Session H02: Searches for Dark Matter

Progress and results from the Cosmic Axion Spin Precession Experiment (CASPEr)

The nature of dark matter, the invisible substance making up over 80{\%} of the matter in the Universe, is one of the most fundamental mysteries of modern physics. Ultralight bosons such as axions, axion-like particles or dark photons could make up most of the dark matter. Couplings between such bosons and nuclear spins may enable their direct detection via nuclear magnetic resonance (NMR) spectroscopy: as nuclear spins move through the galactic dark-matter halo, they couple to dark-matter particles and behave as if they were in an oscillating magnetic field, generating a dark-matter-driven NMR signal. Here we present preliminary CASPEr results obtained via ultralow-field NMR spectroscopy and report progress of the experiment probing the so called axion-wind coupling in the mass range from 1 peV to 10 neV currently under construction in Mainz.   

Quantum Advances in the Search for Dark Matter Axions

The most sensitive experiments searching for dark matter axions today exploit the conversion of axions to microwave photons in a strong magnetic field, resonantly enhanced in a high-quality microwave cavity. After three decades, these experiments have finally achieved the sensitivity to detect dark matter axions over a limited range of mass, whose signal may be no more than a yoctowatt. This achievement has been enabled by dramatic advances in ultralow noise receivers based on devices operating at the Standard Quantum Limit, such as SQUIDs and Josephson Parametric Amplifiers. Further improvements are sought, however, to both increase the sensitivity of these experiments and their scan rate in frequency (mass), and active research and development is ongoing on strategies to circumvent the quantum limit entirely, such as receivers based on squeezed states of vacuum, and qubit-based single photon detectors. Among others in the talk, the HAYSTAC experiment at Yale will be highlighted as an example, where a squeezed-state receiver is currently in commissioning.   

Experiments for quantum gravity and gravitational dark matter detection

We discuss a pair of holy grail experimental goals: detection of the quantum nature of the gravitational field, and direct terrestrial detection of dark matter through its gravitational coupling to the standard model. Both goals could be achievable in the near future, leveraging the considerable progress in quantum-enhanced optomechanical/electromechanical sensing made in recent years. We will suggest some paradigmatic experimental protocols for each. In particular, we will propose a sensor array design capable of detecting any dark matter candidates with constituent mass above around 10^18 GeV.   

Towards the Gravitational Detection of Dark Matter on Earth

Current experimental efforts to see particulate dark matter rely upon the assumption of a non-gravitational interaction with visible matter. Here, we propose an approach for the direct detection of dark matter through its gravitational coupling to terrestrial devices. Relying upon advances in mechanical systems and their detection, we propose that an array of high-quality factor, massive mechanical resonators can detect the tiny classical gravitational forces induced by individual dark matter particles passing through the detector. With current technology and relatively standard assumptions about the distribution of dark matter in our galaxy, we estimate that it is possible to measure Planck-scale dark matter particles. With simple improvements to the technology, the sensitivity floor can reach GUT-scale dark matter candidates. We discuss the scientific challenge of building such a device and the potential implications of dark matter models in this mass range.   

Mapping dark matter in the galaxy via stellar accelerations

Dark matter is the dominant matter in the universe, yet its particle nature and cosmological origin remain mysterious. Knowledge of the distribution of dark matter in the Milky Way Galaxy is crucial to grounding searches for the particles comprising dark matter. Measurements of the Galactic dark matter content currently rely on model assumptions to infer the forces acting upon stars from the distribution of observed velocities. Here, we propose to apply the radial velocity method honed for exoplanet astronomy, to measure the change in the velocity of stars over time. This direct measure of the acceleration of stars would provide a direct probe of the local gravitational potential. We present a realistic strategy to observe the differential accelerations of stars in our Galactic neighborhood with next-generation telescopes, and numerical simulations of the expected sensitivity of such a program.   

Searching for axion-like dark matter in lab-scale experiments

The nature of dark matter is one of the most important open problems in modern physics. Axions, originally introduced to resolve the strong CP problem in quantum chromodynamics (QCD), and axion-like particles (ALPs) are strongly motivated dark matter candidates. I will report on two experimental searches for ultralight axion-like dark matter: a broadband search for interaction with the electromagnetic field using a magnetic material, and a magnetic resonance-based search for interaction with nuclear spins. In both cases we use precision magnetic field sensing in highly-shielded electromagnetic environment.   

Search for light scalar dark matter using optomechanical systems

Although the existence of dark matter (DM) has been indisputably proven by a range of cosmological and astronomical measurements, there is no viable candidate for dark matter in the Standard Model. In this talk, we will explore optomechanical resonators as detectors of scalar dark matter in the $10^{-12} – 10^{-6}$ eV regime. Light DM particles have large occupation numbers and can be phenomenologically described as a classical field. Irrespective of the model used to produce them, such a classical field can have consequences that can be measured by precision measurement setups, such as varying α or me at the frequency associated with DM mass. This effect is enhanced in a solid, and variations in the size of an elastic medium lead to a new force just like the tidal force due to a passing gravitational wave. Moreover, the resonant enhancement over a localized frequency provided by these devices enhances sensitivity to such fields. We will discuss the scalar field parameter space than can be explored by current and future optomechanical devices. Finally, we will comment on how these searches can complement the existing precision measurement based searches based on atomic clocks, spin precession or equivalence principle tests.