- #1
dm4b
- 363
- 4
Hi,
I'm reading Zee's new GR book right now and ran across an action I am having trouble "varying". It's the first term in Eq (9), page 244. Looks like this:
S=-m\int d\tau \sqrt{-\eta _{\mu \nu }\frac{dx^{\mu }}{d\tau }\frac{dx^{\nu }}{d\tau }}
I'm familiar with the trick that gets rid of the square root as outlined by guys like Carrol, as well as Zee. But, I want to tackle this thing head on the hard way w/o the trick ;-)
But, I'm getting stuck reproducing what Zee has in Eq (10)
\delta \left ( -m\int d\tau \sqrt{-\eta _{\mu \nu }\frac{dx^{\mu }}{d\tau }\frac{dx^{\nu }}{d\tau }} \: \right )=m\int d\tau \; \eta _{\mu \nu }\frac{dx^{\mu }}{d\tau }\frac{d\delta x^{\nu }}{d\tau }
I get the same thing, but with a 1/L included, because the root won't go away.
Anybody know the trick? Or does Zee have a typo? Can't be me, right? ;-)
I'm reading Zee's new GR book right now and ran across an action I am having trouble "varying". It's the first term in Eq (9), page 244. Looks like this:
S=-m\int d\tau \sqrt{-\eta _{\mu \nu }\frac{dx^{\mu }}{d\tau }\frac{dx^{\nu }}{d\tau }}
I'm familiar with the trick that gets rid of the square root as outlined by guys like Carrol, as well as Zee. But, I want to tackle this thing head on the hard way w/o the trick ;-)
But, I'm getting stuck reproducing what Zee has in Eq (10)
\delta \left ( -m\int d\tau \sqrt{-\eta _{\mu \nu }\frac{dx^{\mu }}{d\tau }\frac{dx^{\nu }}{d\tau }} \: \right )=m\int d\tau \; \eta _{\mu \nu }\frac{dx^{\mu }}{d\tau }\frac{d\delta x^{\nu }}{d\tau }
I get the same thing, but with a 1/L included, because the root won't go away.
Anybody know the trick? Or does Zee have a typo? Can't be me, right? ;-)
