Zannetti, M (reprint author), Univ Salerno, Dipartimento Fis E Caianiello, Via Giovanni Paolo II 132, I-84084 Fisciano, SA, Italy.
; Corberi, F.] Univ Salerno, Dipartimento Fis E Caianiello, I-84084 Fisciano, SA, Italy
; [Zannetti, M.
; Corberi, F.] Univ Salerno, CNISM, Unita Salerno, I-84084 Fisciano, SA, Italy
; [Zannetti, M.] Chinese Acad Sci, Kavali Inst Theoret Phys China, Beijing 100190, Peoples R China
; [Gonnella, G.] Univ Bari, Dipartmento Fis, I-70126 Bari, Italy
; [Gonnella, G.] Ist Nazl Fis Nucl, Sez Bari, I-70126 Bari, Italy
; [Piscitelli, A.] Nanyang Technol Univ, Sch Phys & Math Sci, Div Phys Sci, Singapore 637371, Singapore
Fluctuations of energy and heat are investigated during the relaxation following the instantaneous temperature quench of an extended system. Results are obtained analytically for the Gaussian model and for the large N model quenched below the critical temperature T-c. The main finding is that fluctuations exceeding a critical threshold do condense. Though driven by a mechanism similar to that of Bose Einstein condensation, this phenomenon is an out-of-equilibrium feature produced by the breaking of energy equipartition occurring in the transient regime. The dynamical nature of the transition is illustrated by phase diagrams extending in the time direction.