Yokota theory, the invariant trace fields of hyperbolic knots and the Borel regulator map

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For a hyperbolic link complement with a triangulation, there are hyperbolicity equations of the triangulation, which guarantee the hyperbolic structure of the link complement. In this paper, we explain that the number of the essential solutions of the equations is equal to or bigger than the extension degree of the invariant trace field of the link. On the other hand, Yokota suggested a potential function of a hyperbolic knot, which gives the hyperbolicity equations and the complex volume of the knot. Applying the fact above to his theory, we explain that the potential function also gives all the values of the Borel regulator map and the complex volumes of the parabolic representations. Furthermore, we explain the maximum value of the imaginary parts of the complex volumes is the volume of the complete hyperbolic structure of the knot complement. Especially, if the number of the essential solutions of the hyperbolicity equations and the extension degree of the invariant trace field are the same, then the evaluation of all essential complex solutions of the hyperbolicity equations to the imaginary part of the potential function is the same with the Borel regulator map. We show these actually happens in the case of the twist knots.