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Ivancevic_Applied-Diff-Geom

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<strong>Geom</strong>etrical Path Integrals and Their Applications 1079The corresponding minimum of potential energy is( √1 + h − 1 + 2hV min = ND− h ln 1 + √ )1 + 2h.22Mean–Field XY Model. In the case of the mean–field XY model(6.120) it is possible to show analytically that a topological change in theconfiguration space exists and that it can be related to the thermodynamicphase transition. Consider again the family M v of submanifolds of theconfiguration space defined in (6.114); now the potential energy per degreeof freedom is that of the mean–field XY model, i.e.,V(ϕ) = V (ϕ)N = J2N 2N∑i,j=1[1 − cos(ϕi − ϕ j ) ] − hN∑cos ϕ i ,where ϕ i ∈ [0, 2π]. Such a function can be considered a Morse function onM, so that, according to Morse theory, all these manifolds have the sametopology until a critical level V −1 (v c ) is crossed, where the topology of M vchanges.A change in the topology of M v can only occur when v passes througha critical value of V. Thus in order to detect topological changes in M v wehave to find the critical values of V, which means solving the equationsi=1∂ϕ i V(ϕ) = 0, (i = 1, . . . , N). (6.126)For a general potential energy function V, the solution of (6.126) would bea formidable task, but in the case of the mean–field XY model, the mean–field character of the interaction greatly simplifies the analysis, allowing ananalytical treatment of (6.126); moreover, a projection of the configurationspace onto a 2D plane is possible [Casetti et al. (1999); Casetti et al.(2003)].6.4.6 Application: Force–Field PsychodynamicsIn this section, which is written in the fashion of the above quantum brainmodelling (see subsection 6.3.8 above), we present the top level of naturalbiodynamics, using geometrical generalization of the Feynman path integral.To formulate the basics of force–field psychodynamics, we use the action–amplitude picture of the BODY ⇄ MIND adjunction:

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