In an efficient market the correlation cofficient between stock returns for two non overlapping time periods should be?

In an efficient market, the correlation coefficient between stock returns for two non-overlapping time periods should be close to zero. This reflects the idea that past stock returns do not predict future returns, as all available information is already reflected in current prices. Consequently, any patterns or trends observed in one period should not persist into another. Thus, the returns are expected to be independent across different time periods.