Here’s a little tutorial on how to make parts of your mesh transparent using transparency maps in Maya Arnold:
1.) Apply an aistandardsurface to your mesh
2.) Using the Attribute Editor (hotkey CTRL+A), go into the Geometry drop-down menu under your material’s tab
3.) Click the checkered box next to Opacity, then select File from the list that pops up
4.) Navigate to your opacity map using the folder next to Image Name, and select it
5.) Click on your mesh, either in your scene or using the Outliner
6.) Locate your mesh’s shape tab in the Attribute editor, then click on the Arnold drop-down menu
7.) Uncheck the Opaque box
8.) Render away!
Helpful Hints: If the opacity on your mesh doesn’t look like what you expected, and your UVs are lined up with your opacity map properly, try inverting the opacity map by navigating to your map file within Maya and selecting ‘Invert’ under the Effects drop-down menu
Let me know in the comments down below (or in the comments on the YouTube video) if you have any questions, thanks!