arXiv subjects

Waltraut Knop

Publications and source records attributed to Waltraut Knop.

4 recordsLinked to original sources

arXiv2026

Where is tree-level heterotic string theory?

We continue the tree-level S-matrix bootstrap program for quantum gravity, now in ten-dimensional theories with half-maximal supersymmetry. This setting includes the heterotic string and allows us to test whether the string-like structures found in the maximally supersymmetric bootstrap persist with less supersymmetry and in non-planar gauge sectors. Imposing analyticity, crossing symmetry, unitarity, and Regge boundedness, we constraint weakly coupled UV completions of supergravity and super Yang-Mills. In the gravitational sector, much of the boundary of the allowed region is explained by extremal amplitudes supported on a single linear Regge trajectory, or by convex combinations of such amplitudes. In the gluon sector, the non-planar problem reveals a tension between representation-channel positivity and the trace decomposition of the EFT data, obstructing a direct normalization by $G$ or $g_{\rm YM}$; a coupled gluon/graviton bootstrap may be necessary to directly constrain the relative strength of gauge and gravitational interactions. Overall, our results support the emergence of linear Regge trajectories as a robust feature of the tree-level quantum-gravity bootstrap.

hep-th↗

arXiv2025

Symmetric Product Orbifold Universality and the Mirage of an Emergent Spacetime

We study thermal two-point functions and four-point functions involving two heavy twisted operators and two light probes in symmetric product orbifolds. We identify cases where they are universal at large $N$, that is, they are only sensitive to the orbifold structure. Surprisingly, such observables mimic correlators obtained from the BTZ background, even though symmetric product orbifolds are not dual to semi-classical gravity. We discuss the interpretation of these results in light of the criteria for emergence of spacetime via Von Neumann algebras. Our analysis implies that a condition on the infinite $N$ thermal two-point functions cannot be stringent enough to define an emergent spacetime and the concept of a sharp horizon.

hep-th↗

arXiv2025

Where is tree-level string theory?

We investigate the space of consistent tree-level extensions of the maximal supergravities in ten dimensions. We parametrize theory space by the first few EFT coefficients and by the on-shell coupling of the lightest massive state, and impose on these data the constraints that follow from $2 \to 2$ supergraviton scattering. While Type II string theory lives strictly inside the allowed region, we uncover a novel extremal solution of the bootstrap problem, which appears to contain a single linear Regge trajectory, with the same slope as string theory. We repeat a similar analysis for supergluon scattering, where we find instead a continuous family of extremal solutionswith a single Regge trajectory of varying slope.

hep-th↗

arXiv2022

Dispersive Sum Rules in AdS$_2$

Dispersion relations for S-matrices and CFT correlators translate UV consistency into bounds on IR observables. In this note, we construct dispersive sum rules for 1D CFTs. We use them to prove bounds on higher-derivative couplings in weakly-coupled non-gravitational EFTs in AdS$_2$. At the leading order in the bulk-point limit, the bounds agree with the flat-space result. We compute the leading universal effect of finite AdS radius on the bounds. Along the way, we give an explicit formula for anomalous dimensions in general higher-derivative contact Witten diagrams in AdS$_2$.

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