# Activities

The Theoretical High Energy Physics Division is performing phenomenological research, with special emphasis on the strong interaction (QCD), including multiparticle production and signals for "new physics" in high energy colliders (in particular at the upcoming Large Hadron Collider, LHC), studies of the strong and weak interaction at lower energies, and the phenomenology of models beyond the Standard model. The topics of research include:

- Studies of the event structure in high energy reactions, e+e- annihilation, lepton-proton and hadron-hadron collisions. This is a very wide field, which includes many separate phenomena such as saturation effects at small x, multiple jet events, the structure of the "underlying event", and diffraction.
- Studies of resummation schemes and initial- and final-state perturbative QCD radiation in the dipole and the parton-shower approaches.
- Matching of such radiation to fixed-order matrix-element calculations, including effects of loop corrections, and study of the resulting radiation patterns in association with gauge boson production in hadron collisions.
- Studies of new physics within and beyond the standard model, including perturbative and nonperturbative QCD effects in top events, Higgs searches, and so on.
- Particle correlations due to Bose-Einstein or Fermi-Dirac effects and fractal structures.
- Soft hadronization effects, further development of the Lund model for quark and gluon jets, and colour interconnection effects in e+e- and in the underlying event in hadronic collisions.
- Modeling of heavy-ion collisions, including various collective effects.
- Development and support of event generators, PYTHIA, ARIADNE, ThePEG and LDCMC. These have found widespread use in the experimental high-energy-physics community, as indispensable tools for comparing theoretical ideas and experimental data, to understand the underlying strong interaction dynamics and to estimate backgrounds for new physics signals.
- Chiral Perturbation Theory and related aspects, including connections to lattice gauge theory.
- Study of Kaon and Eta Decays, meson-meson-scattering.
- Study of non-perturbative aspects of the operator evolution of operators relevant for non-leptonic processes, including modeling of the intermediate energy domain; examples are the Delta I = ½ rule; Hadronic contributions to muon g-2.
- CP violation phenomenology.
- Determination of Quark Masses and CKM matrix elements.
- Modeling a nonperturbative Higgs sector.
- Studies of models with extended Higgs sectors, such as supersymmetric versions of the standard model (MSSM, NMSSM, etc) and more general two Higgs doublet models.
- Prospects of finding additional Higgs bosons at high energy colliders such as the Tevatron and LHC and how this can be used to determine the structure of the Higgs sector.
- Constraints on the Higgs sector from low energy flavour experiments such as Beauty and Kaon factories.
- Prospects of studying fundamental physics at spallation sources, especially neutrino oscillations and dark photons
- Active participation in various workshops on the physics program at current and future accelerators, such as the TeVatron, LHC, ESS, DAPHNE, and e+e- linear colliders.
- Theoretical QCD approach to soft and diffractive processes in pp collisions at LHC. Analysis of vast diffractive phenomenology at the LHC including central and forward exclusive particle/jets production processes. Exclusive QCD backgrounds for the New Physics signals at the LHC. Diffractive Monte-Carlo development.
- Precision study of polarization effects and their sensitivity to QCD production mechanisms and the higher-order QCD corrections in the heavy quarkonia and jets spectra at the LHC. Theoretical aspects of QCD factorisation.
- Analysis of extensions of the Standard Model without the low-scale supersymmetry. LHC phenomenology of extra gauge and Higgs bosons. Cosmological implications of new symmetries and light Dark Matter components. Combined analysis of collider and astrophysical observables of the Dark Matter and other New Physics signals.
- Stability and dynamics of the Vacuum in the Standard Model and beyond. Formation and dynamical properties of the Dark Energy, cosmological Perturbation Theory and the Cosmic Microwave background studies. Astrophysical implications and consequences of the QCD and electro-weak vacuum dynamics in Early Universe.

### Positions

- PhD positions (in Swedish)