Tachyons

In General > s.a. causality violations; modified lorentz symmetry; photon.
* Idea: Particles with negative squared mass; If they transform under the ordinary action of the Lorentz group, as often assumed, they travel along spacelike directions, i.e. faster than light or superluminally.
* Consequences: Existence of tachyons and Lorentz invariance imply causality violations, so a tachyon is considered to be sick in the context of particle mechanics, but in field theory it just indicates an instability of a background.
* Description: Scalar ones can be described by a Klein-Gordon theory, vector ones by a Proca theory, with m² < 0.
* Pseudo-tachyons: Particles which behave like tachyons in momentum space and like subluminal particles (v < c) in ordinary space.
> Related topics: see wave phenomena [superluminal propagation].

References > s.a. casimir effect; observational cosmology.
@ Books, reviews: Kowalczynski 66; Kreisler AS(73); in Gribbin 77; Herbert 89; Stonier 90.
@ General: Feinberg PR(67); Feldman AJP(74)mar [bibliography]; Lévy-Leblond AJP(80)may; Arntzenius BJPS(90); González-Mestres ap/95 [and spacetime geometry]; Kowalczynski APPB(00)he/00 [proposed experimental searches]; Ehrlich AJP(03)nov [and teaching].
@ Quantum: Fanchi FP(90) [parametrized relativistic quantum mechanics].
@ And field theory / matter: Tanaka PTP(61); Bilaniuk et al AJP(62)oct; Bers et al in(71); Moretti & Agresti NCB(95) [Klein-Gordon]; González-Mestres ap/96 [HECRs]; Bollini et al IJTP(99) [and electromagnetism]; Tomaschitz IJMPA(99).
@ And cosmology / inflation: Davidson PRD(87), & Owen PLB(86) [particles as Kaluza-Klein tachyons]; Tomaschitz IJMPD(98) [in FRW spacetime]; Feinstein PRD(02); Gibbons PLB(02)ht [rolling down potential]; Fairbairn & Tytgat PLB(02)ht; Frolov et al PLB(02)ht; Kofman & Linde JHEP(02)ht [problems]; Steer & Vernizzi PRD(04)ht/03; Gorini et al PRD(04); Vernizzi & Steer ap/04-in [vs standard inflation]; Keresztes et al PRD(09)-a0901 [and Big Brake singularity]; > s.a. Rigidity.
@ As dark matter: Shiu & Wasserman PLB(02)ht; Davies IJTP(04)ap.
@ As dark energy: Bagla et al PRD(03)ap/02; Padmanabhan PRD(02)ht; Copeland et al PRD(05)ht/04; de la Macorra et al PLB(06) [late-time behavior]; Calcagni & Liddle PRD(06).
@ Related topics: Asaro AJP(96)apr [and complex velocity]; Davidson PE(01)qp/02 [motion of charged ones]; Salesi IJMPA(97)qp/02 [pseudotachyonic Fermions].

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