I'm working on a problem involving the following action:
$$S_1 = T_{p+1}\int{d^{p+2}\sigma (\frac{1}{4}\alpha'^2 F_{\mu\nu}F^{\mu\nu} + \frac{1}{2} \partial_\alpha X^i \partial^{\alpha} X^J \delta_{ij}+ \text{interaction terms})}$$
which represents the action of an effective free string theory...