The term leitmotif is almost exclusively used in the context of music, but sometimes literature as well. Whether you use the singular form or plural form is irrelevant as long as you use it correctly.
An alternate spelling is leitmotiv, plural leitmotivs.
The two spellings seem to be fairly equally popular until around 1960, when the spelling leitmotif started becoming much more common. (Source: Google Ngram)
So the larger question is this: Who is your audience? And will they understand your use of this term in the context of your discussion?
I question this because of your opening statement, "in an [sic] scientific book". (By the way, "an" there should be "a".) I'm fairly certain this term is not used much in the scientific community, but rather the Arts. That's not to say you shouldn't use it; but keep in mind, you may need to couch it in such a way that it's clear what you mean.