Is it correct to say "... doing so requires the marriage of techniques from different maths fields" I want to express that tackling the problem will need techniques from many different maths fields to be used together. Can you give me some alternatives?
Yes. "Marriage" is obviously a metaphor here, but it's fairly common in English to use "marriage" as a metaphor for combining things.
If you want to be literal, you could say "combining". Or you could reword the sentence to, for example, "Techniques from many different fields must all be used" or "must be used together" or "must be used in conjunction".
If you wanted to be more pretentious you could say "synthesizing".
"Melding" might work.
There are probably other metaphors, but off the top of my head I can't think of one that would be particularly good.