Some meromorphic functions associated to the S-unit equation
Let f ∈ ℚ [X] be a polynomial without multiple roots and with deg(f) ≥ 2. We give conditions for f(X) = AX² + BX + C such that the Diophantine equation f(x)f(y) = f(z)² has infinitely many nontrivial integer solutions and prove that this equation has a rational parametric solution for infinitely many irreducible cubic polynomials. Moreover, we consider f(x)f(y) = f(z)² for quartic polynomials.
We show that the intersection of the images of two polynomial maps on a given interval is sparse. More precisely, we prove the following. Let be polynomials of degrees d and e with d ≥ e ≥ 2. Suppose M ∈ ℤ satisfies , where E = e(e+1)/2 and κ = (1/d - 1/d²) (E-1)/E + ε. Assume f(x)-g(y) is absolutely irreducible. Then .