Supersymmetric flavour physics at LHC at One-Loop Level

The project " Supersymmetric flavour physics at LHC at one-loop level" is a new research project of the Institute for High Energy Physics (HEPHY) of the Austrian Academy of Sciences, Vienna. The main topic of the project is to study the flavour structure in supersymmetric extensions of the Standard Model of particle physics, including radiative corrections due to the strong and electroweak interactions. The framework for our studies will be the Minimal Supersymmetric Standard Model (MSSM). We want to calculate one-loop corrected production and decay rates of Higgs and supersymmetric particles at the Large Hadron Collider (LHC). At present, the LHC allows a direct test of the predictions of different theories of particle physics. The recent discovery of the Higgs boson confirmed the great success of the Standard Model (SM). Due to its high collision energy, LHC will be able to discover also particles predicted by the supersymmetric models. The MSSM in its general form can introduce mixing between different quark flavours in the squark sector that is not related to the SM. Despite the strong constraints from rare meson decays, quark flavour violation in the MSSM can affect the particle phenomenology perceptibly. So far, all studies of quark flavour violating supersymmetric processes have been performed in tree-level approximation. Nevertheless, higher order corrections can often have a large impact on particle phenomenology. In the current project we want to study the effects of quark flavour violation in the MSSM at full one-loop level. At present, there are no computer programs available that calculate processes in the MSSM at one-loop level, including flavour violation. It is our goal to develop a full one-loop computer program for the calculation of flavour sensitive observables in Higgs and sfermion decays in the general MSSM. Such a numerical tool will allow us to study in detail the effects of quark flavour violation on the properties of the Higgs and supersymmetric particles, and in addition its impact on the underlying model parameters and their determination. In our studies we will take into account all existing experimental constraints.

In the project we studied the implication of Supersymmetry (SUSY) at collider experiments in a model where quark flavour mixing in the squark (the superpartners of the quarks) sector is switched on. We found large deviations from the values predicted by the so-called Standard Model of particles in the decay rates of the lightest SUSY Higgs boson decaying into a pair of charm quarks due to quark flavour mixing and in the decays into bottom quark pairs even when this additional quark flavour mixing is off. We also studied the influence of quark flavour mixing when squarks are directly produced at the LHC and further decay to Higgs bosons and/or the weak force particles, and recently also the decay properties of the gluino, the superpartner of the gluon, the first time by including full one-loop corrections. We conclude that this mixing effect can have a significant influence on searches for SUSY particles at LHC. SUSY can also embed gravitation. In this case we have a superpartner of the graviton, the gravitino. We calculated all decay rates for the gravitino decaying into two and three particles, with one of them the lightest SUSY particles which is stable and can therefore be the Dark Matter (DM) particle. We treated also the case when the gravitino itself is the DM candidate. We compiled our results into the numerical package GravitinoPack which is the first world-wide publicly available code of this kind. These findings are especially important within the Early Universe.It is of interest to explain the notion Supersymmetry and its implications in particle physics: Symmetries play a central role in physics - like they also do in arts - because the fundamental principles of Nature are manifested due to them. There even exist a mathematical proof that in the elementary particle world Supersymmetry is the largest possible symmetry of space and time. If it is really realized in Natur, for each of all the particles we know then there must exist a partner particle (e.g. quark - squark, gluon - gluino). But we already know that such particles must be much heavier than the known particles. In the experimental program of the particle accelerator LHC at CERN in Geneva the search for such SUSY partner particles is of great importance. But even the simplest model, the so-called Minimal Supersymmetric Standard Model (MSSM) has many additional free parameters. In its most constrained realizations no SUSY partner particle was found up to now. Therefore it is necessary to study theoretically also more general minimal SUSY models. A logical next step is to allows quark flavour mixing in the sector of the partners of the quarks which is done in our scientific studies.