Epistemic status: the interaction functional is a minimal structural ansatz — not derived from a gauge principle. Defines the interaction architecture, not a complete interacting quantum theory.

From Single States to Interaction

Paper XII established single-state gradient flow: a lone configuration descends its closure functional, converging to an attractor basin that determines the particle identity. But physics requires more than isolated states — it requires interacting configurations.

The central idea of this paper: when multiple states are present, the closure landscape itself depends on the joint configuration. Each state no longer evolves independently — the presence of one deforms the basin structure experienced by the other.


The Total Closure Functional

For a multi-state configuration Ψ = (ψ1, ψ2, …, ψn), the total closure functional separates into individual and interaction terms:

Ftot(Ψ) = Σi F(ψi) + Fint(Ψ)
Sum of individual closure functionals plus an interaction term coupling the joint configuration.

Without the interaction term, the system is separable: each state evolves independently under its own closure pressure. Fint is what couples the evolution — it is the mathematical expression of interaction within the framework.


The Interaction Functional

The interaction functional decomposes into four structural components, each capturing a distinct aspect of how states influence each other:

Fint(Ψ) = λ1Iprox + λ2Ialign + λ3Icomp + λ4Ibind
Four weighted components: proximity, alignment, compatibility, and binding.
  • Proximity (Iprox) — how close the states are in state space. Interaction strength increases with proximity; distant configurations decouple.
  • Alignment (Ialign) — torsional and phase compatibility between interacting states. Aligned phases can interfere constructively; misaligned phases suppress coupling.
  • Compatibility (Icomp) — whether configurations are cooperative or incompatible. Some state pairs lower each other's closure cost; others raise it.
  • Binding (Ibind) — gap penalty on the union of supports. Rewards connected composite configurations; penalises disconnected unions.

Coupled Gradient Flow

Each state evolves under its own closure pressure plus the mutual influence of the interaction term:

i/dt = −Π(∇ψiF(ψi) + ∇ψiFint(Ψ))
Projected gradient flow: each state descends the total closure landscape, not just its own.

The projection Π keeps each state on the admissible manifold. The key structural result: the interaction term redirects gradient flow — states no longer descend toward their individual attractors, but toward joint configurations that minimise the total functional.

Stability

Monotonic descent still holds: dFtot/dt = −‖Π(∇Ftot)‖² ≤ 0. The interacting system is mathematically stable.


Interaction as Basin Deformation

This is the key interpretive insight of the paper. Without interaction, the multi-state basin structure is the product of individual basins — each state has its own attractor landscape, independent of the others.

With interaction, the basins deform. The presence of one state changes the landscape experienced by the other. Concretely:

  • Basin positions shift — attractor locations move in state space
  • Basins merge or split — previously distinct attractors can combine into one, or a single basin can fragment
  • Barriers lower or raise — transitions between basins become easier or harder
  • New joint attractors form — configurations that are not attractors for either state alone become attractors for the pair

This is what interaction means in the framework. There is no separate force carrier or mediating field — interaction is the mutual deformation of basin structure.


Binding as Joint Basin Formation

A bound configuration is a joint attractor whose total closure cost is lower than the sum of the separated parts:

Ftot(Ψ*) < Σi F(ψi*)
The joint attractor is cheaper than the separated configuration. The difference is the binding energy.

The bound state is not held together by a force pulling components inward. It exists because the joint closure landscape has a basin that is deeper than any combination of individual basins.

Binding

Binding is not a force pulling states together. It is the formation of a joint attractor whose total closure cost is lower than the separated configuration.


Scattering-Like Processes

When two states approach in state space, their basins deform. Depending on the interaction structure, several outcomes are possible — classified by what happens to the basin assignments:

Channel Basin Dynamics Outcome
Basin-preserving Basins deform but do not merge or cross States return to their original attractors after interaction
Basin-transition Interaction lowers a barrier; state crosses into a different basin States end in different attractors than they started in
Binding / fusion Basins merge into a single joint attractor Composite bound state forms
Repulsive separation Basins push apart; interaction raises barriers States are driven to greater separation in state space

Worked Examples

(a) Disconnected quark binding

Two disconnected configurations — {2,4} and {3} — interact via the binding term Ibind. The gap penalty on {2,4} is high; the union {2,3,4} is connected. The interaction deforms the basin landscape so that the joint attractor is the connected baryon configuration on {2,3,4}, with lower total closure cost than the separated pair.

(b) Compatible aligned pair

Two states with compatible torsional phases and cooperative closure structure. The alignment and compatibility terms are favourable; a weakly bound composite forms. The joint attractor is slightly deeper than the separated configuration, producing a shallow binding energy.

(c) Incompatible pair

Two states with misaligned phases and incompatible closure structure. The compatibility term raises the joint closure cost. No joint attractor forms — the interaction is repulsive. The states are driven apart in state space.


Conservative Extension

The dissipative gradient flow admits a conservative (time-reversible) extension via a Lagrangian formulation:

Ltot = ½‖Ψ̇‖² − Ftot(Ψ)
Kinetic minus potential. Time-reversible coupled oscillation on the closure landscape.

In this formulation, scattering-like processes become reversible trajectories. States oscillate in the closure landscape rather than irreversibly descending. The dissipative and conservative formulations bracket the physical dynamics from two sides.


Stated Limitations

  • No S-matrix or scattering amplitudes are computed
  • No relativistic kinematics — the framework is non-relativistic at this stage
  • No quantisation of the interaction — all dynamics are classical on state space
  • The interaction functional is an ansatz, not derived from a gauge principle
  • Coupling weights λ1–λ4 are not fixed by the framework
  • No gauge-boson exchange is derived — interaction is basin deformation, not particle exchange
  • Worked examples are schematic — illustrative, not quantitative predictions

From isolated attractors to a relational description — the framework now admits interaction.

Paper open-access. Part of the crystallisation programme at github.com/vfd-org/vfd-crystallisation.