Arisaka Lab at UCLA

Direct Search for Dark Matter

• XENON (Liquid Xenon)
• DarkSide (Liquid Argon)
• MAX and XAX (Future Projects)

Astronomical Observations of Dark Matter

Way back in 1932, from the motion of a cluster of galaxies, the existence of invisible particles were proposed by Jon Oort and Fritz Zwicky. Later on, as shown above, it became evident that the rotational speed of the galaxy is independent from the distance from the galactic center. This fact can be explained only if there is uniform spherical distribution of additional unseen matter which produces enough gravity to hold the galaxy together.

Lastly, in the last two decades, there have been overwhelming indications that dark matter contributes to the major part of Omega of the Universe. The above figure on the left shows the observed fraction of elements (in shaded red vertical bar) as a function of the baryon density. Compered to the critical density (the vertical black line), Omega baryon only counts for 4.6% to the total Omega. The right figure shows the combined results of three observations : CMB doppler peak, distant Supernovae, and the large scale structure, all indicating the striking facts: (1) The total Omega is critical (= 1.0) as predicted by the Inflation, (2) Omega_Matter = 0.27 and (3) Omega_Dark_Energy = 0.73. This means that there is a missing component in Omega_Matter = 0.27 - 0.046 ~ 0.23 that must be the Omega_Dark_Matter. The below figure illustrates the pie chart of the contribution of each component to the total Omega.

Without Dark Matter, We Were Not Here Today

What is the most striking fact of the dark matter is that, without it, we were not here today. It is because dark matter was required to create any structure in the early Universe such as stars and galaxies. Thanks to dark matter which is non-relativistic and attracted only by gravity, the very first structure of our Universe was formed. Today's sophisticated computer simulation allows to investigate the nature of dark matter and it clearly shows necessity of cold dark matter to reproduce the large scale structure of today.

Dark Matter Candidates

There have been various speculation on the true nature of the dark matter, which can be categorized by its mass and cross section illustrated by the figure above on the left. The leading candidate is the WIMPs (Weakly Interacting Massive Particles), such as Neutralino predicted by Supersymmetry (top-right) and the KK photons by Extra Dimensions (bottom-right).

Detection Methods

• Direct detection by the underground experiments
• Production by the accelerator such as LHC
• Indirect Astronomical observations like gamma rays, anti particles and high energy neutrinos.

• Direct Detection ==> XENON, DarkSide, MAX and XAX
• Production by LHC ==> CMS
• Indirect Detection by Ultra High Energy Gamma Rays and Neutrinos ==> Pierre Auger

Useful Review Articles

1) Dark side of the universe.

2) Dark matter: Motivation, candidates and searches.

3) Physics Beyond the Standard Model and Dark Matter.

4) Dark Matter Candidates from Particle Physics and Methods of Detection.

5) Heart of Darkness: The Significance of the Zeptobarn Scale for Neutralino Direct Detection.

6) Revisiting the Higgs Mass and Dark Matter in the CMSSM.