetric spinor indexes is spin-1, so why can't we use this to describe spin-1 fields?
It's a famous claim that spin-0, spin-1 and spin-2 fields are described by scalar, vector and second-rank tensor, respectively. My question is: why not other objects? For example, consider spin-1 field, we can use a field that carries two left spinor indexes. From the group-theoretic relation we...