XEUS: the physics of the hot evolving universe. - Arnaud, Monique; Barcons, Xavier; Barret, Didier; Bautz, Marshall; Bellazzini, Ronaldo; Bleeker, Johan; Böhringer, Hans; Boller, Thomas; Brandt, William; Cappi, Massimo; Carrera, Francisco; Comastri, Andrea; et al. (Experimental Astronomy, 2009)