On a universal mechanism for long ranged volatility correlations
  We propose a general interpretation for long-range correlation effects in the activity and volatility of financial markets. This interpretation is based on the fact that the choice between `active' and `inactive' strategies is subordinated to random-walk like processes. We numerically demonstrate our scenario in the framework of simplified market models, such as the Minority Game model with an inactive strategy. We show that real market data can be surprisingly well accounted for by these simple models. 
Jean-Philippe Bouchaud, Irene Giardina (CEA-Saclay), Marc Mezard   (Orsay)