Spectroscopy of Rubidium atoms in solid matrices of rare gases: experimental results and theoretical analysis

Abstract

Matrix Isolation Spectroscopy of atoms or molecules has recently been proposed also for investigating new physics beyond the Standard Model with atoms and molecules, such as search for time-reversal or CP symmetry violations, electric dipole moment of standard-model particles, as well as DM [4][5][6][7].Cosmological axions are supposed to be one of the possible constituents of the DM of the Universe, whose composition is still unknown [8]. Axions were initially introduced by Peccei and Quinn in order to solve the strong CP problem in quantum chromodynamics [9][10][11][12], and are assumed to interact very weakly with ordinary matter. Successively, it was proposed that they could be one of the possible constituents of DM [13], and Sikivie proposed that they could induce magnetic-type transitions between atomic Zeeman sub-levels, yielding possibility of their indirect detection [14]. It is thus of fundamental importance to envisage possible mechanisms, and relative experiments, to detect these particles. Several possibilities have been recently proposed; for a review, see for example [13,[15][16][17][18][19].Recently, possible detection schemes for cosmological axions in the meV energy range, based on electron transitions between Zeeman-shifted levels of dilute alkali or oxygen atoms [20], or their ionization [21], embedded in