I am a theoretical physicist, working in cosmology, a field which
has been without doubt one the most dynamic and rapidly developing areas of
fundamental science in the last decade or so.
Huge progress has been
made because of the great wealth of experimental data which has been
produced, constraining very strongly our current physical theories
of the universe and challenging them to new levels of precision.
My research has evolved very considerably, in both its subject matter
and methods, since my doctoral thesis (Princeton, USA, 1995). I started
my research working on theoretical problems in ``early universe''
cosmology i.e. in the very hot dense phase of the universe postulated
by cosmological models. I studied notably, and elaborated possible solutions
to, the problem of the origin of the observed excess of particles of
matter over their anti-matter partners in the Universe. Subsequently,
during post-doctoral periods at CERN and Dublin, I investigated specific
modifications of standard cosmologies, in which
the energy driving the expansion of the Universe is in part of an unusual
type (so-called ``dark energy'').
Since about 1998 the underlying motivation
in most of my research has been what is called the problem of ``large scale
structure formation'' : the Universe today is observed to be highly
inhomogeneous up to very large scales, with galaxies
organised in a highly structured way - in walls, voids and
filaments. The theoretical challenge is to understand fully
these observations within a coherent theoretical framework.
Modern cosmology provides such a framework, and even a very
specific model (so called ``Lambda CDM'') which has had extraordinary
success in explaining a whole host of observations in the last couple
of years, most notably the fluctuations of the intensity
of the ``primordial background'' of microwave radiation which have
been measured in great detail by a series of experiments.
However, the clear successes of the model concern the very large scales
at which the Universe is close to homogeneous. Very many questions
remain open concerning its capacity to explain the great wealth
of data on the Universe at the smaller (but still very large !) scales
at which it becomes strongly inhomogeneous.
My research aims to tackle fundamental, and quite general,
open questions in this context. Just one example is the issue at the
centre of a number of my publications in the last few years
(and the subject of the thesis of my doctoral student B. Marcos):
that of ``discreteness effects'' in huge numerical calculations
of structure formation in cosmology. These calculations represent
crudely the smooth distribution of the matter in these models by
large self-gravitating clumps (called ``macro-particles''),
and the question is how this artificial feature affects
the precision of the results. This --- at first sight
technical --- question is actually a very interesting and complex
physical one, which involves understanding basic and unresolved
issues about the clustering of many gravitating bodies, a problem
which goes back to Newton.
What characterises my work and makes it unusual (and particularly
original, I believe), is that it attempts to approach these problems from
a different perspective to the usual one in cosmology : the perspective
given by ``statistical physics'' which is the branch of physics dealing,
in a general manner, with the understanding of systems of large
numbers of constituant elements. My research is thus interdisciplinary,
in the concrete sense that I collaborate with both cosmologists and
statistical physicists. I do so because I am convinced that the
methods of statistical physics, which are much more general
than those of cosmology, can throw new light on the problems in
cosmology, providing new tools and approaches.