fourth generation of fundamental particles



Fields and quanta

field (physics)

standard model of particle physics

force field gauge bosons

scalar bosons

matter field fermions (spinors, Dirac fields)

flavors of fundamental fermions in the
standard model of particle physics:
generation of fermions1st generation2nd generation3d generation
quarks (qq)
up-typeup quark (uu)charm quark (cc)top quark (tt)
down-typedown quark (dd)strange quark (ss)bottom quark (bb)
neutralelectron neutrinomuon neutrinotau neutrino
bound states:
mesonslight mesons:
pion (udu d)
ρ-meson (udu d)
ω-meson (udu d)
ϕ-meson (ss¯s \bar s),
kaon, K*-meson (usu s, dsd s)
eta-meson (uu+dd+ssu u + d d + s s)

charmed heavy mesons:
D-meson (uc u c, dcd c, scs c)
J/ψ-meson (cc¯c \bar c)
bottom heavy mesons:
B-meson (qbq b)
ϒ-meson (bb¯b \bar b)
proton (uud)(u u d)
neutron (udd)(u d d)

(also: antiparticles)

effective particles

hadron (bound states of the above quarks)


minimally extended supersymmetric standard model




dark matter candidates


auxiliary fields



A hypothetical fourth generation of fundamental particles (fermions), beyond the three currently observed.

Still consistent with experiment, suggested by flavour physics, and implied by Spin(16), Spin(18)Spin(18)-GUT.



Exposition and review:

  • David B. Cline, Beyond Truth and Beauty: A Fourth Family of Particles,Scientific American Vol. 259, No. 2 (AUGUST 1988), pp. 60-67 (jstor:24989195)

  • Bob Holdom, WS Hou, Tobias Hurth, Michelangelo L Mangano, Saleh Sultansoy, Gokhan Ünel Four statements about the fourth generation, PMC Phys A 3, 4 (2009) (doi:10.1186/1754-0410-3-4)

Experimental constraints

  • Alexander Lenz, Constraints on a fourth generation of fermions from Higgs Boson searches, Adv. High Energy Phys. 2013 (2013) 910275 (doi:10.1155/2013/910275)

  • Alexander Lenz, How to really kill a physics model, talk notes 2012 (pdf, pdf)

  • N.S. Mankoč Borštnik, H.B.F. Nielsen, Do Present Experiments Exclude the Fourth Family Quarks as Well as the Existence of More Than One Scalar?, Bled Workshops Phys. 17 (2016) no. 2, 128-146 (spire:1510166)

Motivation from flavour physics

Motivation from flavour-physics (B-meson decays)

  • A.K. Ciftci, R. Ciftci, S. Sultansoy, A Search for the Fourth SM Family Fermions and E 6E_6 Quarks at μ +μ \mu^+ \mu^- Colliders, Phys. Rev. D65 (2002) 055001 (arXiv:hep-ph/0106222)

  • Amarjit Soni, Ashutosh Kumar Alok, Anjan Giri, Rukmani Mohanta, Soumitra Nandi, The fourth family: a simple explanation for the observed pattern of anomalies in B-CP asymmetries, Phys. Lett. B683:302-305, 2010 (arXiv:0807.1971)

In string/grand-unified theory

In Spin(16)- and Spin(18)?-GUT (“SO(16)-, SO(18)-GUT”):

In heterotic string theory:

  • A.A. Maslikov, I.A. Naumov, G.G. Volkov, The Fermion Generations Problem in the Gust in the Free World-Sheet Fermion Formulation, Int. J. Mod. Phys. A11 (1996) 1117 (arXiv:hep-ph/9512429)

Last revised on January 8, 2020 at 04:00:42. See the history of this page for a list of all contributions to it.