Completeness from Gravitational Scattering
Pith reviewed 2026-05-16 22:50 UTC · model grok-4.3
The pith
Gravity together with nonabelian symmetry requires the full abelian charge lattice to be populated by single-particle states.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
For theories with a weakly coupled ultraviolet completion of gravity and a nonabelian symmetry G whose Cartan subgroup generates the abelian charge lattice, the existence of a finite set of charged representations necessitates infinitely many charged particles that completely fill the charge lattice. This holds for G equal to SO(N) with N greater than or equal to 5 and SU(N) with N greater than or equal to 3, and implies completeness for related groups like Spin(N), Sp(N), and E8. As a corollary, the SU(5) and SO(10) grand unified theories possess precisely the minimal field content required to derive completeness via this method.
What carries the argument
Consistency requirements on perturbative gravitational scattering amplitudes of charged particles transforming under the nonabelian symmetry G, which force additional states to appear in order to avoid inconsistencies.
If this is right
- The abelian charge lattice is completely filled by single-particle states for SU(N) with N greater than or equal to 3.
- The abelian charge lattice is completely filled by single-particle states for SO(N) with N greater than or equal to 5.
- Completeness follows automatically for the related groups Spin(N), Sp(N), and E8.
- The standard SU(5) and SO(10) grand unified theories already contain the minimal representations needed to obtain completeness from this argument.
Where Pith is reading between the lines
- Partial realizations of nonabelian symmetries become impossible once gravity is included, constraining which representations can appear in ultraviolet completions.
- Model builders must generate the full charge lattice rather than introducing isolated charged states without their partners.
- String theory or other high-energy frameworks that realize gravity and symmetry must automatically produce complete spectra rather than incomplete ones.
- If new charged particles are discovered, gravitational consistency would require the existence of their lattice partners even if they lie beyond direct detection.
Load-bearing premise
The theory admits a weakly coupled ultraviolet completion of gravity, includes a nonabelian symmetry G whose Cartan subgroup generates the charge lattice, and contains at least one finite set of charged representations.
What would settle it
An explicit computation of gravitational scattering amplitudes in a model with SU(3) symmetry containing only fundamental representations that exhibits unitarity violation or poles that cannot be canceled without extra charged states would falsify the claim.
Figures
read the original abstract
We prove that symmetry in the presence of gravity implies a version of the completeness hypothesis. For a broad class of theories, we demonstrate that the existence of finitely many charged particles logically necessitates the existence of infinitely many charged particles populating the entire charge lattice. Our conclusions follow from the consistency of perturbative gravitational scattering and require the following ingredients: 1) a weakly coupled ultraviolet completion of gravity, 2) a nonabelian symmetry $G$, gauged or global, whose Cartan subgroup generates the abelian charge lattice, and 3) a spectrum containing some finite set of charged representations, in the simplest cases taken to be a single particle in the fundamental. Under these conditions, the abelian charge lattice is completely filled by single-particle states for $G=SO(N)$ with $N\geq 5$ and $G=SU(N)$ with $N\geq 3$, which in turn implies completeness for other symmetry groups such as $Spin(N)$, $Sp(N)$, and $E_8$. Curiously, a corollary of our results is that the $SU(5)$ and $SO(10)$ grand unified theories have precisely the minimal field content needed to derive completeness using our methodology.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proves that consistency of perturbative gravitational scattering, in the presence of a nonabelian symmetry G whose Cartan generates the abelian charge lattice and a weakly coupled UV completion of gravity, implies that any finite set of charged representations necessitates an infinite tower of single-particle states that completely fills the charge lattice. This holds specifically for G = SU(N) with N ≥ 3 and G = SO(N) with N ≥ 5 (and extensions to Spin(N), Sp(N), E8), with the SU(5) and SO(10) GUTs identified as having precisely the minimal content required by the argument.
Significance. If the derivation holds, the result supplies a dynamical origin for the completeness hypothesis directly from scattering consistency rather than from ad-hoc assumptions on the spectrum. It furnishes a concrete, representation-theoretic mechanism that forces the full lattice to be populated once a single fundamental representation is present, and it yields falsifiable statements about the minimal field content of grand-unified models. The argument is parameter-free once the three stated conditions are imposed and distinguishes single-particle poles from multi-particle thresholds via residue extraction.
minor comments (3)
- [§2.3] §2.3: the definition of the residue extraction contour could be stated more explicitly (e.g., by writing the explicit small-circle integral around the single-particle pole) to make the separation from multi-particle thresholds immediate for readers unfamiliar with the amplitude techniques.
- [Table 1] Table 1: the column headers for the initial finite representations would benefit from an additional footnote clarifying that the listed charges are normalized with respect to the longest root of G.
- [§1] The discussion of global versus gauged G in §1 could include a one-sentence remark on whether the argument requires the symmetry to be gauged or merely global, since the scattering consistency step appears to use only the global charge lattice.
Simulated Author's Rebuttal
We thank the referee for their positive assessment and recommendation to accept the manuscript. The referee's summary correctly captures our main result: that perturbative gravitational scattering consistency, combined with a nonabelian symmetry G whose Cartan generates the charge lattice and a weakly coupled UV completion of gravity, forces the abelian charge lattice to be fully populated by single-particle states for SU(N) with N≥3 and SO(N) with N≥5 (and extensions). We appreciate the recognition of the result's significance in providing a dynamical origin for completeness and its implications for GUT field content.
Circularity Check
Derivation self-contained from amplitude consistency and representation theory
full rationale
The paper establishes that finite charged representations under a nonabelian G, combined with perturbative gravitational scattering consistency in a weakly coupled UV completion, force the full abelian charge lattice to be populated by single-particle states for SU(N) N≥3 and SO(N) N≥5. This follows from residue analysis distinguishing poles from thresholds and group-theoretic closure, without any parameter fitting, self-definitional loops, or load-bearing self-citations. The initial finite spectrum and symmetry assumptions are external inputs, and the logical implication to completeness is independent of the target result itself.
Axiom & Free-Parameter Ledger
axioms (3)
- domain assumption weakly coupled ultraviolet completion of gravity
- domain assumption nonabelian symmetry G whose Cartan subgroup generates the abelian charge lattice
- domain assumption spectrum containing some finite set of charged representations (e.g., single fundamental)
Forward citations
Cited by 4 Pith papers
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The Equivalence Principle at High Energies Completes the Spectrum
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Sampling the Graviton Pole and Deprojecting the Swampland
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Reference graph
Works this paper leans on
-
[1]
Every possible process is labeled by a pair of charges⃗ q,⃗ q′∈Q
Scatter all possible combinations of charged par- ticles. Every possible process is labeled by a pair of charges⃗ q,⃗ q′∈Q. At the level of the four-point scat- tering amplitude, the external charges are⃗ q1 =−⃗ q4 = ⃗ qand⃗ q2 =−⃗ q3 =⃗ q′. We require this elastic charge configuration so that thet-channel state is neutral. Only then can the graviton cont...
-
[2]
Apply the dispersion relation in Eq. (3) to deduce the existence of a particle either in thesoruchannel, <latexit sha1_base64="/x8EMp6ufFim7M5CGQZMVyKtyww=">AAACA3icbVDLSsNAFJ3UV62vqDvdBIsgKCURqS6LblxWsA9oYplMb9qhk0mcmRRKCLjxV9y4UMStP+HOv3Fas9DWA5d7OOdeZu7xY0alsu0vo7CwuLS8Ulwtra1vbG6Z2ztNGSWCQINELBJtH0tglENDUcWgHQvAoc+g5Q+vJn5rBELSiN+qcQxeiPucBpRgpaWuueeO...
-
[3]
If both⃗ q+⃗ q′/∈Qand⃗ q−⃗ q′/∈Q, then the disper- sion relation in Eq. (3) guarantees the existence of a new charge in the spectrum. We refer to such a scat- tering process as “conclusive.” Conversely, if either ⃗ q+⃗ q′∈Qor⃗ q−⃗ q′∈Q, then no new charges are strictly required. In such a case we deduce nothing, so the scattering process is deemed “inconclusive.”
-
[4]
If any scattering process is conclusive, then we up- dateQto include the required new charges. At this step we compute the orbit of the new charges to gener- ate the full space of charges required by the symmetry Gand any outer automorphismsC. The precise me- chanics of this manuever will depend on the situation. In some cases⃗ q+⃗ q′and⃗ q−⃗ q′will be tr...
work page 2021
-
[5]
On Unitary Representations of the In- homogeneous Lorentz Group,
E. P. Wigner, “On Unitary Representations of the In- homogeneous Lorentz Group,”Annals Math.40(1939) 149
work page 1939
-
[6]
Limits on Massless Parti- cles,
S. Weinberg and E. Witten, “Limits on Massless Parti- cles,”Phys. Lett. B96(1980) 59
work page 1980
-
[7]
Consistency Conditions on the S-Matrix of Massless Particles
P. Benincasa and F. Cachazo, “Consistency Conditions on the S-Matrix of Massless Particles,”arXiv:0705.4305 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv
-
[8]
Higher-spin massless S-matrices in four-dimensions
D. A. McGady and L. Rodina, “Higher-spin massless S-matrices in four dimensions,”Phys. Rev. D90(2014) 084048,arXiv:1311.2938 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2014
-
[9]
N. Arkani-Hamed, T.-C. Huang, and Y.-t. Huang, “Scattering amplitudes for all masses and spins,”JHEP 11(2021) 070,arXiv:1709.04891 [hep-th]
-
[10]
H. Elvang and Y.-t. Huang,Scattering Amplitudes in Gauge Theory and Gravity. Cambridge University Press, 2015
work page 2015
-
[11]
TASI Lectures on Scattering Amplitudes
C. Cheung, “TASI Lectures on Scattering Amplitudes,” inTheoretical Advanced Study Institute in Elementary Particle Physics: Anticipating the Next Discoveries in 12 Particle Physics, p. 571. 2018.arXiv:1708.03872 [hep- ph]
work page internal anchor Pith review Pith/arXiv arXiv 2018
-
[12]
Monopoles, duality, and string theory,
J. Polchinski, “Monopoles, duality, and string theory,” Int. J. Mod. Phys. A19S1(2004) 145,arXiv:hep- th/0304042
-
[13]
Symmetries and Strings in Field Theory and Gravity
T. Banks and N. Seiberg, “Symmetries and Strings in Field Theory and Gravity,”Phys. Rev. D83(2011) 084019,arXiv:1011.5120 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2011
-
[14]
The String Landscape and the Swampland
C. Vafa, “The String Landscape and the Swampland,” arXiv:hep-th/0509212
work page internal anchor Pith review Pith/arXiv arXiv
-
[15]
Constraints on String Vacua with Space-Time Supersymmetry,
T. Banks and L. J. Dixon, “Constraints on String Vacua with Space-Time Supersymmetry,”Nucl. Phys. B307 (1988) 93
work page 1988
-
[16]
B. Heidenreich, J. McNamara, M. Montero, M. Reece, T. Rudelius, and I. Valenzuela, “Non-invertible global symmetries and completeness of the spectrum,”JHEP 09(2021) 203,arXiv:2104.07036 [hep-th]
-
[17]
T.RudeliusandS.-H.Shao, “TopologicalOperatorsand Completeness of Spectrum in Discrete Gauge Theories,” JHEP12(2020) 172,arXiv:2006.10052 [hep-th]
-
[18]
Spectral Constraints on Theories of Colored Par- ticles and Gravity,
A. Hillman, Y.-t. Huang, L. Rodina, and J. Rumbutis, “Spectral Constraints on Theories of Colored Parti- cles and Gravity,”Phys. Rev. Lett.135(2025) 061604, arXiv:2411.04857 [hep-th]
-
[19]
Here the ellipses denote all terms in the low-energy am- plitude that are not the graviton pole. This includes contributions that are regular intcoming from general relativity, as well as higher-dimension operator correc- tions in the effective field theory. Notably, all of these terms exhibit differenttdependence than the graviton pole, so there are alwa...
-
[20]
By in- cluding eikonalization, even better scaling is possible
InRef.[31], Reggeboundswerederivedforgravitational scattering amplitudes as a consequence of analyticity, unitarity, and the partial wave expansion in various con- texts.Themostconservativeofthesebounds, merelyas- suming dominance of single-graviton exchange at large impact parameter, showed in generality that, for tree- level amplitudes,A(s, t)< s 2−D−7 ...
-
[21]
What is the graviton pole made of?,
K. Häring and A. Zhiboedov, “What is the graviton pole made of?,”arXiv:2410.21499 [hep-th]
-
[22]
Positivity of Curvature-Squared Corrections in Gravity
C. Cheung and G. N. Remmen, “Positivity of Curvature-Squared Corrections in Gravity,”Phys. Rev. Lett.118(2017) 051601,arXiv:1608.02942 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2017
-
[23]
Bootstrap Principle for the Spectrum and Scattering of Strings,
C. Cheung, A. Hillman, and G. N. Remmen, “Bootstrap Principle for the Spectrum and Scattering of Strings,” Phys. Rev. Lett.133(2024) 251601,arXiv:2406.02665 [hep-th]
-
[24]
Uniqueness criteria for the Virasoro-Shapiro amplitude,
C. Cheung, A. Hillman, and G. N. Remmen, “Unique- ness criteria for the Virasoro-Shapiro amplitude,”Phys. Rev. D111(2025) 086034,arXiv:2408.03362 [hep-th]
-
[25]
C. Cheung, G. N. Remmen, F. Sciotti, and M. Tarquini, “Strings from Almost Nothing,”arXiv:2508.09246 [hep- th]
-
[26]
Symmetries in quantum field theory and quantum gravity
D.HarlowandH.Ooguri, “Symmetriesinquantumfield theory and quantum gravity,”Commun. Math. Phys. 383(2021) 1669,arXiv:1810.05338 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 2021
-
[27]
Georgi,Lie Algebras in Particle Physics: From Isospin to Unified Theories
H. Georgi,Lie Algebras in Particle Physics: From Isospin to Unified Theories. Frontiers in Physics. The Benjamin/Cummings Publishing Company, Inc., 1982
work page 1982
-
[28]
Unity of All Elementary Particle Forces,
H. Georgi and S. L. Glashow, “Unity of All Elementary Particle Forces,”Phys. Rev. Lett.32(1974) 438
work page 1974
-
[29]
Unified Interactions of Leptons and Hadrons,
H. Fritzsch and P. Minkowski, “Unified Interactions of Leptons and Hadrons,”Annals Phys.93(1975) 193
work page 1975
-
[30]
Throughout this work, we will assume thatGis a single group factor. For a product group,G=⊗iGi, complete- ness of eachGi factor implies completeness ofGunder certain conditions. In particular, consider the case in which a starting spectrumQi is sufficient to prove com- pleteness forG i. First, we require an initial spectrumQ forGcomposed of all states wit...
-
[31]
Multipositivity bounds for scattering amplitudes,
C. Cheung and G. N. Remmen, “Multipositivity bounds for scattering amplitudes,”Phys. Rev. D112(2025) 016017,arXiv:2505.05553 [hep-th]
-
[32]
The string landscape, black holes and gravity as the weakest force,
N. Arkani-Hamed, L. Motl, A. Nicolis, and C. Vafa, “The string landscape, black holes and gravity as the weakest force,”JHEP06(2007) 060,arXiv:hep- th/0601001
-
[33]
Generalized symmetry in dynam- ical gravity,
C. Cheung, M. Derda, J.-H. Kim, V. Nevoa, I. Roth- stein, and N. Shah, “Generalized symmetry in dynam- ical gravity,”JHEP10(2024) 007,arXiv:2403.01837 [hep-th]
-
[34]
This can also be derived using the null constraints in- troduced in Ref. [34]
-
[35]
K. Häring and A. Zhiboedov, “Gravitational Regge bounds,”SciPost Phys.16(2024) 034, arXiv:2202.08280 [hep-th]
-
[36]
N. Arkani-Hamed, T.-C. Huang, and Y.-t. Huang, “The EFT-Hedron,”JHEP05(2021) 259,arXiv:2012.15849 [hep-th]
-
[37]
S. Caron-Huot, Y.-Z. Li, J. Parra-Martinez, and D. Simmons-Duffin, “Causality constraints on cor- rections to Einstein gravity,”JHEP05(2023) 122, arXiv:2201.06602 [hep-th]
-
[38]
S. Caron-Huot and V. Van Duong, “Extremal Effective Field Theories,”JHEP05(2021) 280,arXiv:2011.02957 [hep-th]
-
[39]
Stringy Completions of the StandardModelfromtheBottomUp,
B. Bachu and A. Hillman, “Stringy Completions of the Standard Model from the Bottom Up,” arXiv:2212.03871 [hep-th]
-
[40]
Humphreys,Introduction to Lie Algebras and Rep- resentation Theory
J. Humphreys,Introduction to Lie Algebras and Rep- resentation Theory. Graduate Texts in Mathematics. Springer, 2012
work page 2012
-
[41]
B. C. Hall,Lie groups, Lie algebras, and Representa- tions. Graduate Texts in Mathematics. Springer, 2003
work page 2003
-
[42]
For earlier work bootstrapping ansatze for theories with color and gravity, see Ref. [35]
-
[43]
Our results on charge completeness can be understood in this language. By scattering the charges⃗ qand⃗ q′, we have used that there is a state of charge⃗ q+⃗ q′or ⃗ q−⃗ q′, corresponding to thesoruchannel. This implies that there exists some choice ofvfor which Eq. (C.4) is satisfied where the set of exchanged representationsR contains neither⃗ q+⃗ q′nor⃗ q−⃗ q′
-
[44]
P.Cvitanović,Group Theory: Birdtracks, Lie’s, and Ex- ceptional Groups. Princeton University Press, 2020. 13 Appendix A: Group Theory Review In this appendix, we review some of the group theo- retic structures needed to establish charge completeness. Consider a finite, semisimple, compact Lie groupGwith an associated Lie algebrag. The maximal commuting su...
work page 2020
-
[45]
[14] is to assume certain spectra and then act on Eq
Completeness from Proof by Contradiction The basic strategy of Ref. [14] is to assume certain spectra and then act on Eq. (1) with wisely chosen color projectors to generate a contradiction [38]. Let us now briefly review this approach. Consider the scattering of a pair of particles in the nonabelian representationsR 1 andR 2 of the symmetry groupG=SO(N)....
-
[46]
Completeness with Both Channels If, for whatever reason, we are granted knowledge that bothchannels in Eq. (3) are necessarily nonzero, then we can straightforwardly derive much stronger claims of completeness. In this case, the scattering of charges⃗ q and⃗ q′will necessarily entail new states in the spectrum of charge⃗ q+⃗ q′and also⃗ q−⃗ q′. Mechanical...
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