We have three mutually coprime integers $r,t,M$ where $M\asymp K^{\frac12-2\epsilon}$ and $r,t\asymp K^{\frac14+\epsilon}$ holds with some fixed $\epsilon>0$ and $K>0$ is a large parameter. Assume $M^2-4rt$ is a prime if need be.
What is the largest integer $T$ (preferably prime) with $$2\sqrt{rt}+M\equiv0\bmod T?$$
Is there a fast method to find the largest $T$ allowable and can it be much larger than $K$ (preferably order $\Omega(K^\alpha)$ at arbitrary $\alpha\geq1$)?
Preferably the method should be in $e^{o(\log K)}$ time. Ideally it should be $O(polylog(K))$.
- Also for every possible can $\zeta_r,\zeta_t\asymp T^{\frac12+\beta}$ hold where $\zeta_r^2\equiv r\bmod T$ and $\zeta_t^2\equiv t\bmod T$ while $\beta>0$ is very small and is fixed?