# The invariant momentum-space volume element?

1. Feb 21, 2014

### pellman

When we way that

$$\frac{d^3p}{p_0}=\frac{d^3p}{\sqrt{m^2+\vec{p}^2}}$$

is the invariant volume element, is that with respect to all Lorentz transformations or just proper orthochronous Lorentz transformations?

2. Feb 21, 2014

### WannabeNewton

The latter

3. Feb 21, 2014

Thanks.