arXiv subjects

Torben Skrzypek

Publications and source records attributed to Torben Skrzypek.

10 recordsLinked to original sources

arXiv2026

Exploring the twisted sector of $\mathbb{Z}_{L}$ orbifolds: Matching $α'$-corrections to localisation

We consider type IIB string theory on $\mathrm{AdS}_5\times S^5/\mathbb{Z}_{L}$ orbifold spaces with generic $L$. Recent localisation results in the dual 4d $\mathcal{N}=2$ circular quiver gauge theories provide us with strong coupling expansions of certain correlators involving twisted half-BPS operators. To leading order, these results have been matched to an effective theory for massless twisted string states, which can be constructed by resolving the orbifold singularity and considering localised supergravity modes on the resolution cycles. Applying this reasoning to subleading order in strong coupling, we observe that for $L\neq 2,3,4,6$, a naive reduction of the 10d $(α')^3$-correction does not result in the correct coefficients to match the localisation result. We explain this mismatch by the appearance of twisted sector resonances in string amplitudes involving external twisted sector states. We perform the low-energy expansion of a ``twisted'' Virasoro-Shapiro amplitude and recover the expected coefficients, suggesting that the orbifold resolution and the low-energy expansion can not be interchanged directly. Finally, we comment on the long-quiver limit, $L\to\infty$, in the context of the low-energy effective action.

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arXiv2026

Multiplet Recombination and the CFT Distance Conjecture

Motivated by quantum gravity and the CFT Distance Conjecture, we study infinite-distance limits in four-dimensional ${\cal N}=2$ superconformal field theories with higher-dimensional conformal manifolds and their AdS duals. We focus on partial decoupling limits where a gauge sector becomes weakly coupled while an interacting sector persists. We analyse the structure of towers of states emerging in these limits. The weakly coupled sector contributes, among others, the massless higher-spin tower predicted by the CFT Distance Conjecture exhibiting polynomial degeneracy. The key novelty is the appearance of a protected BPS tower in the interacting sector, characterised by exponential degeneracy and masses at the AdS scale. This structure follows from multiplet recombination in the ${\cal N}=2$ superconformal algebra: As unprotected long multiplets hit the unitarity bound at weak coupling, they recombine into protected short multiplets. We verify this picture through an explicit one-loop computation in the simplest two-node quiver gauge theory with a two-dimensional conformal manifold.

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arXiv2025

Perturbed symmetric-product orbifold: first-order mixing and puzzles for integrability

We study the marginal deformation of the symmetric-product orbifold theory Sym$_N(T^4)$ which corresponds to introducing a small amount of Ramond-Ramond flux into the dual $AdS_3\times S^3\times T^4$ background. Already at first order in perturbation theory, the dimension of certain single-cycle operators is corrected, indicating that wrapping corrections from integrability must come into play earlier than expected. Our results provide a test for integrability computations from the mirror Thermodynamic Bethe Ansatz or Quantum Spectral Curve, akin to the computation of the Konishi anomalous dimension in $\mathcal{N}=4$ supersymmetric Yang--Mills theory. We also discuss a flaw in the original derivation of the integrable structure of the perturbed orbifold. Together, these observations suggest that more needs to be done to correctly identify and exploit the integrable structure of the perturbed orbifold CFT.

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arXiv2025

Interplay of Intersecting Branes and Consistent Embeddings

We explore consistent truncations from 10d/11d supergravity to supergravity theories on brane worldvolumes. Supersymmetric black-brane solutions to these lower-dimensional theories can be uplifted to 10d/11d supergravity and interpreted as intersecting-brane solutions with a particular smearing pattern. We survey this novel family of intersecting-brane solutions which also includes cases that are not related to previously known consistent truncations. Turning the argument on its head, we argue that the knowledge of such solutions allows us to generate appropriate embedding ansätze for consistent truncations. We demonstrate this by deriving new consistent embeddings of pure 5d $\mathcal{N}=4$ supergravity on D4-branes in type IIA theory and of pure 6d $\mathcal{N}=(1,1)$ supergravity on NS5-branes in type IIB theory.

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arXiv2025

Three-point functions from integrability in $\mathcal{N}=2$ orbifold theories

Besides solving the spectral problem of $\mathcal{N}=4$ Super-Yang-Mills (SYM) theory, integrability also provides us with tools to compute the structure constants of the theory, most prominently through the hexagon formalism. We show that, with minor modifications, this formalism can also be applied to orbifolds of $\mathcal{N}=4$ SYM theory, which are integrable theories in their own right. To substantiate this claim, we test our results against a direct gauge-theory calculation at tree-level. We focus here on a family of $\mathcal{N}=2$ supersymmetric $\mathbb{Z}_M$-orbifold theories. BPS correlators in these theories have recently been investigated with independent localisation techniques and a structural matching with wrapping corrections in the hexagon formalism was observed. Together with our weak-coupling evidence, this suggests that a full determination of the structure constants of orbifold theories at finite coupling may be within reach.

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arXiv2024

Compactification on Calabi-Yau threefolds: Consistent truncation to pure supergravity

We study compactifications of eleven- and ten-dimensional maximal supergravity on Calabi-Yau threefolds. We explicitly construct truncations to pure supergravity with eight supercharges in five and four dimensions and show that they are consistent, i.e. that every solution of the lower-dimensional equations of motion fully solves the higher-dimensional ones. We furthermore match the supersymmetry transformations and demonstrate the consistency to full non-linear order in fermions. Our construction is independent of the choice of Calabi-Yau threefold and only involves the universal structures such as the Kähler form and the holomorphic three-form, in agreement with implicit constructions in the generalised geometry literature. As an immediate application, we embed four-dimensional extremal black holes in the higher-dimensional supergravities. We furthermore propose Ansätze for consistent truncations on all universal structures, leading to supergravities with additional matter multiples. An extensive list of equations of motion and supersymmetry transformations for various supergravity theories is provided in the appendix.

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arXiv2024

On AdS/CFT duality in the twisted sector of string theory on $AdS_5 \times S^5/\mathbb{Z}_2$ orbifold background

We consider type IIB string theory on an $AdS_5 \times S^5/\mathbb{Z}_2$ orbifold background, which should be dual to 4d $\mathcal{N}=2$ superconformal $SU(N)\times SU(N)$ gauge theory with two bi-fundamental hypermultiplets. The correlator of two chiral BPS operators from the twisted sector of this quiver CFT exhibits non-trivial dependence on the 't Hooft coupling $λ$ already in the planar limit. This dependence was recently determined using localisation and the expansion at large $λ$ contains a subleading contribution proportional to $ζ(3) λ^{-3/2}$. We address the question of how to reproduce this correction on the string theory side by starting with the $ζ(3) α'^3$ term in the type IIB string effective action. We find a solution of type IIB supergravity which represents a resolution of the $AdS_5 \times S^5/\mathbb{Z}_2$ orbifold singularity and demonstrate that the relevant light twisted sector states may be identified as additional supergravity 2-form modes "wrapping" a finite 2-cycle in the resolution space. Reproducing the structure of the gauge theory result becomes more transparent in the large R-charge or BMN-like limit in which the resolved background takes a pp-wave form with the transverse space being a product of $\mathbb R^4$ and the Eguchi-Hanson space.

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arXiv2023

Integrability treatment of AdS/CFT orbifolds

We elaborate on the treatment of orbifolds of type IIB string theory on $AdS_5\times S^5$ and their dual gauge theories with integrability techniques. The implementation of orbifolds via twisted spin-chains, thermodynamic Bethe Ansatz equations with chemical potentials and $Y$- and $T$-systems with modified asymptotics is confronted with twisted boundary conditions of the string sigma-model. This allows us to consistently twist the quantum spectral curve, which is believed to bridge the two sides of the AdS/CFT duality. We discuss Abelian orbifolds of $PSU(2,2|4)$ and treat the special cases of $\mathcal{N}=2$ supersymmetric $\mathbb{Z}_2$-orbifolds and type 0B string theory on $AdS_5\times S^5$ as primary examples. This opens a pathway to probe the validity of the duality and to study the long-standing question of tachyon stabilisation in non-supersymmetric AdS/CFT. We comment on the current understanding of this issue and point out the next steps in this challenge.

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arXiv2022

On type 0 string theory in solvable RR backgrounds

Motivated by a possibility of solving non-supersymmetric type 0 string theory in $AdS_5 \times S^5$ background using integrability, we revisit the construction of type 0 string spectrum in some solvable examples of backgrounds with RR fluxes that are common to type IIB and type 0B theories. The presence of RR fluxes requires the use of a Green-Schwarz description for type 0 string theory. Like in flat space, the spectrum of type 0 theory can be derived from the type II theory spectrum by a $(-1)^F$ orbifolding, i.e. combining the untwisted sector where GS fermions are periodic with the twisted sector where GS fermions are antiperiodic (and projecting out all spacetime fermionic states). This construction of the type 0 spectrum may also be implemented using a Melvin background that allows to continuously interpolate between the type II and type 0 theories. As an illustration, we discuss the type 0B spectrum in the pp-wave background which is the Penrose limit of $AdS_5 \times S^5$ with RR 5-form flux and also in the pp-wave background which is the Penrose limit of $AdS_3 \times S^3 \times T^4$ supported by mixed RR and NSNS 3-form fluxes. We show that increasing the strength of the RR flux increases the value of the effective normal ordering constant (which determines the mass of the type 0 tachyon) and thus effectively decreases the momentum-space domain of instability of the ground state. We also comment on the semiclassical sector of states of type 0B theory in $AdS_5 \times S^5$.

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arXiv2020

The $F$-term Problem and other Challenges of Stringy Quintessence

We attempt a systematic analysis of string-theoretic quintessence models as an alternative to metastable de Sitter vacua. It appears that, within the boundaries of what is known, large-volume type-IIB flux compactifications are preferred. Here the quintessence scalar is the ratio of certain 4-cycle volumes. It has already been noticed that the volume modulus, which must be stabilized, tends to remain too light. One may call this the "light volume problem". In addition, we identify an "$F$-term problem": The positive energy density of standard-model SUSY breaking is higher than the depth of all known negative contributions. We discuss what it would take to resolve these issues and comment on partially related challenges for axionic quintessence. In particular, large cancellations between positive and negative potential terms appear unavoidable in general. As a further challenge, one should then explain why a small de-tuning cannot be used to uplift into a deep slow-roll regime, violating de Sitter swampland conjectures.

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