## >> Publications at DIEP

###### DIEP aims at performing groundbreaking interdisciplinary research that connects different fields and shines light on aspects of emergence. Below you find a list of publications of some of the researchers associated with DIEP in 2024. To access older publications starting in late 2020, you can check the publication archives.

## >> Field theories and quantum methods for stochastic reaction-diffusion systems

## by Mauricio J. del Razo, Tommaso Lamma, Wout Merbis| September 2024

###### Complex systems are composed of many particles or agents that move and interact with one another. The underlying mathematical framework to model many of these systems must incorporate the spatial transport of particles and their interactions, as well as changes to their copy numbers, all of which can be formulated in terms of stochastic reaction-diffusion processes. The probabilistic representation of these processes is complex because of combinatorial aspects arising due to nonlinear interactions and varying particle numbers. This review presents the main field theory representations of stochastic reaction-diffusion systems, which handle these issues `under-the-hood'. First, we focus on bringing techniques familiar to theoretical physicists -- such as second quantization, Fock space, and path integrals -- back into the classical domain of reaction-diffusion systems. We demonstrate how various field theory representations can all be unified under a single basis-independent representation. We then extend existing quantum-based methods and notation to work directly on the level of the unifying representation, and we illustrate how they can be used to consistently obtain previous known results, such as numerical discretizations and relations between model parameters at multiple scales. Throughout the work, we contextualize how these representations mirror well-known models of chemical physics depending on their spatial resolution, as well as the corresponding macroscopic limits. The framework presented here may find applications in a diverse set of scientific fields, including physical chemistry, theoretical ecology, epidemiology, game theory and socio-economical models of complex systems. The presentation is done in a self-contained educational and unifying manner such that it can be followed by researchers across several fields.

## >> Time, Spacetime and F-Theory

## by Enrico Cinti, Marco Sanchioni| August 2024

###### This Chapter explores the philosophical and ontological implications of F-theory, a non-perturbative extension of Type IIB string theory, mainly focusing on the apparent existence of two temporal dimensions. The paper proposes an interpretation that advocates for a single temporal dimension grounded in a brane-based ontology, challenging the conventional understanding of time and spacetime in F-theory. Moreover, it discusses the implications of a brane-based ontology for spacetime emergence, providing a novel understanding of the relations between spatiotemporal and non-spatiotemporal structures.

## >> Anchoring as a Structural Bias of Deliberation

## by Sebastian Till Braun, Soroush Rafiee Rad, Olivier Roy| July 2024

###### We study the anchoring effect in a computational model of group deliberation on preference rankings. Anchoring is a form of path-dependence through which the opinions of those who speak early have a stronger influence on the outcome of deliberation than the opinions of those who speak later. We show that anchoring can occur even among fully rational agents. We then compare the respective effects of anchoring and three other determinants of the deliberative outcome: the relative weight or social influence of the speakers, the popularity of a given speaker’s opinion, and the homogeneity of the group. We find that, on average, anchoring has the strongest effect among these. We finally show that anchoring is often correlated with increases in proximity to single-plateauedness. We conclude that anchoring can constitute a structural bias that might hinder some of the otherwise positive effects of group deliberation

## >> Reassessing the alternative ecosystem states proposition in the African savanna-forest domain

## by Steven I. Higgins, Swarnendu Banerjee, Mara Baudena, David M. J. S. Bowman, Timo Conradi, Pierre Couteron, Laurence M. Kruger, Robert B. O'Hara, Grant J. Williamson| July 2024

###### Ecologists are being challenged to predict how ecosystems will respond to climate changes. According to the Multi-Colored World (MCW) hypothesis, climate impacts may not manifest because consumers such as fire and herbivory can override the influence of climate on ecosystem state. One MCW interpretation is that climate determinism fails because alternative ecosystem states (AES) are possible at some locations in climate space. We evaluated theoretical and empirical evidence for the proposition that forest and savanna are AES in Africa. We found that maps which infer where AES zones are located were contradictory. Moreover, data from longitudinal and experimental studies provide inconclusive evidence for AES. That is, although the forest-savanna AES proposition is theoretically sound, the existing evidence is not yet convincing. We conclude by making the case that the AES proposition has such fundamental consequences for designing management actions to mitigate and adapt to climate change in the savanna-forest domain that it needs a more robust evidence base before it is used to prescribe management actions.

## >> Operator Entanglement Growth Quantifies Complexity of Cellular Automata

## by Calvin Bakker, Wout Merbis | June 2024

###### Cellular automata (CA) exemplify systems where simple local interaction rules can lead to intricate and complex emergent phenomena at large scales. The various types of dynamical behavior of CA are usually categorized empirically into Wolfram’s complexity classes. Here, we propose a quantitative measure, rooted in quantum information theory, to categorize the complexity of classical deterministic cellular automata. Specifically, we construct a Matrix Product Operator (MPO) of the transition matrix on the space of all possible CA configurations. We find that the growth of entropy of the singular value spectrum of the MPO reveals the complexity of the CA and can be used to characterize its dynamical behavior. This measure defines the concept of operator entanglement entropy for CA, demonstrating that quantum information measures can be meaningfully applied to classical deterministic systems.

## >> New asymptotically (Anti)-de Sitter black holes in (super)gravity

## by Jay Armas, Gianbattista-Piero Nicosia | June 2024

###### We use the duality between gravitational dynamics and fluids living on dynamical surfaces carrying multiple charges, known as the blackfold approach, to perturbativaly construct new asymptotically global (Anti)-de Sitter multi-spinning, non-extremal, multi-charged black holes in theories of higher-dimensional gravity minimally coupled to a dilaton and higher-form gauge fields in spacetime dimensions D≥5, and new asymptotically AdSl×Sm black holes in type IIB and eleven-dimensional supergravity. These solutions include the generalisation of the Kerr-Newman solution to (A)dS carrying either electric or string charge, generalisations of black rings to higher-dimensions with 𝕊p×𝕊n+1 horizon topology, static de Sitter solutions carrying arbitrary q-brane charge, as well as various asymptotically AdSl×Sm multi-charged and multi-spinning black hole solutions, some of which correspond to novel thermal states in N=4 Super-Yang-Mills theory

## >> Fractonic solids

## by Akash Jain | June 2024

###### Fractons are exotic quasiparticles whose mobility in space is restricted by symmetries. In potential real-world realisations, fractons are likely lodged to a physical material rather than absolute space. Motivated by this, we propose and explore a new symmetry principle that restricts the motion of fractons relative to a physical solid. Unlike models with restricted mobility in absolute space, these fractonic solids admit gauge-invariant momentum density, are compatible with boost symmetry, and can consistently be coupled to gravity. We also propose a holographic model for fractonic solids.

## >> Enriched Quantales Arising from Complete Orthomodular Lattices

## by Soroush Rafiee, Joshua Sack, Shengyang Zhong | June 2024

###### This paper connects complete orthomodular lattices to two enriched quantale structures. Complete orthomodular lattices emphasize a static perspective of a quantum system, helping us reason about testable properties of a quantum system. Quantales offer a dynamic perspective, helping us reason about the structure of quantum actions. We enrich quantales with an orthocomplementation-inducing operator, and call these structures orthomodular dynamic algebras. One type of orthomodular dynamic algebra distinguishes the joins of any two different sets of atoms, while the other distinguishes elements by the collective behavior of the atoms below it. We show that both orthomodular dynamic algebras are unital, and the unit is the top element of an induced orthomodular lattice. We provide a categorical equivalence between both orthomodular dynamic algebras and complete orthomodular lattices with isomorphisms, and we show that this equivalence is preserved when augmenting the orthomodular dynamic algebras with an involution. These equivalences help clarify the relationship between static and dynamic quantum structures.

## >> Beyond the Quantum Membrane Paradigm: A Philosophical Analysis of the Structure of Black Holes in Full QG

## by Enrico Cinti, Marco Sanchioni | June 2024

###### This paper presents a philosophical analysis of the structure of black holes, focusing on the event horizon and its fundamental status. While black holes have been at the centre of countless paradoxes arising from the attempt to merge quantum mechanics and general relativity, recent experimental discoveries have emphasised their importance as objects for the development of Quantum Gravity. In particular, the statistical mechanical underpinning of black hole thermodynamics has been a central research topic. The Quantum Membrane Paradigm, proposed by Wallace (Stud Hist Philos Sci Part B 66:103-117, 2019), posits a real membrane made of black hole microstates at the black hole horizon to provide a statistical mechanical understanding of black hole thermodynamics from an exterior observer’s point of view. However, we argue that the Quantum Membrane Paradigm is limited to low-energy Quantum Gravity and needs to be modified to avoid reference to geometric notions, such as the event horizon, which presumably do not make sense in the non-spatiotemporal context of full Quantum Gravity. Our proposal relies on the central dogma of black hole physics. It considers recent developments, such as replica wormholes and entanglement wedge reconstruction, to provide a new framework for understanding the nature of black hole horizons in full Quantum Gravity.

## >> Odd viscous flow past a sphere at low but nonzero Reynolds numbers

## by Ruben Lier | May 2024

###### Measuring lift force on symmetrically shaped obstacles immersed in laminar flow is the quintessential way of signalling odd viscosity. For flow past cylinders, such a lift force does not arise when incompressibility and no-slip boundary conditions hold, whereas for spheres, a lift force was found in Stokes flow, applying to cases where the Reynolds number is negligible and convection can be ignored. When considering the role of convection at low but nonzero Reynolds numbers, two arising hurdles are the Whitehead paradox and the breaking of axial symmetry, which are overcome by asymptotic matching and the Lorentz reciprocal theorem respectively. We also consider the case where axial symmetry is retained because the translation of the sphere is aligned with the anisotropy vector of odd viscosity. We find that while lift vanishes, the interplay between odd viscosity and convection gives rise to a stream-induced non-vanishing torque.

## >> Hydrodynamics of thermal active matter

## by Jay Armas, Akash Jain, Ruben Lier | May 2024

###### Active matter concerns many-body systems comprised of living or self-driven agents that collectively exhibit macroscopic phenomena distinct from conventional passive matter. Using Schwinger-Keldysh effective field theory, we develop a novel hydrodynamic framework for thermal active matter that accounts for local temperature variations and the ensuing stochastic effects. This framework provides a deeper understanding of energy balance, second law of thermodynamics, and thermostated steady states in active matter, while also addressing the systematic violations of fluctuation-dissipation theorem and detailed balance. We use our framework of active hydrodynamics to develop effective field theory actions for active superfluids and active nematics that offer a first-principle derivation of various active transport coefficients and feature activity-induced phase transitions.

## >> Duality, Underdetermination, and the Uncommon Common Core

## by Daniel Grimmer, Enrico Cinti, Rasmus Jaksland| March 2024

Dualities arise when two seemingly different descriptions of the world are physically equivalent, suggesting that either description can be used to describe a given system. This raises the question of which description, if any, is true and raises worries of empirical underdetermination. This paper explores the underdetermination problem in the context of dualities and focuses on the viability of a common core ontology as a solution. The common core suggests that one should only ontologically commit to what is invariant under the duality map between the dual descriptions. The paper examines this solution through the lens of Fourier duality in non-relativistic quantum mechanics and raises con- cerns about the existence and adequacy of the common core. It argues that the common core might not be ontologically rich enough to support a genuine realist commitment and questions whether it should be preferred over the dual descriptions. By doing so, the analysis highlights the challenges of employing the common core interpretation in quan- tum mechanics and also in other dualities such as T-duality and AdS/CFT, especially for purposes of breaking underdetermination. Dualities are, we conclude, likely examples

of underdetermination and therefore a challenge to scientific realism.

## >> SUSY, Spin-Statistics, and all that... On the contrast between Spin-Statistics and Wigner’s Theorem

## by Enrico Cinti, Marco Sanchioni| March 2024

Supersymmetry is a conjectured symmetry that relates standard model's bosons and

fermions. The spin-statistics theorem, which states that a particle's statistics depends on its spin, is a crucial component of quantum field theory's analysis of matter. Prima facie, supersymmetry creates problems for the theoretical structure underpinned by the spin-statistics theorem. Since supersymmetry relates bosons and fermions, the distinction between particles obeying Bose-Einstein or Fermi-Dirac statistics seems to collapse since, ultimately, they are part of a single supermultiplet, that is, the actual degree of freedom of supersymmetric quantum field theory. This article aims to evaluate the status of the spin- statistics theorem within supersymmetric quantum field theories and which strategies one can implement to make sense of this state of affairs. In particular, we argue that there are two main options in the face of the conflict between Wigner's theorem and the spin-statistics theorem: either we abandon the validity of the spin-statistics theorem and adopt an invariant superfield ontology, or we abandon Wigner's theorem and uphold spin-statistics theorem, at the price, however, of introducing a significant redundancy in our ontological. Moreover, we explore how these two options relate to important philosophical debates, such as the nature of superspace and spacetime ontologies, and the debates between motivationalists and interpretationalist regarding physical symmetry.