Let $X_1,X_2,...$ be iid random variable with mean zero. If $X_1$ has second moment thatthen by the CLT we have $P(X_1+X_2+...+X_n\geq 0)\rightarrow \frac{1}{2}$, as $n$ goes to infinity. I am curious about thatwhether does this hold without the second moment assumption? I think this might be a well studied problem. Could anyone provide an answer or reference to me? Many thank!