Twin Higgs Asymmetric Dark Matter

Abstract

We study Asymmetric Dark Matter (ADM) in the context of the minimal (Fraternal) Twin Higgs solution to the little hierarchy problem, with a twin sector with gauged $SU(3)' \times SU(2)'$, a twin Higgs, and only third generation twin fermions. Naturalness requires the QCD$^\prime$ scale $\Lambda'_{\rm QCD} \simeq 0.5 - 20 \ {\rm GeV}$, and $t'$ to be heavy. We focus on the light $b'$ quark regime, $m_{b'} \lesssim \Lambda'_{\rm QCD}$, where QCD$^\prime$ is characterised by a single scale $\Lambda'_{\rm QCD}$ with no light pions. A twin baryon number asymmetry leads to a successful DM candidate: the spin-3/2 twin baryon, $\Delta' \sim b'b'b'$, with a dynamically determined mass ($\sim 5 \Lambda'_{\rm QCD}$) in the preferred range for the DM-to-baryon ratio $\Omega_{\rm DM}/\Omega_{\rm baryon} \simeq 5$. Gauging the $U(1)'$ group leads to twin atoms ($\Delta'$ - $\bar {\tau'}$ bound states) that are successful ADM candidates in significant regions of parameter space, sometimes with observable changes to DM halo properties. Direct detection signatures satisfy current bounds, at times modified by dark form factors.