# Tagged Questions

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### Is $\phi^4$ theory in 4d conformally invariant at the classial level?

I used to believe the three following statements to be true (at the classical level only): From scale invariance full conformal invariance follows. Scale invariance is present if there are no ...
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### Hermiticity of the Lagrangian density [duplicate]

In quantum mechanics, the dynamical variables are replaced by hermitian operators. However, the Lagrangian density in quantum field theory is not an observable but we also make sure that it is ...
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### Why is the spacelike conserved charge due to spacetime translations the momentum?

Whilst reading several books on QFT, I have come across the derivation of the conserved charges due to the symmetry under spacetime-translations. I can follow the derivations, and have that the ...
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### Is there a classification scheme for linear classical field theories?

Central to a mathematical understanding of the Bogolyubov transformation is the study and classification of linear lattice field theories. What follows might be familiar to many people, but I just ...
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### Noether's theorem in classical field theory (proof)

Noether's theorem for classical field theory state that if for each closed region $\Omega \in \mathbb{R}^4$ the action $I_{\Omega}$[$\phi$] is invariant under a differentiable transformation of one ...
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### Significance of symplectic form in classical field theory

I'm trying to understand the significance of construction presented to me in field theory class. Let me first briefly describe it and then ask questions. Given two solutions $\phi_1$, $\phi_2$ of the ...
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### Time independent Yang-Mills field coupled to scalar field

Let $A$ be a Yang-Mills field with $A_0 = 0$ and we also have time independent scalar field $\phi$ in the adjoint representation of our gauge group with zero potential (no mass too). I have to show ...
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### Jet bundles for physicists

In order to make Classical Field Theory rigorous we need the idea of jet bundles. I've seem some books on the subject, but most of them are aimed at mathematicians and tend to go quite deep in the ...
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