arXiv subjects

Joe Marshall

Publications and source records attributed to Joe Marshall.

6 recordsLinked to original sources

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

Grand Challenges around Designing Computers' Control Over Our Bodies

Advances in emerging technologies, such as on-body mechanical actuators and electrical muscle stimulation, have allowed computers to take control over our bodies. This presents opportunities as well as challenges, raising fundamental questions about agency and the role of our bodies when interacting with technology. To advance this research field as a whole, we brought together expert perspectives in a week-long seminar to articulate the grand challenges that should be tackled when it comes to the design of computers' control over our bodies. These grand challenges span technical, design, user, and ethical aspects. By articulating these grand challenges, we aim to begin initiating a research agenda that positions bodily control not only as a technical feature but as a central, experiential, and ethical concern for future human-computer interaction endeavors.

cs.HC↗

arXiv2025

On in-in correlators for spinning theories and their shadow formulation

In-in correlators are the basic observables in cosmology and are traditionally computed using the Schwinger-Keldysh formalism. In this paper we revisit this formalism for photons, gluons, and gravitons coupled to scalars in four dimensional de Sitter space and provide a novel treatment of boundary gauge-fixing of the underlying path integral. We also derive effective actions in Euclidean Anti-de Sitter space whose Feynman rules compute the in-in correlators of these theories in de Sitter space, generalising the shadow formalism recently obtained for scalar theories. We illustrate this formalism in a number of examples at tree-level and 1-loop, demonstrating its relative simplicity compared to other approaches. Moreover, we initiate the study of color/kinematics duality and the double copy for in-in correlators using dressing rules which uplift flat space Feynman diagrams to de Sitter space.

hep-th↗

arXiv2025

Tangles: Unpacking Extended Collision Experiences with Soma Trajectories

We reappraise the idea of colliding with robots, moving from a position that tries to avoid or mitigate collisions to one that considers them an important facet of human interaction. We report on a soma design workshop that explored how our bodies could collide with telepresence robots, mobility aids, and a quadruped robot. Based on our findings, we employed soma trajectories to analyse collisions as extended experiences that negotiate key transitions of consent, preparation, launch, contact, ripple, sting, untangle, debris and reflect. We then employed these ideas to analyse two collision experiences, an accidental collision between a person and a drone, and the deliberate design of a robot to play with cats, revealing how real-world collisions involve the complex and ongoing entanglement of soma trajectories. We discuss how viewing collisions as entangled trajectories, or tangles, can be used analytically, as a design approach, and as a lens to broach ethical complexity.

cs.RO↗

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↗

arXiv2023

Magnetic Order and Magnetic Excitations in FeTe: How Good is a Short-Range Heisenberg Model?

We revisit the fitting of the Fang-Bernevig-Hu model [Europhys. Lett. 86, 67005 (2009)] to inelastic neutron scattering data carried out by Lipscombe et al. [Phys. Rev. Lett. 106, 057004 (2011)]. We demonstrate that there are many quite different parameter choices within the experimentally observed phase (AFM3) that provide approximately equally good fits to the neutron data. We note that (a) all of these parameter sets lie very close to a point of transition between the AFM3 phase and one of its neighbors in the classical phase diagram, and (b) many of them involve rather large values of the third-neighbor coupling $J_3$. In light of these observations, we discuss whether the modeling of FeTe may need revision to allow for a slightly non-AFM3 ground state, orbital as well as spin physics on the Fe sites, the effects of electron itinerancy, or a combination of these.

cond-mat.str-el↗