1. Department of Economics and Statistics, University of Siena, Piazza San Francesco, 7-8 53100 Siena, Italy
2. IPAG Business School Paris, 10-12 rue du Théâtre 75015 Paris, France
3. Paris School of Economics-Centre d’Economie de la Sorbonne, Maison des Science Economiques, University of Paris-I Panthon-Sorbonne, 106-112 boulevard de l’Hôpital 75647 Paris, France
4. Leibniz Institute for Financial Research SAFE, Theodor-W.-Adorno-Platz 3, 60629 Frankfurt am Main, Germany
5. Department of Information Engineering and Mathematics, University of Siena, via Roma, 56 - 53100 Siena, Italy