Spin in the dark matter problem
- PDF / 1,680,012 Bytes
- 38 Pages / 612 x 792 pts (letter) Page_size
- 21 Downloads / 165 Views
pin in the Dark Matter Problem¶ V. A. Bednyakov Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, 141980 Russia e-mail: [email protected] Abstract—Weakly interacting massive particles (WIMPs) are among the main candidates for the relic dark matter (DM). The idea of direct DM detection relies on elastic spin-dependent (SD) and spin-independent (SI) interaction of WIMPs with target nuclei. In this review, formulas for the DM event rate calculations are collected. The importance of the SD WIMP–nucleus interaction for reliable DM detection is argued and the spin nuclear structure functions relevant to DM search are discussed. The effective low-energy minimal supersymmetric standard model (MSSM) is used for calculation of the DM cross sections, provided the lightest neutralino is the WIMP. It is shown that the absolute lower bound for the rate of direct DM detection is due to the SD WIMP–nucleon interaction and a new-generation experiment aimed at detecting DM with sensitivity higher than 10–5 event/day/kg should have a non-zero-spin target to avoid missing of the DM signal. The mixed spin– scalar couplings approach is argued. Prospects of DM experiments with high-spin Ge-73 are discussed in the mixed coupling scheme. The DAMA experiment has claimed observation of WIMPs due to annual signal modulation. Some important consequences of the DAMA claim for the other DM searches as well as for collider physics are considered. PACS numbers: 95.35.+d, 12.60.Jv, 14.80.Ly DOI: 10.1134/S1063779607030033
1. INTRODUCTION By definition, galactic Dark Matter (DM) does not emit detectable amounts of electromagnetic radiation and only gravitationally affects other, visible, celestial bodies. The best (and historically among the first) evidence of this kind comes from the study of galactic rotation curves, when one measures the velocity with which globular stellar clusters, gas clouds, or dwarf galaxies orbit around their centers. If the mass of these galaxies were concentrated in their visible parts, the orbital velocity at large radii r should decrease as 1/ r (Fig. 1). Instead, it remains approximately constant to the largest radius where it can be measured. This implies that the total mass M(r) felt by an object at a radius r must increase linearly with r (Fig. 2). Studies of this type imply that 90% or more of the mass of large galaxies is dark. The mass density averaged over the entire Universe is usually expressed in units of critical density ρc ≈ 10–29 g/cm3; the dimensionless ratio Ω ≡ ρ/ρc = 1 corresponds to a flat Universe. Analyses of galactic rotation curves imply Ω ≥ 0.1. Studies of clusters and superclusters of galaxies through gravitational lensing or through measurements of their X-ray temperature, as well as studies of the large-scale streaming of galaxies, favor larger values of the total mass density of the Universe Ω ≥ 0.3 (see, for example, [3]). Finally, naturalness arguments and inflationary models prefer Ω = 1.0
to a high accuracy. The requirement that the Universe be at
Data Loading...
