nLab fourth generation of fundamental particles



Fields and quanta

fields and particles in particle physics

and in the 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

hadrons (bound states of the above quarks)


in grand unified theory

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 09:00:42. See the history of this page for a list of all contributions to it.