arXiv subjects

Linus Wulff

Publications and source records attributed to Linus Wulff.

At least 19 recordsLinked to original sources

arXiv2025

One loop in $D=11$ vs $D=10$: 4-point check

The one-loop correction to eleven-dimensional supergravity involves a cubically divergent term $t_8t_8R^4$, with four Riemann tensors. A similar term (with finite coefficient) has been argued to be present in the M-theory effective action. It is expected to reduce to a similar one-loop term present in the type IIA effective action. This has previously been verified in the NSNS sector at the 4-point level. Here we extend this result to couplings of NSNS and RR fields, which have been computed using the pure spinor formalism. In particular, we check all couplings of RR fields to the dilaton as well as all couplings involving the metric and RR three-form. Correcting some minor mistakes in the literature we find complete agreement. We also give a complete analysis of 4-point terms in eleven dimensions computed previously from superparticle amplitudes and present a very simple form for these.

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arXiv2024

No manifest T-duality at order $\alpha'^3$

When reduced from $10$ to $10-d$ dimensions tree-level string theory exhibits an $O(d,d)$ symmetry. This symmetry, which is closely related to T-duality, appears only after certain field redefinitions. We find a simple form for a subset of these redefinitions at order $\alpha'^3$ and show that they cannot be lifted to ten dimensions. This is inconsistent with ``manifestly T-duality invariant'' approaches such as generalized geometry (in the uncompactified setting). Such formulations therefore seem not to be the correct language to describe string theory.

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arXiv2024

Second order bosonic string effective action from $O(d,d)$

The corrections to the tree-level effective action for the bosonic string up to second order in $\alpha'$ are fixed by requiring its dimensional reduction to $26-d$ dimensions to be compatible with $O(d,d)$ symmetry. The result is in agreement with the literature, but takes a simpler form than previously know expressions. We identify some structures in the Lagrangian which appear at least at the first three orders in $\alpha'$.

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arXiv2024

Tree-level $R^4$ correction from $O(d,d)$: NS-NS five-point terms

The tree-level string effective action reduced from $D$ to $D-d$ dimensions possesses a continuous $O(d,d)$ symmetry, closely related to T-duality. A necessary condition for a higher derivative correction to preserve this symmetry is that certain $O(d,d)$ violating terms which appear in the dimensional reduction have to cancel out. We use this idea to complete the quartic Riemann correction with all terms involving five NS-NS sector fields. The resulting Lagrangian is considerably simpler than expressions that have previously appeared in the literature.

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arXiv2022

The $\alpha'^2$ correction from double field theory

It is known that the order $\alpha'$ correction to the tree-level effective action for the bosonic and heterotic string can be described in the framework of Double Field Theory (DFT). Here we determine the DFT action and transformations at order $\alpha'^2$ by a direct calculation. The result is vastly simpler than previous proposals. We show that this correction reproduces the known $\alpha'^2$ correction to the heterotic string effective action. The relation of our action to an (implicit) all order proposal coming from the so-called generalized Bergshoeff-de Roo identification is also discussed.

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arXiv2021

Completing $R^4$ using $O(d,d)$

The tree-level string effective action is known to contain quartic Riemann terms with coefficient $\zeta(3)\alpha'^3$. In the case of the type II string this is the first $\alpha'$ correction. We use the requirement that the action reduced on a $d$-torus should have an $O(d,d)$ symmetry to find the B-field couplings up to fifth order in fields. The answer turns out to have a surprisingly intricate structure.

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arXiv2021

String theory at order $\alpha'^2$ and the generalized Bergshoeff-de Roo identification

It has been shown by Marques and Nunez that the first $\alpha'$-correction to the bosonic and heterotic string can be captured in the $O(D,D)$ covariant formalism of Double Field Theory via a certain two-parameter deformation of the double Lorentz transformations. This deformation in turn leads to an infinite tower of $\alpha'$-corrections and it has been suggested that they can be captured by a generalization of the Bergshoeff-de Roo identification between Lorentz and gauge degrees of freedom in an extended DFT formalism. Here we provide strong evidence that this indeed gives the correct $\alpha'^2$-corrections to the bosonic and heterotic string by showing that it leads to a cubic Riemann term for the former but not for the latter, in agreement with the known structure of these corrections including the coefficient of Riemann cubed.

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arXiv2020

O(D,D) and the string $\alpha'$ expansion: An obstruction

Double Field Theory (DFT) is an attempt to make the O(d,d) T-duality symmetry of string theory manifest, already before reducing on a d-torus. It is known that supergravity can be formulated in an O(D,D) covariant way, and remarkably this remains true to the first order in $\alpha'$. We set up a systematic way to analyze O(D,D) invariants, working order by order in fields, which we carry out up to order $\alpha'^3$. At order $\alpha'$ we recover the known Riemann squared invariant, while at order $\alpha'^2$ we find no independent invariant. This is compatible with the $\alpha'$ expansion in string theory. However, at order $\alpha'^3$ we show that there is again no O(D,D) invariant, in contradiction to the fact that all string theories have a quartic Riemann invariant with coefficient proportional to $\zeta(3)$. We conclude that DFT and similar frameworks cannot capture the full $\alpha'$ expansion in string theory.

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arXiv2020

Relaxing unimodularity for Yang-Baxter deformed strings

We consider so-called Yang-Baxter deformations of bosonic string sigma-models, based on an $R$-matrix solving the (modified) classical Yang-Baxter equation. It is known that a unimodularity condition on $R$ is sufficient for Weyl invariance at least to two loops (first order in $\alpha'$). Here we ask what the necessary condition is. We find that in cases where the matrix $(G+B)_{mn}$, constructed from the metric and $B$-field of the undeformed background, is degenerate the unimodularity condition arising at one loop can be replaced by weaker conditions. We further show that for non-unimodular deformations satisfying the one-loop conditions the Weyl invariance extends at least to two loops (first order in $\alpha'$). The calculations are simplified by working in an $O(D,D)$-covariant doubled formulation.

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arXiv2020

Quantum correction to generalized T-dualities

Poisson-Lie duality is a generalization of abelian and non-abelian T-duality, and it can be viewed as a map between solutions of the low-energy effective equations of string theory, i.e. at the (super)gravity level. We show that this fact extends to the next order in $\alpha'$ (two loops in $\sigma$-model perturbation theory) provided that the map is corrected. The $\alpha'$-correction to the map is induced by the anomalous Lorentz transformations of the fields that are necessary to go from a doubled $O(D,D)$-covariant formulation to the usual (super)gravity description.

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arXiv2020

The first $\alpha'$-correction to homogeneous Yang-Baxter deformations using $O(d,d)$

We use the $O(d,d)$-covariant formulation of supergravity familiar from Double Field Theory to find the first $\alpha'$-correction to (unimodular) homogeneous Yang-Baxter (YB) deformations of the bosonic string. A special case of this result gives the $\alpha'$-correction to TsT transformations. In a suitable scheme the correction comes entirely from an induced anomalous double Lorentz transformation, which is needed to make the two vielbeins obtained upon the YB deformation equal. This should hold more generally, in particular for abelian and non-abelian T-duality, as we discuss.

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arXiv2019

Two-loop conformal invariance for Yang-Baxter deformed strings

The so-called homogeneous Yang-Baxter (YB) deformations can be considered a non-abelian generalization of T-duality--shift--T-duality (TsT) transformations. TsT transformations are known to preserve conformal symmetry to all orders in $\alpha'$. Here we argue that (unimodular) YB deformations of a bosonic string also preserve conformal symmetry, at least to two-loop order. We do this by showing that, starting from a background with no NSNS-flux, the deformed background solves the $\alpha'$-corrected supergravity equations to second order in the deformation parameter. At the same time we determine the required $\alpha'$-corrections of the deformed background, which take a relatively simple form. In examples that can be constructed using, possibly non-commuting sequences of, TsT transformations we show how to obtain the first $\alpha'$-correction to all orders in the deformation parameter by making use of the $\alpha'$-corrected T-duality rules. We demonstrate this on the specific example of YB deformations of a Bianchi type II background.

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arXiv2019

Constraining integrable AdS/CFT with factorized scattering

We consider (warped) AdS string backgrounds which allow for a GKP spinning string/null cusp solution. Integrability implies that the worldsheet S-matrix should factorize, which in turn constrains the form of the warp factor as a function of the coordinates of the internal space. This constraint is argued to rule out integrability for all supersymmetric AdS7 and AdS6 backgrounds as well as AdS5 Gaiotto-Maldacena backgrounds and a few highly supersymmetric AdS4 and AdS3 backgrounds.

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arXiv2018

Marginal deformations of WZW models and the classical Yang-Baxter equation

We show how so-called Yang-Baxter (YB) deformations of sigma models, based on an R-matrix solving the classical Yang-Baxter equation (CYBE), give rise to marginal current-current deformations when applied to the Wess-Zumino-Witten (WZW) model. For non-compact groups these marginal deformations are more general than the ones usually considered, since they can involve a non-abelian current subalgebra. We classify such deformations of the AdS(3) x S(3) string.

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arXiv2018

Non-abelian T-duality and Yang-Baxter deformations of Green-Schwarz strings

We perform non-abelian T-duality for a generic Green-Schwarz string with respect to an isometry (super)group G, and we derive the transformation rules for the supergravity background fields. Specializing to G bosonic, or G fermionic but abelian, our results reproduce those available in the literature. We discuss also continuous deformations of the T-dual models, obtained by adding a closed B-field before the dualization. This idea can also be used to generate deformations of the original (un-dualized) model, when the 2-cocycle identified from the closed B is invertible. The latter construction is the natural generalization of the so-called Yang-Baxter deformations, based on solutions of the classical Yang-Baxter equation on the Lie algebra of G and originally constructed for group manifolds and (super)coset sigma models. We find that the deformed metric and B-field are obtained through a generalization of the Seiberg-Witten map. When applied to integrable sigma models these deformations preserve the integrability.

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arXiv2018

Trivial solutions of generalized supergravity vs non-abelian T-duality anomaly

The equations that follow from kappa symmetry of the type II Green-Schwarz string are a certain deformation, by a Killing vector field $K$, of the type II supergravity equations. We analyze under what conditions solutions of these `generalized' supergravity equations are trivial in the sense that they solve also the standard supergravity equations. We argue that for this to happen $K$ must be null and satisfy $dK=i_KH$ with $H=dB$ the NSNS three-form field strength. Non-trivial examples are provided by symmetric pp-wave solutions. We then analyze the consequences for non-abelian T-duality and the closely related homogenous Yang-Baxter sigma models. When one performs non-abelian T-duality of a string sigma model on a non-unimodular (sub)algebra one generates a non-vanishing $K$ proportional to the trace of the structure constants. This is expected to lead to an anomaly but we show that when $K$ satisfies the same conditions the anomaly in fact goes away leading to more possibilities for non-anomalous non-abelian T-duality.

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arXiv2017

Classifying integrable symmetric space strings via factorized scattering

All symmetric space $AdS_n$ solutions of type II supergravity have recently been found for $n>2$. For the supersymmetric solutions (and their T-duals) it is known that the Green-Schwarz string is classically integrable. We complete the classification by ruling out integrability for the remaining non-supersymmetric solutions. This is achieved by showing that tree-level scattering on the worldsheet of a GKP or BMN string fails to factorize for these cases.

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arXiv2017

Condition on Ramond-Ramond fluxes for factorization of worldsheet scattering in anti-de Sitter space

Factorization of scattering is the hallmark of integrable 1+1 dimensional quantum field theories. For factorization of scattering to be possible the set of masses and momenta must be conserved in any two-to-two scattering process. We use this fact to constrain the form of the Ramond-Ramond fluxes for integrable supergravity anti-de Sitter backgrounds by analysing tree-level scattering of two AdS bosons into two fermions on the worldsheet of a BMN string. We find a condition which can be efficiently used to rule out integrability of AdS strings and therefore of the corresponding AdS/CFT dualities, as we demonstrate for some simple examples.

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