Nonzero Values of Dirichlet L-Functions in Vertical Arithmetic Progressions

Let L(s, χ) be a fixed Dirichlet L-function. Given a vertical arithmetic progression of T points on the line ℜs = ½, we show that at least cT/ log T of them are not zeros of L(s, χ) (for some positive constant c). This result provides some theoretical evidence towards the conjecture that all nonnegative ordinates of zeros of Dirichlet L-functions are linearly independent over the rationals. We also establish an upper bound (depending upon the progression) for the first member of the arithmetic progression that is not a zero of L(s, χ).