There are worlds we name, and worlds we summon into being. The Arab World has long inhabited both roles—invoked in international law as geopolitical reality, yet shaped by repetition, signification, and remembered alignments. It appears over the centuries not as a subject with agency, but as a revenant: referenced for its solidarity and unity, yet rarely allowed either coherence or consequence. What holds the “Arab World” together in international law, this essay argues, is not essence but performance, not institutional substance, but the staging of collectivity. Bandung (1955) made this dynamic briefly visible: nine Arab states, fragmented in voice and agenda, appeared united; Palestine, symbolically central, remained formally absent. The pattern endures, from the choreography of the Arab League to strategic posturing in relation to Gaza’s ongoing genocide by Israel. The “Arab World,” in this light, is not an unfulfilled project, but a legal and political arrangement, summoned, displayed, and sustained in a state of permanent deferral.

We study an abstract group of reversible Turing machines. In our model, each machine is interpreted as a homeomorphism over a space which represents a tape filled with symbols and a head carrying a state. These homeomorphisms can only modify the tape at a bounded distance around the head, change the state, and move the head in a bounded way. We study three natural subgroups arising in this model: the group of finite-state automata, which generalizes the topological full groups studied in topological dynamics and the theory of orbit-equivalence; the group of oblivious Turing machines whose movement is independent of tape contents, which generalizes lamplighter groups and has connections to the study of universal reversible logical gates, and the group of elementary Turing machines, which are the machines which are obtained by composing finite-state automata and oblivious Turing machines.

We show that both the group of oblivious Turing machines and that of elementary Turing machines are finitely generated, while the group of finite-state automata and the group of reversible Turing machines are not. We show that the group of elementary Turing machines has undecidable torsion problem. From this, we also obtain that the group of cellular automata (more generally, the automorphism group of any uncountable one-dimensional sofic subshift) contains a finitely generated subgroup with undecidable torsion problem. We also show that the torsion problem is undecidable for the topological full group of a full $\mathbb {Z}^d$-shift on a nontrivial alphabet if and only if $d \geq 2$.

With reference to Elon Musk’s FinTech strategy for X, the social media platform formerly known as Twitter, this essay critically interrogates the evolution of North American and European FinTech economies toward what is typically called ‘embedded finance’; that is, the technological integration of monetary and financial services into discrete social interactions and economic transactions by nonfinancial companies. We argue that embedded finance furthers the disappearance of FinTech as an evident market domain of technologically facilitated monetary and financial relations. Specialist FinTech startup intermediaries are receding into the background of an institutional and digital landscape shaped by strong monopolization tendencies. FinTech economies are increasingly dominated by major platform firms with the assistance of banks. Relatedly, FinTech services have become ubiquitous to the extent that they are taken for granted by people who are configured as platform users that are ripe for rent capture, rather than as sovereign consumers searching for products. The disappearance of FinTech should not be confused with its demise, however. Disappearance is the fullest expression of the transformative appearance of FinTech in people’s everyday monetary and financial lives over the last quarter century.

The recent ascendance of American conservative ideology within Israel’s political Right is puzzling given its historical absence. Furthermore, prevailing theories—which focus on the role of other countries, experts, or transnational networks as ideational importers—cannot account for it. Accordingly, utilizing insights from the diaspora politics literature, we develop an alternative explanation that focuses on the cooperation between diaspora actors and local actors (diaspora–local cooperation, DLC) as a source of ideational importation and ideological change. Like other sources of outside ideas, DLC-based ideational importation depends on the establishment of organizational infrastructure for ideological dissemination—and ideational localization—for the adaptation and translation of external ideas to the local context. Unlike other kinds of transnational ideational networks, such cooperation is primarily based on national kinship that transcends specific ideational commitments. Such national kinship, we argue, legitimizes DLC and supports multidimensional ideational importation that can potentially amount to ideological change. We further suggest that the actual ideological change this process triggers depends on how imported ideas align with core ideological components and how they serve the needs of local actors in a given political context. We use detailed process-tracing analysis to demonstrate how DLC has led to an ideological change in Israel’s political Right.

This article argues that a pervasive but confused theory of free will is driving unwarranted resistance to behavioral genetic research and undermining the concept of personal responsibility enshrined in our moral and legal conventions. We call this the theory of ‘free-will-by-subtraction’. A particularly explicit version of this theory has been propounded by the psychologist Eric Turkheimer, who has proposed that human agency can be scientifically quantified as the behavioral variation that remains unexplained after known genetic and environmental causes have been accounted for. This theory motivates resistance to research that suggests genetic differences substantially account for differences in human behavior because that is seen to reduce the scope of human freedom. In academic philosophy, free-will-by-subtraction theory corresponds to a position called ‘libertarian incompatibilism’, which holds that human beings are not responsible for behavior that has antecedent causes yet maintains that free will nonetheless exists because some fraction of human behavioral variation is self-caused. However, this position is rejected by most professional philosophers. We argue that libertarian incompatibilism is inconsistent with a secular materialist outlook in which all human behavior is understood to have antecedent causes whether those causes are known to science or not — an outlook Turkheimer shares. We show that Turkheimer sustains this contradiction by adopting an untenable position we call ‘epistemic libertarianism’, which holds that antecedent causes of our behavior only infringe on our freedom if we know about them. By contrast, the overwhelming majority of secular materialist philosophers support a position called ‘compatibilism’, which maintains that free will is compatible with the comprehensive causation of human behavior. We show that compatibilism neutralizes the threat that genetic explanation poses to human agency and rescues a generous conception of personal responsibility that aligns with our moral intuitions.

In plasmas and in astrophysical systems, particle diffusion faster than normal, namely superdiffusion, has been detected, calling for a generalisation of Fick’s law and of the transport equation. Formally, superdiffusive transport is often described by fractional diffusion equations, where the second-order spatial derivative is changed into a spatial derivative of fractional order less than two, usually in the form of the so-called Riesz derivative. Fractional operators are non-local, so that this involves the contribution of very distant points (far from the particle source) to the particle flux at a given position in the system. To consider the property of non-locality in the case of anomalous transport, we give a simple analytical derivation of the fractional Fick’s law, where the contribution to the flux of distant points is weighted by an inverse power law, and show that this is consistent with use of the Riesz derivative in the transport equation. A numerical procedure for the computation of the non-local flux is presented and applied to both a simple Gaussian density profile and also to density profiles coming from test particle simulations of one-dimensional collisionless shocks. In these simulations, energetic particles can move diffusively or superdiffusively. The latter case naturally gives rise to the emergence of uphill transport in the downstream region, which means a flux of particles in the same direction of the density gradient. This analysis contributes to the interpretation of energetic particle fluxes accelerated at collisionless shock waves in the interplanetary medium.

This article offers a possible context for the late eighth- to early ninth-century sculptures identified by James Lang as apostle pillars: stone columns and shafts featuring representations of the apostles, which he recorded in the southern part of Northumbria. That context, it is argued, is the cult of St Wilfrid, promoted by Stephen’s Life of Bishop Wilfrid which focuses on his pastoral activities and estates in the western parts of the Deiran province of Northumbria – those areas where apostle pillars were subsequently erected in ‘shire’ estates close to Wilfrid’s cult centre at Ripon. Their restricted distribution may reflect the constraints imposed by the rival episcopal centre at Lindisfarne, which, with support from its affiliated religious community at Whitby, successfully contested the influence of Wilfrid’s cult in the eastern parts of the Deiran province, and in the archiepiscopal centre at York.

Some scholars argue that democratic stability requires political elites to practice forbearance: roughly speaking, “restraint in deploying their institutional prerogatives” (Levitsky and Ziblatt, How Democracies Die, 2018). The article proposes a novel conception of forbearance as a mechanism of democratic stability. According to this view, public officials exercise forbearance when they refrain from actions of uncertain legitimacy, actions that, while in fact compatible with democracy’s constitutive rules, are not commonly known to be. The argument is that such actions, by provoking divergent reactions among citizens, create uncertainty about the extent to which others are willing to resist breaches of democracy’s rules. This uncertainty undermines their ability to coordinate responses to genuine abuses of power in the future. The article concludes with observations about the normative implications of the theory, introducing the concept of the “Democrat’s Dilemma” to illustrate the difficulties of knowing when democrats ought to practice forbearance.

We give a short and relatively elementary proof of the Hilton–Milner Theorem.

In recent years, a wide range of mortality models has been proposed to address the diverse factors influencing mortality rates, which has highlighted the need to perform model selection. Traditional mortality model selection methods, such as AIC and BIC, often require fitting multiple models independently and ranking them based on these criteria. This process can fail to account for uncertainties in model selection, which can lead to overly optimistic prediction intervals, and it disregards the potential insights from combining models. To address these limitations, we propose a novel Bayesian model selection framework that integrates model selection and parameter estimation into the same process. This requires creating a model-building framework that will give rise to different models by choosing different parametric forms for each term. Inference is performed using the reversible jump Markov chain Monte Carlo algorithm, which is devised to allow for transition between models of different dimensions, as is the case for the models considered here. We develop modeling frameworks for data stratified by age and period and for data stratified by age, period, and product. Our results are presented in two case studies.

Emerging scholarship suggests that willingness to engage in violent or risky behavior relates to Need for Chaos – a trait-state combination reflecting disaffection with society and politics, independent of political identity and beliefs. While previous research links Need for Chaos to a stronger gain-seeking mentality, it remains unclear whether those higher in Need for Chaos respond differently to gain and loss frames. We use a framing experiment based on prospect theory to test whether Need for Chaos moderates decision making about two salient policy issues in the United States: the debt ceiling and government shutdown negotiations in US Congress in 2023. Results from both studies (n = 2,704; 3,002) suggest that individuals low in Need for Chaos are risk-averse toward gains but risk-seeking toward losses, whereas those high in Need for Chaos exhibit the opposite pattern, seeking risk when anticipating gains and avoiding risk when anticipating losses. Our findings add important nuance to existing research by demonstrating that individuals higher in Need for Chaos are not merely indifferent to framing; rather, they also systematically respond to gain and loss frames. This work underscores how individual differences may help to shape judgment and decision making, particularly in times of societal and political uncertainty.

In reflexive methodology in terrorism studies and international security broadly, there are arguments about the absence of African voices, the lack thereof contributing to standardizing the fieldwork experiences of Western terrorism scholars as ‘one-size-fits-all’. However, while the voices of African-based scholars, particularly those based in the West, are increasingly being reflected in reflexive methodology in international security, we know little about how shared national belongingness and its associated cultural norms between the researcher and the researched influence the process of elite interviewing. This article addresses these limitations by reflecting on my experiences as a Nigerian conducting elite interviews with fellow nationals who are counter-terrorism security elites (CTSE) in Nigeria. In doing so, I examine the concepts of seniority, hierarchy, and reciprocity – important social norms that, while present in many contexts, take on distinctive meanings within counter-terrorism institutions in Nigeria – on data access and knowledge production. I contend that the shared cultural understanding between the researcher and CTSE study participants leads them to deploy these norms to foster post-fieldwork relational positionalities, which are used to advance their personal or career interests. This situation results in specific methodological and ethical dilemmas, which are addressed by engaging with and integrating these norms to resolve them. This article contributes to reflexive methodology in terrorism by nuancing the debate on situational ethics management in fieldwork dilemmas and advocating for context-based positionality.

Antimicrobial resistance (AMR) is a global public health challenge that, like climate change, demands urgent, coordinated, multi-sectoral action. Yet, responses to AMR may be ill-suited to local contexts, overlook historical inequalities, or dismiss marginalised knowledge systems. Some of these concerns can be discussed using the concept of a just transition, which aims to ensure that “no one is left behind,” “all voices are heard,” and past injustices are addressed. However, framing justice in these terms is insufficient. We argue for a more multifaceted and broader-scoped understanding of what justice demands in a just transition for AMR. We examine existing justice frameworks in AMR literature and discuss two cases that motivate our call for including both more forms of justice in a multifaceted concept of a just transition and a broader scope of justice. The first case involves over-the-counter antibiotic access in the Kibera informal settlement near Nairobi, highlighting structural injustices resulting from colonial oppression and what an Ubuntu philosophy would show as injustice. The second case concerns veterinary prescription requirements for Maasai pastoralists’ livestock farming in southern Kenya and highlights epistemic and distributive injustices, as well as injustices that befall non-human animals. These examples reveal distinct injustices shaped by socio-cultural and ecological contexts.

Using the $\infty $-categorical enhancement of mixed Hodge modules constructed by the author in a previous paper, we explain how mixed Hodge modules canonically extend to algebraic stacks, together with all the six operations and weights. We also prove that Drew’s approach to motivic Hodge modules gives an $\infty $-category that embeds fully faithfully in mixed Hodge modules, and we identify the image as mixed Hodge modules of geometric origin.

The escalating complexity of global migration patterns renders evident the limitation of traditional reactive governance approaches and the urgent need for anticipatory and forward-thinking strategies. This Special Collection, “Anticipatory Methods in Migration Policy: Forecasting, Foresight, and Other Forward-Looking Methods in Migration Policymaking,” groups scholarly works and practitioners’ contributions dedicated to the state-of-the-art of anticipatory approaches. It showcases significant methodological evolutions, highlighting innovations from advanced quantitative forecasting using Machine Learning to predict displacement, irregular border crossings, and asylum trends, to rich, in-depth insights generated through qualitative foresight, participatory scenario building, and hybrid methodologies that integrate diverse knowledge forms. The contributions collectively emphasize the power of methodological pluralism, address a spectrum of migration drivers, including conflict and climate change, and critically examine the opportunities, ethical imperatives, and governance challenges associated with novel data sources, such as mobile phone data. By focusing on translating predictive insights and foresight into actionable policies and humanitarian action, this collection aims to advance both academic discourse and provide tangible guidance for policymakers and practitioners. It underscores the importance of navigating inherent uncertainties and strengthening ethical frameworks to ensure that innovations in anticipatory migration policy enhance preparedness, resource allocation, and uphold human dignity in an era of increasing global migration.