Session 38 - Modeling & Numerical Methods.
Display session, Wednesday, June 11
South Main Hall,

## [38.05] Probing Hierarchical Clustering by Scale-Scale Correlations of Wavelet Coefficients

J. Pando, L. Z. Fang (U. Arizona), P. Lipa (Institut fur Hochenergiephysik der Osterreichischen Akademi der Wissenschaften), M. Greiner (Theoretische Physik, Technische U.)

It is of fundamental importance to determine if and how hierarchical clustering is involved in large-scale structure formation of the universe. Hierarchical evolution is characterized by rules which specify how dark halos are formed by merging of halos at smaller scales. We show that scale-scale correlations of the matter density field are direct and sensitive measures to quantify this merging tree. Such correlations are most conveniently determined from discrete wavelet transforms. Analyzing two samples of Ly\alpha forests of QSO's absorption spectra, we find significant scale-scale correlations whose scale dependence is typical for branching processes. Therefore, models which predict a history'' independent evolution are ruled out and the halos hosting the Ly\alpha clouds must have gone through a history'' dependent merging process during their formation.