Higgsino

In particle physics, supersymmetry is a theory that says every particle we know has a heavier partner. The higgsino is the supersymmetric partner of the Higgs boson. It’s a particle with spin ½, meaning it’s a type of Fermion.

When the forces of nature split during a process called electroweak symmetry breaking, the higgsino mixes with other supersymmetric particles called gauginos. This creates four neutral particles (called neutralinos) and two charged particles (called charginos). The charginos carry positive or negative charge, while the neutralinos are neutral.

In models that follow a rule called R-parity, the lightest neutralino becomes the lightest supersymmetric particle (LSP). This matters because the LSP is stable — it won’t decay — and it’s a good candidate for dark matter, the invisible material that makes up most of the universe’s mass. The neutralino itself is a mix of different parts called bino, wino, and higgsino, and depending on which one it’s mostly made of, it behaves differently and can have different masses.

In versions of supersymmetry where particles like top squarks, bottom squarks, gluinos, and higgsino-heavy neutralinos and charginos are expected to be light, these particles should be easier to create in high-energy experiments. Scientists at the Large Hadron Collider (LHC) have searched for higgsinos by trying to produce them directly through particle collisions, but as of 2017, no evidence for them has been found.

Mass

If dark matter is made entirely of higgsinos, calculations show that the higgsino’s mass would need to be about 1.1 TeV in order to account for the amount of dark matter we observe in the universe. But if dark matter is made up of different types of particles, not just higgsinos, then the exact mass needed for the higgsino to play its role depends on how those different particles are spread out or distributed in the multiverse — a concept where different possible universes might have different physical constants or particle properties. In those scenarios, the higgsino wouldn’t need to be as heavy and could have a lower mass while still contributing to the total amount of dark matter.

mħ ≈ 1.1 (Ωħ/ΩDM)1/2 TeV

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