Among the prominent candidates for dark matter are bosonic fields with small scalar couplings to the Standard-Model particles. Several techniques are employed to search for such couplings and the current best constraints are derived from tests of gravity or atomic probes. In experiments employing atoms, observables would arise from expected dark-matter-induced oscillations in the fundamental constants of nature. These studies are primarily sensitive to underlying particle masses below 10 −14 eV. We present a method to search for fast oscillations of fundamental constants using atomic spectroscopy in cesium vapor. We demonstrate sensitivity to scalar interactions of dark matter associated with a particle mass in the range 8 · 10 −11 to 4 · 10 −7 eV. In this range our experiment yields constraints on such interactions, which within the framework of an astronomicalsize dark matter structure, are comparable with, or better than, those provided by experiments probing deviations from the law of gravity.

The weak force is the only fundamental interaction known to violate the symmetry with respect to spatial inversion (parity). This parity violation (PV) can be used to isolate the effects of the weak interaction in atomic systems, providing a unique, low-energy test of the Standard Model [see for example reviews 1, 2, 3]. These experiments are primarily sensitive to the weak force between the valence electrons and the nucleus, mediated by the neutral Z 0 boson and dependent on the weak charge of the nucleus, Q w . The Standard Model (SM) parameter Q w was most precisely determined in cesium (Cs) [4, 5] and has provided a stringent test of the SM at low energy. The SM also predicts a variation of Q w with the number of neutrons in the nucleus, an effect whose direct observation we are reporting here for the first time. Our studies, made on a chain of ytterbium (Yb) isotopes, provide a measurement of isotopic variation in atomic PV, confirm the predicted SM Q w scaling and offer information about an additional Z´ boson.The large PV observable in Yb was first predicted by DeMille [6], a prediction further supported by subsequent calculations [7,8,9] and confirmed by experiment [10,11]. The PV effect in Yb is approximately 100 times larger than that in Cs. Moreover, Yb has a chain of stable isotopes, allowing for an isotopic comparison of the effect [12]. Such a comparison has the potential to be a probe of neutron distributions in the Yb nuclei [13] and is sensitive to physics beyond the SM [14,15]. A related measurement, in which the PV effects are compared for different hyperfine components of isotopes with non-zero nuclear spin, is expected to improve the understanding of the weak interaction within the nucleus [3,16,17,18].The principle of our measurements is similar to that of the 1 st -generation experiment [10,11]. We optically excite Yb atoms in a beam, on the 6s 2 1 S 0 → 5d6s 3 D 1 transition ( fig. 1), in a region in which in addition to the applied optical field, static electric and static magnetic fields are applied to the atoms [19].The directions of the magnetic and static electric field and that of the optical-field polarization define the handedness for the experimental coordinate system. As the 1 S 0 and 3 D 1 states are of nominally same parity, an electric-dipole (E1) transition between them is forbidden by selection rules. In the presence of the weak interaction, however, mixing of the 1 P 1 state into 3 D 1 results in a E1 PV amplitude for the transition. The applied dc (or quasi-static) electric field results in additional mixing of these states, allowing for a larger and controlled Stark-induced E1 amplitude [20]. The Stark-induced and PV amplitudes will interfere with appropriate choice of field geometry. Field reversals flip the handedness of the field geometry, leading to a sign reversal of the Stark-PV interference term and a change in the transition rate. This change provides an experimental observable.We measured the PV effect in four nuclear-spin-zero isotopes ( 170 Yb, 172 Yb, 174 Yb a...

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