In the last century, new observational techniques and discoveries such as the Cosmic Microwave
Background Radiation have brought a new dimension of knowledge about the
Universe. Therefore new theories and models have been proposed to explain the observed
Universe. Computer simulations are a very important tool because they lay a bridge between
theory, often over-simpli ed, and observations, which reveal the complexity of our
Universe.
In this thesis, it is given a review of observations including the most important discoveries
and results that help to describe the Universe and have been used to develop the models
considered nowadays. The cosmological theory behind the large-scale structure formation
is explained, from the basis of the Friedman model to the formation of structures through
the linear, quasi-linear and non-linear regime, including the Zeldovich approximation and
the spherical collapse model. Furthermore, the di erent types of codes used for cosmological
simulations are introduced, focusing on the N-body codes and presenting the code
used in this thesis, developed by Klypin & Holtzman (1997). The tools used to analyse
the results: density plots, power spectrum and mass variance are described as well.
Three main sets of simulations have been performed: a basic simulation (RUN0) with
standard cosmological parameters, simulations of CDM and simulations of Hot+Cold
Dark Matter (HCDM). All the simulations use 323 particles, while di erent cosmological
parameters have been changed e.g. 8,
m,
and n. Thus, it is observed that higher
values of
m and low values of
lead to more clustering and hence more developed
structures. Moreover, the e ect of 8 appears to be critical, since it determines the amplitude
of the density
uctuations at the initial redshift of the simulation. When studying
the presence of hot dark matter, the main di erence comes from the cut-o in the power
spectrum due to the hot dark matter free-streaming, resulting in less developed structures.
Similarly to the previous case, the e ects of the cosmological parameters are explained for
this model.
Finally, some additional simulations regarding dark halos populations and density pro-
les are included in the Appendix. |