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1d
comment Invariant amplitude in QED in terms of Mandelstam variables
Yes exactly - for example, $P_i \cdot P_j $ are expressible entirely in terms of the mandelstam variables so that e.g $P_1 \cdot P_2 = s/2$ for example.
1d
comment Invariant amplitude in QED in terms of Mandelstam variables
In the relativistic regime, you may ignore the mass terms so that $s+t+u=0$.
1d
awarded  Enthusiast
Apr
29
asked Superficial degree of divergence for scalar theories
Apr
27
comment Wick contraction in proton-pion production
I see. But why is it that they contribute the same under integral? The contraction in term (a) involves an outgoing proton at $x_1$ and an incoming proton at $x_2$. The contraction in term (c) has an outgoing proton at $x_2$ and an incoming proton at $x_1$. Is it because only under the integral we can swap $x_1 \leftrightarrow x_2$ and thus have the proton going from $x_1$ to $x_2$ in both cases say? Thanks!
Apr
27
comment Wick contraction in proton-pion production
@AccidentalFourierTransform: I was just wondering how we expect them to be equal in the first place - it seems to imply that $$:(ig \bar \Psi \gamma_5 \psi \phi)_{x_1} (e \bar \psi \gamma_{\mu} \Psi A^{\mu})_{x_2}: = :(ig \bar \psi \gamma_5 \Psi \phi)_{x_2} (e \bar \Psi \gamma_{\mu} \psi A^{\mu})_{x_1}:$$ but why is this true? Thanks!
Apr
26
asked Wick contraction in proton-pion production
Apr
24
asked Crossing Symmetry in Bhabha scattering and Moller scattering
Apr
21
accepted Derivation of the full generator of the Lorentz transformations
Apr
21
accepted Resources to learn about the Higgs theory at undergraduate level
Apr
21
accepted Dependence on UV cut off of some $\phi^4$ diagrams
Apr
21
accepted Hartree-Fock correction to $e$-$e$ interaction
Apr
21
accepted Conceptual question about field transformation
Apr
21
accepted Classical and Semi-classical treatments of the ideal gas
Apr
20
revised Decimation of a triangular lattice
added 213 characters in body
Apr
20
comment Decimation of a triangular lattice
The physics concept I am trying to understand is if the transfer matrix method is appropriate for this question where the interaction is not simply of the form $\sigma_i \sigma_{i+1}$. I have edited this into my answer. Please now reopen.
Apr
18
revised Raising and lowering operators for a composite isospin $SU(2)$ system
edited title
Apr
18
asked Raising and lowering operators for a composite isospin $SU(2)$ system
Apr
18
comment Transformation properties of $2 \times 2$ matrix involving Pauli matrices
2) It says one can check that $\phi'$ and $\phi$ are related by a rotation - but isn't this just a definition already given (first line of the OP really with the exponential $\exp(-i\alpha \cdot t)$?
Apr
18
comment Transformation properties of $2 \times 2$ matrix involving Pauli matrices
Ok many thanks :) My final questions would be: 1) Do we have to assume anything about the $\phi_i$ to show that $\sigma'$ is also hermitian? I know that an $SU(2)$ triplet consists of the $\pi$ mesons and under hermitian conjugation I suppose $(\pi^+, \pi^0, \pi^-) \rightarrow (\pi^-, \pi^0, \pi^+)$ so that it goes into itself but perhaps there exists another triplet such that this doesn't happen. Thanks :)