I have been reading Witten's paper Perturbative Gauge Theory As A String Theory In Twistor Space (http://arxiv.org/pdf/hep-th/0312171v2.pdf ). This is a long paper to read.
My sense of what you describe as twistor theory based on H^2 is that H^2 ~ C^4, and of course we have a different meaning to projective spaces. The standard theory has T = C^4 with projective twistor space CP^3 = P(C^4) < --- F_12(T) --- > G_{2,4}(C). The G_{2,4}(C) = U(4)/U(2)^2, or in signatured spacetime SU(2,2)/SU(2)xSU(1,1). The quotient between SU(2,2) = SO(4,2) and SU(2)xSU(1,1) ~ SO(3,1) is the Grassmannian space of this space of 2-planes in 4-space. The quotient SO(4,2)/SO(4,1) is the AdS_5 or moduli space for the quaternion bundle. This has a relationship to G_{2,4}(C) as its quotient is with SO(3,1) вЉ‚ SO(4,1). The CP^3 is projective twistor space PT and the manifold F_{12}(T) is a five dimensional space that through this double fibration maps information in this space to CP^3.
The double fibration has the equivariant action of SL(4,C). For H^2 this action is likely replaced by SL(2,H). Both of these are dim = 15 and ~ SU(4) or SU(2,2). The structure above has to be modified in some ways. I would propose that the product of elements in the two H's is given by the Jordon product or the general product
U*V = Uв--¦V - ВЅ(U tr(V) + V tr(U)) + ВЅ(trU tr(V) - trV tr(U))I.
The Freudenthal determinant of a matrix U is det(U)I = tr[(U*U)в--¦U], which gives the eigenvalued problem
det(U - О»I) = О»^3 - О»^2Tr U - О»tr(U*U) - det(U)I = 0
This cubic involves the eigenvalues О»1, О»2, О»3 with eigen-vectors x, y, z. The determinant det(U - О»I) = (U - О»I)в--¦[(U - О»I)*(U - О»I)], where have (U - О»I)*(U - О»I) = 0, so that if U - О»I = P_О» a projector on the Fano plane then this is an orthogonality condtion. We then have for instance two projectors P_{О»1} = xx^†and P_{О»2} = yy^†so that P_{О»1}в--¦P_{О»2} = 0 as an orthogonality condition.
Given K the Jordan algebra h_n(K) = RвЉ•h_{n-1}(K)вЉ•K^n. Given T = C^4 this is h_5(C) = RвЉ•h_4(C)вЉ•C^4. By SL(4,C) ~ SL(2,H) we have a representation
h_3(H) = RвЉ•h_2(H)вЉ•H^2.
The quaternion x = (p, q) is then such that
xx^†=
|p_1p_1^†, p_1q_2^†|
|q_2p_1^†, p_2q_2^†|
as a 2x2 matrix of 2-spinors or quaternions. For this exterior product between x with positive helicity and x' with negative helicity this is a null quaternion momentum for a massless particle. Inner products may also be easily defined for + and - helicity fields. Further analysis along these lines will lead to maximal helicity violating amplitudes and the BCFW theory.
The h_3(H) is is a matrix of the form
|П†, П€|
|П€, r|
for П† \in h_2(H), П€ \in H^2 and r \in R. The two quaternions with four components defines four dimensions complex or 8 real dimensions, we have 2 + 1 dimensions from the remaining parts of the matrix, which gives the HP^{2|3} =~ CP^{4|3} coordinates (8 - 3 = 5).
The matrix U \in J3(O) is diagonalizable by the F4 group. The partition of the matrix as
U = sum_iP_i = sum_i(λ_i x_ix_i^†).
The matrix above, is a 5x5 matrix that transforms under SO(10) or SO(9,1). The SO(9) вЉ‚ SO(9), which is also a subgroup of F4. This serves to conserve the eigenvalues, and further it is a subgroup of the E6 exotic group.
Cheers LC