Isospin (isotopic spin, isobaric spin) is a physical quantity which is mathematically analogous to spin. Isospin was introduced by Werner Heisenberg to explain the fact that the strength of the strong interaction is almost the same between two protons or two neutrons as between a proton and a neutron, unlike the electromagnetic interaction which depends on the electric charge of the interacting particles. Heisenberg's idea was that protons and neutrons were essentially two states of the same particle, the nucleon, analogous to the 'up' and 'down' states of a spin-1/2 particle. The proton, for example, was analogous to the 'spin-up' state and the neutron to the 'spin-down' state. Even if one ignores charge, the proton and neutron are still not completely symmetric, the neutron is slightly more massive, and so isospin is not a perfect symmetry of the strong force. In physics, spin is an intrinsic angular momentum associated with microscopic particles. ... Werner Heisenberg Werner Karl Heisenberg (December 5, 1901 – February 1, 1976) was a celebrated German physicist and Nobel laureate, one of the founders of quantum mechanics. ... The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ... Properties In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... Electric charge is a fundamental FATTY STASHEconserved property of some subatomic particles, which determines their electromagnetic interactions. ... A state is an organized political community occupying a definite territory, having an organized government, and possessing internal and external sovereignty. ... Nucleon is the common name used in nuclear chemistry to refer to a neutron or a proton, the components of an atoms nucleus. ... In physics, spin is an intrinsic angular momentum associated with microscopic particles. ...

Isospin infinitesimal generators transform as the three-dimensional adjoint representation of SU(2). The generators of isospin are described by Pauli matrices. In the original formulation of Yang-Mills theory, protons and neutrons were described as two components of an isospin doublet, belonging to the fundamental representation of SU(2), and interacting by means of the SU(2) gauge bosons. In mathematics, a Lie group is an analytic real or complex manifold that is also a group such that the group operations multiplication and inversion are analytic maps. ... The adjoint representation of a Lie group G is the linearized version of the action of G on itself by conjugation. ... In mathematics, the special unitary group of degree n is the group of n by n unitary matrices with determinant 1 and entries from the field C of complex numbers, with the group operation that of matrix multiplication. ... The Pauli matrices are a set of 2 × 2 complex Hermitian matrices developed by Pauli. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... Properties In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Categories: Stub ... In mathematics, a fundamental representation is a representation of a mathematical structure, such as a group, that satisfies the following condition: All other irreducible representations of the group can be found in the tensor products of the fundamental representation with many copies of itself. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ...

In the framework of the Standard Model, isospin invariance of the strong interaction is a result of the fact that particles differing only in the replacement of an up quark for a down quark (such as protons (uud) and neutrons (udd)) behave the same, since strong interactions are independent of the flavor of particles. Thus, isospin invariance appears as a consequence of the flavor invariance of strong interactions. Isospin invariance is absent in electromagnetic and weak interactions since they do depend on quark flavour. The Standard Model of Fundamental Particles and Interactions The Standard Model of particle physics is a theory which describes the strong, weak, and electromagnetic fundamental forces, as well as the fundamental particles that make up all matter. ... Invariant may have meanings invariant (computer science), such as a combination of variables not altered in a loop invariant (mathematics), something unaltered by a transformation invariant (music) invariant (physics) conserved by system symmetry This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... In particle physics, flavor is a property of a fermion that identifies it, a label that specifies the name of the particle. ... A particle is In particle physics, a basic unit of matter or energy. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ...