TITLE: Cyrillic alphabet in math
QUESTION [16 upvotes]: There are a lot of variables and constants in a paper that I am writing. Is anything wrong to use Cyrillic letters for constants and Latin and Greek letters for variables? I wonder why the letters are not used in other papers when they need extra symbols.
(Image is provided by @Ryan)

$2ж+цc$ looks better than $2b'+Cc$.
I know some readers may not know the name of these letters, but this is true for some Greek letters too. What is more important: beautiful and easy to understand equations or knowing the name of the letters? Are these letters used in the academic material of the countries that their language are written in Cyrillic?  
(Personally, I do not know the name of most Cyrillic letters. But I think using them is interesting and useful.)

REPLY [6 votes]: I suppose my answer is more cosmopolitan. I would entirely welcome a Cyrillic letter with three caveats:

Tell me how to pronounce it so that I can actually read it aloud in my head. This is easy enough to accomplish with a footnote and the IPA.
Have mercy on me and make it a letter that I can actually transcribe by hand without much difficulty and wouldn't be confused with another Latin or Greek letter. I would welcome a Б, Я, or a И (or even the Old English þ) any day over having to write $\xi$, $\Xi$,  or even $\zeta$ on a bad day. And I'd prefer to use those Cyrillic letters over $\eta$, $\chi$, $\tau$ when I have to use $h$, $n$, $x$, or $t$ already. 
Make sure the letter is fulfilling a purpose that isn't already being handled, or could be handled, by some other letter or symbol.

The complaints against the Cyrillic alphabet because it's non-canonical or difficult-to-pronounce are pretty trivial. I still remember when I learned the Greek alphabet for the first time and wondered why they were necessary and was annoyed and discomforted by having to learn how to transcribe and pronounce new letters. Learning a handful of Cyrillic letters wouldn't have been too much to ask from me in addition to learning the Greek alphabet at the same time. Those who don't recall the Greek alphabet being difficult to learn should have no complaint---they've either forgotten it was difficult and learning a few more letters would be no more difficult, or it was easy for them and learning a few more letters should be just as easy.
I did eventually find out the Greek letters weren't necessary---they were convenient. Marching through subscripts, primes, overlines, uppercase, calligraphy, fraktur, etc. there really shouldn't be any reason why we'd have to dip into another alphabet. But we do, and we can't imagine going back. Probably because we have dipped into the Greek alphabet, these previous tweaks to letters have received their own associated implicit meanings which must be overcome when you wish to use it in a different fashion. The human eye consistently finds lowercase easier to read. Thus we use magascule forms only occasionally. Uppercase letters denote sets. Calligraphy represents sets of sets. Fraktur represents abysmal sets of sets of sets. Subscripts are things that don't move and are somehow related or under collective investigation. Overlines and primes represent quantities which are somehow related to (usually in a determined by fashion) the un-overlined or un-primed quantities.  Dipping into the Cyrillic alphabet would probably open up new doors if people were willing to do so.
However, I imagine the reason why we don't dip too frequently into other alphabets is that the Latin and Greek alphabets are accommodating enough to the majority of people. And only a handful wish for more because of necessity. This means that the third point that I listed is probably going to be the hardest to fulfill. If you use a non-orthodox letter for a purpose that could be fulfilled by a Latin or Greek letter equally well, I'd question your compositional skills.
If you find a usage for these letters, please don't type-cast them into a fixed constant. That would murder the potential. And convince a respected mathematician that your usage is good. I want more letters.