Gravitinos and hidden Supersymmetry at the LHC - Universität ...

inflation in a process called reheating, which is also not understood so far. Another process
which cannot be described by the Standard Model is the generation of the matter-antimatter
asymmetry - baryogenesis. Any initial baryon asymmetry (being itself a peculiar initial condition)
would be diluted by inflation, making a dynamical creation process necessary. The
conditions for successful baryogenesis, which are called Sakharov conditions [26], cannot be
satisfied by the particle content and the interactions of the SM 3 . However, it is important to
note that baryogenesis can be linked to seemingly unrelated problem of neutrino masses, in
particular to the see-saw extension of the Standard Model, a fact vindicating the motto of
this chapter.
So far we haven’t considered the meaning of the name given to the concordance model,
albeit this name itself characterizes quantities lying beyond the Standard Model of particle
physics. The greek letter lambda is reserved in cosmology for the constant term proportional
to the metric in Einstein’s equation of motion. One view is that the cosmological constant is
an additional freedom in the definition of the theory arising from the renormalization of the
energy momentum tensor [30]. However, the general belief is that the constant is determined
by the matter content of the theory as the energy density of the vacuum [31]. The observed
positive value of the cosmological constant, while being responsible for seventy percent of the
current total energy content of the universe, is an extremely small number which cannot be
explained within the scope of the Standard Model or even any quantum field theory to date.
The CDM part in the model name abbreviates cold dark matter - another unresolved
problem in cosmology and particle physics. The term dark matter refers to non-luminous
source of gravitation which was proposed already in the thirties by Fritz Zwicky to explain
radial velocities of the galaxies in the Coma cluster [32]. While the existence of dark matter
is firmly established on the basis of astrophysical and cosmological observations, its nature
is unknown [33, 34]. It has been proposed, that the observed gravitational effects might be
explained by a modification of the theory of gravity [35] or that they might be caused by nonluminous
astrophysical objects in the halo of galaxies [36,37]. However, these explanations are
strongly disfavored by current experimental data. Again, the best explanation seem to come
from the layer of microphysics, dark matter being a new kind of elementary particle obeying
all observational constraints, since the Standard Model has no viable candidates [38, 39].
Summing up, one clearly sees that, even not taking into account various purely internal
theoretical reasons and quantum gravity, our current description of the elementary particle
physics is by far incomplete. However, there is a tension between this certainty originating
from astrophysical observations and the lack of direct evidence from the high-energy experiments.
This situation has lead to a multitude of theoretical models trying to accommodate
the observations and to become a successor of the Standard Model. A definite further progress
can only be achieved if we gain new insights into the nature of the phenomena, preferably,
from high-energy experiments where new processes happen in the laboratory, and one is able
to measure repeatedly a high number of observables. A lot of hope is associated with the
Large Hadron Collier, a proton-proton accelerator with a design center-of-mass energy of 14
TeV. It seems probable that the LHC not only allows us to pose further questions concerning
the nature of the Higgs mechanism, but also gives us the possibility to shed light on the nature
of dark matter. Having summarized the current situation in particle physics and cosmology,
we now turn our attention to promising dark matter candidates.
3 The phase transition occurring in the early universe during electroweak symmetry breaking is not strong
enough for a successful electroweak baryogenesis [27–29].
3