" V. References [1] Stachowiak, H . ; "Modell" (In German); In: Seiffert, H. Handlexikon zur Wissenschaftstheorie; Deutscher Taschenbuch Verlag; 1989; pp. 219 - 222. [2] Wieringa, R. J. G Scale Model Railroad; "Algebraic foundations for dynamic conceptual models"; PhD dissertation Free University of Amsterdam; 17 May 1990. [3] Kaschek, R. "

" Since then, physicists have revised the Standard Model to allow neutrinos to have mass, which make up additional free parameters beyond the initial 19. A further extension of the Standard Model can be found in the theory of supersymmetry, which proposes a massive supersymmetric "partner" for every particle in the conventional Standard Model. Supersymmetric particles have been suggested as a candidate for explaining dark matter. Although supersymmetric particles have not been observed experimentally to date, the theory is one of the most popular avenues of research in theoretical particle physics. References Textbooks Griffiths, David J. (1987) Introduction to Elementary Particles, Wiley, John & Sons, Inc. ISBN 0471603864 Journal Articles Y. Model Railroad News Hayato et al. , Search for Proton Decay through p → νK+ in a Large Water Cherenkov Detector. "