**Is the cosmological constant really understood?**

The interpretation of the coefficient of the volume term as cosmological constant has been a longstanding interpretational issue and caused many moments of despair during years. The intuitive picture has been that cosmological constant obeys p-adic length scale scale evolution meaning that Λ would behave like 1/L_{p}^{2}= 1/p≈ 1/2^{k}.

This would solve the problems due to the huge value of Λ predicted in GRT approach: the smoothed out behavior of Λ would be Λ∝ 1/a^{2}, a light-cone proper time defining cosmic time, and the recent value of Λ - or rather, its value in length scale corresponding to the size scale of the observed Universe - would be extremely small. In the very early Universe - in very short length scales - Λ would be large.

It has however turned out that I have not really understood how this evolution could emerge! Twistor lift seems to allow only a very slow (logarithmic) p-adic length scale evolution of Λ. Is there any cure to this problem?

- The magnetic energy decreases with the area of string like 1/p≈ 1/2
^{k}, where p defines the transversal length scale of the flux tube. Volume energy (magnetic energy associated with the twistor sphere) is positive and increases like S. The sum of these has minimum for certain radius of flux tube determined by the value of Λ. Flux tubes with quantized flux would have thickness determined by the length scale defined by the density of dark energy: L∼ ρ_{vac}^{-1/4}, ρ_{dark}= Λ/8π G. ρ_{vac}∼ 10^{-47}GeV^{4}(see this) would give L∼ 1 mm, which would could be interpreted as a biological length scale (maybe even neuronal length scale).

- But can Λ be very small? In the simplest picture based on dimensionally reduced 6-D Kähler action this term is not small in comparison with the Kähler action! If the twistor spheres of M
^{4}and CP_{2}give the same contribution to the induced Kähler form at twistor sphere of X^{4}, this term has maximal possible value!

The original discussions treated the volume term and Kähler term in the dimensionally reduced action as independent terms and Λ was chosen freely. This is however not the case since the coefficients of both terms are proportional to 1/α

_{K}^{2}S, where S is the area of the twistor sphere which is same for the twistor spaces of M^{4}and CP_{2}if CP_{2}size defines the only fundamental length scale. I did not even recognize this mistake.

- The induction of the twistor structure by dimensional reduction involves the identification of the twistor spheres S
^{2}of the geometric twistor spaces T(M^{4})= M^{4}× S^{2}(M^{4}) and of T_{CP2}having S^{2}(CP_{2}) as fiber space. What this means that one can take the coordinates of say S^{2}(M^{4}) as coordinates and imbedding map maps S^{2}(M^{4}) to S^{2}(CP_{2}). The twistor spheres S^{2}(M^{4}) and S^{2}(CP_{2}) have in the minimal scenario same radius R(CP_{2}) (radius of the geodesic sphere of CP_{2}. The identification map is unique apart from SO(3) rotation R of either twistor sphere. Could one consider the possibility that R is not trivial and that the induced Kähler forms could almos cancel each other?

- The induced Kähler form is sum of the Kähler forms induced from S
^{2}(M^{4}) and S^{2}(CP_{2}) and since Kähler forms are same apart from a rotation in the common S^{2}coordinates, one has J_{ind}= J+R(J), where R denotes the rotation. The sum is J_{ind}=2J if the relative rotation is trivial and J_{ind}=0 if R corresponds to a rotation Θ→ Θ+π changing the sign of J= sin(Θ)dΘ ∧dΦ.

- Could p-adic length scale evolution for Λ correspond to a sequence of rotations - in the simplest case Θ → Θ + Δ
_{k}Θ taking gradually J from 2J at very short length scales to J=0 corresponding to Δ_{∞}Θ=π at very long length scales? A suitable spectrum for Δ_{k}(Θ) could reproduce the proposal Λ ∝ 2^{-k for Λ. } - One can of course ask whether the resulting induced twistor structure is acceptable. Certainly it is not equivalent with the standard twistor structure. In particular, the condition J
^{2}= -g is lost. In the case of induced Kähler form at X^{4}this condition is also lost. For spinor structure the induction guarantees the existence and uniqueness of the spinor structure, and the same applies also to the induced twistor structure being together with the unique properties of twistor spaces of M^{4}and CP_{2}the key motivation for the notion.

- Could field equations associated with the dimensional reduction allow p-adic length scale evolution in this sense?

- The sum J+R(J) defining the induced Kähler form in S
^{2}(X^{4}) is covariantly constant since both terms are covariantly constant by the rotational covariance of J.

- The imbeddings of S
^{2}(X^{4}) as twistor sphere of space-time surface to both spheres are holomorphic since rotations are represented as holomorphic transformations. This in turn implies that the second fundamental form in complex coordinates is a tensor having only components of type (1,1) and (-1,-1) whereas metric and energy momentum tensor have only components of type (1,-1) and (-1,1). Therefore all contractions appearing in field equations vanish identically and S^{2}(X^{4}) is minimal surface and Kähler current in S^{2}(X^{4}) vanishes since it involves components of the trace of second fundamental form. Field equations are indeed satisfied.

- The solution of field equations becomes a family of space-time surfaces parametrized by the values of the cosmological constant Λ as function of S
^{2}coordinates satisfying Λ/8π G = ρ_{vac}=J∧(*J)(S^{2}). In long length scales the variation range of Λ would become arbitrary small.

- The sum J+R(J) defining the induced Kähler form in S
- If the minimal surface equations solve separately field equations for the volume term and Kähler action everywhere apart from a discrete set of singular points, the cosmological constant affects the space-time dynamics only at these points. The physical interpretation of these points is as seats of fundamental fermions at partonic 2-surface at the ends of light-like 3-surfaces defining their orbits (induced metric changes signature at these 3-surfaces). Fermion orbits would be boundaries of fermionic string world sheets.

One would have family of solutions of field equations but particular value of Λ would make itself visible only at the level of elementary fermions by affecting the values of coupling constants. p-Adic coupling constant evolution would be induced by the p-adic coupling constant evolution for the relative rotations R for the two twistor spheres. Therefore twistor lift would not be mere manner to reproduce cosmological term but determine the dynamics at the level of coupling constant evolution.

- What is nice that also Λ=0 option is possible. This would correspond to the variant of TGD involving only Kähler action regarded as TGD before the emergence of twistor lift. Therefore the nice results about cosmology obtained at this limit would not be lost.

For a summary of earlier postings see Latest progress in TGD.

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