A Why Can We Drop Constant Terms in Quantum Field Theory Lagrangians?

spaghetti3451
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Why can we always drop any constant term in a Lagrangian density in quantum field theory?

This issue is somehow related to the constant term being some kind of cosmological constant?

Can you please explain this issue?
 
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Well, in classical field theory the constant is superfluous, because the field equations are calculated in terms of the partial derivatives of the Lagrangian density.
In QFT the constant term should not influence the path integral (generating functional for the various Green functions). Can you show that?
 
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