Hyperstealth dark matter and long-lived particles

A new dark matter candidate is proposed that arises as the lightest baryon from a confining <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>S</a:mi><a:mi>U</a:mi><a:mo stretchy="false">(</a:mo><a:mi>N</a:mi><a:mo stretchy="false">)</a:mo></a:math> gauge theory which equilibrates with the Standard Model only through electroweak interactions. Surprisingly, this candidate can be as light as a few GeV. The lower bound arises from the intersection of two competing requirements: (i) the equilibration sector of the model must be sufficiently heavy, at least several TeV, to avoid bounds from colliders, and (ii) the lightest dark meson (that may be the dark <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msup><e:mi>η</e:mi><e:mo>′</e:mo></e:msup></e:math>, <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>σ</g:mi></g:math>, or the lightest glueball) has suppressed interactions with the SM and must decay before big bang nucleosynthesis. The low-energy dark sector consists of one flavor that is electrically neutral and an electroweak singlet. The dark matter candidate is the lightest baryon consisting of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>N</i:mi></i:math> of these light flavors leading to a highly suppressed elastic scattering rate with the Standard Model (SM). The equilibration sector consists of vectorlike dark quarks that transform under the electroweak group, ensuring that the dark sector can reach thermal equilibrium with the SM in the early Universe. The lightest dark meson lifetimes vary between <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msup><k:mn>10</k:mn><k:mrow><k:mo>−</k:mo><k:mn>3</k:mn></k:mrow></k:msup><k:mo>≲</k:mo><k:mi>c</k:mi><k:mi>τ</k:mi><k:mo>≲</k:mo><k:msup><k:mn>10</k:mn><k:mn>7</k:mn></k:msup><k:mtext> </k:mtext><k:mtext> </k:mtext><k:mi mathvariant="normal">m</k:mi></k:math>, providing an outstanding target for LHC production and experimental detection. We delineate the interplay between the lifetime of the light mesons, the suppressed direct detection cross section of the lightest baryon, and the scale of equilibration sector that can be probed at the LHC.