Phenomenology of ELDER dark matter
HJE
Phenomenology of ELDER dark matter
Eric Ku ik 0 1 3 4 5
Maxim Perelstein 0 1 3 5
Nicolas Rey-Le Lorier 0 1 3 5
Yu-Dai Tsai 0 1 2 3 5
0 Waterloo , ON N2J 2W9 , Canada
1 Indianola , IA 50125 , U.S.A
2 Perimeter Institute for Theoretical Physics
3 Ithaca , NY 14853 , U.S.A
4 Racah Institute of Physics, Hebrew University of Jerusalem
5 Laboratory for Elementary Particle Physics, Cornell University
We explore the phenomenology of Elastically Decoupling Relic (ELDER) dark matter. ELDER is a thermal relic whose present density is determined primarily by the cross-section of its elastic scattering o this scattering is mediated by a kinetically mixed dark photon, we argue that the ELDER scenario makes robust predictions for electron-recoil direct-detection experiments, as well as for dark photon searches. These predictions are independent of the details of interactions within the dark sector. Together with the closely related Strongly-Interacting Massive Particle (SIMP) scenario, the ELDER predictions provide a physically motivated, well-de ned target region, which will be almost entirely accessible to the next generation of searches for sub-GeV dark matter and dark photons. We provide useful analytic approximations for various quantities of interest in the ELDER scenario, and discuss two simple renormalizable toy models which incorporate the required strong number-changing interactions among the ELDERs, as well as explicitly implement the coupling to electrons via the dark photon portal.
Beyond Standard Model; Cosmology of Theories beyond the SM
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2.1
2.2
2.3
3.1
3.2
3.3
4.1
4.2
1 Introduction 2
ELDER dark matter 3
Dark photon portal and phenomenology
The thermal history of ELDERs
ELDER mass estimates
ELDERs, SIMPs and WIMPs, oh my!
Dark photon portal Direct detection Dark photon searches
4
5
Models of ELDERs
3 model
Choi-Lee model
Conclusions
A Boltzmann equations B
Kinetic decoupling and approximate analytic solution
C Thermally-averaged 3 ! 2 rate
1
Introduction
Cosmological observations at a variety of length scales, from individual galaxies to the
Hubble scale, indicate that most of the matter in the universe is in the form of dark matter
(DM). DM cannot consist of any of the known elementary particles, and its existence
provides solid experimental evidence for physics beyond the Standard Model (SM). The
microscopic nature of dark matter is one of the major mysteries in fundamental physics. For
many years, both theoretical work and experimental searches for dark matter focused on a
short list of possible candidates independently motivated by particle physics | primarily
QCD axions and weakly-interacting massive particles (WIMPs) realized within
supersymmetry or other extensions of the SM at the weak scale. Despite decades of experimental
e ort, no evidence for these candidates has been found. While neither WIMP nor axion
dark matter is ruled out and the experimental searches are ongoing, there has been renewed
interest in exploring alternative particle dark matter candidates.
{ 1 {
A promising new direction is to consider models in which dark matter particles have
strong number-changing self-interactions [1{18]. If the DM is a thermal relic, its current
density in such models can be determined either by the cross section of the number-changing
self-interaction processes (\Strongly-Interacting Massive Particle", or SIMP, scenario [19])
or by the cross section of elastic scattering between the DM and SM (\Elastically
Decoupling Relic", or ELDER, scenario [7]). In both cases, the observed DM density is naturally
obtained if the mass of the DM particles is parametrically close to the QCD con nement
scale, mDM
10
100 MeV. This leads to an attractive particle physics framework: a
\dark sector" of elds not charged under the SM gauge groups, containing a non-Abelian
\dark QCD" gauge group that con nes at a scale similar to
QCD. The proximity of the
SM and \dark" con nement scales may be due to a discrete symmetry relating the dark
QCD gauge coupling to the SM g3 at a high energy scale [20{24]. The dark matter may
then consist of mesons that emerge from dark QCD upon con nement [2]. If the dark
sector also contains an Abelian gauge eld, kinetic mixing between this eld and the SM
electromagnetic eld naturally provides the requisite interaction between the dark matter
particle and the SM, via the dark photon portal [4, 8].
The goal of this paper is to study the above possibilities in more detail, in particular,
the ELDER scenario proposed in ref. [7]. In ref. [7], we demonstrated the viability of this
scenario in a general framework, without reference to a speci c model of either the dark
sector or the portal connecting it to the SM. Instead, we used a simple parametrization
of the DM number-changing self-scattering and DM-SM elastic scattering cross sections.
Moreover, the analysis of ref. [7] was primarily based on numerical solution of Boltzmann
equations. Here, we expand that analysis in (...truncated)