Although this seems like unfair criticism, I found this paper to be dense, boring, and unnecessarily long. Given that, this post will be drier and terser than my other posts (apologies to my big fans).
The authors try to find the optimal frequency for an ET civilization (or I suppose possibly even Earth) to communicate with for long distances. In particular, they look to maximize the data rate. While this is all well and good, and is an interesting thing to think about, I’m not going to bother going into their analysis or even their conclusions because I frankly find them to be useless. All of the analysis assumes Earth technology and Earth knowledge and Earth communication. It irks me. While these assumptions are fair to a degree for when you are designing a search (with current technology we could produce this signal and detect this signal, etc), I feel that expanding them into such a deep analysis is not fruitful. I feel there is merit into looking into most wavelengths, and since a lot of SETI will turn into parasite searches or hopefully get its own funding to do its thing, most wavelengths will be analyzed, especially if time stretches on for a while without a detection. So I don’t think this paper is very useful for SETI.
That being said, there is merit to this for mankind and our possibly inevitable expansion in the solar system and maybe beyond. If there is a specific wavelength that, with our knowledge and technology, works best for long distance travel in terms of data rate, then maybe we should keep this in mind as an alternative to radio (if it’s better). I’m not sure our technology is currently advanced enough to communicate with x-rays, but in the near future I wouldn’t be surprise if it becomes feasible.