Index Concordia

Minimal area in arbitrary background (I)

Posted in Gravity, String Theory by Index Guy on August 7, 2008

Let us start with the following background metric:

ds^2 = A\eta_{mn}dx^m dx^n + Bdr^2 ,

where the functions A and B are functions of the extra coordinate r. The case of anti-de Sitter space corresponds to

A = B = \displaystyle\frac{R^2}{r^2}.

Under the “T-duality” transformation

\partial_{a}y^m = i A \epsilon_{ab}\partial_{b}x^m   and   \rho = \displaystyle\frac{R^2}{r}

the metric in the dual space takes the form

ds^2 = \tilde{A}\eta_{mn}dy^m dy^n + \tilde{B}d\rho^2 ,

but now

\tilde{A} = \left[A(\rho)\right]^{-1}   and   \tilde{B} = \displaystyle\frac{R^4}{\rho^4}B(\rho).

Since we can always bring the metric in this form, we will just consider the initial case and see what can we do with it. Note that it could be the case that the change of variables between (r,\rho) could be of the general form

\rho = Ar   which means   dr^2 = \left(r\displaystyle\frac{\partial A}{\partial r} + A\right)^{-2}d\rho^2 .

This case could be more complicated… For now we will just stick with the first change of variables introduced.