Undergrad Q: What Subscript Should I Use for Physics Quantity?

[nomadreid]

I am almost ashamed to put this question, as it verges on the silly, but it is a real question, and Physics Forums has come to my rescue so often...
I am translating a physics article from Russian, and at one place the author puts quantities (such as σ for standard deviation, etc.) with a double subscript: one indicating the particle involved, and the second the axis upon which the quantity is projected. I am not one to ask the author to change his style (let alone the content), but I do have to change the Russian letter he uses for "particle" to an English subscript. He uses the first letter of the Russian word for "particle", so that with a projection to the x-axis, this looks like σ_чx. If I used "p", this would look too much like momentum. I can't think of another natural single letter. Any suggestions?
I could then use a syllable instead of a letter: if I use, say, "par", then I have to come up with a natural way to combine them (without second-level subscripts such as σ_parx or σ_xpar): parx is obviously no good, but I am not sure about something like par(x), par-x, par.x, or par/x. So, any suggestions?
Thanks.

 

[mfb]

$\sigma_{par,x}$?
If the particle has some index or name, that could be used.

 

[nomadreid]

$\sigma_{par,x}$?
If the particle has some index or name, that could be used.

Thanks for the suggestion, mfb. That sounds pretty good.
(But I am willing to hear other suggestions, for anyone else who reads this.)
Unfortunately, the generalized particle has no particular name; the author is trying to prove statements about particles in chaotic motion around a central point (no, not Brownian motion), and although he sometimes uses an electron as an example, the statements are supposed to be general. So no particular name. Alas.

 

[jtbell]

Does the article refer to any articles in English? If so, those might give examples of the customary notation for that field.

 

[nomadreid]

Does the article refer to any articles in English? If so, those might give examples of the customary notation for that field.

Thanks for the good suggestion, jtbell, and I will keep this idea in mind in future. Alas, all the sources referred to in this article are in Russian. However, I decided to take mfb's suggestion. Since much of the rest of the article introduces the author's own notation, and since when I asked him what he would like, he gave me a free hand, he appears not too interested in keeping to convention. I am just his translator, not his editor or peer reviewer, so I am satisfied with mfb's notation, and thereby declare this topic closed. Again, thanks to both of you for responding.