Manifestations of Dark Matter and Variations of the Fundamental Constants of Nature in Atoms and Astrophysical Phenomena
Astrophysical observations indicate that there is five times more dark matter - an 'invisible' form of matter whose identities and properties still remain shrouded in mystery - in the Universe than the ordinary 'visible' matter that makes up stars, planets, dust and interstellar gases. Conventional schemes for the direct detection of dark matter involve processes (such as collisions with, absorption by or inter-conversion with ordinary matter) which are either quartic (g^4) or quadratic (g^2) in an underlying interaction constant g. In this thesis, I explore the possibility of searching for new effects of dark matter that are linear in g. Searching for linear effects of dark matter may provide an enormous advantage over conventional schemes, since the interaction constant g is very small, g << 1. Indeed, by investigating linear effects, I have derived new limits on certain interactions of dark matter with ordinary matter that have improved on previous limits by up to 15 orders of magnitude, as well as the first ever limits on several other interactions. Linear effects may arise for low-mass (sub-eV/c^2), bosonic (integral spin) dark matter particles. Such particles can be produced in the early Universe with negligible kinetic energy and form an oscillating classical field, \phi(t) = \phi_0*\cos(m_\phi*c^2*t/\hbar). Alternatively, these low-mass bosons may also form topological defects, such as domain walls, strings and monopoles. The interactions of these oscillating fields or topological defects with ordinary matter can produce effects that are linear in the interaction constant g. Possible linear effects of dark matter include the induction of a cosmological evolution of the fundamental constants (such as the electromagnetic fine-structure constant \alpha and the particle masses), which may be sought for with atomic clock spectroscopy and laser interferometry measurements in the laboratory, as well as astrophysical big bang nucleosynthesis measurements. Other linear effects of dark matter include spin-precession effects and oscillating spin-gravity couplings, and parity and time-reversal-invariance violating effects: oscillating nuclear Schiff and magnetic quadrupole moments, oscillating atomic and nuclear anapole moments, and oscillating atomic and molecular electric dipole moments; these effects may be sought for with a variety of magnetometric techniques.
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