Since October 1st, 2015 Dr. Alex Vikman from LMU (Munich), recipient of Purkyně Fellowship, has joined our group. His research focuses on cosmology and the puzzles of dark matter and dark energy.
In the past two decades cosmology experienced a golden age. During these
years we learned several fundamental striking facts about the universe where we
live in.
First it was observed that the universe expansion is currently accelerated by
some unknown substance called Dark Energy (DE). The latter approximately
builds 70% of the energy budget of our universe. Observations only allow for
negligibly weak interactions of this substance with light and other standard
model (SM) fields. So far Dark Energy reveals itself only through gravity. Even
more astonishing is that in accordance with the observations the pressure of DE
is negative with the magnitude approximately equal to the DE energy density.
Thus DE has the equation of state close to that of vacuum in quantum field
theories (QFT). In turn, the gravitational effects of the quantum vacuum are
indistinguishable from those cased by the cosmological constant (CC) introduced
by Einstein at the dawn of the theory of General Relativity. General Relativity
does not predict the value of CC, while our current estimations of the vacuum
energy from QFT are many orders of magnitude larger than the observational
results. The origin of Dark Energy and the theory behind the proper value
of the cosmological constant remains one of the biggest puzzles of theoretical
physics.
Further, it turned out that out of the remaining 30% of the energy budget of
our universe only 5% correspond to the ordinary SM luminous matter whereas
the rest is still dark and unknown. The good news here is that for cosmological
purposes these 25% behave like dust. This dark dust is called Dark Matter
(DM). Despite of all recent efforts, no interaction of DM with the SM fields
has been detected so far. Thus, similarly to DE, the only manifestation of
DM is purely gravitational. However, contrary to DE, there are tremendous
amount of particle physics models beyond the SM which can be candidates to
explain the DM phenomenon. The origin of DM is another fundamental problem
of theoretical physics and so far the only observational fact which necessarily
requires physics beyond the Standard Model.
Finally, during recent years we observed that the spatial sections of the universe
have Euclidean geometry with a very high precision. We have also learned
that the cosmological density perturbations have a slightly red-tilted spectrum.
This means that the amplitude of these fluctuations away from homogeneity
and isotropy (large scale structure of the universe) is slightly increasing towards
larger scales. These two observational facts confirm main predictions of inflation
and of the quantum origin of the cosmological perturbations. This is a fantastic
success of the theoretical cosmology. However, the exact particle physics model
behind inflation and the quantum creation of the large scale structure is still
unknown. Usually such models require new fundamental physics beyond the
SM.
These main problems of cosmology is an active area of current research of
the cosmology group. For the most recent publications of the members of the
cosmology group see
here.
