I'm new to this exchange so please bear with me regarding notation. I would like to know what the differential operator $d^n$ means as seen in some physics equations. Normally, one would have an integral with a $dx$ or $dy$ (whatever the case might be), but the differentials I am talking about are of the form $(d^n)x$. (please note that I'm aware of those in tensor calculus, of the form $d(x^n)$ - I'm not referring to those.) Please help.
An example: $d^3x = dxdydz$, In general $d^n x$ is a symbol used for the volume element under integration.
For example $\int f(x_1,x_2,x_3,x_4) d^4 x$ means you have to perform 4 integrals, not just one, over a 4-volume domain.
$$ d^n x = d x_1 dx_2 \cdots dx_n $$ In this sense $d^n$ is not an operator, but rather a shorthand.