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Severin Lüst

Publications and source records attributed to Severin Lüst.

At least 19 recordsLinked to original sources
arXiv2026

Warped Numerical Calabi-Yau Metrics

We compute numerical warped Type IIB flux backgrounds on Calabi-Yau threefolds following the construction of Giddings, Kachru, and Polchinski. Using physics-informed neural networks, we approximate all three ingredients required by the GKP setup: the Ricci-flat Calabi-Yau metric, the harmonic (2,1)-forms representing the imaginary self-dual three-form flux, and the warp factor, which solves a sourced Poisson equation on the internal manifold. We apply our pipeline to the Dwork family of quintics for two different flux vacua, one near a conifold point and one away from it, the latter serving as a numerical cross-check. With these tools, we study the singular bulk problem, and find that for our benchmark point close to the conifold, approximately 0.5 percent of the total Calabi-Yau volume sits in the throat, and the warp factor is an order of magnitude larger as compared to the bulk. We also introduce several improvements to techniques used for numerical studies of CY metrics and quantities derived from them that might be of interest independently of our application. These include an improved point sampling algorithm that produces samples that are more uniform under the Calabi-Yau measure, a feature-engineered spectral network for the metric, multi-step physics-informed training, and a weighted Huber loss tailored to stiff PDEs with highly non-uniform sources.

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arXiv2026

Effective potentials, warping, and implications for F-term uplifting

We analyse warping corrections to the scalar potential in flux compactifications of Type IIB string theory, focusing on their effect on $F$-term de Sitter uplifting in Calabi-Yau orientifold models. A systematic inverse-volume expansion allows us to derive the four-dimensional off-shell potential in the presence of warping and non-ISD 3-form fluxes. This corresponds to integrating out all massive Kaluza-Klein modes using the ten-dimensional equations of motion. We further propose a warped Kähler potential in four-dimensional $\mathcal{N}=1$ supergravity, and show that it is consistent with our ten-dimensional results. In the KKLT framework, we find that classical warping corrections, as well as mixed corrections involving non-ISD fluxes and quantum effects, are dominant, rendering the scenario effectively uncontrollable with current methods. By contrast, in LVS-like constructions these corrections are suppressed by inverse powers of the volume, specifically $\mathcal{V}^{1/2}$ or $\mathcal{V}^{1/6}$, depending on the concrete model.

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arXiv2026

Species Quantum Mechanics

In this note we introduce some concepts of Species Quantum Mechanics. Specifically, we consider quantum operators that correspond to the species number $N_s$ and the tower mass scale $m_t$ in the context of the swampland distance conjecture. We discuss the commutation relations, a possible wave function, and symplectic duality transformations on the conjugate variables. Furthermore, we argue that the Castellano-Ruiz-Valenzuela (CRV) pattern is a consequence of the canonical commutation rules of moduli space quantum mechanics. We also connect the canonical quantization to the periods of ${\cal N}=2$ Calabi-Yau compactifications to explore other aspects of the CRV pattern, including its possible connection to the Ooguri-Vafa-Verlinde black hole quantization procedure.

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arXiv2025

More Effective RS Field Theory

In this paper we derive the effective theory for a stabilized five-dimensional warped geometry, addressing several outstanding issues in this derivation. These include allowing for a non-zero 4d cosmological constant, accounting for constraints from both the UV and IR branes, and determining how the stabilized theory responds to an energy perturbation on each brane. We show how a consistent low-energy effective theory from a stable warped solution must respect a constraint that follows from the higher-dimensional Einstein equation. Satisfying the constraint requires that the 4d cosmological constant must be the same everywhere throughout the bulk, which means the stabilizing fields must adjust to allow for the same 4d curvature everywhere in the extra dimension. We show explicitly how this works in a 5d model, and how the correct 4d effective potential reproduces this behavior. We find that the cosmological constant generated from adding energy to one of the branes is unaffected by the details of the stabilization mechanism at leading order, despite the need for the stabilizing fields to adjust. In anticipation of a companion paper, we also briefly discuss how supersymmetry can be realized consistently in the 5d theory. In particular, we show how the stabilization mechanism remains consistent with sequestering, even as the supersymmetry-breaking energy is reflected in the stabilizing field throughout the bulk.

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arXiv2025

An index for flux vacua

We propose to use the winding number of the gradient of a scalar potential as a simple topological index that relates critical points in the interior of the scalar field space to the behavior of the potential at the (asymptotic) boundary of the field space. We demonstrate this technique for supersymmetric flux compactifications of M-theory on Calabi-Yau four-folds, and use the Fermat sextic as a simple, one-parameter example.

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arXiv2024

KKLT Ex Nihilo

Flux compactifications that give three- or four-dimensional Anti de Sitter vacua with a parametrically small negative cosmological constant are claimed to be ubiquitous in String Theory. However, the 1+1 and 2+1 dimensional CFT duals to such vacua should have very large central charges and rather unusual properties. We construct brane configurations that source these would-be AdS flux compactifications, and identify certain UV AdS geometries that these branes source. The central charge of the CFT duals to these UV AdS geometries place lower bounds on the absolute values of the cosmological constants of the AdS vacua. These bounds are incompatible with the scale separation needed to construct realistic cosmological models.

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arXiv2024

Effective Theory of Warped Compactifications and the Implications for KKLT

We argue that effective actions for warped compactifications can be subtle, with large deviations in the effective potential from naive expectations owing to constraint equations from the higher-dimensional metric. We demonstrate this deviation in a careful computation of the effective potential for the conifold deformation parameter of the Klebanov-Strassler solution. The uncorrected naive effective potential for the conifold was previously used to argue that the Klebanov-Strassler background would be destabilized by antibranes placed at the conifold infrared tip unless the flux was uncomfortably large. We show this result is too strong because the formerly neglected constraint equations eliminate the features of the potential that allowed for the instability in the de Sitter uplift of the KKLT scenario.

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arXiv2023

Tadpoles and Gauge Symmetries

The tadpole conjecture proposes that complex structure moduli stabilisation by fluxes that have low tadpole charge can be realised only at special points in moduli space, leading generically to (large) gauge symmetries. Here we provide an exhaustive survey of the gauge symmetries arising in F-theory flux compactifications on products of attractive $\mbox{K3}$ surfaces, with complex structure moduli fully stabilised. We compute the minimal rank of the left-over non-abelian gauge group for all flux configurations within the tadpole bound, finding that it is always non-zero. It decreases in a roughly linear fashion with the tadpole charge, reaching zero at charge 30. By working out possible gauge algebras for different values of the tadpole, we find that all simple ADE Lie algebras of rank $\le 18$ appear.

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arXiv2022

Holography and the KKLT Scenario

The KKLT scenario, one of the few ideas to realize dS vacua in string theory, consists of two steps: the first involves the construction of a supersymmetric AdS vacuum with a small negative cosmological constant, and the second involves breaking supersymmetry and uplifting the energy to achieve dS. In this paper we use conventional holography to argue why it is not possible to complete the first step. We obtain this by putting a bound on the central charge of the dual theory which involves branes wrapping special Lagrangian cycles in CY 4-folds. We find that $l_{\rm AdS}^2 \lesssim χ(CY_4)$. Since $l_{\rm species}^2\gtrsim χ(CY_4)$ this leads to $l_{\rm AdS}/l_{\rm species}\lesssim 1$ leading at best to a highly curved AdS which is beyond the validity of the EFT.

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arXiv2022

The Tadpole Conjecture in the Interior of Moduli Space

We revisit moduli stabilization on Calabi-Yau manifolds with a discrete symmetry. Invariant fluxes allow for a truncation to a symmetric locus in complex structure moduli space and hence drastically reduce the moduli stabilization problem in its dimensionality. This makes them an ideal testing ground for the tadpole conjecture. For a large class of fourfolds, we show that an invariant flux with non-zero on-shell superpotential on the symmetric locus necessarily stabilizes at least 60% of the complex structure moduli. In case this invariant flux induces a relatively small tadpole, it is thus possible to bypass the bound predicted by the tadpole conjecture at these special loci. As an example, we discuss a Calabi-Yau hypersurface with $h^{3,1}=3878$ and show that we can stabilize at least 4932 real moduli with a flux that induces M2-charge $N_\text{flux} =3$.

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arXiv2021

Holographic BCFTs and Communicating Black Holes

We study the AdS/BCFT duality between two-dimensional conformal field theories with two boundaries and three-dimensional anti-de Sitter space with two Karch-Randall branes. We compute the entanglement entropy of a bipartition of the BCFT, on both the gravity side and the field theory side. At finite temperature this entanglement entropy characterizes the communication between two braneworld black holes, coupled to each other through a common bath. We find a Page curve consistent with unitarity. The gravitational result, computed using double-holographically realized quantum extremal surfaces, matches the conformal field theory calculation. At zero temperature, we obtain an interesting extension of the AdS$_3$/BCFT$_2$ correspondence. For a central charge $c$, we find a gap $(\frac{c}{16},\frac{c}{12})$ in the spectrum of the scaling dimension $Δ_{\text{bcc}}$ of the boundary condition changing operator (which interpolates mismatched boundary conditions on the two boundaries of the BCFT). Depending on the value of $Δ_{\text{bcc}}$, the gravitational dual is either a defect global AdS$_3$ geometry or a single sided black hole, and in both cases there are two Karch-Randall branes.

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arXiv2021

An update on moduli stabilization with antibrane uplift

It was recently shown that in warped compactifications based on a Klebanov-Strassler throat there is a light complex structure field, governing the size of the throat and the redshift at its tip. We show that after uplift of the cosmological constant by an anti-D3 brane at the tip of the throat, the contribution to supersymmetry breaking coming from the new light field is large. We work out the mass scales, in particular the condition for this field to be heavier than the Kähler modulus. We check that for the range of parameters relevant for the destabilization we find agreement with de Sitter swampland conjecture. Adding matter fields on distant branes, we discuss the effects on supersymmetry breaking in the observable sector. A hierarchically small scale of supersymmetry breaking translates generically into large values of localized D3 charges in the manifold.

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arXiv2021

On the weak gravity conjecture in string theory with broken supersymmetry

We use type I string models with supersymmetry broken by compactification (à la Scherk-Schwarz) in order to test the weak gravity conjecture in the presence of runaway potentials in a perturbative string theory setting. For a finite value of the supersymmetry breaking radius there is a runaway potential, which is the only possibility if one accepts the non-existence of de Sitter vacua. Although the weak gravity conjecture is valid in the decompactification limit, for fixed values of the radius we show that there are short-ranged attractive D1 brane-brane interactions. We argue however that at one-loop level the effective tension of the branes decreases and becomes smaller than the effective charge such that there is a long-ranged repulsive force and the weak gravity conjecture is respected. Moreover, for very small $g_s$ we expect a large number of stable bound states to be present.

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arXiv2021

Algorithmically solving the Tadpole Problem

The extensive computer-aided search applied in [arXiv:2010.10519] to find the minimal charge sourced by the fluxes that stabilize all the (flux-stabilizable) moduli of a smooth K3xK3 compactification uses differential evolutionary algorithms supplemented by local searches. We present these algorithms in detail and show that they can also solve our minimization problem for other lattices. Our results support the Tadpole Conjecture: The minimal charge grows linearly with the dimension of the lattice and, for K3xK3, this charge is larger than allowed by tadpole cancelation. Even if we are faced with an NP-hard lattice-reduction problem at every step in the minimization process, we find that differential evolution is a good technique for identifying the regions of the landscape where the fluxes with the lowest tadpole can be found. We then design a "Spider Algorithm," which is very efficient at exploring these regions and producing large numbers of minimal-tadpole configurations.

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arXiv2021

The Tadpole Problem

We examine the mechanism of moduli stabilization by fluxes in the limit of a large number of moduli. We conjecture that one cannot stabilize all complex-structure moduli in F-theory at a generic point in moduli space (away from singularities) by fluxes that satisfy the bound imposed by the tadpole cancelation condition. More precisely, while the tadpole bound in the limit of a large number of complex-structure moduli goes like 1/4 of the number of moduli, we conjecture that the amount of charge induced by fluxes stabilizing all moduli grows faster than this, and is therefore larger than the allowed amount. Our conjecture is supported by two examples: K3 x K3 compactifications, where by using evolutionary algorithms we find that moduli stabilization needs fluxes whose induced charge is 44% of the number of moduli, and Type IIB compactifications on CP^3, where the induced charge of the fluxes needed to stabilize the D7-brane moduli is also 44% of the number of these moduli. Proving our conjecture would rule out de Sitter vacua obtained via antibrane uplift in long warped throats with a hierarchically small supersymmetry breaking scale, which require a large tadpole.

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arXiv2020

Swampland, Gradient Flow and Infinite Distance

In the first part of this paper we will work out a close and so far not yet noticed correspondence between the swampland approach in quantum gravity and geometric flow equations in general relativity, most notably the Ricci flow. We conjecture that following the gradient flow towards a fixed point, which is at infinite distance in the space of background metrics, is accompanied by an infinite tower of states in quantum gravity. In case of the Ricci flow, this conjecture is in accordance with the generalized distance and AdS distance conjectures, which were recently discussed in the literature, but it should also hold for more general background spaces. We argue that the entropy functionals of gradient flows provide a useful definition of the generalized distance in the space of background fields. In particular we give evidence that for the Ricci flow the distance $Δ$ can be defined in terms of the mean scalar curvature of the manifold, $Δ\sim\log \bar R$. For a more general gradient flow, the distance functional also depends on the string coupling constant. In the second part of the paper we will apply the generalized distance conjecture to gravity theories with higher curvature interactions, like higher derivative $R^2$ and $W^2$ terms. We will show that going to the weak coupling limit of the higher derivative terms corresponds to the infinite distance limit in metric space and hence this limit must be accompanied by an infinite tower of light states. For the case of the $R^2$ or $W^2$ couplings, this limit corresponds to the limit of a small cosmological constant or, respectively, to a light additional spin-two field in gravity. In general we see that the limit of small higher curvature couplings belongs to the swampland in quantum gravity, just like the limit of a small $U(1)$ gauge coupling belongs to the swampland as well.

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