M8-H duality as analog of momentum-position duality for 3-surfaces as particles (see this, this, this and this) is a central part of TGD. I have already earlier considered several variants of what the twistor lift at the level of M8 could mean. There are several questions to be answered.
Identification of the twistor spaces
What are the twistor spaces of T(M8) and T(Y4) for the M8-H dual Y4 of the space-time surfaces X4⊂ H?
- The 12-D space of light-like geodesics in M(1,7) would be the naive guess for the twistor space of M8. Now however the Minkowski metric of M8 is number theoretic and given by real part of octonionic product and 14-D G2, is the number theoretic symmetry group so that the 12-D G2/U(1)× U(1) is the natural candidate for the octonionic twistor space of M8. U(1)× U(1) has an interpretation as color Cartan algebra.
- Without further conditions, the twistor sphere defined by light-like rays at a given point of M8 is a 6-D and the space S6=G2/SU(3) is the natural identification for it. With this identification, the dimension of the total twistor space T(M8) would be 8+6=14, the dimension of G2. This does not conform with the identification as T(M8)=G2. It is also an open question whether S6 possesses the twistorially highly desirable Kähler structure.
- How could one reduce the dimension of the space of light-like rays of M8 from 6 to 4? Could the condition that the light-rays are associated with a point of M8-H dual Y4 ⊂ M8 are quaternionic, allow to achieve this. M8-H duality in its recent form indeed requires that the normal space for a given point of Y4⊂ M8 as M8-H dual of X4⊂ H is quaternionic and Minkowskian in number theoretic sense (see this). This suggests a direct connection between twistorialization and M8-H duality.
- Could one require that the light-like 8-momentum has vanishing tangential component to Y4 and is therefore quaternionic? This would replace the twistor sphere with a union of twistor spheres associated with Minkowskian mass shells p2=m2. The space of light rays would be 3- rather than 4-D and the wistor space of M8 would be 11-D rather than 12-D. One dimension is missing.
- The physical intuition suggests that the light rays do not have a momentum component in the direction of the tangent space of Y3 defining the 3-D holographic data but that they have a component tangential to Y4 in a direction normal to Y3. This would conform with non-point-likeness: by general coordinate invariance, the momentum component tangential to Y3 would not correspond to anything physical.
The additional condition would be that these light-like vectors are quaternionic. The space of allowed 8-D light-like vectors would be 4-D and the twistor space could be G2. The associativity of the dynamics at the level of M8 requires that the normal space is quaternionic and thus Minkowskian and also contains a commutative subspace. Can these two quaternionicity conditions be consistent with each other? If so, 8-D associative light-likeness respecting the 3-dimensality of holographic data implies the desired 4-dimensionality of the analog of the twistor sphere.
- The section of the twistor bundle assigned to Y4 assigns to each point of Y4 a light-like vector. If also quaternionic units are chosen in an integrable way, this would define the M8 counterpart of the H-J structure which, when mapped to H by M8-H duality, would provide the H-J structure of H.
If the selected light-like vectors have a vanishing tangential component in Y4, the light-like vectors in H are in M4. If this is not the case, the light-like vectors in M4 have also CP2 component. For instance, light-like geodesics in M4× S1, S1⊂ CP2 are possible. It therefore seems that the TGD view of twistorialization indeed makes possible the twistor description of massive particles.
Spinorial aspects of M8 twistorialization
What about the spinorial aspects of M8 twistorialization? One should generalize a) the map of the points of sphere S2 to the 2× 2 matrices defined by a bi-spinor and its dual, b) the masslessness condition as vanishing of a determinant of the analog of the quaternionic matrix and c) the coincidence relation. One should also understand how the counterparts of the electroweak couplings are represented and solve the Dirac equation in M8.
- In the case of M4, the map of massless momenta are mapped to the bispinors providing a matrix representation of quaternions in terms of Pauli sigma matrices. A possible way to achieve this is to introduce octonionic spinor structure (see this, this and this) in which massless 8-D momenta correspond to octonions, which should be associative and therefore quaternionic. This would conform with the above identification of light rays.
- Octonionic spinors, presumably complexified with i=(-1)1/2 commuting with the octonionic units, should be also defined. The map of quaternionic massless 8-momenta to the octonionic counterparts of the Pauli spin matrices representing quaternionic basis would define octonionic spinors satisfying the quaternionicity condition.
- The condition that the twistor space allows Käahler structure and has S2× S2 as fiber might leave only the product T(M8)=T(M4)× T(E4), which is consistent with M8= M4× E4. The mechanism of the dimensional reduction would be the same as in the case of H. Whether one can identify T(E4) as CP3 is quite not clear.
- Very naively, in the spinorial approach the extended twistor space C4 is replaced with C8. Division with 2-complex-dimensional planes CP2 would give Grassmannian Grc(2,8) with dimension 2× (8-2)=12, which is a complex manifold having the representation U(8)/U(2)× U(6). The fiber would be CP2. Minkowskian signature would suggest that U(6) is replaced with U(5,1) and U(8) with U(7,1).
- The number theoretic G2/U(1)× U(1) is the third possible identification but it is not clear whether it is consistent with the number theoretic M4 signature and CP2 fiber.
- The matrices defined by bi-spinor pairs associated with M4 twistors can be regarded as quaternions. The quaternionicity condition means that the octonionic spinor pairs actually reduce to M4 bi-spinor pairs on a suitable basis, which however depends on the point of Y4?
If commutative i is introduced and quaternions are not replaced with their 2× 2 matrix representations involving commuting imaginary units, a doubling of degrees of freedom takes place. Does this mean that both M4 chiralities are obtained? Could this solve the googly problem in M4?
- What happens to M8 spinors as tensor products of Minkowski spinors and electroweak spinors when the octonionic Dirac operator acts on a quaternionic subspace. The electroweak degrees of freedom do not disappear but become passive. One has 8-D complex spinors, which are enough to represent a single H-chirality if the octonionic gamma matrices, which are quaternionic at Y4, are not represented in terms of Pauli sigma matrices and i is introduced.
- The electroweak gauge potentials as induced spinor connection represent the geometric view of physics realized at the level of H. Number theoretical vision suggests that the M8 spinor connection cannot involve sigma matrices, which would be defined as commutators of octonionic units and be octonionic units themselves. Kähler coupling is however possible.
What could the form of the Kähler gauge potential be? The Kähler form should be apart from a multiplicative imaginary unit i equal to the theoretical flat metric of M8 so that the Kähler function would represent harmonic oscillator potential. The octonionic Dirac equation would have a unique coupling to the Kähler gauge potential with Kähler coupling constant absorbed to it. This would guarantee that the solutions of the modified Dirac equation in M8 have a finite norm. Presumably the solutions can be found by generalizing the procedure to solve Dirac equation in harmonic oscillator potential.
- The octonionic Dirac operator, which reduces to the quaternionic M4 Dirac operator and for the local quaternionic M4 identified as a normal space, the fermions are massless. How to solve this problem? As found, the non-vanishing M4 mass requires that the light-like M8 momentum has a component in the direction of Y4 having a natural interpretation as the analog of the square root of the Higgs field.
- Complexified octonionic spinors form a complex 8-D space, which corresponds to a single fermion chirality. Do different H chiralities emerge from the mere octonionic picture or must one introduce them in the same way in the case of H? The couplings of quarks and leptons to the induced Kähler form are different and this should be true also at the level of M8: it seems that both quarks and leptons should be introduced unless on is read consider either leptons or quarks as fundamental fermions.
- Color SU(3) acts as a number theoretic symmetry of octonions. SU(3) as an automorphism group transforms to each other different quaternionic normal spaces represented as points of CP2. This representation is realized at the level of H in terms of spinor harmonics. The idea that the low energy and higher energy models for hadron in terms of SO(4) and SU(3) symmetries are dual suggest that fermionic SO(4) harmonics in M8 could be analogous to the representation of color as spinor harmonics in CP2.
See the article Twistors and holography= holomorphy vision or the chapter with the same title.
For a summary of earlier postings see Latest progress in TGD.
For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.