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arXiv:2509.18966

Non-Lagrangian phases of matter from Wilsonian renormalization of 3D Wess-Zumino-Witten theory on Stiefel manifolds

Shouryya Ray

Published Sep 23, 2025• 0 citations
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Abstract

I study the renormalization of D-dimensional level-k Wess-Zumino-Witten theory with Stiefel-manifold target space $\mathrm{St}_{N,N-D-1} \cong \mathrm{SO}(N)/\mathrm{SO}(D+1)$, with a particular focus on $D = 3$. I investigate in particular whether such a theory admits IR-stable fixed points of the renormalization group flow. Such fixed points have been suggested to describe conformal phases of matter that do not have a known dual (super-)renormalizable Lagrangian for $N \geq 7$ in $D = 3$. They are hence of interest both from the point of view of quantum phases of matter as well as pure field theory. The $D$-dimensional expressions enable the computation, by analytic computation, of beta functions in $D = 2 + ε$, at least to first non-trivial order. In $D = 2$, a stable fixed point is found, serving a generalization of the famed $\mathrm{SU}(2)_k$ Wess-Zumino-Witten conformal field theory; it annihilates in $D = 2 + ε$ with an unstable fixed point which splits off from the Gaussian one for $ε> 0$. Although the story is thus qualitatively similar to that of SO(5) deconfined (pseudo-)criticality, for $N \geqslant 6$, the annihilation appears to occur only for $ε> 1$, suggesting the existence of a stable phase in $D = 3$. Comparisons of the scaling dimension of the lowest singlet operator are made with known results for $N = 6$, which is dual to QED$_3$ with $N_\mathrm{f} = 4$ fermion flavors. The predictions for the $N = 7$ Stiefel liquid represent to my knowledge the first computation of this kind for a Wess-Zumino-Witten theory without a known gauge theory dual.

DOI
10.48550/arxiv.2509.18966

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I study the renormalization of D-dimensional level-k Wess-Zumino-Witten theory with Stiefel-manifold target space StN,N−D−1≅SO(N)/SO(D+1)\mathrm{St}_{N,N-D-1} \cong \mathrm{SO}(N)/\mathrm{SO}(D+1)StN,N−D−1​≅SO(N)/SO(D+1), with a particular focus on D=3D = 3D=3. I investigate in particular whether such a theory admits IR-stable fixed points of the renormalization group flow. Such fixed points have been suggested to describe conformal phases of matter that do not have a known dual (super-)renormalizable Lagrangian for N≥7N \geq 7N≥7 in D=3D = 3D=3. They are hence of interest both from the point of view of quantum phases of matter as well as pure field theory. The DDD-dimensional expressions enable the computation, by analytic computation, of beta functions in D=2+εD = 2 + εD=2+ε, at least to first non-trivial order. In D=2D = 2D=2, a stable fixed point is found, serving a generalization of the famed SU(2)k\mathrm{SU}(2)_kSU(2)k​ Wess-Zumino-Witten conformal field theory; it annihilates in D=2+εD = 2 + εD=2+ε with an unstable fixed point which splits off from the Gaussian one for ε>0ε> 0ε>0. Although the story is thus qualitatively similar to that of SO(5) deconfined (pseudo-)criticality, for N⩾6N \geqslant 6N⩾6, the annihilation appears to occur only for ε>1ε> 1ε>1, suggesting the existence of a stable phase in D=3D = 3D=3. Comparisons of the scaling dimension of the lowest singlet operator are made with known results for N=6N = 6N=6, which is dual to QED3_33​ with Nf=4N_\mathrm{f} = 4Nf​=4 fermion flavors. The predictions for the N=7N = 7N=7 Stiefel liquid represent to my knowledge the first computation of this kind for a Wess-Zumino-Witten theory without a known gauge theory dual.
We suggest the possibility that the two-dimensional SU(2)k\mathrm{SU}{(2)}_{k}SU(2)k​ Wess-Zumino-Witten (WZW) theory, which has global SO(4)\mathrm{SO}(4)SO(4) symmetry, can be continued to $2+\ensuremath{\epsilon}$ dimensions by enlarging the symmetry to $\mathrm{SO}(4+\ensuremath{\epsilon})$. This is motivated by the three-dimensional sigma model with SO(5)\mathrm{SO}(5)SO(5) symmetry and a WZW term, which is relevant to deconfined criticality. If such a continuation exists, the structure of the renormalization group flows at small $\ensuremath{\epsilon}$ may be fixed by assuming analyticity in $\ensuremath{\epsilon}$. This leads to the conjecture that the WZW fixed point annihilates with a new, unstable fixed point at a critical dimensionality dc>2{d}_{c}>2dc​>2. We suggest that dc<3{d}_{c}<3dc​<3 for all kkk, and we compute dc{d}_{c}dc​ in the limit of large kkk. The flows support the conjecture that the deconfined phase transition in SU(2)\mathrm{SU}(2)SU(2) magnets is a ``pseudocritical'' point with approximate SO(5)\mathrm{SO}(5)SO(5), controlled by a fixed point slightly outside the physical parameter space.
We propose a new type of quantum liquids, dubbed Stiefel liquids, based on (2 þ 1)-dimensional nonlinear sigma models on target space SOðNÞ=SOð4Þ, supplemented with Wess-Zumino-Witten terms.We argue that the Stiefel liquids form a class of critical quantum liquids with extraordinary properties, such as large emergent symmetries, a cascade structure, and nontrivial quantum anomalies.We show that the well-known deconfined quantum critical point and Uð1Þ Dirac spin liquid are unified as two special examples of Stiefel liquids, N ¼ 5 and N ¼ 6, respectively.Furthermore, we conjecture that Stiefel liquids with N > 6 are non-Lagrangian, in the sense that under renormalization group they flow to infrared (conformally invariant) fixed points that cannot be described by any renormalizable continuum Lagrangian.Such non-Lagrangian states are beyond the paradigm of parton gauge mean-field theory familiar in the study of exotic quantum liquids in condensed matter physics.The intrinsic absence of (conventional or partonlike) mean-field construction also means that, within the traditional approaches, will be difficult to decide whether a non-Lagrangian state can actually emerge from a specific UV system (such as a lattice spin system).For this purpose we hypothesize that a quantum state is emergible from a lattice system if its quantum anomalies match with the constraints from the (generalized) Lieb-Schultz-Mattis theorems.Based on this hypothesis, we find that some of the non-Lagrangian Stiefel liquids can indeed be realized in frustrated quantum spin systems, for example, on triangular or kagome lattice, through the intertwinement between noncoplanar magnetic orders and valence-bond-solid orders.
It has been proposed that the deconfined criticality in (2+1)d(2+1)d(2+1)d---the quantum phase transition between a N\'eel antiferromagnet and a valence-bond solid (VBS)---may actually be pseudocritical, in the sense that it is a weakly first-order transition with a generically long correlation length. The underlying field theory of the transition would be a slightly complex (nonunitary) fixed point as a result of fixed points annihilation. This proposal was motivated by existing numerical results from large scale Monte Carlo simulations as well as a conformal bootstrap. However, an actual theory of such a complex fixed point, incorporating key features of the transition such as the emergent SO(5) symmetry, is so far absent. Here we propose a Wess-Zumino-Witten (WZW) nonlinear sigma model with level k=1k=1k=1, defined in $2+\ensuremath{\epsilon}$ dimensions, with target space ${S}^{3+\ensuremath{\epsilon}}$ and global symmetry $\text{SO}(4+\ensuremath{\epsilon})$. This gives a formal interpolation between the deconfined criticality at d=3d=3d=3 and the SU(2)1\text{SU}{(2)}_{1}SU(2)1​ WZW theory at d=2d=2d=2 describing the spin-1/21/21/2 Heisenberg chain. The theory can be formally controlled, at least to leading order, in terms of the inverse of the WZW level 1/k1/k1/k. We show that at leading order there is a fixed point annihilation at ${d}^{*}\ensuremath{\approx}2.77$, with complex fixed points above this dimension including the physical d=3d=3d=3 case. The pseudocritical properties such as correlation length, scaling dimensions, and the drifts of scaling dimensions as the system size increases, calculated crudely to leading order, are qualitatively consistent with existing numerics.
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It is known that the U ( 2 ) Wess-Zumino-Witten model is dual to the free fermion theory in two dimensions via non-Abelian bosonization. While it is decomposed into the S U ( 2 ) Wess-Zumino-Witten model and a free compact boson, the former is believed to be equivalent to the O ( 3 ) nonlinear sigma model with the theta term at θ = π . In this work, we reexamine this duality through the lens of nonperturbative renormalization group (RG) flow. We analyze the RG flow structure of the O ( 3 ) nonlinear sigma model with the theta term in two dimensions using the functional renormalization group. Our results reveal a nontrivial fixed point with a nonzero value of the topological coupling. The scaling dimensions (critical exponents) at this fixed point suggest the realization of a duality between the O ( 3 ) nonlinear sigma model with the theta term and the free fermion theory, indicating that these models belong to the same universality class.