Sometimes, there is an absolute limit on the number of terms an officeholder can serve, while, in other cases, the restrictions are merely on the number of consecutive terms.
For example, Maxwell's Equations would always be capitalized, while quantum mechanics is usually un-capitalized. I searched half a dozen sites for an answer to this but found no clue about a rule. So go either way that makes you happy, but (most of all) be consistent.
Note. Values and accuracies are from the Review of Particle Physics [reference 1] . Italicized symbols represent variable names; nonitalicized symbols represent unit names. The figures in parentheses after the values give the 1-standard-deviation uncertainties in the last digits.