REVIEW
Two and three-point functions in Liouville theory
High Energy Physics - Theory · Submitted 23 Mar 1994 · 19 references
Pith's verdict: The pre-DOZZ construction of generic-β Liouville two- and three-point functions: the closed forms are right in hindsight, but the continuation's normalization and α↔2/α duality are never independently pinned down.
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Referee report
The paper
The paper claims
The paper constructs closed-form two- and three-point functions for Liouville exponentials with arbitrary real exponent, and checks the three-point function against the Liouville equation of motion.
The reading
What carries the argument
The engine is the continued function $f(a,b|s)$, defined for integer $s$ as $Σ_{j=0}^{s-1}Γ(a+bj)$ and extended to arbitrary complex arguments by an integral representation. It obeys four functional relations — shift in $s$, shift in $a$, shift by $b$, and a reflection $b→-b$ — which let the authors move gamma-function arguments around without ever leaving the continued domain. The poles and zeros of $e^{f}$ are then read off from those relations: poles at $a = -bj-ℓ$ and zeros at $a+bs = -bj-ℓ$ for nonnegative integers $j,ℓ$. This is what makes the otherwise formal continuation controllable, and it is what produces the pole-zero spectrum of $A_2$ and $A_3$ that the paper later uses to argue about mass shells. A second piece of machinery is the treatment of the residual Möbius volume: the two-punctured sphere has one conformal Killing vector, so the naive $β_3→0$ limit of $A_3$ diverges, and the authors divide by the explicit volume $V^{(2)}_{CKV}$ of the subgroup fixing $z_1,z_2$ to obtain a finite $A_2$.
Extended reading notes
Core claim
The paper's central claim is that the two- and three-point functions of Liouville exponentials $e^{β_jφ}$ exist in closed form for generic real $β_j$. The three-point function is reduced, by a Möbius transformation argument, to the standard conformal structure with a $β$-dependent amplitude $A_3$ given by a Dotsenko–Fateev integral over $s_3 = (Q-Σβ_j)/α$ screening insertions; evaluating that integral and continuing in $s_3$ produces $A_3$ as a product of gamma functions times three factors $F_i$ built from a continued sum $f(a,b|s)$ of log-gamma terms. The two-point function follows either by taking a $β_3→0$ limit of $A_3$ with the volume of the residual Möbius subgroup divided out, or by differentiating the two-point function with respect to $μ^2$ and matching against the once-integrated three-point function; both routes give the compact expression for $A_2(β)$ in eq. (33). The load-bearing check is eq. (42): the authors verify that $4(Δ_2-Δ_3)^2 ∂_{β_1}A_3|_{β_1=0}$ equals $αμ^2/2$ times $A_3(α,β_2,β_3)$, which is precisely the Liouville equation of motion $∂^2φ = (αμ^2/2)e^{αφ}$ promoted to a statement about three-point functions. They read this as strong evidence that the continuation procedure is the right one, since a uniqueness proof was previously available only for the rational coefficients needed to dress minimal models.
Load-bearing premise
The whole result rests on continuing a sum of log-gamma terms from integer to arbitrary complex values, and on one convention for the otherwise meaningless product $Γ(0)sin(πs)$ — a sign choice the authors say is fixed by requiring the Liouville-equation check to come out right, rather than derived independently.
Editorial extensions
If this is right
- Gravitational dressing factors for two- and three-point functions become available at arbitrary real dressing charge, not only at the rational values tied to minimal models.
- The pole-zero structure of $A_2(β)$ yields a candidate mass-shell condition: the tachyon zero at $β = Q/2$ gives $(k-P/2)^2 = (D-1)/12$, with the graviton case shifted to $(k-P/2)^2 = (D-25)/12$.
- All zeros of $A_2$ other than $β=Q/2$ lie above $Q/2$ and correspond to wave functions that are not normalizable as $φ→+∞$, so they are excluded and the microscopic puncture sits on the boundary of the allowed set.
- Because $A_3$ vanishes whenever any one of the three $β_j$ is taken from the zero table of $A_2$, and no configuration of three coinciding poles can rescue it, the three-point string $S$-matrix element vanishes for on-shell external states — the property factorization of higher $S$-matrix elements would need.
- The quasiclassical limit $Q→∞$ reproduces the previously known structure of the normalized two-point function, $G_2/Z ∝ (2b-1)^{-1}(-m^2/8)^{-2b}|z_1-z_2|^{-4b}$, now in explicit form.
Reading between the lines
- The Liouville-equation check is a one-parameter test of a two-parameter continuation: it fixes the ambiguous $\sin(πs)Γ(0)$ convention but cannot by itself confirm that the $β$-dependence away from $β_1=0$ is right, so the natural next test is a four-point function or an independent canonical free-field computation of $A_2$.
- The mass-shell conjecture is stated in $D$ target-space dimensions rather than $D+1$, and the authors themselves note that the $(D+1)$-dimensional reading of the on-shell condition works cleanly only at $μ=0$; whether the conjecture survives at $μ≠0$ is decidable once the special four-point cases are computed.
- If the mass-shell zeros of $A_2$ are the right on-shell condition, then the tower of excluded zeros above $β=Q/2$ is a prediction about which would-be states are absent from the noncritical spectrum — a statement that a matrix-model or continuum computation at $c_M<1$ could in principle check.
- The failure of the one-point function to be well defined in this scheme, which the authors trace to the absence of an $SL(2,\mathbb{C})$-invariant vacuum, suggests that any correlator of the Liouville field itself must be defined with at least two spectator exponentials — a structural constraint that would carry over to any alternative construction of $φ$ correlators.
Original abstract
Based on our generalization of the Goulian-Li continuation in the power of the 2D cosmological term we construct the two and three-point correlation functions for Liouville exponentials with generic real coefficients. As a strong argument in favour of the procedure we prove the Liouville equation of motion on the level of three-point functions. The analytical structure of the correlation functions as well as some of its consequences for string theory are discussed. This includes a conjecture on the mass shell condition for excitations of noncritical strings. We also make a comment concerning the correlation functions of the Liouville field itself.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
Based on our generalization of the Goulian-Li continuation in the power of the 2D cosmological term we construct the two and three-point correlation functions for Liouville exponentials with generic real coefficients. As a strong argument in favour of the procedure we prove the Liouville equation of motion on the level of three-point functions. The analytical structure of the correlation functions as well as some of its consequences for string theory are discussed. This includes a conjecture on the mass shell condition for excitations of noncritical strings. We also make a comment concerning the correlation functions of the Liouville field itself.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Based on our generalization of the Goulian-Li continuation in the power of the 2D cosmological term we construct the two and three-point correlation functions for Liouville exponentials with generic real coefficients. | contribution 0.90 | 0.95 | 0.49 | asserted 1.00 |
| s1 | As a strong argument in favour of the procedure we prove the Liouville equation of motion on the level of three-point functions. | result 0.81 | 0.95 | 0.25 | asserted 0.97 |
| s2 | The analytical structure of the correlation functions as well as some of its consequences for string theory are discussed. | contribution 0.74 | 0.81 | 0.10 | asserted 0.81 |
| s3 | This includes a conjecture on the mass shell condition for excitations of noncritical strings. | interpretation 0.51 | 0.82 | 0.10 | speculative 0.96 |
| s4 | We also make a comment concerning the correlation functions of the Liouville field itself. | contribution 0.90 | 0.83 | 0.04 | unclear 0.76 |
What was examined, and what was not
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References
How later papers used it
179 later papers cite it
2 later papers by other authors are listed below: 2 used its method or tool and 1 compared its own results with it. 1 of them appears under more than one label.
Uses its method or tool 2 of 9 papers with this label
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Defined its 2-point function as the limit of the 3-point function when one insertion tends to the identity as in this paper, and used the DOZZ formula for the 3-point structure constant to compute the overall normalization.
Boundary timelike Liouville theory: bulk 1-point & boundary 2-point functions (2021) · 0.83 · paraphrased: the licence does not allow quoting
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Expressed its F-matrix in terms of the quantum 6j-symbol, with the DOZZ three point function of this paper appearing in the formula.
Solving the Schwarzian via the Conformal Bootstrap (2017) · 0.87 · paraphrased: the licence does not allow quoting
Compares with it 1 of 11 papers with this label
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Found that the integral giving the amplitude between its states matches exactly with the b to 0 limit of this paper's DOZZ formula.
Solving the Schwarzian via the Conformal Bootstrap (2017) · 0.93 · paraphrased: the licence does not allow quoting
How the literature uses it
161 arXiv papers cite this in 228 sentences
Papers citing it · 152 sentences without a confident label
Uses its method or tool 9 papers
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In order to do this we are going to use the DOZZ formulation of Liouville theory [ref] .
Bootstrapping closed string field theory · Classical bootstrap for string vertices · 0.99
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Nevertheless, we can leverage the exact solution of the worldsheet CFT ([ref]) [ref] to deduce the analytic structure of the string amplitudes viewed as analytic functions of the external momenta.
The complex Liouville string: the worldsheet · Introduction · 0.92
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At each point in the base, we then perform the integration along the fiber: [equation] where in going from the second to the third line we used the Verlinde inner product [ref] between Liouville blocks [equation] and used the compact notation [ref] [equation] $𝒞$ being a choice of channel decomposition, $𝐏$ being the internal momenta, $ρ_0$ being the Cardy density, and $C_0$ being the DOZZ formula [ref] up to some normalization [ref] .
On random matrix statistics of 3d gravity · Other amplitudes · 0.93
Uses its data or values 1 paper
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The structure constant $C(α,α_1,α_2)$ of the Liouville field theory was computed [ref] [ref] [ref] to be [equation] where $Υ(x)$ is defined by [equation] for $0<Re(x) <Q$ and analytically continued to the whole complex plane.
Dangerous Liouville Wave -- exactly marginal but non-conformal deformation · Quantum Liouville wave · 0.84
Compares with it 10 papers
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The final result reads [equation] where $Δ_i = η_i (1-η_i)/b^2$ and $C_123$ is given by [equation] with [equation] This matches with the classical limit of the DOZZ formula [ref] .
Liouville Theory, AdS$_2$ String, and Three-Point Functions · Solving the functional equation · 0.99
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By comparing to the exact correlation functions, known from [ref] , the authors of [ref] identified the saddles that contribute to the corresponding functional integrals.
Semi-Classical Analysis of the String Theory Cigar · Introduction and Overview · 0.88
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Incorporating these leg factors, we finally get f(_1)f(_2)/f(^∗_3) F__1,_2,_3 F__1^∗,_2^∗,_3^∗ ∼'_0 (2_1)(2_2)(2_3)/( _1+_2+_3 -Q)(_2+_3-_1)(_3+_1-_2)(_1+_2-_3) , where [equation] This is precisely the DOZZ formula [ref] apart from the extra normalization factor [equation] Notice that this normalization factor depends on the coefficient $$ of the exponential term $∫d^2z e^2bφ$ in the Liouville action which can be shifted away by shifting $→+$ const, and is therefore clearly scheme-depedent.
Non-Perturbative Topological Strings And Conformal Blocks · Three-Point Functions · 0.91
Cites it as support 1 paper
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However, the OPE in the unphysical range of the Liouville momentum formally makes sense, and indeed it was even used in the original derivation of the three-point function [ref] [ref] [ref] .
Refined Cigar and Omega-deformed Conifold · Refined cigar and $Ω$-deformation · 0.96
Cites it as background 48 papers
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These partition functions were until recently [ref] unknown, with the sole exception of the W$_2$ case, i.e. the Liouville case, whose three point structure constants are given by the famous DOZZ formula [ref] .
Toda 3-Point Functions From Topological Strings · Introduction · 0.81
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The spacelike structure constants $C(a_1 , a_2, a_3)$ are given by the Dorn–Otto–Zamolodchikov–Zamolodchikov (DOZZ) formula [ref] (see [ref] for more discussions).
Quantum Gravity from Timelike Liouville theory · Conformal bootstrap for Liouville · 0.83
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The Virasoro primaries of the $c=25$ Liouville CFT are scalar operators $V_P$ labeled by their Liouville momenta $P≥0$, of scaling dimensions $Δ_P=2+2P^2$, subject to the normalization ⟨V_P_1(z,z̅)V_P_2(0)⟩=πδ(P_1-P_2)/|z|^2Δ_P_1 Their structure constants are given by the DOZZ formula [ref] .[Explicitly, in our normalization convention, the $c=25$ Liouville structure constants are given in (2.9) of [ref] .] The closed string asymptotic states, as insertions on the worldsheet, are given by the BRST cohomology representatives of the form V^±_ω= g_s cc̃ e^±i ωX^0 V_P=ω/2, where the superscript $+$ and $-$ corresponds to in- and out-states, respectively.
Multi-Instanton Calculus in c = 1 String Theory · Multiple ZZ-instantons from the worldsheet perspective · 0.81
Discussion
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