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The Standard Model of particle physics is extraordinarily successful, and deeply unsatisfying. Among its most glaring wounds is the hierarchy problem: the Higgs boson's mass should be driven by quantum corrections to values 10¹⁷ times larger than what is observed. Every virtual particle in the quantum vacuum contributes to the Higgs mass, and these contributions are enormous. For the Higgs to sit at its measured value requires a cancellation of 34 decimal places of precision between contributions, a fine-tuning so extreme it offends every physicist who contemplates it. Nature doesn't accidentally cancel things to 34 decimal places. Something must be making it happen.

Supersymmetry (SUSY) was the most elegant proposed solution. It posits a deep symmetry between fermions and bosons: every known particle has a supersymmetric partner with the same mass but opposite spin statistics. Electrons have selectrons. Quarks have squarks. Photons have photinos. The quantum corrections to the Higgs mass from fermions and bosons come with opposite signs, and if SUSY is exact, they cancel perfectly, automatically, without any fine-tuning. The hierarchy problem dissolves. The cancellation is not a coincidence but a consequence of symmetry.

There is one problem. The Large Hadron Collider has found no supersymmetric particles, not one. After decades as the leading candidate for physics beyond the Standard Model, SUSY has been pushed to energy scales where it can no longer naturally solve the hierarchy problem. The symmetry, if it exists, is broken, the superpartners are heavier than they should be, and nobody knows why. Physicists are left in the uncomfortable position of having the most beautiful solution to a real problem, with no experimental evidence that the solution exists. Supersymmetry may be true, broken, hidden at higher energies, or it may be the most elegant wrong idea in the history of physics. The universe, as usual, has not said which.

FB Quantum Physics group

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