Dark matter from particle physics

Abstract

Eventually, the properties of particles relevant to the possible amounts of dark matter from various particle physics sources (lightest superpartner (LSP), massive neutrinos, axions, etc.) will be well determined. I discuss how well $\text{Ω}{}_{\mathrm{<mtext>LSP</mtext>}}\text{h}{}^2$ can be calculated once there is collider data on the properties of the LSP. Study of the supersymmetry Lagrangian implies that current limits on WIMPs are not general.

Introduction

By the early 1980s particle physics had proposed three main candidates for non-baryonic dark matter, massive neutrinos, axions, and the supersymmetry LSP. All of them automatically give interesting $\text{Ωh}{}^2\text{∼0.1}$ for reasonable values of the relevant parameters. Once the neutrino and axion masses are measured their contribution to $\text{Ωh}{}^2$ can be calculated. The main purpose of this talk is to discuss how well that can be done for the LSP [1].

It should be noted that from the point of view of particle theory all these candidates are natural, and occur together in a typical theory. Unified theories (with or without a GUT gauge group) typically have a stable LSP and massive neutrinos – it would require explanation if they did not. If there are any broken global symmetries they are likely to have an axion. In principle, the ratios of $\text{Ω}{}_{\mathrm{<mtext>LSP</mtext>}}$, $\text{Ω}{}_{\mathrm{<mtext>v</mtext>}}$, $\text{Ω}{}_{\mathrm{<mtext>a</mtext>}}$, $\text{Ω}{}_{\mathrm{<mtext>baryon</mtext>}}$ are calculable from the particle physics, although we do not yet understand such theories well enough to do so at present.

In this talk I will focus on calculating $\text{Ω}{}_{\mathrm{<mtext>LSP</mtext>}}$ once there is collider data on its properties. First, it should be emphasized that detection of an LSP escaping a detector will imply that it has a lifetime about 10¹⁵ times longer than other sparticles, consistent with being stable, but not demonstrating that. It will be necessary to observe LSP scattering or annihilation to prove it is indeed a significant part of the CDM.

Once M_LSP and its couplings to other particles are known, $\text{Ω}{}_{\mathrm{<mtext>LSP</mtext>}}$ can be calculated. The calculation gives a density so it is actually $\text{Ωh}{}^2$ that results, but by then h² should be well enough known so it is not a large source of error. Then two main possible sources of error remain, the cosmology, and how well the needed parameters can be measured at colliders.