Signatures of Dark Matter: molecular detectors of oscillating fundamental constants

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Although dark matter (DM) is much more abundant in the universe than normal matter, it has not yet been detected beyond doubt in laboratory experiments. This project aims to develop an experiment that will be sensitive to certain dark matter signatures. Dark matter could consist partly of particles of low mass (in the range neV/c^2). It could behave as a field oscillating at the Compton frequency, coupling to the Standard Model (SM) fields. This would result in oscillating fundamental constants, e.g. the fine structure constant, the quark masses, the coupling constant of the strong force. In this project we consider vibrational transitions in molecules. These are sensitive to the electron mass, the nuclear mass, and the fine structure constant. Via the nuclear mass, there is also a dependence on the quark masses and the coupling constant of the strong force. The apparatus to be developed will be used to search for oscillations in the frequency of vibrational transitions in a room-temperature molecular gas. Laser spectroscopy at 1.5 µm of acetylene (C2H2) will be used for this purpose. The resonance frequency of an optical resonator will be used as a reference frequency. The experiment will be optimised in several respects. A very large Compton frequency range will be investigated (10 Hz - 100 MHz), two spectroscopy variants will be used, the shot noise level of sensitivity will be achieved, the molecular transition is advantageously chosen, a correlation technique will allow the suppression of interferences, and the experiment will record extensive data over up to 1 year of measurement time. At the end of the project, we expect to achieve a reduction of the upper limits for the coupling strength of a DM field to the fields of the SM by factors between 100 and 1000.