Lagrangian equation in special relativity

IPhO' 2008
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Can we use the method of Lagrangian equation in the very high velocity system and how to use it?

Thank you.
 
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IPhO' 2008 said:
Can we use the method of Lagrangian equation in the very high velocity system and how to use it?

Thank you.

Yes, we can. You can check out the attachment "Lagrangian definition of relativistic momentum" in my blog for details.
 
The Landau series has a good treatment of this as well. It starts off with a Lagrangian formulation.
 
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From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu} \delta g_{\mu\nu} = -g_{\mu\nu} \delta g^{\alpha\mu} \,\, . $$ Multiply both sides by ##g_{\alpha\beta}## to get $$\delta g_{\beta\nu} = -g_{\alpha\beta} g_{\mu\nu} \delta g^{\alpha\mu} \qquad(*)$$ (This is Dirac's eq. (26.9) in "GTR".) On the other hand, the variation ##\delta g^{\alpha\mu} = \bar{g}^{\alpha\mu} - g^{\alpha\mu}## should be a tensor...
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