Description:

Title: Atom Interferometry: Gravity, Blackbody Radiation and Chameleons

Speaker: Philipp Haslinger, UC Berkeley

Abstract: If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field it might be detectable as a “fifth force” between normal-matter objects. In order to be consistent with cosmological observations and laboratory experiments, some leading theories use a screening mechanism to suppress this interaction. However, atom-interferometry presents a tool to reduce this screening on so-called chameleon models. By sensing the gravitational acceleration of a 0.19 kg in vacuum source mass which is 10^-9 times weaker than Earth´s gravity, we reached a natural bound for cosmological motivated scalar field theories and were able to place tight constraints.
Blackbody (thermal) radiation is emitted by objects at finite temperature with an outward energy-momentum flow, which exerts an outward radiation pressure. At room temperature e. g. a cesium atom scatters on average less than one of these blackbody radiation photons every 10^8 years. Thus, it is generally assumed that any scattering force exerted on atoms by such radiation is negligible. However, particles also interact coherently with the thermal electromagnetic field and this leads to a surprisingly strong force acting in the opposite direction of the radiation pressure.