Interactions and overlap between the programme topics
The research directions outlined above for the three topics Fundamental Particles and Forces, Cosmic Matter in the Laboratory and Matter and Radiation from the Universe are closely intertwined, with relations ranging from pure complementarity of questions and methods to points of concrete overlap and to potential for direct collaboration. This may be illustrated by a number of examples, which are sketched as key research objectives in the figure below. Behind every objective is at least one fundamental scientific question: the scientists in the Matter and the Universe have the competence to formulate the relevant questions and to approach the answers in a systematic way. In the figure, items marked with an asterisk indicate a subject that is dealt with in more than one topic.
The research landscape of the programme.
Scientic objectives are located in a 3-axes coordinate system, which represents the topics.
Objectives marked with an asterisk are common to at least two topics.
The investigation of neutrino properties is common to all three topics due to the unique role of neutrinos in shaping large-scale structures, the generation of baryon asymmetries of the Universe and as messengers from astrophysical objects. They provide access to novel mass-generating mechanisms beyond the Standard Model. An important cross-topic activity will thus be to combine model-independent information on the absolute mass scale of neutrinos by KATRIN and of the mass hierarchy by the PINGU extension of IceCube with model-dependent results from cosmology and searches for neutrinoless double beta decay. In the past decades neutrino physics has led to major surprises and it can be expected that this tradition will continue.
Astrophysics experiments have gathered direct evidence for the existence of Dark Matter (DM) on large scales, as well as in our galaxy and its centre. This observation provides constraints for scenarios of New Physics investigated at the LHC and limits the possibilities for supersymmetric models or other extensions of the Standard Model that incorporate DM candidate particles. The exploration of the nature of Dark Matter is therefore a natural cross-topic activity in the programme Matter and the Universe. Activities in the topic Matter and Radiation from the Universe concentrate on experimental searches (direct and indirect) with particle detectors and telescopes, whereas topic Fundamental Particles and Forces focuses on identifying potential DM candidates in theories beyond the SM that are consistent both with searches at colliders and with astrophysical constraints and — once such particles are discovered — on studying their properties.
A unification of fundamental forces mediated by gauge bosons is suggested by super-symmetric extensions of the Standard Model at an energy scale of 1016 GeV, just a few orders of magnitude below the Planck scale where quantum gravity effects can no longer be neglected. Meaningful model building at such ultra-high-energy scales at which the very nature of space and time becomes fuzzy, requires a combination of experimental constraints from particle colliders such as the LHC with all available astrophysical and cosmological signals. The latter include gravitational waves, the cosmic microwave background, the most energetic cosmic and gamma rays, or helioscopes. In particular, constraints on the structure of space–time could arise from observations with Fermi, CTA or the Pierre Auger Observatory.
The preponderance of matter over antimatter in the Universe is one of the striking puzzles of modern physics. It requires CP violation at the level of fundamental interactions, but the CKM mechanism of the SM is insufficient to quantitatively explain the cosmological matter dominance. Studies of CP-violation are carried out in all three topics. The AMS-02 experiment will soon provide first results on the direct search for antimatter nuclei in space. At the same time, neutrino astroparticle physics is trying to investigate CP-violating effects. The Belle II experiment will have unprecedented sensitivity to new sources of CP violation, which naturally appear in theories beyond the Standard Model and involve scales well above the reach of present collider experiments. The proposed JEDI experiment aims to measure the electric dipole moment (EDM) of protons and deuterons with unprecedented precision. A non-zero value of this EDM could on the one hand shed light on the long-standing CP puzzle of the strong interaction and on the other hand point to a source of additional CP violation required for cosmology.
One of the most intriguing aspects in the quest to identify the nature of the fundamental interactions and the structure of space–time is the generation of mass of the elementary particles arising from a non-trivial structure of the vacuum, i.e. the origin of mass. After the discovery of a Higgs boson at the LHC the in-depth study of mass generation by electroweak symmetry breaking will be a prime focus in Fundamental Particles and Forces. The masses of hadrons receive in addition large contributions from the non-perturbative interactions between quarks and gluons, which are studied in Cosmic Matter in the Laboratory .
Strongly interacting matter plays a prominent role for many investigations in all three topics of the programme. The quark–gluon structure of hadrons will be probed in complementary ways at PANDA and at the LHC. There is also synergy between PANDA, BESIII and Belle II in the spectroscopy of heavy-quark systems. A wide range of questions regarding the strong interaction is addressed within both Fundamental Particles and Forces and Cosmic Matter in the Laboratory using lattice computations. Methods from string theory can provide new insights into several aspects of QCD, including its phase diagram, which will be studied experimentally at ALICE and CBM. The scattering of hadrons at very high energies will be studied at the LHC and is of prime importance for understanding the interactions of cosmic rays with the atmosphere.
These are some examples of the science issues that are also indicated in the figure above. It shows the beauty of fundamental research and its far-reaching consequences. The topics will naturally reach beyond their own fields and provide consistent answers across topics.