Spin Dependence of Dark Matter Scattering

TL;DR

The paper investigates how spin-dependent and spin-independent DM scattering cross sections can diagnose the underlying particle physics responsible for dark matter, by comparing six beyond-the-Standard-Model scenarios plus a model-independent framework under relic-density constraints.Using a Bayesian Markov Chain Monte Carlo approach, it maps predicted SI/SD cross sections across parameter space, highlighting how exchange mechanisms (notably $Z$- and Higgs-mediated processes) and particle spin shape the detection prospects in direct detectors and in IceCube.Key outcomes include a strong SD signal in the FP region of mSUGRA and in Dirac-neutrino and mUED scenarios, a large SD cross section in the nMSSM tadpole model, and suppressed SD signals in xSM and LHT, illustrating how SD/SI planes can differentiate models and guide experimental priorities.The study also provides model-independent expressions for SI/SD scattering across spins and emphasizes how hadronic uncertainties in sigma terms impact the interpretation of direct-detection results.

Abstract

New experiments designed to discover a weakly interacting dark matter (DM) particle via spin dependent scattering can distinguish models of electroweak symmetry breaking. The plane of spin dependent versus spin independent DM scattering cross sections is a powerful model diagnostic. We detail representative predictions of mSUGRA, singlet extended SM and MSSM, a new Dirac neutrino, Littlest Higgs with T-parity (LHT) and Minimal Universal Extra Dimensions (mUED) models. Of these models, the nMSSM has the largest spin dependent (SD) cross section. It has a very light neutralino which would give lower energy nuclear recoils. The Focus Point region of mSUGRA, mUED and the right handed neutrino also predict a very large SD cross section and predict a large signal of high energy neutrinos in the IceCube experiment from annihilations of dark matter in the Sun. We also describe a model independent treatment of the scattering of DM particles of different intrinsic spins.

Figures (13)

• Figure 1: Scan over the common scalar, $m_{0}$, and gaugino mass, $m_{1/2}$, to satisfy relic density and LEP2 constraints on mSUGRA with specific values of $A_{0}$ and $\tan \beta$ ($A_{0}=0$, $\tan\beta=30, 55$). Open squares (in red) show parameter values that have a relic density within $\pm 10\%$ of the measured value; solid points (in black) have lower relic density values.
• Figure 2: Neutralino relic density and LEP2 allowed regions in the mSUGRA model obtained from a scan over the common scalar, $m_{0}$, and gaugino mass, $m_{1/2}$, while allowing variations of the parameters $A_{0}, \tan \beta$ and $m_{t}$. One, two and three sigma contours are shown
• Figure 3: Posterior distributions of SI and SD cross sections in the mSUGRA model. The region of high SI and SD cross sections corresponds to the FP region and should be probed fully by the XENON10 and Super CDMS 25 Kg experiments. The tail that extends to lower SI and SD values corresponds to the AF and CA regions. The proposed COUPP1T experiment should probe these regions Bertone:2007xj.
• Figure 4: Posterior distributions of the induced muon flux at the Super-Kamiokande detector (cm$^{-2}$s$^{-1}$ units) from high energy neutrinos created by DM annihilations in the Sun for mSUGRA. Only the low neutralino mass FP region is constrained by the Super-K limit.
• Figure 5: Posterior distributions of SI and SD cross sections that satisfy the relic density and LEP2 constraints in the tadpole extended SUSY model. This model has light neutralinos with relatively large SI and SD cross sections that make the prospects for discovery promising.