Use the polygonal lasso tool to create that black cut shape then fill it with black on a new layer
Select basic brushes and choose a small (5px or so) with no hardness
create a white line right under (or above) the black shape >> apply Gaussian blur (around 6)
lower the opacity of the white stroke and thin it from the sides with a soft eraser brush
In the above image i definetly should have drawn the white brush stroke above the cut to give it the right depth
instead i should twist things and call the wallpaper (Up)