Nonlinear Supergravity

Supergravity is a theory that was discovered exactly forty years ago. It combines Einsteins general relativity with a new speculative symmetry that is called supersymmetry. This supersymmetry relates particles with different properties to each other. This means for example that the electron would have a partner that is a new yet undiscovered particle, the so called selectron. The existence of this new supersymmetry has many advantages. It can for example provide us naturally with a new particle that could explain the so far not yet understood dark matter in our universe. Supersymmetry can also help to better explain the mass of the Higgs particle that was discovered in 2012 at the Large Hadron Collider. Furthermore, theories with supersymmetry are much easier to analyze and thanks to supersymmetry we have been able to understand certain theories of particle physics in regimes that are impossible to study in theories without supersymmetry. So the last decades have seen tremendous theoretical breakthroughs thanks to supersymmetry. However, up to date we have not yet discovered the supersymmetric partners of the standard particles, like the electron. This means that the supersymmetric partners, like the selectron, have to be heavier than all the particles we have observed so far. In order to achieve this in our theories, we have to `break supersymmetry to create an asymmetry between the particles and their `superpartners. This breaking of supersymmetry leads, at low energies, to what is called a `nonlinear realization of supersymmetry. Such nonlinear realizations of supersymmetry have been intensely studied recently in the context of supergravity, i.e. in the context of a supersymmetric generalization of Einsteins theory of general relativity. One of the huge breakthroughs in this context was the discovery that upon adding a particular particle that transforms nonlinearly under supersymmetry, it becomes trivial to get a positive cosmological constant in the supergravity theory. This is of tremendous importance since it was observed in 1998 that the cosmological constant in our universe is positive. This has initiated the study of nonlinear realizations of supersymmetry in the context of supergravity. The goals of this research project are 1) to systematically study the couplings between supergravity and particles that transform nonlinearly under supersymmetry, 2) the investigation of potential applications to cosmology and particle physics and 3) the exploration of an intriguing connection to string theory which is a theory of quantum gravity that at low energies gives rise to supergravity.

Supergravity is a theory that was discovered forty years ago. It combines Einstein's general relativity with a new speculative symmetry that is called supersymmetry. This supersymmetry relates particles with different properties to each other. This means for example that the electron would have a partner that is a new yet undiscovered particle, the so called selectron. Up to date we have not yet discovered the supersymmetric partners of the standard particles, like the electron. This means that the supersymmetric has to be `broken' in order to create an asymmetry between the particles and their so-called `superpartners'. This research project, which was carried out at the Technical University (TU) Vienna, has studied particular theories in which supersymmetry is broken and realized in an intricate way. We investigated how this can be realized by higher dimensional membrane like objects and studied implications for our own universe. In particular, the so-far mysterious dark energy that we observe in our universe is closely connected to such a broken supersymmetry and was a central part of this research project. Our related publications have received a lot of attention in local, national and international new outlets, see for example: https://www.quantamagazine.org/dark-energy-may-be-incompatible-with-string-theory-20180809/ https://www.spektrum.de/news/fuehrt-die-stringtheorie-ins-sumpfland/1584718 https://www.meinbezirk.at/wieden/c-lokales/von-der-wieden-ins-universum_a2945607 https://www.welt.de/print/die_welt/wissen/article181825292/Eine-Minute-Physik-Dehnt-sich-das-All-ewig-aus.html Other research publications during this project worked out the underlying mathematical structures for theories in which supersymmetry is spontaneously broken and developed the necessary technical tools for future applications to theories that describe our own universe. During this project we had joined publications with researchers at the Stanford University in the USA and in Europe with the universities in Leuven, Liverpool, Munich, Padova and Heidelberg. We also organized a weeklong workshop at the TU Wien with visitors from France, Belgium and Germany. The research outcomes obtained during this stand-alone project did result in the awarding of one PhD (doctorate). Furthermore, the postdoc that was working on this project moved on to a prestigious postdoc position at the Max-Planck-Institute for Physics in Munich and the principal investigator obtained a professorship positions at Lehigh University in the USA during this research project. This shows the high quality and relevance of this research project and proves that it was a great success.