commit algebra
Floor 6, Les continus · introduced in Chapter 13, Orientation et charge
Which operators commute with every move at a point of the Fano plane?
At a unit of the octonions, the algebra generated by the six left multiplications by the other units, each tensored with a flip of a two-state counter, and by the counter’s sign. It is the complex Clifford algebra , a sum of two matrix algebras, and its centre is spanned by the identity and one sign, the chirality read with the parity of the number of moves.
In fix an imaginary unit and put . For each of the six imaginary units orthogonal to , and anticommutes with , hence with ; the product of the six is . These statements do not depend on the signs of the units.
So along a word of moves of the tetrahedron , each paired with the left multiplication of a unit orthogonal to and acting on , the first factor keeps the class of the spinor system while changes sign at each move: the product of the class and is reversed by every move, and after moves the preserved operator is .
By alternativity , which is for imaginary . The seven therefore generate a Clifford algebra on , whose volume element is central of square 1 and so acts as ; the product of six is . Changing the sign of a unit changes only signs.
Fix a point of the Fano plane, with unit , and the table . For the three lines through , ordered so that , put and , and on a second factor write and for the Pauli matrices. The commit algebra at is
and .
For each of the seven points: (1) the six , , generate , with commutant ; (2) the seven generators of anticommute in pairs, six square to and one to , and their product is , so is the complex Clifford algebra , of dimension 128; (3) the commutant of is its centre, , and , with central projections of rank 8; (4) , so ; (5) complex conjugation of fixes every generator and exchanges with .
(1) The six anticommute and square to , so they generate a quotient of , which is simple; on the image is all of . (2) anticommutes for , each anticommutes with , and the six multiply to . (3) On an odd number of generators the centre of the complex Clifford algebra is spanned by and the volume element, here ; since , both simple summands act. (4) , so . (5) The generators are real matrices, and is imaginary. All five were also checked for all seven points, the dimensions by ranks over a prime field and the commutants with explicit commuting elements.
On the seven anticommute and their product is , since the six multiply to and . So is a single module of , whose volume element is a scalar, and there is one sector. The commit algebra rebuilds from six of the seven and , which stands in the place of ; its volume element is then , which is not a scalar, and its two eigenspaces are the sectors.
Replacing by , with the generators for the shift and every function of the count, leaves the commutant spanned by and : an element commuting with every function of the count is , commuting with every gives , so commutes with the even products and . The parity carries all of the counter’s contribution.
(1) Each , , changes by . A function of , tensored with or with , commutes with only if it lies in , and the products generate on each eigenspace of . (2) With , for every imaginary unit, so no sends to ; does not commute with , so it is not in . (3) for every point, so the -eigenspaces of and of are isoclinic: , the sign depending on conventions.
With a further factor for the spinor, each of the two sectors has dimension 16. In the gauge in which , the sector holds , , , which is for , together with , , , which is ; the sector holds the other two combinations. Neither nor is constant on a sector.
(1) and flip the occupation of the mode ; commutation of with every forces constant, and for it forces . The products span , irreducible on each eigenspace of . (2) for . (3) If two complex structures satisfy , then ; here . All three items were also checked by computation.
At , with the quartet the -eigenspace of , put and . (1) The fifteen products , , span and commute with ; those annihilating 1 span . (2) On the -invariants have dimension 2 and the -invariants dimension 1, spanned by . (3) Every -invariant vector of is annihilated by , and .
So an element of invariant under and is unique up to scale, .
A bilinear pairing realized by operators as is symmetric for the anticommutator and antisymmetric for the commutator, so a symmetric pairing admits only the canonical anticommutation relations. On the stabilizer of in , the dicyclic group of order twelve, is irreducible with Frobenius–Schur indicator , so its invariant bilinear forms are the multiples of the antisymmetric : the pairing of the spinor alone selects no statistics.
Identify with the complex matrices and put . A tensor with for all seven is a multiple of , the tensor of the octonion norm, which is symmetric; at one point the -invariant ones are spanned by and the antisymmetric tensor of , and .
Let have symmetry under the swap of its factors and put , a tensor on the sixteen modes of . In the Fock space of these modes with exchange sign , for fermions and for bosons, the pair is nonzero if and only if . As a two-particle tensor has eigenvalue under the swap and under a rotation by of one particle, and the two agree exactly when is symmetric. So the invariant pair has a half that makes pairs only for fermions and a half only for bosons, and a pair neutral for all seven points is up to scale and makes pairs only for fermions.
. With the matrix of , neutrality reads , and the seven left multiplications generate , so for all seven points is scalar. Since , the pair depends only on the part of of symmetry , and has symmetry because is antisymmetric; the rotation by is on . Checked with Jordan–Wigner fermions and truncated bosons on the sixteen modes.
At , let and be the projections onto the plane and onto the six units orthogonal to it. The symmetric pair tensors that are -invariant and annihilated by are spanned by and , and , where . For each of the fifteen generators of , and for , the tensor is antisymmetric, and commutes with no , .
If each generation’s lepton and quark pair coefficients are equal, and the lepton and quark terms are dressed by factors that do not depend on the generation, then . If instead the second generation carries only the second structure and the third only the first, the ratio of ratios is in absolute value.
The invariant neutral tensors are spanned by the parts of and on and on the six units, and the symmetric ones are the parts of . With and , ; since commutes with , is symmetric, equal to on and on the six units. With one structure ; with two, the second generation’s quark entry carries the extra factor . The rest was computed at one point.
- Built from
- spinor systemorientation
- Objects
- the seven points
- The volume’s word
- fiber
- In the volume
- XVSpin from the Double CoverXVIThe Quartet