The physics case for axions and axion-like particles is reviewed and an overview of ongoing and near-future laboratory searches is presented.
We review the physics case for very weakly coupled ultralight particles beyond the Standard Model, in particular for axions and axion-like particles (ALPs): (i) the axionic solution of the strong CP problem and its embedding in well motivated extensi
ons of the Standard Model; (ii) the possibility that the cold dark matter in the Universe is comprised of axions and ALPs; (iii) the ALP explanation of the anomalous transparency of the Universe for TeV photons; and (iv) the axion or ALP explanation of the anomalous energy loss of white dwarfs. Moreover, we present an overview of ongoing and near-future laboratory experiments searching for axions and ALPs: haloscopes, helioscopes, and light-shining-through-a-wall experiments.
We show that supersymmetric Dark Force models with gravity mediation are viable. To this end, we analyse a simple string-inspired supersymmetric hidden sector model that interacts with the visible sector via kinetic mixing of a light Abelian gauge bo
son with the hypercharge. We include all induced interactions with the visible sector such as neutralino mass mixing and the Higgs portal term. We perform a detailed parameter space scan comparing the produced dark matter relic abundance and direct detection cross sections to current experiments.
We study supersymmetric scenarios where the dark matter is the gaugino of an unbroken hidden U(1) which interacts with the visible world only via a small kinetic mixing with the hypercharge. Strong constraints on the parameter space can be derived fr
om avoiding overclosure of the Universe and from requiring successful Big Bang Nucleosynthesis and structure formation. We find that for typical values of the mixing parameter, scenarios with neutralino NLSP are excluded, while scenarios with slepton NLSP are allowed when the mixing parameter lies in the range chi~O(10^(-13) - 10^(-10)). We also show that if the gravitino is the LSP and the hidden U(1) gaugino the NLSP, the bounds on the reheating temperature from long lived charged MSSM relics can be considerably relaxed and we comment on the signatures of these scenarios at future colliders. Finally, we discuss the case of an anomalously small mixing, chi<<10^(-16), where the neutralino becomes a decaying dark matter candidate, and derive constraints from gamma ray experiments.
We point out that chameleon field theories might reveal themselves as an afterglow effect in axion-like particle search experiments due to chameleon-photon conversion in a magnetic field. We estimate the parameter space which is accessible by current
ly available technology and find that afterglow experiments could constrain this parameter space in a way complementary to gravitational and Casimir force experiments.In addition, one could reach photon-chameleon couplings which are beyond the sensitivity of common laser polarization experiments. We also sketch the idea of a Fabry-Perot cavity with chameleons which could increase the experimental sensitivity significantly.
