In quantum mechanics and statistical mechanics, parastatistics is one of several alternatives to the better known particle statistics models (Bose–Einstein statistics, Fermi–Dirac statistics and Maxwell–Boltzmann statistics). Other alternatives include anyonic statistics and braid statistics, both of these involving lower spacetime dimensions. Herbert S. Green is credited with the creation of parastatistics in 1953. Formalism Consider the operator algebra of a system of N identical particles. This is a *-algebra. There is an SN group (symmetric group of order N) acting upon the operator algebra with the intended interpretation of permuting the N particles. Quantum mechanics requires focus on observables having a physical meaning, and the observables would have to be invariant under all possible permutations of the N particles. For example, in the case N = 2, R2 − R1 cannot be an observable because it changes sign if we switch the two particles, but the distance between the two particles : |R2 − R1| is a legitimate observable. In other words, the observable algebra would have to be a *-subalgebra invariant under the action of SN (noting that this does not mean that every element of the operator algebra invariant under SN is an observable). This allows different superselection sectors, each parameterized by a Young diagram of SN. In particular: For N identical parabosons of order p (where p is a positive integer), permissible Young diagrams are all those with p or fewer rows. For N identical parafermions of order p, permissible Young diagrams are all those with p or fewer columns. If p is 1, this reduces to Bose–Einstein and Fermi–Dirac statistics respectively. If p is arbitrarily large (infinite), this reduces to Maxwell–Boltzmann statistics. Quantum field theory A paraboson field of order p, where if x and y are spacelike-separated points, and if where [,] is the commutator and {,} is the anticommutator. Note that this disagrees with the spin-statistics theorem, which is for bosons and not parabosons. There might be a group such as the symmetric group Sp acting upon the φ(i)s. Observables would have to be operators which are invariant under the group in question. However, the existence of such a symmetry is not essential. A parafermion field of order p, where if x and y are spacelike-separated points, and if . The same comment about observables would apply together with the requirement that they have even grading under the grading where the ψs have odd