vectorlike

Vectorlike is an adjective used in physics and mathematics to describe objects whose left- and right-handed components transform identically under a symmetry group. In particle physics, it most often refers to vectorlike fermions, whose chiralities carry the same gauge quantum numbers.

In the Standard Model, fermions are chiral: left- and right-handed fields transform differently under SU(2)L × U(1)Y, and their masses arise from Yukawa couplings after electroweak symmetry breaking. Vectorlike fermions, by contrast, can have gauge-invariant Dirac mass terms independent of the Higgs field and may mix with ordinary fermions, leading to modified electroweak couplings and flavor effects.

Common realizations are vectorlike quarks and vectorlike leptons. They can appear as SU(2) singlets, doublets or higher multiplets with various hypercharges, giving electric charges such as 2/3 or -1/3 for quarks and 0 or -1 for leptons. Their decays include W, Z, or Higgs bosons when they transform into Standard Model fermions.

Production at colliders occurs via QCD for pair production if colored, or electroweak processes for single production when mixing with Standard Model fermions. Experimental searches at the LHC set lower mass bounds that depend on decay modes and assumed branching ratios, typically in the hundreds of GeV to TeV range.

In mathematics, vectorlike representations are those equivalent to their complex conjugates, enabling gauge-invariant mass terms without anomalies. They appear in beyond-Standard Model theories such as extra dimensions, composite Higgs models, and certain grand unified frameworks.