- #1
binbagsss
- 1,259
- 11
Homework Statement
i am stuck on part d , see below
Homework Equations
parts a to c are fine
polyakov action:
## \frac{1}{2} \int \frac{1}{e(t)} \frac{dX^u}{dt}\frac{dX_u}{dt}-m^2 e(t) dt ##
EoM of ##e(t)##:
##\frac{-1}{(e(t))^2} \frac{dX^u}{dt}\frac{dX_u}{dt}-m^2=0## [1]you plug the EoM of ##e(t)## (which is equivalent to the mass-shell constraint) into the polykov action to recover the Nambu-Goto action.
The Attempt at a Solution
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More than anything, I am confused as to why we are given the mass, since the dimension of the space-time is not given, ##u=0,1...d##, ##d## is not specified. If it were ##d=1## I guess we would use it as something like computing the other space-time coordinate.
Whilst ##e(t)## has a transformation rule, ##X^u(t)## just acts as a scalar on the world-sheet in string theory? or in this case on the world-line, and as such has no transformation rule and so it is just a case of plugging in.
I interpret the trajectory in terms of ##t## as (apologies i have done ##\tau=t## and will also do ##\tau'=t'##) ##X^0(t)=t## and ##X^i(t)=0 ## for ##i=0,1,..,d##
So that the mass-shell constraint reads ##\frac{\partial X^0}{\partial t}\frac{\partial X_0}{\partial t}=1/2 ## and via the chain rule of t' and t it is easy to check that this is consistent.
So simply plugging in I get ## X^0(t'(t))=t' ^2##
However I'm guessing this is wrong since I have no idea why we are given the mass, any help much appreciated,ta.