Building on recent work of Harper, and using various results of Chang and Iwaniec on the zerofree regions of L-functions Lps, χq for characters χ with a smooth modulus q, we establish a conjecture of Soundararajan on the distribution of smooth numbers over reduced residue classes for such moduli q. A crucial ingredient in our argument is that, for such q, there is at most one 'problem character' for which Lps, χq has a smaller zero-free region. Similarly, using the 'Deuring-Heilbronn' phenomenon on the repelling nature of zeros of L-functions close to one, we also show that Soundararajan's conjecture holds for a family of moduli having Siegel zeros.
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