The Standard Model (SM) of particle physics is currently the most precise theory describing fundamental physics and drives research at a global level. As the discovery of the Higgs particle further confirms the SM's range of application, it also denied the existence of new physics – physics Beyond the Standard Model (BSM) – up to the highest engery scale we can currently test. This finding challenges our current understanding of physics as our theories cannot yet explain macroscopic observations like the existence of Dark Matter or the asymmetry between matter and antimatter. The essential question is, therefore: where does one expect signals beyond the standard model on a microscopic level, and how can one describe this?
Complementary to the collider investigations of BSM signatures that take place at the high-energy frontier, it is also possible to probe for these signals with experiments at low energy via precision measurements. Indeed, one can argue that such indirect searches may have greater reach, with sensitivities in some cases approaching the Grand Unified scale. Examples for such sensitive low-energy tests of BSM physics include searches for nucleon, electron, and atomic Electric Dipole Moments; efforts to directly detect Dark Matter through its scattering off atomic nuclei; measurements of lepton number violating processes like the neutrinoless double beta decay; and sensitive tests for new sources of flavor violation through the conversion of a muon to an electron in the nuclear field. Though there is a variety of ideas on how to detect such signals, the common ground of these low-energy experiments is the measurement of BSM signals on a nuclear level – ranging from large nuclear cores such as Xenon to planned experiments on light nuclei like Helium.
The variety of possible BSM theories answers these questions differently and leads to distinctive beyond-the-SM phenomena. Thus, linking these experiments to the fundamental level is of relevance for two reasons:
Identification of BSM sources
While a non-vanishing signal would confirm the existence of BSM structures, to identify the sources of these signals, one needs to propagate the signal from the target (nuclear many-body level) to the level of the fundamental theory.
Once one is able to propagate possible BSM interactions to the level of nuclear cores, it might be possible to identify special nuclei which feature a coherent enhancement or suppression of such structures and thus guide experimental efforts.
Theoretical descriptions of such phenomena still suffer from large uncontrolled uncertainties – mostly associated with the nuclear many-body methods or an insufficient treatment or relevant interactions. Over the last years, method-dependent uncertainties could be significantly reduced. However, they can still be as big as 100% in some cases. Since expected signals are supposed to be small, an accurate and precise description is needed to discriminate between different BSM structures. Therefore it is essential to understand the effects of all relevant uncertainties associated with the propagation of scales.
As the main objective of my current research, I intend to set up a consistent and accurate framework for analyzing BSM effects on a nuclear level, which can be systematically improved to increase the desired precision of the description.