I'm not sure if this question would be more appropriate here or on SO. My hope is that someone has already had this need and found a solution.
Periodically, I search for a specific research topic on arXiv. Unfortunately it doesn't correspond to a specific arXiv subject: papers of interest can be found under very different subjects, since it's somewhat multidisciplinary. Currently, arXiv only supports sending periodic emails concerning either an entire archive, or one or more subjects inside an archive. There's no way I know of to receive only the results of a specific keyword search. However, I've heard of someone who has been able to get that, but I couldn't get them to explain me what they did.
Have you ever had this need? Did you find a solution?
You can set up a Google Scholar alert. Google Scholar indexes, among other things, arXiv preprints (they typically take 2-3 days to show up), so you will get these in the email alerts.
Be warned that it also indexes journals, other repositories... And while it is possible to restrict advanced searches to arXiv, I haven't been able to set up an alert that only looks at arXiv. So if you are only interested in what shows up on the arXiv, you will have to weigh the pros and cons of also having alerts about papers you might already have seen elsewhere.