Dark Atoms of the Universe: towards OHe nuclear physics

TL;DR

This paper explores the nuclear physics of hypothetical O-helium atoms formed by stable negatively charged particles binding with helium nuclei, assessing their potential role as dark matter and implications for detection experiments.

Contribution

It develops a model for OHe-nucleus interactions using the Schrödinger equation and identifies parameter ranges where bound states could explain dark matter detection signals.

Findings

OHe can form bound states with certain nuclei at keV energies.

The existence of these states depends on nuclear parameters and the size of nuclei.

Results suggest possible explanations for DAMA experiment signals without conflicting with other detectors.

Abstract

The nonbaryonic dark matter of the Universe is assumed to consist of new stable particles. A specific case is possible, when new stable particles bear ordinary electric charge and bind in heavy "atoms" by ordinary Coulomb interaction. Such possibility is severely restricted by the constraints on anomalous isotopes of light elements that form positively charged heavy species with ordinary electrons. The trouble is avoided, if stable particles $X^{--}$ with charge -2 are in excess over their antiparticles (with charge +2) and there are no stable particles with charges +1 and -1. Then primordial helium, formed in Big Bang Nucleosynthesis, captures all $X^{--}$ in neutral "atoms" of O-helium (OHe). Schrodinger equation for system of nucleus and OHe is considered and reduced to an equation of relative motion in a spherically symmetrical potential, formed by the Yukawa tail of nuclear scalar isoscalar attraction potential, acting on He beyond the nucleus, and dipole Coulomb repulsion between the nucleus and OHe at small distances between nuclear surfaces of He and nucleus. The values of coupling strength and mass of $\sigma$-meson, mediating scalar isoscalar nuclear potential, are rather uncertain. Within these uncertainties and in the approximation of rectangular potential wells and wall we find a range of these parameters, at which the sodium nuclei have a few keV binding energy with OHe. The result also strongly depend on the precise value of parameter $d_o$ that determines the size of nuclei. At nuclear parameters, reproducing DAMA results, OHe-nucleus bound states can exist only for intermediate nuclei, thus excluding direct comparison with these results in detectors, containing very light (e.g. $^3He$) and heavy nuclei (like Xe).