Coupling Constants Of Axion-like Particles Research Articles

Dark Matter Axions, Non-Newtonian Gravity and Constraints on Them from Recent Measurements of the Casimir Force in the Micrometer Separation Range

We consider axionlike particles as the most probable constituents of dark matter, the Yukawa-type corrections to Newton’s gravitational law and constraints on their parameters following from astrophysics and different laboratory experiments. After a brief discussion of the results by Prof. Yu. N. Gnedin in this field, we turn our attention to the recent experiment on measuring the differential Casimir force between Au-coated surfaces of a sphere and the top and bottom of rectangular trenches. In this experiment, the Casimir force was measured over an unusually wide separation region from 0.2 to 8μm and compared with the exact theory based on first principles of quantum electrodynamics at nonzero temperature. We use the measure of agreement between experiment and theory to obtain the constraints on the coupling constant of axionlike particles to nucleons and on the interaction strength of a Yukawa-type interaction. The constraints obtained on the axion-to-nucleon coupling constant and on the strength of a Yukawa interaction are stronger by factors of 4 and 24, respectively, than those found previously from gravitational experiments and measurements of the Casimir force but weaker than the constraints following from a differential measurement where the Casimir force was nullified. Some other already performed and planned experiments aimed at searching for axions and non-Newtonian gravity are discussed, and their prospects are evaluated.

The State of the Art in Constraining Axion-to-Nucleon Coupling and Non-Newtonian Gravity from Laboratory Experiments

Constraints on the Yukawa-type corrections to Newton’s gravitational law and on the coupling constant of axionlike particles to nucleons obtained from different laboratory experiments are reviewed and compared. The constraints on non-Newtonian gravity under discussion cover the wide interaction range from nanometers to millimeters and follow from the experiments on neutron scattering, measuring the Casimir force and Cavendish-type experiments. The constraints on the axion-to-nucleon coupling constant following from the magnetometer measurements, Cavendish-type experiments, Casimir physics, and experiments with beams of molecular hydrogen are considered, which refer to the region of axion masses from 10−10 to 200 eV. Particular attention is given to the recent constraints obtained from measuring the Casimir force at nanometer separation distance between the test bodies. Several proposed experiments focussed on constraining the non-Newtonian gravity, axionlike particles and other hypothetical weakly interacting particles, such as chameleons and symmetrons, are discussed.

Constraints on non-Newtonian gravity and axionlike particles from measuring the Casimir force in nanometer separation range

We obtain constraints on the Yukawa-type corrections to Newton's gravitational law and on the coupling constant of axionlike particles to nucleons following from the experiment on measuring the Casimir force between an Au-coated microsphere and a silicon carbide plate. For this purpose, both the Yukawa-type force and the force due to two-axion exchange between nucleons are calculated in the experimental configuration. In the interaction range of Yukawa force exceeding 1 nm and for axion masses above 17.8 eV, the obtained constraints are much stronger than those found previously from measuring the lateral Casimir force between sinusoidally corrugated surfaces. These results are compared with the results of other laboratory experiments on constraining non-Newtonian gravity and axionlike particles in the relevant interaction ranges.

Constraints on axionlike particles and non-Newtonian gravity from measuring the difference of Casimir forces

We derive constraints on the coupling constants of axion-like particles to nucleons and on the Yukawa-type corrections to Newton's gravitational law from the results of recent experiment on measuring the difference of Casimir forces between a Ni-coated sphere and Au and Ni sectors of a structured disc. Over the wide range of axion masses from 2.61\,meV to 0.9\,eV the obtained constraints on the axion-to-nucleon coupling are up to a factor of 14.6 stronger than all previously known constraints following from experiments on measuring the Casimir interaction. The constraints on non-Newtonian gravity found here are also stronger than all that following from the Casimir and Cavendish-type experiments over the interaction range from 30\,nm to $5.4\,\mu$m. They are up to a factor of 177 stronger than the constraints derived recently from measuring the difference of lateral forces. Our constraints confirm previous somewhat stronger limits obtained from the isoelectronic experiment, where the contribution of the Casimir force was nullified.

Recent breakthrough and outlook in constraining the non-Newtonian gravity and axion-like particles from Casimir physics

The strongest constraints on the Yukawa-type corrections to Newton’s gravitational law and on the coupling constants of axion-like particles to nucleons, following from recently performed experiments of Casimir physics, are presented. Specifically, the constraints obtained from measurements of the lateral and normal Casimir forces between sinusoidally corrugated surfaces, and from the isoelectronic experiment are considered, and the ranges of their greatest strength are refined. Minor modifications in the experimental setups are proposed which allow for strengthening the resultant constraints up to an order of magnitude. The comparison with some weaker constraints derived in the Casimir regime is also made.

Improved constraints on the coupling constants of axion-like particles to nucleons from recent Casimir-less experiment

We obtain improved constraints on the coupling constants of axion-like particles to nucleons from a recently performed Casimir-less experiment. For this purpose, the differential force between a Au-coated sphere and either Au or Si sectors of a rotating disc, arising due to two-axion exchange, is calculated. Over a wide region of axion masses from 1.7 meV to 0.9 eV the obtained constraints are stronger up to a factor of 60 than the previously known ones following from the Cavendish-type experiment and measurements of the effective Casimir pressure.

First results from the new PVLAS apparatus: A new limit on vacuum magnetic birefringence

Several groups are carrying out experiments to observe and measure vacuum magnetic birefringence, predicted by Quantum Electrodynamics (QED). We have started running the new PVLAS apparatus installed in Ferrara, Italy, and have measured a noise floor value for the unitary field magnetic birefringence of vacuum $\Delta n_u^{\rm (vac)}= (4\pm 20) \times 10^{-23}$ T$^{-2}$ (the error represents a 1$\sigma$ deviation). This measurement is compatible with zero and hence represents a new limit on vacuum magnetic birefringence deriving from non linear electrodynamics. This result reduces to a factor 50 the gap to be overcome to measure for the first time the value of $\Delta n_u^{\rm (vac,QED)}$ predicted by QED: $\Delta n_u^{\rm (vac,QED)}= 4\times 10^{-24}$ ~T$^{-2}$. These birefringence measurements also yield improved model-independent bounds on the coupling constant of axion-like particles to two photons, for masses greater than 1 meV, along with a factor two improvement of the fractional charge limit on millicharged particles (fermions and scalars), including neutrinos.

Constraints on axion-nucleon coupling constants from measuring the Casimir force between corrugated surfaces

We obtain stronger laboratory constraints on the coupling constants of axion-like particles to nucleons from measurements of the normal and lateral Casimir forces between sinusoidally corrugated surfaces of a sphere and a plate. For this purpose, the normal and lateral additional forces arising in the experimental configurations due to the two-axion exchange between protons and neutrons are calculated. Our constraints following from measurements of the normal and lateral Casimir forces are stronger than the laboratory constraints reported so far for masses of axion-like particles larger than 11 and 8 eV, respectively. A comparison between various laboratory constraints on the coupling constants of axion-like particles to nucleons obtained from the magnetometer measurements, E\"otvos- and Cavendish-type experiments, and from the Casimir effect is performed over the wide range of masses of axion-like particles from $1{0}^{\ensuremath{-}10}$ to 20 eV.