Prof Andre Lukas

Abstract:

We study heterotic Calabi-Yau compactifications with NSNS three-form flux in view of moduli stabilisation and investigate whether the value |W0| of the flux superpotential evaluated at supersymmetric minima can be small. Unlike in type IIB string theory, heterotic compactifications lack a no-scale structure, so that a non-vanishing flux superpotential generically induces a tree-level scalar potential for all moduli. Controlled moduli stabilisation therefore requires the flux superpotential to be sufficiently small in order to compete with non-perturbative effects. Working within a four-dimensional effective field theory and exploiting the special geometry of Calabi-Yau complex structure moduli spaces, we analyse the complex structure F-term equations and derive two no-go theorems: (1) supersymmetric vacua with vanishing |W0|, which would lead to a vanishing tree-level scalar potential as in type IIB, occur only at singular loci in moduli space, and (2) no supersymmetric vacua with small |W0| exist in the large complex structure limit. Motivated by these results, we analyse explicit models away from the large complex structure regime using exact period expressions and identify one- and two-parameter examples in which suitable flux choices allow for values of |W0| of order unity, with some one-parameter models admitting values moderately below unity. Our findings show that small heterotic flux superpotentials are highly constrained, with the values of |W0| found in the examples studied being only marginally compatible with moduli stabilisation.

Abstract:

We outline a method to determine analytic Kähler potentials with associated approximately Ricci‐flat Kähler metrics on Calabi–Yau manifolds. Key ingredients are numerically calculating Ricci‐flat Kähler potentials via machine learning techniques and fitting the numerical results to Donaldson's ansatz. We apply this method to the Dwork family of quintic hypersurfaces in P 4 $\mathbb {P}^4$ and an analogous one‐parameter family of bi‐cubic CY hypersurfaces in P 2 × P 2 $\mathbb {P}^2\times \mathbb {P}^2$ . In each case, a relatively simple analytic expression is obtained for the approximately Ricci‐flat Kähler potentials, including the explicit dependence on the complex structure parameter. We find that these Kähler potentials only depend on the modulus of the complex structure parameter.

Abstract:

Abstract We present a method to construct approximate analytic expressions for Ricci-flat K"ahler metrics on Calabi–-Yau threefolds with explicit dependence on the K"ahler moduli. Our strategy combines numerical data obtained from machine learning with an explicit analytic Ansatz for the K"ahler potential and symbolic regression methods. Specifically, we use neural networks to learn the K"ahler potential at selected points in K"ahler moduli space, fit this data to analytic expressions with K"ahler moduli-dependent parameters, and determine an analytic form of these coefficients as functions of the K"ahler moduli using symbolic regression. In this way, we reconstruct closed-form approximations to the Ricci-flat metric that retain explicit K"ahler-moduli dependence. We apply this method to two Calabi–-Yau threefolds with $h^{1,1}=2$, namely a bicubic hypersurface in $\mathbb{P}^2 \times \mathbb{P}^2$ and a bi-degree $(2,4)$ hypersurface in $\mathbb{P}^1 \times \mathbb{P}^3$, both of which admit nontrivial discrete symmetry groups that simplify the structure of the metric. In both cases, the resulting analytic expressions reproduce the numerically learned K"ahler potentials with percent-level accuracy and yield a Ricci-flatness measure that remains sufficiently small across the sampled region. Our results represent a concrete bridge between purely numerical results for Calabi–-Yau metrics and analytic constructions, opening the door to a systematic study of their dependence on K"ahler moduli.