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[P2 analysis] Confluent Potts projector tomography at Q→1: separate singlet, [2], and logarithmic residues #262

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@LightChainr

Motivation

The latest repository state makes the global-symmetry label itself an observable that should be differentiated, not just a name attached after the fact.

Two recent results sharpen the point:

  1. [P2 theory/analysis] Explain the missing x=17/4 spin-4 four-leg primary before attributing local H4 to thermal Q4 #257 / PR analysis: add exact Q=1 spin-4 competitor preflight #260 identifies the exact lower-dimensional four-leg spin-4 primary
V_(2,2): x=17/4, spin=-4,

and the Potts state-space analysis places its integer-shift family in the nontrivial [2] representation rather than the singlet. This gives a natural reason why an ordinary S_Q-invariant bulk anisotropy need not couple linearly to it.

  1. [P2 exact/breakthrough] Critical-manifold Q-score tomography: observe Potts representation collisions before taking Q→1 #258 constructs an exact critical-manifold Q score at Q=1, but correctly warns that
measure derivative != derivative of a Q-dependent field.

A generic-Q observable carries explicit Q dependence through its representation projector, normalization and mixing coefficients.

I propose making that missing field derivative explicit using the finite partition-algebra / categorical S_Q projectors themselves.

Conceptual shift

Instead of asking only

which Potts representation does this continuum field belong to?

construct the finite-volume generic-Q projector/invariant tensor

P_lambda(Q)

for the low-leg connectivity space and study both

P_lambda(1)

and its confluent tangent

d_Q P_lambda(Q)|_(Q=1).

At generic Q, the Potts state space is organized by S_Q representations through the partition algebra. At integer/special Q, categorical dimensions can become zero or negative and semisimplicity can fail; therefore ordinary finite-group Hilbert-space intuition is not sufficient. The correct question is whether the Gram/projector data of the analytically continued connectivity tensors develop degeneracies whose finite parts or derivatives realize the logarithmic mixing.

This is not an assertion that every projector has a pole at Q=1. Which low-leg projectors remain regular, become null, or collide should be derived exactly.

Phase A — exact low-leg Potts tensor algebra

Start with the smallest connectivity spaces relevant to the current questions:

2 marked clusters / two-leg sector,
4 marked clusters / four-leg sector.

Using the partition-algebra diagram basis, construct the generic-Q Gram matrix and the invariant-tensor/projector decomposition into the representations that actually occur, in particular

[]   singlet,
[1],
[2],
[11].

Cross-check the decomposition against the twisted-state formulas of Jacobsen--Ribault--Saleur and the invariant-tensor counting in the Potts global-symmetry bootstrap.

Record symbolically/rationally as functions of Q:

projector matrices,
Gram determinants and eigenvalues,
categorical dimensions,
projector traces,
intertwiner / tensor-product coefficients.

Then expand around Q=1.

Phase B — turn #257's selection statement into an explicit lattice projector

For the four-leg spin-4 candidate V_(2,2) use an explicitly [2]-covariant lattice insertion rather than four-arm geometry alone.

The first useful observables are

O_[2]^a(x),
<O_[2]^a(x) O_[2]^b(y)> projected to [],

and neutral three-point tensors allowed by

[2] x [2] x lambda -> [].

This gives a direct positive construction of the charged sector whose one-point singlet matrix element is absent.

Compare the resulting lattice phase/leg convention with the character-weighted V_(r,s) construction in arXiv:2604.05503 / 2510.04701. The target is not merely the x=17/4 power; it is the full [2] invariant-tensor pattern.

Phase C — exact decomposition of a Q derivative

Let a generic-Q projected observable be

O_lambda(Q) = P_lambda(Q) O_bare(Q).

Along the square-bond critical manifold, #258 supplies the exact measure score T=k+b/2 (with its bulk-even / homology-odd decomposition treated separately). Then

d_Q <O_lambda(Q)>
 = measure-score contribution
 + < (d_Q P_lambda) O_bare >
 + < P_lambda d_Q O_bare >.

This is the finite-volume version of the field-definition counterterm that the collision literature requires.

Implement this identity on tiny FK tori where direct symbolic generic-Q differentiation is possible. It would calibrate which part of a logarithmic tangent comes from

probability measure,
representation projector,
explicit operator definition.

That decomposition is substantially more informative than calling Cov(O,T) the top field.

Phase D — search for confluent projector geometry

At Q=1, examine whether two generic-Q representation tensors that are distinct for Q!=1 become linearly dependent, zero-norm or otherwise degenerate.

If so, construct basis-independent confluent data such as

rank loss of the Gram matrix,
finite normalized residues,
derivative of the projector subspace,
principal angle / wedge between colliding tensor directions,
minimal polynomial of the induced transfer action on the confluent space.

This supplies a representation-theoretic analogue of #218's eigenvector coalescence, now at the level of explicit Potts symmetry tensors.

A particularly interesting possibility is that the energy/two-cluster logarithmic pair can be recognized as a collision not only of scaling dimensions but also of categorical projector data. If that works for the known Vasseur--Jacobsen--Saleur pair, apply the same construction after the common spin-4 differential.

Phase E — connect to charged OPE spectroscopy (#250)

The normalized loop three-point constant omega_123 removes ordinary multiplicative field normalization. Combine it with the explicit Potts tensor projector:

continuum number: omega_123(Q)
representation tensor: I_{lambda1 lambda2 lambda3}(Q).

Then distinguish two kinds of Q -> 1 structure:

conformal/OPE derivative,
S_Q invariant-tensor/projector derivative.

The proposed tangent

T_123 = d_Q log omega_123 |_(1)

should be supplemented by the derivative of the categorical invariant tensor whenever the external fields carry nontrivial Potts charge.

This is especially relevant to [2] fields: a scalar-normalized structure constant does not by itself specify which invariant tensor in a multidimensional S_Q tensor-product space is being measured.

Phase F — connect to #249 minimal realization

Add the representation projector/invariant-tensor label as an instrument descriptor in the context-Hankel manifest.

Then ask separately:

rank of the singlet endpoint realization,
rank after [2]-charged instruments are admitted,
rank after Q-derivative/confluent projector instruments are admitted.

A rank increase only after charged/confluent instruments is structurally different from a third ordinary bulk scalar field.

Bold conjecture

My current risky guess is:

the leading global square-site H4 endpoint sector is genuinely singlet and therefore does not linearly see V_(2,2)_[2]; the local four-arm geometry contains strong overlap with the same four-leg conformal family only after an explicit [2] cluster-label projector is inserted. The unlabelled marked-pivotal H4 mixes singlet descendants and charged four-leg information and is therefore not itself an RG eigenoperator.

This would explain three otherwise awkward facts at once:

x=17/4 exists but does not dominate global matching,
local H4 is strong but has complicated radial flow,
charged deck/leg information disappears from scalar one-point responses.

A more radical possibility is that the Q->1 derivative of the representation projector itself contributes to the logarithmic partner. The known energy/two-cluster collision is the right exact control for deciding whether that idea is real or merely formal.

Literature anchors

  • Jacobsen--Ribault--Saleur, arXiv:2208.14298 — Potts state spaces, twisted torus partition functions, partition-algebra decomposition and S_Q representation labels.
  • Nivesvivat, arXiv:2205.09349 — Potts four-point bootstrap with explicit S_Q invariant tensors, representation spectra and fusion constraints.
  • Binder--Rychkov, arXiv:1911.07895 — categorical symmetry/Deligne-category interpretation of noninteger-rank symmetry and its preservation under RG.
  • Ang et al., arXiv:2604.05503 — exact charged loop three-point constants and lattice leg-character construction.
  • Vasseur--Jacobsen--Saleur, arXiv:1206.2312 — explicit Q->1 representation collision producing a percolation logarithmic observable.
  • Nivesvivat--Ribault, arXiv:2007.04190 — logarithmic fields as confluent/derivative limits of generic conformal representations.

Relation to current work

Scientific boundary

This is an exact/theory analysis program, not a new evidence count. Categorical dimensions at noninteger or special Q are not ordinary positive multiplicities. A negative or zero analytic dimension must not be interpreted as a literal negative/absent number of states without the full partition-algebra/categorical construction.

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