Phenomenology of ELDER dark matter

Journal of High Energy Physics, Aug 2017

Abstract 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 off Standard Model (SM) particles. Assuming that 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-defined 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.

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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 - 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)


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Eric Kuflik, Maxim Perelstein, Nicolas Rey-Le Lorier, Yu-Dai Tsai. Phenomenology of ELDER dark matter, Journal of High Energy Physics, 2017, pp. 78, Volume 2017, Issue 8, DOI: 10.1007/JHEP08(2017)078