Fields with imaginary mass Tachyon

in paper coined term tachyon , gerald feinberg studied lorentz invariant quantum fields imaginary mass. because group velocity such field superluminal, naively appears excitations propagate faster light. however, understood superluminal group velocity not correspond speed of propagation of localized excitation (like particle). instead, negative mass represents instability tachyon condensation, , excitations of field propagate subluminally , consistent causality. despite having no faster-than-light propagation, such fields referred tachyons in many sources.

tachyonic fields play important role in modern physics. perhaps famous higgs boson of standard model of particle physics, has imaginary mass in uncondensed phase. in general, phenomenon of spontaneous symmetry breaking, closely related tachyon condensation, plays important role in many aspects of theoretical physics, including ginzburg–landau , bcs theories of superconductivity. example of tachyonic field tachyon of bosonic string theory.

tachyons predicted bosonic string theory , neveu-schwarz (ns) , ns-ns sectors, respectively open bosonic sector , closed bosonic sector, of rns superstring theory prior gso projection. such tachyons not possible due sen conjecture, known tachyon condensation. resulted in necessity gso projection.