Lattice field theoryIn physics, lattice field theory is the study of lattice models of quantum field theory, that is, of field theory on a space or spacetime that has been discretised onto a lattice. Although most lattice field theories are not exactly solvable, they are of tremendous appeal because they can be studied by simulation on a computer, often using Markov chain Monte Carlo methods. One hopes that, by performing simulations on larger and larger lattices, while making the lattice spacing smaller and smaller, one will be able to recover the behavior of the continuum theory as the continuum limit is approached.
Destin de l'Universvignette|alt=Une animation du comportement supposé d'un Big Crunch.|Une animation du comportement supposé d'un Big Crunch. La question du destin de l'Univers fait partie des questions fondamentales de la cosmologie. Elle a trait à l'évolution future de l'expansion de l'Univers. Pendant longtemps elle a été focalisée sur la question de savoir si l'expansion observée actuellement se poursuivrait indéfiniment, ou bien s'interromprait pour laisser place à une phase de contraction menant au Big Crunch, un effondrement général de l'Univers, analogiquement inverse du Big Bang.
Classical unified field theoriesSince the 19th century, some physicists, notably Albert Einstein, have attempted to develop a single theoretical framework that can account for all the fundamental forces of nature – a unified field theory. Classical unified field theories are attempts to create a unified field theory based on classical physics. In particular, unification of gravitation and electromagnetism was actively pursued by several physicists and mathematicians in the years between the two World Wars.
Gluon field strength tensorIn theoretical particle physics, the gluon field strength tensor is a second order tensor field characterizing the gluon interaction between quarks. The strong interaction is one of the fundamental interactions of nature, and the quantum field theory (QFT) to describe it is called quantum chromodynamics (QCD). Quarks interact with each other by the strong force due to their color charge, mediated by gluons. Gluons themselves possess color charge and can mutually interact.
Lattice model (physics)In mathematical physics, a lattice model is a mathematical model of a physical system that is defined on a lattice, as opposed to a continuum, such as the continuum of space or spacetime. Lattice models originally occurred in the context of condensed matter physics, where the atoms of a crystal automatically form a lattice. Currently, lattice models are quite popular in theoretical physics, for many reasons. Some models are exactly solvable, and thus offer insight into physics beyond what can be learned from perturbation theory.
Gauge covariant derivativeIn physics, the gauge covariant derivative is a means of expressing how fields vary from place to place, in a way that respects how the coordinate systems used to describe a physical phenomenon can themselves change from place to place. The gauge covariant derivative is used in many areas of physics, including quantum field theory and fluid dynamics and in a very special way general relativity. If a physical theory is independent of the choice of local frames, the group of local frame changes, the gauge transformations, act on the fields in the theory while leaving unchanged the physical content of the theory.
Warm inflationIn physical cosmology, warm inflation is one of two dynamical realizations of cosmological inflation. The other is the standard scenario, sometimes called cold inflation. In warm inflation radiation production occurs concurrently with inflationary expansion. This is consistent with the conditions necessary for inflation as given by the Friedmann equations of general relativity, which simply require that the vacuum energy density dominates the energy content of the universe at time of inflation, and so does not prohibit some radiation to be present.
Background independenceBackground independence is a condition in theoretical physics that requires the defining equations of a theory to be independent of the actual shape of the spacetime and the value of various fields within the spacetime. In particular this means that it must be possible not to refer to a specific coordinate system—the theory must be coordinate-free. In addition, the different spacetime configurations (or backgrounds) should be obtained as different solutions of the underlying equations.
Organe électriquethumb|Une torpille Certains poissons électriques, comme la torpille, sont dotés d'organes électriques qui leur permettent de produire des décharges électriques de forte intensité. Ces organes sont composés de cellules électriques (dites « électroplaques », ou « électrocyte ») qui sont des cellules musculaires modifiées, et de terminaisons de neurone électromoteur cholinergique. Quand un influx nerveux arrive au niveau des terminaisons cholinergiques, elles libèrent de l'acétylcholine qui va activer des récepteurs à la surface de la membrane des électrocytes au niveau de la plaque motrice.
Catégorie préabélienneEn mathématiques, plus précisément en théorie des catégories, une catégorie préabélienne est une catégorie additive qui contient tous les noyaux et conoyaux. De manière plus détaillée, cela signifie qu'une catégorie C est pré-abélienne si: C est préadditive, c'est-à-dire enrichie sur une catégorie monoïdale de groupes abéliens (de manière équivalente, toutes les collections de morphismes d'un objet de C vers un objet de C sont des groupes abéliens et une composition de morphismes est bilinéaire) C contient tous les produits finis (de manière équivalente, tous les coproduits finis).
