Session H15: Cosmology with Ultra Low Mass Fields

Precision measurement for particle physics and cosmology

Axions and other light particles are strongly motivated. For example, the axion is the crucial element in the recently proposed solution to the hierarchy problem using dynamical relaxation in the early universe. However, such particles are challenging to search for experimentally. Precision measurement technologies such as atom interferometry, nuclear magnetic resonance, high precision magnetometry, and torsion balances allow novel, highly sensitive experiments for direct detection of such light dark matter and of gravitational waves. Thus precision measurement technologies open new avenues for probing the origin and composition of the universe.   

Magnetometer Searches for Ultra Low Mass Fields

New spin interactions arise in a variety of extensions to the Standard Model. Well-known spin-dependent effects, such as permanent electric dipole moments and violations of Lorentz and CPT symmetries, have been searched for in many experiments. The existence of low-mass axion-like particles would also generate spin-dependent effects that can be searched for in similar experiments, but often with unique signatures. Since particles with spin also have a magnetic moment, such experiments are automatically sensitive to ordinary magnetic fields and one of the challenges is to eliminate such effects, using for example, two different spin species in a co-magnetometer arrangement. I will describe several past and on-going experiments using co-magnetometers based on nuclear spin-polarized noble gases. These experiments are used to search for both axion-like dark matter and for axion-mediated forces that are independent of dark matter.   

Torsion-balance experiments and ultra-low-mass fields

Many of the solutions to outstanding problems in modern cosmology posit new, ultra-light fields. Unifying General Relativity and Quantum Mechanics appears to require new ultra-light fields at some level. Such fields are also invoked to drive inflation and dark energy. Ultra-light fields may also make up much or all of the dark matter density of the universe. Torsion pendulums, a technology that dates to the 18th century, remain one of the most sensitive experimental techniques to search for ultra-light, weakly interacting fields. I will explain how torsion balance experiments can search for beyond-the-standard-model fields using laboratory-based as well as galactic sources, and the important cosmological implications of these measurements. I will also describe a new experimental signature for which certain torsion balance geometries make very sensitive direct dark matter detectors over a broad range of interesting dark matter parameter space.