Handful of problems with a common resolution
Theory building could be compared to pattern recognition or to a solving a crossword puzzle. It is essential to make trials, even if one is aware that they are probably wrong. When stares long enough to the letters which do not quite fit, one suddenly realizes what one particular crossword must actually be and it is soon clear what those other crosswords are. In the following I describe an example in which this analogy is rather concrete. Let us begin by listing the problems.
 The condition that modified Dirac action allows conserved charges leads to the condition that the symmetries in question give rise to vanishing second variations of Kähler action. The interpretation is as quantum criticality and there are good arguments suggesting that the critical symmetries define an infinitedimensional superconformal algebra forming an inclusion hierarchy related to a sequence of symmetry breakings closely related to a hierarchy of inclusions of hyperfinite factors of types II_{1} and III_{1}. This means an enormous generalization of the symmetry breaking patterns of gauge theories.
There is however a problem. For the translations of M^{4} the resulting fermionic charges vanish. The trial for the crossword in absence of nothing better would be the following argument. By the abelianity of these charges the vanishing of quantal representation of fourmomentum is not a problem and that classical representation for fourmomentum or the representation coming from SuperVirasoro representations is enough.
 Irrespective of whether the 4D modified Dirac action or its 3dimensional dimensional reduction defines the propagator, it seems impossible to obtain a stringy propagator without adding it as a kind of mass insertion. A second trial for a crossword which does not look very convincing. This is certainly a problem at the level of formalism since stringy picture follows in finite measurement resolution from the slicing of spacetime sheets with string world sheets.
 Quantum classical correspondence requires that the geometry of the spacetime sheet should correlate with the quantum numbers characterizing positive (negative) energy part of the quantum state. One could argue that by multiplying WCW spinor field by a suitable phase factor depending on charges of the state, the correspondence follows from stationary phase approximation. Also this crossword looks unsatisfactory.
 In quantum measurement theory classical macroscopic variables identified as degrees of freedom assignable to the interior of the spacetime sheet correlate with quantum numbers. Stern Gerlach experiment is an excellent example of the situation. The generalization of the imbedding space concept by replacing it with a book like structure implies that imbedding space geometry at given page and for given causal diamond (CD) carries information about the choice of the quantization axes (preferred plane M^{2} of M^{4} resp. geodesic sphere of CP_{2} associated with singular covering/factor space of CD resp. CP_{2} ). This is a big step but not enough. Modified Dirac action as such does not seem to provide any hint about how to achieve this correspondence. One could even wonder whether dissipative processes characterizing the outcome of quantum jump sequence should have spacetime correlate. How to achieve this? There are no guesses for the crosswords here.
Each of these problems makes one suspect that something is lacking from the modified Dirac action: there should be a manner to feed information about quantum numbers of the state to the modified Dirac action in turn determining vacuum functional as an exponent Kähler function identified as Kähler action for the preferred extremal assumed to be dictated by by quantum criticality and equivalently by hyperquaternionicity.
This observation leads to what might be the correct question. Could a general coordinate invariant and Poincare invariant modification of the modified Dirac action consistent with the vacuum degeneracy of Kähler action allow to achieve this information flow somehow? This seems to be possible. In the following I proceed step by step by improving the trial to get the final result.
1. The first guess
The idea is simple: add to the modified Dirac action a source term which is analogous to the Dirac action in M^{4}×CP_{2}.
 The additional term would be essentially the analog of ordinary Dirac action at the imbedding space level.
S_{int}= Σ_{A}Q_{A}∫Ψbar g^{AB} j_{Bα} Γ^{α}Ψ g^{1/2}d^{4}x ,
g_{AB}= j_{A}^{k}h_{kl}j_{B}^{l} ,
g^{AB}g_{BC}=δ^{A}_{C} ,
j_{Bα}=j_{B}^{k}h_{kl}∂_{α}h^{l}.
The gamma matrices in question are modified gamma matrices defined by Kähler action with possible instanton term included. The sum is over isometry charges Q_{A} interpreted as quantal charges and j^{Ak} denotes the Killing vector field of the isometry. g^{AB} is the inverse of the tensor g_{AB} defined by the local inner products of Killing vectors fields in M^{4} and CP_{2}. The spacetime projections of the Killing vector fields j_{Bα} have interpretation as classical color gauge potentials in the case of SU(3). In M^{4} degrees of freedom j_{Bα} reduce to the gradients of linear M^{4} coordinates in case of translations.
 An important restriction is that by fourdimensionality of M^{4} and CP_{2} the rank of g_{AB} is 4 so that g^{AB} exists only when one considers only four conserved charges. In the case of M^{4} this is achieved by a restriction to translation generators Q_{A}=p_{A}. g_{AB} reduces to Minkowski metric and Killing vector fields are constants. The Cartan subalgebra could be however replaced by any four commuting charges in the case of Poincare algebra. In the case of SU(3) one must restrict the consideration either to U(2) subalgebra or its complement. CP_{2}=SU(3)/SU(2) decomposition would suggest the complement as the correct choice. One can indeed build the generators of U(2) as commutators of the charges in the complement.
 The added term containing quantal charges must make sense in the modified Dirac equation. This requires that the physical state is an eigenstate of momentum and color charges. This allows only color hypercharge and color isospin so that there is no hope of obtaining exactly the stringy formula for the propagator. The modified Dirac operator is given by
D_{tot}= D+ D_{int}= Γ^{α}D_{α}+ Σ_{A}Q_{A}g^{AB} j_{Bα}Γ^{α} .
The conserved fermionic isometry currents are
J^{Aα}= Σ_{B}Q_{B}Ψbar g^{BC} j_{C}^{k}h_{kl}j_{A}^{l}Γ^{α}Ψ
=Q_{A}Ψbar Γ^{α}Ψ .
Here the sum is restricted to a Cartan subalgebra of Poincare group and color group.
2. Does one obtain stringy propagator?
Before trying to answer to the question whether one really obtains stringy propagator one must define what one means with "stringy propagator".
 The first guess would be that the added term corresponds to Q_{A}γ^{A} involving sum over momenta and color charges analogous to p_{A}γ^{A} term in super generator G_{0} and the modified Dirac operator D=Γ^{α}D_{α} corresponds to the analog of superKac Moody contribution. Here Γ^{α} denotes modified gamma matrix defined by Kähler action. I have considered this option earlier and the detailed analysis shows that the generalized eigenvalues of the 3D modified Dirac operator should behave like n^{1/2}. This ad hoc assumption does not make this option convincing.
 Could one consider a generalization of the additional term to include also charges associated with Super KacMoody algebra acting on lightlike 3surfaces? The first problem is that the matrix g_{AB} is invertible only for four vector fields so that one should give up the assumption that charges are conserved. Second problem is that super generators carry fermion number and it seems impossible to define bosonic counterparts for them.
The next question is "What do we really need?". Only the information about quantum numbers of quantum state in superconformal representation at partonic 2surface must be feeded to the propagator. The minimum of this kind is information about isometry charges: that is conserved fourmomentum and color quantum numbers. This observation inspires the third guess. All that is needed is that the eigenvalue of p_{A} belongs to the mass shell defined by Super Virasoro conditions at partonic 2surface. Same applies to the eigenvalues of color hypercharge and isospin. Let us forget for a moment electroweak quantum numbers and look what this gives.
 The modified Dirac operator D would take the role of p_{A}γ^{A} which looks quite a reasonable generalization and that added term carries information about the momentum and color quantum numbers.
 One can avoid the difficulties due to the fact that G_{n} carry fermion number and just the relevant information about states of Super Virasoro representation is feeded to the modes and spectrum of the modified Dirac equation and to the classical spacetime physics defined by the exponent of Kähler action which must receive an additional term coupling it to isometry charges.
 The modified Dirac operator D+D_{int} would annihilate the spinor modes in the interior of the spacetime surface expect at the lightlike 3surfaces or partonic 2surfaces at the ends of lightlike 3surface serving as sources. This gives to the induced spinor field additional terms expressible in terms of the stringy propagator. The propagator would not have exactly stringy character  in particular, only the color hyper charge and isospin appear in it but there is no absolute need for this. What is essential is that the information about mass and color quantum numbers of the state of superconformal representation is feeded into the spacetime physics.
 D_{int} represents also a mass term in the modified Dirac equation so that particle massivation has a spacetime correlate. For instance, the mass calculated by padic thermodynamics makes itself visible at the level of classical physics.
3. Should one assume that the source term is almost topological?
Kähler function contains besides real part also imaginary part which does not however contribute to the configuration space metric since it is induced by instanton term assignable to Kähler action and corresponding modified Dirac action. The CP breaking term is unavoidable in the previous scenario and is expected to relate to the small CP breaking of particle physics and to the generation of matter antimatter asymmetry. It is not completely clear what the situation is in the recent case.
 The most general option is that the modified gamma matrices appearing in the added term could correspond to a sum of modified gamma matrices assignable to Kähler action and its instanton counterpart.
 One can also consider the analog ChernSimons term with 3D modified gamma matrices defined by ChernSimons action and assigned to the lightlike wormhole throats at which the induced metric changes its signature from Euclidian to Minkowskian. Wormhole throats define the lines of generalized Feynman diagrams so that the assignment of 3D stringy propagator with them looks sensible and conforms with quantum holography. Instanton action reduces to ChernSimons action assignable to wormhole throats but it is not clear whether the instanton term in Dirac action and its counterpart involving coupling to isometry charges are subject to a similar reduction.
There is support for ChernSimons option. In the case of Kähler action the dimensional reduction of the modified Dirac operator at wormhole throats is problematic because the determinant of the induced 4metric vanishes: the dimensional reduction of D to D_{3} can be defined only through a limiting procedure (this is however nothing unheardof: in AdS/CFT correspondence similar situation is encountered). For ChernSimons action situation is different and it defines modified gamma matrices and couplings to isometry charges are welldefined.
A careful consideration of the CP breaking effects predicted by various options should make it possible to make a unique choice.
4. The definition of Dirac determinant and the additional term in Kähler action
The modification forces also to reconsider the definition of the Dirac determinant.
 The earlier definition was based on the slicing of spacetime sheets by 3D lightlike surfaces and dimensional reduction to 3D Dirac operator D_{3} with Dirac determinant identified as a product of generalized eigenvalues of D_{3}. This definition generalizes to the recent context and implies that instead of massless particle one has massive particle carrying also other quantum numbers.
 The interaction term induced to Kähler action should be consistent with vacuum degeneracy of Kähler action. The interaction term of form
L_{int}= C(m^{2},I_{3},Y) Q_{A}g^{AB}j_{Bα} (J^{α}_{K}+iJ^{α}_{I})(g_{4})^{1/2}
satisfies this condition. The coefficient C(m^{2},I_{3},Y) can depend on mass and color charges. J^{α}_{K} and J^{α}_{I} denote Kähler current and instanton current respectively. 3D ChernSimons term is equivalent with instanton term.
This term is not the most general possible. One can add also couplings to conserved isometry currents as well as to currents whose existence is guaranteed by quantum criticality. For these currents only the covariant divergence vanishes. This would support the interpretation in terms of a measurement interaction feeding information to classical spacetime physics about the eigenvalues of the observables of the measured system. The resulting field equations remained second order partial differential equations since the second order partial derivatives appear only linearly in the added terms.
 The CP breaking term in the modified Dirac equation means a breaking of time reflection symmetry at the level of fundamental physics. The vision is that the classical nondeterminism of Kähler action allows to have spacetime correlates for quantum jumps sequences and therefore also for dissipation. This motivates the question whether the CP breaking term could give rise to dissipative effects allowing description in terms of the coupling of the conserved charges to Kähler current and to conserved isometry currents.
5. A connection with quantum measurement theory
It is encouraging that isometry charges and also other charges could make themselves visible in the geometry of spacetime surface as they should by quantum classical correspondence. This suggests the interpretation in terms of quantum measurement theory.
 The interpretation resolves the problem caused by the fact that the choice of the commuting isometry charges is not unique. Cartan algebra corresponds naturally to the measured observables. For instance, one could choose the Cartan algebra of Poincare group to consist of energy and momentum, angular momentum and boost (velocity) in particular direction as generators of the Cartan algebra of Poincare group. In fact, the choices of a preferred plane M^{2} subset M^{4} and geodesic sphere S^{2} subset CP_{2} allowing to fix the measurement subalgebra to a high degree are implied by the replacement of the imbedding space with a book like structure forced by the hierarchy of Planck constants. Therefore the hierarchy of Planck constants seems to be required by quantum measurement theory. One cannot overemphasize the importance of this connection.
 What about the spacetime correlates of electroweak charges? The earlier proposal explains this correlation in terms of the properties of quantum states: the coupling of electroweak charges to ChernSimons term could give the correlation in stationary phase approximation. It would be however very strange if the coupling of electroweak charges with the geometry of the spacetime sheet would not have the same universal description based on quantum measurement theory as isometry charges have.
 The hint as how this description could be achieved comes from a long standing unanswered question motivated by the fact that electroweak gauge group identifiable as the holonomy group of CP_{2} can be identified as U(2) subgroup of color group. Could the electroweak charges be identified as classical color charges? This might make sense since the color charges have also identification as fermionic charges implied by quantum criticality. Could electroweak charges be only represented as classical color charges by mapping them to classical color currents in the measurement interaction term in the modified Dirac action? At least this question might make sense.
 It does not however make sense to couple both electroweak and color charges to the same fermion current. There are also other fundamental fermion currents which are conserved. All the following currents are conserved.
J^{α}=Ψbar OΓ^{α}Ψ ,
where O belongs to the set {1,J== J_{kl}Σ^{kl},Σ_{AB}, Σ_{AB}J} .
Here J_{kl} is the covariantly constant CP_{2} Kähler form and Σ_{AB} is the (also covariantly) constant sigma matrix of M^{4} (flatness is absolutely essential).
 Electromagnetic charge can be expressed as a linear combination of currents corresponding to O=1 and O=J and vectorial isospin current corresponds to J. It is natural to couple of electromagnetic charge to the the projection of Killing vector field of color hyper charge and coupling it to the current defined by O_{em}=a+bJ. This allows to interpret the puzzling finding that electromagnetic charge can be identified as anomalous color hypercharge for induced spinor fields made already during the first years of TGD. There exist no conserved axial isospin currents in accordance with CVC and PCAC hypothesis which belong to the basic stuff of the hadron physics of old days.
 There is also an infinite variety of conserved currents obtained as the quantum critical deformations of the basic fermion currents identified above. This would allow in principle to couple an arbitrary number of observables to the geometry of the spacetime sheet by mapping them to Cartan algebras of Poincare and color group for a particular conserved quantum critical current. Quantum criticality would therefore make possible classical spacetime correlates of observables necessary for quantum measurement theory.
 Note that various coupling constants would appear in the couplings. Quantum criticality should determine the spectrum of these couplings.
 Quantum criticality implies fluctuations in long length and time scales and it is not surprising that quantum criticality is needed to produce a correlation between quantal degrees of freedom and macroscopic degrees of freedom. Note that quantum classical correspondence can be regarded as an abstract form of entanglement induced by the entanglement between quantum charges Q_{A} and fermion number type charges assignable to zero modes.
 Spacetime sheets can have several wormhole contacts so that the interpretation in terms of measurement theory coupling short and long length scales suggests that the measurement interaction terms are localizable at the wormhole throats. This would favor ChernSimons term or possibly instanton term if reducible to ChernSimons terms. The breaking of CP and T might relate to the fact that state function reductions performed in quantum measurements indeed induce dissipation and breaking of time reversal invariance.
 The experimental arrangement quite concretely splits the quantum state to a quantum superposition of spacetime sheets such that each eigenstate of the measured observables in the superposition corresponds to different spacetime sheet already before the realization of state function reduction. This relates interestingly to the question whether state function reduction really occurs or whether only a branching of wave function defined by WCW spinor field takes place as in multiverse interpretation in which different branches correspond to different observers. TGD inspired theory consciousness requires that state function reduction takes place. Maybe multiversalist might be able to find from this picture support for his own beliefs.
 One can argue that "free will" appears not only at the level of quantum jumps but also as the possibility to select the observables appearing in the modified Dirac action dictating in turn the Kähler function defining the Kähler metric of WCW representing the "laws of physics". This need not to be the case. The choice of CD fixes M^{2} and the geodesic sphere S^{2}: this does not fix completely the choice of the quantization axis but by isometry invariance rotations and color rotations do not affect Kähler function for given CD and for a given type of Cartan algebra. In M^{4} degrees of freedom the possibility to select the observables in two manners corresponding to linear and spherical Minkowski coordinates could imply that the resulting Kähler functions are different. The corresponding Kähler metrics do not differ if the real parts of the Kähler functions associated with the two choices differ by a term f(Z)+(f(Z))^{*}, where Z denotes complex coordinates of WCW and ^{*} complex conjugation, the Kähler metric remains the same. The holomorphic function f can depend also on zero modes. If this is the case then one can allow in given CD superpositions of WCW spinor fields for which the measurement interactions are different. This condition is expected to pose nontrivial constraints on the measurement action and quantize coupling parameters appearing in it.
6. New view about gravitational mass and matter antimatter asymmetry
The physical interpretation of the additional term in modified Dirac action forces quite a radical revision of the ideas about matter and antimatter.
 The term p_{A}∂_{α}m^{A} contracted with the fermion current is analogous to a gauge potential coupling to fermion number. Since the additional terms in the modified Dirac operator induce stringy propagation, a natural interpretation of the coupling to the induced spinor fields is in terms of gravitation. One might perhaps say that the measurement of four momentum induces gravitational interaction. Besides momentum components also color charges take the role of gravitational charges. As a matter fact, any observable takes this role via coupling to the projections of Killing vector fields of Cartan algebra. The analogy of color interactions with gravitational interactions is indeed one of the oldest ideas in TGD.
 One could wonder whether the two terms in the modified Dirac equation be analogous to Einstein tensor and energy momentum tensor in Einstein's equations. Coset construction in which gravitational and inertial fourmomenta are replaced by supersymplectic and super KacMoody algebras does not support this idea.
 The coupling to fourmomentum is through fermion number (both quark number and lepton number). For states with a vanishing fermion number isometry charges therefore vanish. In this framework matter antimatter asymmetry would be due to the fact that matter (antimatter) corresponds to positive (negative) energy parts of zero energy states for massive systems so that the contributions to the net gravitational fourmomentum are of same sign. Antimatter would be unobservable to us because it resides at negative energy spacetime sheets. As a matter fact, I proposed already years ago that gravitational mass is magnitude of the inertial mass but gave up this idea.
 Bosons do not couple at all to gravitation if they are purely local bound states of fermion and antifermion at the same spacetime sheet (say represented by generators of super conformal KacMoody algebra). Therefore the only possible identification of gauge bosons is as wormhole contacts. If the fermion and antifermion at the opposite throats of the contact correspond to positive and negative energy states the net energy receives a positive contribution from both sheets. If both correspond to positive (negative) energy the contributions to the net fourmomentum have opposite signs.
For background and more reader friendly formulas see the section "Handful of problems with a common solution" of the new chapter Does the modified Dirac action define the fundamental variational principle?.
