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Lagrangian, scalar or pseudoscalar? 
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#1
Jan1011, 12:04 PM

P: 24

Hi,
My question is. Can in principle, a Lagrangian density for some theory be a pseudoscalar. Normally people say that the Lagrangian needs to be a scalar, but it case it is a pseudoscalar it would also be a eigaen function of the parity operator. This topic could well be on the classical physics section, but as this is more relevant in quantum theory I decided to place it here. Thanks 


#2
Jan1011, 04:04 PM

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P: 11,894

The normal requirement is that the fields transform irreducibly under the spacetime symmetry group and that the lagrangian density is a scalar under the spacetime symmetry group. The symmetry requirement for QFT in Minkowski spacetime is restricted Poincare group plus CPT plus gauge invariance. The Lagrangian density should be a scalar wrt to the 3 altogether or each taken separately.



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