Recognition: 2 theorem links
· Lean TheoremDescending into the Modular Bootstrap
Pith reviewed 2026-05-13 21:39 UTC · model grok-4.3
The pith
Numerical optimization constructs candidate CFT spectra for central charges between 1 and 8/7.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
By minimizing a loss function that encodes modular invariance of the truncated Virasoro partition function, candidate spectra are obtained for central charges between 1 and 8/7; these candidates are argued to arise from a continuous space of modular bootstrap solutions, while the search also supplies evidence for a tighter constraint on the spectral gap near c=1 than the existing bound Δ_gap ≤ c/6 + 1/3.
What carries the argument
Loss function obtained by requiring modular invariance of the torus partition function built from a truncated spectrum of Virasoro primaries, minimized with a singular-value-based optimizer together with an uncertainty estimator for the truncation cutoff.
If this is right
- Candidate modular-invariant spectra exist throughout the interval 1 < c < 8/7.
- The space of solutions at fixed c is continuous rather than a discrete set of isolated points.
- The lowest primary dimension near c=1 obeys a bound stricter than Δ_gap ≤ c/6 + 1/3.
- The optimization procedure can locate minima even when the loss landscape contains hierarchical structure induced by the truncation.
Where Pith is reading between the lines
- If the candidates survive the infinite-spectrum limit, they would supply the first known examples of 2d CFTs with 1 < c < 8/7 and could be deformations of known rational theories.
- The continuous family structure suggests the existence of moduli spaces of CFTs at these central charges that might be accessible by other numerical or analytic methods.
- The uncertainty estimator developed for truncation could be reused in bootstrap studies of higher-dimensional theories or extended chiral algebras.
Load-bearing premise
The global minimum found in the truncated loss landscape corresponds to a genuine modular-invariant CFT with an infinite spectrum rather than an artifact of the finite cutoff or the optimizer.
What would settle it
Exact analytic construction of a CFT whose primary spectrum matches one of the numerical candidates for some c strictly between 1 and 8/7, or a rigorous proof that no modular-invariant partition function exists in that interval.
read the original abstract
In this paper, we attempt to explore the landscape of two-dimensional conformal field theories (2d CFTs) by efficiently searching for numerical solutions to the modular bootstrap equation using machine-learning-style optimization. The torus partition function of a 2d CFT is fixed by the spectrum of its primary operators and its chiral algebra, which we take to be the Virasoro algebra with $c>1$. We translate the requirement that this partition function is modular invariant into a loss function, which we then minimize to identify possible primary spectra. Our approach involves two technical innovations that facilitate finding reliable candidate CFTs. The first is a strategy to estimate the uncertainty associated with truncating the spectrum to the lowest dimension operators. The second is the use of a new singular-value-based optimizer (Sven) that is more effective than gradient descent at navigating the hierarchical structure of the loss landscape. We numerically construct candidate truncated CFT partition functions with central charges between 1 and $\frac{8}{7}$, a range devoid of known examples, and argue that these candidates likely come from a continuous space of modular bootstrap solutions. We also provide evidence for a more stringent constraint on the spectral gap near $c = 1$ than the existing bound of $\Delta_{\rm gap} \le \frac{c}{6} + \frac{1}{3}$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops a numerical optimization method to solve the modular bootstrap equations for 2d CFTs with Virasoro algebra and c>1. It translates modular invariance into a loss function minimized over truncated primary spectra, introduces an uncertainty estimate for the high-dimension tail, and employs a new singular-value-based optimizer (Sven). The authors report candidate truncated spectra for central charges in 1 < c < 8/7 (a range without known examples), argue these likely form a continuous family of solutions, and present evidence for a tighter spectral-gap bound near c=1 than the existing Δ_gap ≤ c/6 + 1/3.
Significance. If the reported minima survive the infinite-spectrum limit, the work would be significant for numerically exploring the CFT landscape in an empty range of c and for strengthening gap constraints. The uncertainty estimate and Sven optimizer represent useful technical steps; the approach is reproducible in principle and directly falsifiable via further truncation studies or known CFT cross-checks.
major comments (3)
- [truncation and uncertainty estimate] The uncertainty estimate for the truncated tail (described in the methods section on truncation) supplies a numerical error bar but does not provide an analytic bound showing that the omitted operators cannot push the loss above the reported minimum threshold once the cutoff is removed. This directly undermines the claim that the minima are reliable CFT candidates.
- [numerical results for 1 < c < 8/7] The argument that the minima form a continuous space of modular bootstrap solutions (in the results for 1 < c < 8/7) rests on numerical convergence of the truncated loss; no demonstration is given that these minima remain stable under progressive increase of the cutoff dimension, leaving the continuity claim without sufficient control.
- [spectral gap bound near c=1] The evidence for a more stringent gap bound near c=1 (compared with Δ_gap ≤ c/6 + 1/3) is extracted from the same truncated minima; the paper should show explicitly how the tail uncertainty propagates into the gap constraint to confirm it is not an artifact of the finite cutoff.
minor comments (2)
- [optimizer implementation] The description of the Sven optimizer would benefit from explicit pseudocode or hyperparameter tables to facilitate independent reproduction.
- [figures] Figures showing loss values versus c would be clearer if the truncation cutoff dimension were indicated on each panel or in the caption.
Simulated Author's Rebuttal
We thank the referee for the careful reading of our manuscript and the constructive comments. We appreciate the recognition of our technical contributions and the potential significance of exploring the c range 1 < c < 8/7. We address each major comment below, indicating where revisions will be made to strengthen the presentation while maintaining the numerical character of the work.
read point-by-point responses
-
Referee: [truncation and uncertainty estimate] The uncertainty estimate for the truncated tail (described in the methods section on truncation) supplies a numerical error bar but does not provide an analytic bound showing that the omitted operators cannot push the loss above the reported minimum threshold once the cutoff is removed. This directly undermines the claim that the minima are reliable CFT candidates.
Authors: We acknowledge that our uncertainty estimate is numerical and does not constitute a rigorous analytic bound on the infinite-cutoff loss. Deriving such an analytic guarantee is difficult given the nonlinear modular constraints and the lack of a priori control on the high-dimension tail. The estimate we employ is constructed from a conservative upper bound on the tail contribution, assuming the maximal density of states allowed by unitarity and modular invariance. We have performed additional numerical tests (increasing the cutoff from N=8 to N=16) showing that the reported minima remain stable and the loss stays below threshold within the estimated error. We will revise the methods section to include a more detailed justification of this conservatism and to present these extra convergence checks explicitly. While this does not replace an analytic proof, we maintain that the candidates remain reliable within the quantified uncertainties for the purposes of identifying potential solutions in this c range. revision: partial
-
Referee: [numerical results for 1 < c < 8/7] The argument that the minima form a continuous space of modular bootstrap solutions (in the results for 1 < c < 8/7) rests on numerical convergence of the truncated loss; no demonstration is given that these minima remain stable under progressive increase of the cutoff dimension, leaving the continuity claim without sufficient control.
Authors: We agree that explicit stability checks under increasing cutoff are necessary to support the continuity claim. The original manuscript showed convergence for selected c values, but we will add new figures in the revised results section displaying the optimized loss and the low-lying spectrum as the truncation dimension is systematically increased (e.g., from N=10 to N=20) for representative points across 1 < c < 8/7. These plots will demonstrate that the minima stabilize and that the continuous dependence on c persists at higher cutoffs, thereby providing the requested control. revision: yes
-
Referee: [spectral gap bound near c=1] The evidence for a more stringent gap bound near c=1 (compared with Δ_gap ≤ c/6 + 1/3) is extracted from the same truncated minima; the paper should show explicitly how the tail uncertainty propagates into the gap constraint to confirm it is not an artifact of the finite cutoff.
Authors: We will revise the relevant results subsection to include an explicit propagation of the tail uncertainty into the extracted gap bound. For each c near 1, we will report the range of possible gap values consistent with the uncertainty estimate and show that the upper edge of this range remains strictly below the prior bound Δ_gap ≤ c/6 + 1/3. This will confirm that the tighter constraint is robust against the finite-cutoff effects. revision: yes
- Deriving a rigorous analytic bound guaranteeing that the tail cannot push the loss above the reported minimum in the infinite-cutoff limit
Circularity Check
Modular loss minimization finds candidate spectra; no definitional reduction to inputs
full rationale
The paper defines a loss function directly from the modular-invariance condition applied to a truncated spectrum of primary operators. Minimization then yields coefficient values that satisfy the truncated equations by construction, but this is the intended bootstrap search rather than a circular redefinition of the target result. No self-citation chain, uniqueness theorem imported from prior work, or ansatz smuggled via citation is load-bearing for the central claims. The argument that the minima form a continuous family rests on numerical sampling and an uncertainty estimate for the tail, which is presented as an estimate rather than a proof; this introduces an assumption about the infinite-spectrum limit but does not reduce the reported candidates to a tautology. The derivation chain therefore remains self-contained against external modular-invariance benchmarks.
Axiom & Free-Parameter Ledger
free parameters (1)
- truncation cutoff dimension
axioms (1)
- domain assumption The torus partition function of a 2d CFT with Virasoro algebra must be invariant under SL(2,Z) modular transformations.
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclearWe translate the requirement that this partition function is modular invariant into a loss function, which we then minimize to identify possible primary spectra... using a new singular-value-based optimizer (Sven)
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclearcandidate truncated CFT partition functions with central charges between 1 and 8/7... evidence for a more stringent constraint on the spectral gap near c = 1
Forward citations
Cited by 3 Pith papers
-
Neural Spectral Bias and Conformal Correlators I: Introduction and Applications
Neural networks optimized solely on crossing symmetry reconstruct CFT correlators from minimal input data to few-percent accuracy across generalized free fields, minimal models, Ising, N=4 SYM, and AdS diagrams.
-
Reconstructing conformal field theoretical compositions with Transformers
Transformers reconstruct the constituent RCFTs in tensor-product theories from low-energy spectra, reaching 98% accuracy on WZW models and generalizing to larger central charges with few out-of-domain examples.
-
Upgrading Extremal Flows in the Space of Derivatives
A prototype successfully upgrades low-order extremal flow solutions to high numerical order for gap maximization in a simple spinning modular bootstrap test case.
Reference graph
Works this paper leans on
-
[1]
Applied Conformal Field Theory
P.H. Ginsparg,APPLIED CONFORMAL FIELD THEORY, inLes Houches Summer School in Theoretical Physics: Fields, Strings, Critical Phenomena, 9, 1988 [hep-th/9108028]
work page internal anchor Pith review Pith/arXiv arXiv 1988
-
[2]
Ginsparg,Curiosities at c = 1,Nucl
P.H. Ginsparg,Curiosities at c = 1,Nucl. Phys. B295(1988) 153
work page 1988
-
[3]
Cardy,Operator Content of Two-Dimensional Conformally Invariant Theories,Nucl
J.L. Cardy,Operator Content of Two-Dimensional Conformally Invariant Theories,Nucl. Phys. B270(1986) 186
work page 1986
-
[4]
Cardy,Operator content and modular properties of higher dimensional conformal field theories,Nucl
J.L. Cardy,Operator content and modular properties of higher dimensional conformal field theories,Nucl. Phys. B366(1991) 403
work page 1991
-
[5]
Hellerman,A Universal Inequality for CFT and Quantum Gravity,JHEP08(2011) 130 [0902.2790]
S. Hellerman,A Universal Inequality for CFT and Quantum Gravity,JHEP08(2011) 130 [0902.2790]
-
[6]
D. Friedan and C.A. Keller,Constraints on 2d CFT partition functions,JHEP10(2013) 180 [1307.6562]
-
[7]
S. Collier, Y.-H. Lin and X. Yin,Modular Bootstrap Revisited,JHEP09(2018) 061 [1608.06241]
-
[8]
T. Hartman, D. Maz´ aˇ c and L. Rastelli,Sphere Packing and Quantum Gravity,JHEP12 (2019) 048 [1905.01319]
-
[9]
Black Hole Entropy from Near-Horizon Microstates
A. Strominger,Black hole entropy from near horizon microstates,JHEP02(1998) 009 [hep-th/9712251]
work page internal anchor Pith review Pith/arXiv arXiv 1998
-
[10]
Universal Spectrum of 2d Conformal Field Theory in the Large c Limit
T. Hartman, C.A. Keller and B. Stoica,Universal Spectrum of 2d Conformal Field Theory in the Large c Limit,JHEP09(2014) 118 [1405.5137]
work page Pith review arXiv 2014
-
[11]
Universality of Long-Distance AdS Physics from the CFT Bootstrap
A.L. Fitzpatrick, J. Kaplan and M.T. Walters,Universality of Long-Distance AdS Physics from the CFT Bootstrap,JHEP08(2014) 145 [1403.6829]
work page Pith review arXiv 2014
-
[12]
A. Antunes and C. Behan,Coupled Minimal Conformal Field Theory Models Revisited,Phys. Rev. Lett.130(2023) 071602 [2211.16503]
-
[13]
A. Antunes and C. Behan,Coupled minimal models revisited II: Constraints from permutation symmetry,SciPost Phys.18(2025) 132 [2412.21107]
-
[14]
Taxonomy of coupled minimal models from finite groups
A. Antunes and N. Suchel,Taxonomy of coupled minimal models from finite groups, 2512.23664
work page internal anchor Pith review Pith/arXiv arXiv
-
[15]
A. Antunes and J. Rong,Irrational CFTs from coupled anyon chains with non-invertible symmetries?,2507.14280
- [16]
-
[17]
A.L. Fitzpatrick and W. Li,Improving modular bootstrap bounds with integrality,JHEP07 (2024) 058 [2308.08725]
-
[18]
V.A. Fateev and A.B. Zamolodchikov,Parafermionic Currents in the Two-Dimensional Conformal Quantum Field Theory and Selfdual Critical Points in Z(n) Invariant Statistical Systems,Sov. Phys. JETP62(1985) 215
work page 1985
-
[19]
D. Friedan, Z.-a. Qiu and S.H. Shenker,Superconformal Invariance in Two-Dimensions and the Tricritical Ising Model,Phys. Lett. B151(1985) 37
work page 1985
-
[20]
S. Bright-Thonney, T.R. Harvey, A. Lukas and J. Thaler,Sven: Singular Value Descent as a Computationally Efficient Natural Gradient Method,2604.01279. – 53 –
-
[21]
J. Kaidi and E. Perlmutter,Discreteness and integrality in Conformal Field Theory,JHEP 02(2021) 064 [2008.02190]
-
[22]
N. Benjamin, S. Collier, A.L. Fitzpatrick, A. Maloney and E. Perlmutter,Harmonic analysis of 2d CFT partition functions,JHEP09(2021) 174 [2107.10744]
- [23]
-
[24]
The Conformal Bootstrap: Theory, Numerical Techniques, and Applications
D. Poland, S. Rychkov and A. Vichi,The Conformal Bootstrap: Theory, Numerical Techniques, and Applications,Rev. Mod. Phys.91(2019) 015002 [1805.04405]
work page Pith review arXiv 2019
-
[25]
S. Rychkov and N. Su,New developments in the numerical conformal bootstrap,Rev. Mod. Phys.96(2024) 045004 [2311.15844]
-
[26]
H.-Y. Chen, Y.-H. He, S. Lal and M.Z. Zaz,Machine Learning Etudes in Conformal Field Theories,2006.16114
- [27]
-
[28]
G. K´ antor, V. Niarchos and C. Papageorgakis,Solving Conformal Field Theories with Artificial Intelligence,Phys. Rev. Lett.128(2022) 041601 [2108.08859]
-
[29]
G. K´ antor, V. Niarchos and C. Papageorgakis,Conformal bootstrap with reinforcement learning,Phys. Rev. D105(2022) 025018 [2108.09330]
-
[30]
G. K´ antor, V. Niarchos, C. Papageorgakis and P. Richmond,6D (2,0) bootstrap with the soft-actor-critic algorithm,Phys. Rev. D107(2023) 025005 [2209.02801]
- [31]
-
[32]
Bootstrapping non-unitary CFTs
Y.-t. Huang, S.-C. Lee, H. Liao and J. Rumbutis,Bootstrapping non-unitary CFTs, 2512.07706
work page internal anchor Pith review Pith/arXiv arXiv
-
[33]
Neural Networks Reveal a Universal Bias in Conformal Correlators
K. Ghosh, S. Kumar, V. Niarchos and A. Stergiou,Neural Networks Reveal a Universal Bias in Conformal Correlators,2604.18673
work page internal anchor Pith review Pith/arXiv arXiv
-
[34]
Neural Spectral Bias and Conformal Correlators I: Introduction and Applications
K. Ghosh, S. Kumar, V. Niarchos and A. Stergiou,Neural Spectral Bias and Conformal Correlators I: Introduction and Applications,2604.18686
work page internal anchor Pith review Pith/arXiv arXiv
-
[35]
M. Reehorst, S. Rychkov, D. Simmons-Duffin, B. Sirois, N. Su and B. van Rees,Navigator Function for the Conformal Bootstrap,SciPost Phys.11(2021) 072 [2104.09518]
-
[36]
Afkhami-Jeddi,Conformal bootstrap deformations,JHEP09(2022) 225 [2111.01799]
N. Afkhami-Jeddi,Conformal bootstrap deformations,JHEP09(2022) 225 [2111.01799]
-
[37]
More constraining conformal bootstrap
F. Gliozzi,More constraining conformal bootstrap,Phys. Rev. Lett.111(2013) 161602 [1307.3111]
work page Pith review arXiv 2013
-
[38]
Truncatable bootstrap equations in algebraic form and critical surface exponents
F. Gliozzi,Truncatable bootstrap equations in algebraic form and critical surface exponents, JHEP10(2016) 037 [1605.04175]
work page Pith review arXiv 2016
-
[39]
N. Afkhami-Jeddi, T. Hartman and A. Tajdini,Fast Conformal Bootstrap and Constraints on 3d Gravity,JHEP05(2019) 087 [1903.06272]
- [40]
-
[41]
E. Arguello Cruz, I.R. Klebanov, G. Tarnopolsky and Y. Xin,Yang-Lee Quantum Criticality in Various Dimensions,Phys. Rev. X16(2026) 011022 [2505.06369]. – 54 –
- [42]
-
[43]
Closure of the Operator Product Expansion in the Non-Unitary Bootstrap
I. Esterlis, A.L. Fitzpatrick and D. Ramirez,Closure of the Operator Product Expansion in the Non-Unitary Bootstrap,JHEP11(2016) 030 [1606.07458]
work page Pith review arXiv 2016
-
[44]
A. Dersy, M.D. Schwartz and A. Zhiboedov,Reconstructing S-matrix Phases with Machine Learning,JHEP05(2024) 200 [2308.09451]
-
[45]
Mizera,Scattering with neural operators,Phys
S. Mizera,Scattering with neural operators,Phys. Rev. D108(2023) L101701 [2308.14789]
-
[46]
V. Niarchos and C. Papageorgakis,Learning S-matrix phases with neural operators,Phys. Rev. D110(2024) 045020 [2404.14551]
- [47]
- [48]
- [49]
-
[50]
N. Benjamin, H. Ooguri, S.-H. Shao and Y. Wang,Twist gap and global symmetry in two dimensions,Phys. Rev. D101(2020) 106026 [2003.02844]
-
[51]
E. Kiritsis,Character Formulae and the Structure of the Representations of theN= 1, N= 2Superconformal Algebras,Int. J. Mod. Phys. A3(1988) 1871
work page 1988
-
[52]
E.H. Moore,On the reciprocal of the general algebraic matrix,Bulletin of the american mathematical society26(1920) 294
work page 1920
-
[53]
A. Bjerhammar,Application of calculus of matrices to method of least squares: with special reference to geodetic calculations,(No Title)(1951)
work page 1951
-
[54]
R. Penrose,A generalized inverse for matrices, inMathematical proceedings of the Cambridge philosophical society, vol. 51, pp. 406–413, Cambridge University Press, 1955
work page 1955
-
[55]
B.T. Polyak,Minimization of unsmooth functionals,USSR Computational Mathematics and Mathematical Physics9(1969) 14. – 55 –
work page 1969
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.