detection of alignments. Section 3 contains the analysis of observational samples of galaxies from the Sloan Digital Sky Survey. The comparison between models and observations as well as the discussion of the results is presented in Section 4, and Section 5 contains the final conclusions from this work.

Anisotropies in the 3D Correlation function
===========================================

In this section we analyse the three-dimensional two-point correlation function, using cluster-particle pairs, measured using $\Lambda$CDM numerical simulations, taking into account the orientation with respect to the centre halo angular momentum. To this end, we have run two periodic simulations of $500$ and $60$ $h^{-1 }$Mpc computational box sizes, for a flat low-density Universe, with a matter density $\Omega_{\rm m}=1-\Omega_{\Lambda}=0.3$, Hubble constant $H_{\circ}=70$ km s$^{-1}$ Mpc$^{-1}$, and normalisation parameter $\sigma_{8}=0.8$. The particle resolutions are $m_{\rm p}\ge 
7.2\times 10^{10}\,h^{-1}\,M_{\odot}$ for the large simulation, and $m_{\rm p}\ge 1.2\times 10^{8}\,h^{-1}\,M_{\odot}$ for the small one. The identification of particle clumps has been carried out by means of a standard friends-of-friends algorithm with a percolation length given by $l=0.17$ $\bar{\nu}^{-1/3}$, where $\bar{\nu}$ is the mean number density of DM particles. Both simulations have been performed using the first version of the GADGET code developed by Springel et al. (2001). We 