On the critical line zeros of $L$ -- functions attached to automorphic   cusp forms
  We prove for L-function attached to an automorphic cusp form for the Hecke congruence group $\Gamma_0(D)$, which is also an eigenfunction of all the Hecke operators, that a positive proportion of its non-trivial zeros lie on the critical line. This result extends the work of J.L. Hafner of 1983 where the case of the full modular group is considered. 
Irina Rezvyakova
math.NT