In a Colloquium lecture of Juan Maldecena, He states that weak coupling states the theory is hard to change the metric. And tolds that weakly coupled system requires a lot of fields.
Can you give me more explanation for weakly coupled in gravity theories? And i don't understand the relation between the metric and a number of field.
weakly coupled system requires a lot of fields.
In string theory we can consider theories in which the number of D-branes in the theory, N, is proportional to $\frac{1}{{{g_s}}}$ where ${g_s}$ is the closed string coupling constant. A weak coupling would imply that that coupling constant is very small. If the coupling constant, ${g_s}$, is small, and the number of D-branes in the theory is proportional to $\frac{1}{{{g_s}}}$, then that would mean there would be a lot of D-branes in the theory. In order to maintain the amount of degrees of freedom required by supersymmetry, each D-brane has a corresponding world-volume gauge field. So if there are a lot of D-branes, there will be a lot of these fields.