Investigating pseudoscalar and scalar dark matter

TL;DR

This work investigates keV-scale light bosonic dark matter candidates—pseudoscalar and scalar—using underground detectors and the annual modulation signature to probe a broad range of couplings. It develops and analyzes the direct-detection channels (Compton-like, axioelectric/photoelectric-like, and Primakoff) and computes the expected counting-rate spectra in NaI(Tl) detectors, highlighting axioelectric dominance for pseudoscalars and hadronic-coupling sensitivity for scalars. By performing a model-independent DAMA/NaI analysis over seven annual cycles, the authors extract allowed regions in the parameter spaces $(m_a,g_{a\bar{e}e})$ and $(m_h,g_{h\bar{N}N})$, identifying cosmologically interesting lifetimes and showing compatibility with the DAMA modulation signal alongside WIMP scenarios. The study argues that pseudoscalar and scalar light boson DM can account for the DAMA/NaI observations under specific couplings and lifetimes, and it suggests that DAMA/LIBRA and future underground experiments will further constrain or confirm these candidates, particularly in the keV mass range around a few keV. The appendices provide explicit non-relativistic cross-section formulas essential for precise rate calculations and feature detailed derivations for all three detection channels across both pseudoscalar and scalar cases.

Abstract

In this paper another class of Dark Matter candidate particles: the pseudoscalar and scalar light bosonic candidates, is discussed. Particular care is devoted to the study of the processes for their detection (which only involves electrons and photons/X-rays) in a suitable underground experimental set-up. For this purpose the needed calculations are developed and various related aspects and phenomenologies are discussed. In particular, it is shown that - in addition to the WIMP cases already discussed elsewhere - there is also possibility for a bosonic candidate to account for the 6.3 sigma C.L. model independent evidence for the presence of a particle DM component in the galactic halo observed by DAMA/NaI. Allowed regions in these scenarios are presented also paying particular care on the cosmological interest of the bosonic candidate.

Figures (6)

• Figure 1: Possible diagrams for the direct detection processes of a light boson particle. On the left: "Compton - like" effect; on the center: "Axioelectric" or photoelectric-like effect; on the right: Primakoff effect. See text.
• Figure 2: Coupling of the pseudoscalar $a$ particle to the fermions $f$ (a case) and to the photons through the loop of charged fermions (b case).
• Figure 3: Pseudoscalar case: region in the plane $g_{a\bar{e}e}$ vs $m_a$ allowed by the DAMA/NaI annual modulation data in the considered model framework. See text.
• Figure 4: DAMA/NaI allowed region at 3$\sigma$ C.L. in the plane $g_{a\gamma\gamma}$ vs $m_a$ for a light pseudoscalar candidate ( crossed hatched region). All the configurations in this region can be allowed depending on the values of all the $g_{a \bar{f}f}$. Examples of two of the many possible models: i) upper black region: coupling only to electrons; ii) lower black region: coupling (proportional to the $m_a$) through the (weak) isospin to quarks and leptons. For details see text. The indicative region of the Kaluza-Klein (K.K.) pseudoscalar axion credited in ref. DiLella from the analysis of indirect observations and the region of the DFSZ and KSVZ models (P.Q. axion) are shown as well. The solid line corresponds to $a$ particle with lifetime equal to the age of the Universe; at least all the $g_{a \gamma\gamma}$'s below this line are of cosmological interest. See text. Thus, a pseudoscalar DM candidate could also account for the DAMA/NaI model independent result as well as the WIMP solutions already discussed elsewhere.
• Figure 5: DAMA/NaI allowed region at 3$\sigma$ C.L. in the plane $g_{h\bar{N}N}$ vs $m_h$ for a scalar light boson DM candidate coupled only to the hadronic matter in the given frameworks. To account for cosmological interesting lifetimes, here only the configurations with negligible Primakoff effect contribution have been selected. See text.