Exploration of new experimental strategies for the detection of ultralight dark matter: laboratory searches on ground and in space

Ultralight dark matter (ULDM), as a class of low mass (< 1 eV) dark matter (DM) candidates, is a compelling alternative to historically dominant models such as WIMPs and has recently gained significant attention in the scientific community. In this thesis, we study various experimental schemes for the direct detection of ULDM, both on ground and in space. More precisely, we propose a theoretical modeling of current and futuristic experiments, and we derive an estimation of their respective sensitivity.

We mainly concentrate on three distinct phenomenologies.

The first one is the coupling between a DM (1) field, known as the dark photon (DP), and electromagnetism, which induces a small electric field oscillating at the DP Compton frequency. We first propose an innovative way of detecting this small electric field by measuring the quadratic Stark shift of Rydberg atoms inside a microwave cavity, and we show that such an experiment could reach competitive constraints compared to existing laboratory experiments. Another possibility of detecting this electric field is to use a spherical mirror, which reflects it and focuses the electromagnetic power at its center of curvature, where a horn antenna is located (e.g. SHUKET experiment at CEA Saclay). We analytically investigate the effects of diffraction and mode matching in this type of experiment, and we show that the expected signal intensity can be significantly reduced compared to usual estimates. In this study, we also propose an optimization of the experimental parameters in order to increase the signal.

The second main phenomenology considered in this thesis is the oscillation of rest mass and transition frequencies of atoms and test masses. These oscillations could be produced by the non-universal coupling of standard matter with a scalar ULDM candidate (dilaton or axion-like particle). We extensively study the impact of such oscillations on various atom interferometer schemes and classical tests of the universality of free fall, and we demonstrate how these different experiments could probe unconstrained regions of the parameter space. The oscillation of rest mass could also be observed in space-based gravitational wave (GW) detectors, such as LISA, and we investigate the possibility of such detection using more realistic orbits of spacecraft compared to previous studies. In particular, using Bayesian methods, we show that LISA could disentangle scalar ULDM signals from monochromatic GWs. We also show that the small velocity of the DM wave is not resolvable for most frequencies in the LISA band, which induces a decrease in sensitivity to scalar ULDM couplings, with respect to previous studies.

 Finally, we study the effect of vacuum birefringence and dichroism induced by the coupling between axions and photons, and how it could be detected with optical cavities, fibers, and LISA. In particular, we show that a slight modification of LISA’s optical benches would make LISA the most sensitive experiment to the axion-photon coupling at low axion masses.

ultralight dark matter, axion, dilaton, dark photon, quantum sensors, atomic clock, atom interferometry, optical interferometry, LISA, equivalence principle, fundamental physics

Full document (EN) : TEL-04750272