" The Standard Model did not accommodate massive neutrinos, because it assumed the existence of only "left-handed" neutrinos, which have spin aligned counter-clockwise to their axis of motion. If neutrinos have non-zero mass, they necessarily travel slower than the speed of light . Therefore, it would be possible to "overtake" a neutrino, choosing a reference frame in which its direction of motion is reversed without affecting its spin (making it right-handed). 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. Man Health Cover Model Workout References Textbooks Griffiths, David J. (1987) Introduction to Elementary Particles, Wiley, John & Sons, Inc. "

" & Roth-Berghofer, Th. (Eds. ) Professional knowledge management; LNCS 3782 Springer Verlag; 2005. Models as people artist model — in art school modeling, a person who poses for purposes of art. model — person whose occupation is to display clothing (eg. a "fashion model") or other personal items of artistic or aesthetic value, and who is often physically attractive; a model who attains celebrity status or is otherwise widely known is said to be a "supermodel". promotion model— promotes a product or service role model — person who acts as a behavioural or moral example to others. Man Calendar Model Models as physical objects physical model — physical representation of an object; in engineering, similitude is used in the scientific testing of physical models. scale model — a replica or prototype of an object built as a hobby or for research. "