arXiv subjects

Simon Schreyer

Publications and source records attributed to Simon Schreyer.

8 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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arXiv2025

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 K\"ahler 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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arXiv2024

Higher order corrections to KPV: The nonabelian brane stack perspective

In this work, we study the decay of $\overline{D3}$-branes in the setup of Kachru, Pearson, and Verlinde (KPV) at higher order in $\alpha'$ from the perspective of a nonabelian $\overline{D3}$-brane stack. We extend the leading order analysis of KPV by including higher order commutators as well as higher derivative corrections. Recently, the KPV setup has been studied at higher order in $\alpha'$ from the NS5-brane perspective. It was found that in order to control $\alpha'$ corrections the quantity $g_sM^2$ determining the amount of warping in the Klebanov-Strassler throat has to be much larger than expected. This leads to serious issues when using the $\overline{D3}$-branes as an uplift to dS. The benefit of the analysis in this work is that the $\overline{D3}$-brane perspective is controlled when the distance between the branes inside the brane stack is substringy which is a regime not controlled on the NS5-brane side. As a main result, we find that the strong bound $g_sM^2\sim \mathcal{O}(100)$ obtained on the NS5-brane also holds in the regime accessible from the $\overline{D3}$-brane perspective. We also show that the novel way of uplifting proposed in the recent work on $\alpha'$ corrections to the KPV setup can only work for small warped throats.

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arXiv2023

No Asymptotic Acceleration without Higher-Dimensional de Sitter Vacua

There has recently been considerable interest in the question whether and under which conditions accelerated cosmological expansion can arise in the asymptotic regions of field space of a $d$-dimensional EFT. We conjecture that such acceleration is impossible unless there exist metastable de Sitter vacua in more than $d$ dimensions. That is, we conjecture that `Asymptotic Acceleration Implies de Sitter' (AA$\Rightarrow$DS). Phrased negatively, we argue that the $d$-dimensional `No Asymptotic Acceleration' conjecture (a.k.a.~the `strong asymptotic dS conjecture') follows from the de Sitter conjecture in more than $d$ dimensions. The key idea is that the relevant field-space asymptotics almost always correspond to decompactification and that the only positive energy contribution which decays sufficiently slowly in this regime is the vacuum energy of a higher-dimensional metastable vacuum. This result is in agreement with recent Swampland bounds on the potential in the asymptotics in field space from e.g. the species bound, but is significantly more constraining. We further note that for our asymptotic decompactification limits based on higher-dimensional de Sitter, the Kaluza-Klein scale always falls below the Hubble scale asymptotically. In fact, this occurs whenever $|V'|/V \leq 2 \sqrt{(d+k-2)/k(d-2)}$ asymptotically, with $k$ the number of decompactifying internal directions. This is steeper than what is needed for accelerated expansion.

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arXiv2022

$\alpha'$ corrections to KPV: An uplifting story

In earlier work, the effect of $\alpha'^2$ curvature corrections on the NS5-brane responsible for the decay of anti-D3-branes in the set-up of Kachru, Pearson, and Verlinde (KPV) was considered. We extend this analysis to include all known $\alpha'^2$ corrections to the action of an abelian fivebrane which involve not just curvature but also gauge fields and flux. We compute the value of these terms at the tip of the Klebanov-Strassler throat to obtain the $\alpha'^2$ corrected potential for the NS5-brane of KPV. The resulting potential provides a novel uplifting mechanism where one can obtain metastable vacua with an arbitrarily small positive uplifting potential by fine-tuning $\alpha'$ corrections against the tree-level potential. This mechanism works for small warped throats, both in terms of size and contribution to the D3-tadpole, thereby sidestepping the issues associated with a standard deep warped throat uplift which are deadly in KKLT and, as we explicitly check, severely constraining in the Large Volume Scenario.

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arXiv2022

Curvature corrections to KPV: Do we need deep throats?

We consider $\alpha'^2$ curvature corrections to the action of an NS5-brane which plays the key role in the metastability analysis of warped anti-D3-brane uplifts by Kachru, Pearson and Verlinde (KPV). Such corrections can dramatically alter the KPV analysis. We find that for the $\alpha'^2$-corrections to be sufficiently small to recover essentially the leading-order KPV potential one needs a surprisingly large $S^3$ radius, corresponding to $g_sM > 20$. In the context of the Large Volume Scenario (LVS) this implies a D3-tadpole of at least $\mathcal{O}(10^3-10^4)$. However, large $\alpha'^2$-corrections do not necessarily spoil the uplift in KPV. Rather, as the curvature corrections lower the tension of the brane, a novel uplifting mechanism suggests itself where the smallness of the uplift is achieved by a tuning of curvature corrections. A key underlying assumption is the existence of a dense discretuum of $g_s$. This new mechanism does not require a deep warped throat, thereby sidestepping the main difficulty in uplifting KKLT and LVS. However, all of the above has to be treated as a preliminary exploration of possibilities since, at the moment, not all relevant correction at the order $\alpha'^2$ are known.

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arXiv2022

Loops, Local Corrections and Warping in the LVS and other Type IIB Models

To establish metastable de Sitter vacua or even just scale-separated AdS, control over perturbative corrections to the string-derived leading-order 4d lagrangian is crucial. Such corrections can be classified in three types: First, there are genuine loop effects, insensitive to the UV completion of the 10d theory. Second, there are local $\alpha'$ corrections or, equivalently, 10d higher-dimension operators which may or may not be related to loop-effects. Third, warping corrections affect the 4d Kahler potential but are expected not to violate the 4d no-scale structure. With this classification in mind, we attempt to derive the Berg-Haack-Pajer conjecture for Kahler corrections in type-IIB Calabi-Yau orientifolds and extend it to include further terms. This is crucial since the interesting applications of this conjecture are in the context of generic Calabi-Yau geometries rather than in the torus-based models from which the main motivation originally stems. As an important by-product, we resolve a known apparent inconsistency between the parametric behaviour of string loop results and field-theoretic expectations. Our findings lead to some interesting new statements concerning loop effects associated with blowup-cycles, loop corrections in fibre inflation, and possible logarithmic effects in the Kahler and scalar potential.

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arXiv2022

The LVS Parametric Tadpole Constraint

The large volume scenario (LVS) for de Sitter compactifications of the type IIB string is, at least in principle, well protected from various unknown corrections. The reason is that, by construction, the Calabi-Yau volume is exponentially large. However, as has recently been emphasised, in practice the most explicit models are rather on the border of parametric control. We identify and quantify parametrically what we believe to be the main issue behind this difficulty. Namely, a large volume implies a shallow AdS minimum and hence a small uplift. The latter, if it relies on an anti-D3 in a throat, requires a large negative tadpole. As our main result, we provide a simple and explicit formula for what this tadpole has to be in order to control the most dangerous corrections. The fundamental ingredients are parameters specifying the desired quality of control. We comment on the interplay between our constraint and the tadpole conjecture. We also discuss directions for future work which could lead to LVS constructions satisfying the tadpole constraint with better control, as well as further challenges that may exist for the LVS. Our formula then represents a very concrete challenge for future searches for and the understanding of relevant geometries.

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