Supersymmetry

Supersymmetry (SUSY) is a theoretical symmetry that relates fermions and bosons, proposing that for every known fermion there exists a corresponding bosonic superpartner, and vice versa. It is one of the most promising extensions of the Standard Model of particle physics, offering solutions to several theoretical problems including the hierarchy problem and dark matter.


Key Concepts

  1. Relates particles with different spin statistics: fermions ↔ bosons
  2. Each Standard Model particle has a superpartner with spin differing by 1/2
  3. Superpartners of fermions are called “sfermions” (e.g., selectron, squark)
  4. Superpartners of bosons are called “inos” (e.g., photino, gluino, higgsino)
  5. If exact, supersymmetry would require superpartners to have the same mass as their Standard Model counterparts

Standard Model vs SUSY Names

  1. Fermions → Sfermions (bosonic superpartners): electron → selectron, quark → squark, neutrino → sneutrino
  2. Gauge Bosons → Gauginos (fermionic superpartners): photon → photino, gluon → gluino, W boson → wino, Z boson → zino
  3. Higgs Boson → Higgsinos (fermionic superpartners): Higgs → higgsino
  4. Naming pattern: fermions get “s-” prefix (sfermions), bosons get “-ino” suffix (gauginos, higgsinos)
  5. Examples: electron (e⁻) → selectron (ẽ), up quark (u) → sup quark (ũ), photon (γ) → photino (γ̃)

Why Supersymmetry?

  1. Addresses the hierarchy problem: stabilizes the Higgs mass against quantum corrections
  2. Provides a natural candidate for dark matter (the lightest supersymmetric particle, or LSP)
  3. Allows unification of the three gauge couplings at high energy scales
  4. Connects to string theory, which requires supersymmetry for consistency
  5. Offers a more elegant mathematical structure for quantum field theory

Broken Supersymmetry

  1. Supersymmetry must be broken, as no superpartners have been observed at Standard Model particle masses
  2. Superpartners are expected to be much heavier than their Standard Model counterparts
  3. The mechanism of supersymmetry breaking is one of the key open questions in particle physics
  4. Current experimental searches at the LHC have placed lower limits on superpartner masses
  5. If supersymmetry exists, it may be discovered at higher energy colliders or through indirect evidence