In elementary particle physics and mathematical physics, in particular in effective field theory, a form factor is a function that encapsulates the properties of a certain particle interaction without including all of the underlying physics, but instead, providing the momentum dependence of suitable matrix elements. It is further measured experimentally in confirmation or specification of a theory—see experimental particle physics. For example, at low energies the interaction of a photon with a nucleon is a complicated calculation involving interactions between the photon and a sea of quarks and gluons, the calculation cannot be performed from first principles. In this context, form factors are called "structure functions", since they can be used to describe the structure of the nucleon. However, the generic Lorentz-invariant form of the matrix element for the electromagnetic current interaction is known, ε μ N ¯ N where q μ represents the photon momentum; the three functions: α, β, κ are associated to the electric and magnetic form factors for this interaction, are measured experimentally.

This matrix element serves to determine the transition amplitude involved in the scattering interaction or the respective particle decay—cf. Fermi's golden rule. In general, the Fourier transforms of form factor components correspond to electric charge or magnetic profile space distributions of the hadron involved; the analogous QCD structure functions are a probe of the gluon distributions of nucleons. Brown, Lowell S.. Quantum Field Theory. Cambridge University Press. ISBN 978-0-521-46946-3. P 400 Gasiorowicz, Elementary Particle Physics, John Wiley & Sons, ISBN 978-0471292876Wilson, R.. "Form factors of elementary particles", Physics today 22 p 47, doi:10.1063/1.3035356 Charles Perdrisat and Vina Punjabi. "Nucleon Form factors", Scholarpedia 5: 10204. Online article Structure function Quantum field theory Standard model Quantum mechanics Special relativity Photon Structure Function Electric form factor Magnetic form factor Charge radius

Weber's sailfin lizard, is an agamid lizard found in Indonesia. It is endemic to Halmahera and Ternate Islands of Maluku, it has a life-span of between 10–15 years. H. weberi is the smallest of the three recognized species of Hydrosaurus, attaining an avg. total length between 2–3 ft. Some argue that full species status may be invalid and claim this agamid should be classified a subspecies of the larger H. pustulatus, Philippine Sailfin. The third species, H. amboinensis, Indonesian Sailfin is the largest of the group. Although much research is still needed, it is known that this lizard is omnivorous. In captivity, juveniles are maintained on a 60% insect / 40% vegetation diet. Adults consume 75% vegetation and 25% insects and other non-vegetation life. H.weberi 2–3 ft H.pustulatus 2.5–3 ft H.amboinensis 2.5–3 ft+ The specific name, weberi, is in honor of German-Dutch zoologist Max Wilhelm Carl Weber van Bosse. Photos of Hydrosaurus weberi Barbour, T.. New a new toad from the Dutch East Indies, with notes on other species.

Proc. Biol. Soc. Washington 24: 15-22. Barts, M. & Wilms, T. 2003. Die Agamen der Welt. Draco 4: 4-23 Colwell, G. J. 1993. Hydrosaurus weberi. Morphology Herpetological Review 24: 150 de Rooij, N. de 1915. The Reptiles of the Indo-Australian Archipelago. I. Lacertilia, Emydosauria. Leiden, xiv + 384 pp. Gábris, J. 2003. Zur Haltung von philippinischen Segelechsen. Draco 4: 24-33 Werning, H. 2002. Wasseragamen und Segelechsen. Natur und Tier Verlag, 127 pp. Werning, H. 2004. Bibliographie der Gattungen Physignathus, Lophognathus und Hydrosaurus. Iguana Rundschreiben 17: 18-31