Open Questions in Cosmic-Ray Research at Ultrahigh Energies

Rafael Alves Batista, Jonathan Biteau, Mauricio Bustamante, Klaus Dolag, Ralph Engel, Ke Fang, Karl-Heinz Kampert, Dmitriy Kostunin, Miguel Mostafa, Kohta Murase, Günter Sigl, Foteini Oikonomou, Angela V. Olinto, Mikhail I. Panasyuk, Andrew Taylor, Michael Unger