About the least action principle

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  • Thread starter yancey
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hello, everyone. When a vector field ##A_{\mu}## has the Lagrangian of the form as
##L=Const.{\times}F^{\mu\nu}F_{\mu\nu}##, where
[itex]F_{\mu\nu}=({\partial}_{\mu}-{\alpha}{\partial}^{\rho}{\partial}_{\rho}{\partial}_{\mu})A_{\nu}-({\partial}_{\nu}-{\alpha}{\partial}^{\rho}{\partial}_{\rho}{\partial}_{\nu})A_{\mu}[/itex]. Now I will apply the least action principle to it. Which one of the following two choices is the right one?
[itex]{\delta}S=\frac{{\partial}S}{{\partial}A_{\mu}}{\delta}A_{\mu}+\frac{{\partial}S}{{\partial}({\partial}_{\mu}A_{\nu})}{\delta}({\partial}_{\mu}A_{\nu})=0,[/itex]
or
[itex]{\delta}S=\frac{{\partial}S}{{\partial}A_{\mu}}{\delta}A_{\mu}+\frac{{\partial}S}{{\partial}({\partial}_{\mu}A_{\nu})}{\delta}({\partial}_{\mu}A_{\nu})+\frac{{\partial}S}{{\partial}({\partial}_{\mu}{\partial}_{\nu}{\partial}_{\rho}A_{\lambda})}{\delta}({\partial}_{\mu}{\partial}_{\nu}{\partial}_{\rho}A_{\lambda})=0.[/itex]
 

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  • #2
Orodruin
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Which do you think and why?
 
  • #3
haushofer
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What is that alpha in your field strength? I'd say F=dA.

You can include higher derivatives in your functional derivative; if you use partial integrations, you'll see that every higher order derivative swaps a sign.
 
  • #4
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What is that alpha in your field strength? I'd say F=dA.

You can include higher derivatives in your functional derivative; if you use partial integrations, you'll see that every higher order derivative swaps a sign.
Thanks for your attention. I was reading a paper on a model of generalized uncertainty principle which originated from quantum gravity effect. ##\alpha## represents the parameter of quantum gravity effect.
 

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