%0 Journal Article %T Time-dependent loss of derivatives for hyperbolic operators with non regular coefficients %A Ferruccio Colombini %A Daniele Del Santo %A Francesco Fanelli %A Guy M¨¦tivier %J Mathematics %D 2013 %I arXiv %R 10.1080/03605302.2013.795968 %X In this paper we will study the Cauchy problem for strictly hyperbolic operators with low regularity coefficients in any space dimension $N\geq1$. We will suppose the coefficients to be log-Zygmund continuous in time and log-Lipschitz continuous in space. Paradifferential calculus with parameters will be the main tool to get energy estimates in Sobolev spaces and these estimates will present a time-dependent loss of derivatives. %U http://arxiv.org/abs/1305.1095v1