TY - JOUR AU - Cicoli, Michele AU - Guidetti, Veronica AU - Muia, Francesco AU - Pedro, Francisco G. AU - Vacca, Gian Paolo TI - On the choice of entropy variables in multifield inflation JO - Classical and quantum gravity VL - 40 IS - 2 SN - 0264-9381 CY - Bristol PB - IOP Publ. M1 - PUBDB-2023-07949 M1 - arXiv:2107.03391 M1 - DESY-21-106 SP - 025008 PY - 2023 N1 - 20 pages + appendices, 3 figures AB - We discuss the usefulness and theoretical consistency of different entropy variables used in the literature to describe isocurvature perturbations in multifield inflationary models with a generic curved field space. We clarify which is the proper entropy variable to be used to match the evolution of isocurvature modes during inflation to the one after the reheating epoch in order to compare with observational constraints. In particular, we find that commonly used variables, as the relative entropy perturbation or the one associated to the decomposition in tangent and normal perturbations with respect to the inflationary trajectory, even if more useful to perform numerical studies, can lead to results which are wrong by several orders of magnitude, or even to apparent destabilisation effects which are unphysical for cases with light kinetically coupled spectator fields. KW - entropy: perturbation (INSPIRE) KW - inflation: model (INSPIRE) KW - isocurvature: perturbation (INSPIRE) KW - trajectory (INSPIRE) KW - reheating (INSPIRE) KW - spectator (INSPIRE) KW - curvature (INSPIRE) KW - stability (INSPIRE) KW - coupling (INSPIRE) KW - kinetic (INSPIRE) KW - multifield inflation (autogen) KW - isocurvature modes (autogen) KW - entropy perturbations (autogen) LB - PUB:(DE-HGF)16 UR - <Go to ISI:>//WOS:000905279400001 DO - DOI:10.1088/1361-6382/acabf7 UR - https://bib-pubdb1.desy.de/record/600392 ER -