Ultra-low-mass bosonic dark matter may form a coherently oscillating classical field. Scalar-type interactions of this field with ordinary matter induce apparent variations of the fundamental “constants”, including the fundamental interaction strengths and particle masses. I discuss how these varying constants can be sought with precision, low-energy (and often table-top-scale) experiments, including: spectroscopy (clocks), optical cavities, interferometry, and torsion pendula. Existing and new experimental data have allowed us to improve on previous bounds on scalar-field dark-matter interactions by up to 15 orders of magnitude. Ultra-low-mass bosons may also form macroscopic topological defects, such as domain walls. I discuss previously overlooked signatures in models of scalar-field topological defects, including an environmental dependence of and spatial variations of the fundamental constants in the vicinity of dense bodies such as Earth due to the formation of a “bubblelike” defect structure surrounding the dense body. These novel quasi-non-transient signatures have allowed us to significantly improve on previous bounds on models of scalar-field domain walls.
 Stadnik and Flambaum, Physical Review Letters 114, 161301 (2015).
 Stadnik and Flambaum, Physical Review Letters 115, 201301 (2015).
 Stadnik and Flambuam, Physical Review A 93, 063630 (2016).
 Stadnik and Flambaum, Physical Review A 94, 022111 (2016).
 Hees, Minnazzoli, Savalle, Stadnik and Wolf, Physical Review D 98, 064051 (2018).
 Grote and Stadnik, Physical Review Research 1, 033187 (2019).
 Stadnik, Physical Review D 102, 115016 (2020).
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