X-ray sources as tracers of the large-scale structure in the Universe
  We review the current status of studies of large-scale structure in the X-ray Universe. After motivating the use X-rays for cosmological purposes, we discuss the various approaches used on different angular scales including X-ray background multipoles, cross-correlations of the X-ray background with galaxy catalogues, clustering of X-ray selected sources and small-scale fluctuations and anisotropies in the X-ray background. We discuss the implications of the above studies for the bias parameter of X-ray sources, which is likely to be moderate for X-ray selected AGN and the X-ray background (~1-2). We finally outline how all-sky X-ray maps at hard X-rays and medium surveys with large sky coverage could provide important tests for the cosmological models. 
X. Barcons (1), F.J. Carrera (2 and 1), M.T. Ceballos (1), S.   Mateos(1) ((1) Instituto de Fisica de Cantabria CSIC-UC, (2)...