arXiv subjects

Ivo Sachs

Publications and source records attributed to Ivo Sachs.

At least 19 recordsLinked to original sources

arXiv2026

Inflationary Bispectra and IR Physics from Quantum Simulators

Bose-Einstein condensates have been used successfully as quantum simulators for early-universe particle production. Here we extend this analogy to the interacting theory. To this end, we compute the leading interaction terms expected in a general experimental setup that determine the 3-point correlations. We apply them to cosmologically motivated expanding model universes, but also periodically oscillating ones. While expanding scale factors do not necessarily lead to easily observable signatures due to experimental constraints on the realizable scale factor, periodically driven ones produce resonant correlators that grow linearly over time and lend themselves well to experimental detection. One direct application of this analysis is the experimental study of late-time infrared divergencies often discussed in the context of massless scalars in de Sitter space.

hep-th↗

arXiv2026

Gravitational instantons from closed superstring field theory

We test exact marginality of the deformation describing the resolution of a $\mathbb{Z}_2$ orbifold by analyzing the closed superstring equations of motion to third order in the size, including $\alpha'$ corrections. We find that the third order correction is unobstructed for all deformation moduli. We are also able to reproduce the Eguchi-Hanson gravitational instanton up to the second order in the field theory limit with a suitable choice of moduli.

hep-th↗

arXiv2026

Probing of colliding wave spacetimes and a quantum Weyl conjecture

We perform a quantum probing of colliding plane-wave space-times. In particular, we consider the Khan-Penrose and the Ferrari-Ib\'a\~nez solutions, which admit a strong and a weak singularity after the two waves collide. While we find that, like Schwarzschild, for the Khan-Penrose solution the singularity cannot be probed by quantum field theory, the Ferrari-Ib\'a\~nez singularity can be traversed. Our results culminate in a quantum Weyl conjecture: The significant geometric property to classify space-times with respect to quantum probes is given by the Coulomb part of the Weyl tensor. We then use this conjecture to sketch a possible backreaction scenario for plane waves.

hep-th↗

arXiv2026

Split Representations and Bubble Resummation for Massive de Sitter Correlators

We combine spectral- and split representations to factorize multi-loop momentum space diagrams, in the Schwinger-Keldysh formulation for cosmological correlators, with massive scalars in the loop. This allows us to extend the resummation of loop contributions from flat to de Sitter space. Furthermore, in our split representation the signal part of the correlators can be identified directly on the integrand level from the spectral function. We apply this to describe the non-perturbative flow of the EFT background and the cosmological collider signals in a large-N model.

hep-th↗

arXiv2026

The 2-Dimensional Dual of $\phi^4$ in AdS$_3$

We study the correlation functions of a conformally coupled $\phi^4$-interacting theory in AdS$_3$ and its dual CFT$_2$. The one-loop diagram is not expressible in terms of known transcendental functions, but is shown to be expressible as an infinite sum of previously well-studied tree-level diagrams, and we compute this sum using several number-theoretic conjectures. This enables us to extract recursively, the analytic expressions of anomalous dimensions of all dual double-trace operators. In the $s$-channel various consistency checks were performed against established bootstrap method, while our results in the $t$- and $u$-channel are not available in any previous literature to our knowledge.

hep-th↗

arXiv2026

Cosmological Correlator Discontinuities from Scattering Amplitudes

Recent theoretical work has revealed that basic observables of quantum field theory in de Sitter space, known as in-in or cosmological correlators, exhibit surprisingly simple mathematical structure reminiscent of scattering amplitudes in flat space. For many theories, this simplicity can be made manifest using a set of ``cosmological dressing rules'' which uplift flat-space Feynman diagrams to in-in correlators in de Sitter space by attaching auxiliary propagators to the interaction vertices. In this paper, we show that discontinuities of cosmological correlators with respect to internal energy variables can be obtained by applying auxiliary propagators to unitarity cuts of flat space Feynman diagrams. Moreover, discontinuities with respect to external energy variables can be obtained by cutting auxiliary propagators attached to Feynman diagrams. This observation in turn implies highly non-trivial constraints on cosmological correlators in the form of simple sum rules. We illustrate these ideas in a number of examples at tree-level and 1-loop for conformally coupled scalar theories, although they hold more generally. Finally, we show how to reconstruct cosmological correlators from their discontinuities using dispersion relations, providing a powerful new approach to computing cosmological observables by systematically reconstructing them from data uplifted from flat space.

hep-th↗

arXiv2026

On Duality Invariant Yang-Mills Theory

We provide an explicit construction of a manifestly duality invariant, interacting deformation of Maxwell theory in four dimensions in terms of mutually local, but interacting 1- and 3-forms. Interestingly, our theory is formulated directly as a BRST quantized gauge theory, while the underlying gauge invariant Lagrangian before gauge fixing is obscured. Furthermore, the underlying gauge invariance is based on an associative, rather than a Lie symmetry.

hep-th↗

arXiv2025

Yang-Mills Theory and the $\mathcal{N}=2$ Spinning Path Integral

We embed the perturbative Fock state of the Yang-Mills BV-multiplet in the vertex operator algebra of the path-integral for the $\mathcal{N}=2$ supersymmetric world line and evaluate the pull-back of the latter to an integral form on supermoduli space. Choosing a suitable Poincar\'e dual on the latter, we show that this integral form describes an extension of Yang-Mills theory. Upon projection back to the Fock space, we recover the Yang-Mills action from the world line. This furthermore gives an a priori justification for the construction of Yang-Mills equations of motion as emerging from deformations of the BRST differential.

hep-th↗

arXiv2025

Resummation of Cosmological Correlators and their UV-Regularization

Cosmological correlators are important observables in cosmology. They are often approximated by de Sitter space correlators. In this paper, we give a first precise diagrammatical computation of higher loop diagrams to all orders for a conformally coupled scalar in four dimensions. We show that, in contrast to flat space, diagrams of necklace topology do not resum using the natural application of de Sitter-invariant regularization and are thus hard to evaluate. We propose a modification to the UV-regularization of the loops, compatible with de Sitter invariance, but much easier to work with. The modified diagrams can be resummed to give a glimpse at non-perturbative effects for de Sitter correlators. Furthermore, they fit nicely with recently proposed cosmological dressing rules.

hep-th↗

arXiv2025

BCOV on the Large Hilbert Space

We formulate the BCOV theory of deformations of complex structures as a pull-back to the super moduli space of the worldline of a spinning particle. In this approach the appearance of a non-local kinetic term in the target space action has the same origin as the mismatch of pictures in the Ramond sector of super string field theory and is resolved by the same type of auxiliary fields in shifted pictures. The BV-extension is manifest in this description. A compensator for the holomorphic 3-form can be included by resorting to a description in the large Hilbert space.

hep-th↗

arXiv2025

On Spinning Particles, their Partition Functions and Picture Changing Operators

We compute the partition function for the $N=1$ spinning particle, including pictures and the large Hilbert space, and show that it counts the dimension of the BRST cohomology in two- and four-dimensional target space. We also construct a quadratic action in the target space. Furthermore, we find a consistent interaction as a derived bracket based on the associative product of world line fields, leading to an interacting theory of multiforms in space-time. Finally, we comment on the equivalence of the multiform theory with a Dirac fermion. We also identify the chiral anomaly of the latter with a Hodge anomaly for the multiform theory, which manifests itself as a deformation of the gauge fixing.

hep-th↗

arXiv2025

Cosmological Dressing Rules

The basic observables in cosmology are known as in-in correlators. Recent calculations have revealed that in-in correlators in four dimensional de Sitter space exhibit hidden simplicity stemming from a close relation to scattering amplitudes in flat space. In this paper we explain how to make this property manifest by dressing flat space Feynman diagrams with certain auxiliary propagators. These dressing rules are derived for conformally coupled and massless scalar theories and we show that they reproduce the same infrared divergences predicted by the Schwinger-Keldysh formalism.

hep-th↗

arXiv2025

Yang-Mills Theory From Super Moduli Space

For the spinning superparticle we construct the pull-back of the world-line path integral to super moduli space in the Hamiltonian formulation. We describe the underlying geometric decomposition of super moduli space. Algebraically, this gives a realization of the cyclic complex. The resulting space-time action is classically equivalent to Yang-Mills theory up to boundary terms and additional non-local interactions.

hep-th↗

arXiv2024

The Subtle Simplicity of Cosmological Correlators

We investigate cosmological correlators for conformally coupled $ϕ^4$ theory in four-dimensional de Sitter space. These \textit{in-in} correlators differ from scattering amplitudes for massless particles in flat space due to the spacelike structure of future infinity in de Sitter. They also require a regularization which preserves de Sitter-invariance, which makes the flat space limit subtle to define at loop-level. Nevertheless we find that up to two loops, the \textit{in-in} correlators are structurally simpler than the wave function and have the same transcendentality as flat space amplitudes. Moreover, we show that their loop integrands can be recast in terms of flat space integrands and can be derived from a novel recursion relation.

hep-th↗

arXiv2024

On Superparticles and their Partition Functions

We describe a family of twisted partition functions for the relativistic spinning particle models. For suitable choices of fugacities this computes a refined Euler characteristics that counts the dimension of the physical states for arbitrary picture and, furthermore, encodes the complete BV-spectrum of the effective space-time gauge theory originating from this model upon second quantization. The relation between twisted world-line partition functions and the spectrum of the space-time theory is most easily seen on-shell but we will give an off-shell description as well. Finally we discuss the construction of a space-time action in terms of the world-line fields in analogy to string field theory.

hep-th↗

arXiv2023

Bulk Landau Pole and Unitarity of Dual Conformal Field Theory

The singlet sector of the $O(N)$ $ϕ^4$-model in AdS$_4$ at large-$N$, gives rise to a dual conformal field theory on the conformal boundary of AdS$_4$, which is a deformation of the generalized free field. We identify and compute an AdS$_4$ three-point one-loop fish diagram that controls the exact large-$N$ dimensions and operator product coefficients (OPE) for all ``double trace'' operators as a function of the renormalized $ϕ^4$-couplings. We find that the space of $ϕ^4$-coupling is compact with a boundary at the bulk Landau pole. The dual CFT is unitary only in an interval of ${\it negative}$ couplings bounded by the Landau pole where the lowest OPE coefficient diverges.

hep-th↗

arXiv2022

A toy model for background independent string field theory

We study gauge theories of background fields associated to BRST quantized spinning particle models and identify background-independent algebraic structures which allow to systematically reduce the spectrum of fields and subject some of them to dynamical equations of motion. More specifically, we construct a manifestly background-independent extension of the model based on $N=2$ spinning particle. The resulting system describes an on-shell spin-1 field coupled to off-shell background fields including metric and dilaton. Tensoring with a given Lie algebra results in a non-abelian extension of the model.

hep-th↗

arXiv2022

Quantum probing of null-singularities

We adapt the dual-null foliation to the functional Schrödinger representation of quantum field theory and study the behavior of quantum probes in plane-wave space-times near the null-singularity. A comparison between the Einstein-Rosen and the Brinkmann patch, where the latter extends beyond the first, shows a seeming tension that can be resolved by comparing the configuration spaces. Our analysis concludes that Einstein-Rosen space-times support exclusively configurations with non-empty gravitational memory that are focussed to a set of measure zero in the focal plane with respect to a Brinkmann observer. To conclude, we provide a rough framework to estimate the qualitative influence of back-reactions on these results.

hep-th↗