Action for massless particles in GR
34788
Lagrangian for relativistic massless point particle
38673
General relativity: For massless particles, is the momentum and velocity 4-vectors equal?
88525
Action and Action integral: Different kinds of variational principles
92532
Conservation of Mass during Electron - Positron Annihilation
92297
Relativistic Mass and Dark Matter
53170
Energy conservation in General Relativity
131016
Question about Klein-Gordon field Lagrangian
157321
Why does the action have to be hermitian?
128937
Lie theory and particle physics
72721
Do an action and its Euler-Lagrange equations have the same symmetries?
105660
Invariance of action $\Rightarrow$ covariance of field equations?
7291
Gravity as a gauge theory
63098
Properly discontinuous actions and discrete groups in complete Riemannian manifolds.
94173
Deriving the Lagrangian for a free particle
22279
Local and Global Symmetries
124863
Performing Wick Rotation to get Euclidean action of a scalar field $\Psi$
121914
Unitary representations of the diffeomorphism group in curved spacetime