International Solvay Institutes

We review aspects of entanglement entropy in the quantum mechanics of matrices, i.e., matrix quantum mechanics (MQM), at large N. In doing so, we review standard models of MQM and their relation to string theory, D-brane physics, and emergent non-commutative geometries. We overview, in generality, definitions of subsystems and entanglement entropies in theories with gauge redundancy and discuss the additional structure required for definining subsystems in MQMs possessing a gauge redundancy. In connecting these subsystems to non-commutative geometry, we review several works on ‘target space entanglement,’ and entanglement in non-commutative field theories, highlighting the conditions in which target space entanglement entropy displays an ‘area law’ at large N. We summarize several example calculations of entanglement entropy in non-commutative geometries and MQMs. We review recent work in connecting the area law entanglement of MQM to the Ryu–Takayanagi formula, highlighting the conditions in which invariance implies a minimal area formula for the entanglement entropy at large N. Finally, we make comments on open questions and research directions.

Early access to innovative therapies offers a critical lifeline for patients with severe or life-threatening conditions, yet substantial disparities persist across the United States (US), the European Union (EU), China (CH), and Japan (JP). These disparities arise from diverging definitions of unmet medical need (UMN), heterogeneous timelines for regulatory review, and uneven implementation of Early and Expanded Access mechanisms. This policy review provides a comparative analysis of regional frameworks, emphasizing how clinical trial geography, eligibility rules, and access mechanisms interact to shape pre-approval opportunities for patients. While regulatory innovations such as the FDA's Breakthrough Therapy designation, the EMA's PRIME scheme, the PMDA's Sakigake program, and recent reforms in China have accelerated access in selected contexts, cross-border misalignments and fragmented health technology assessment (HTA) processes continue to generate inequities. The EU's new HTA Regulation (2021/2282) represents a step forward by embedding joint clinical assessment and real-world evidence, but persistent structural inconsistencies hinder timely and equitable uptake. This article argues for a paradigm shift from static approval models to adaptive licensing approaches, including live licenses and regulatory sandboxes. It calls for internationally coordinated benefit–risk governance that integrates early access planning into drug development from Phase II onward. By reframing uncertainty as a shared responsibility among regulators, developers, payers, clinicians, and patients, early access governance can be redesigned to promote equity, transparency, and responsiveness particularly for rare and high-burden diseases.

International audience

In (super)gravity theories, T-duality relates solutions with an exact isometry which can have wildly different asymptotic behaviors: A well-known example is the duality between BTZ black holes and (non-extremal) three-dimensional black strings. Using this dual pair, we show how the knowledge of a phase space which includes one set of solutions (here, BTZ black holes embedded in the Brown-Henneaux phase space) allows to obtain a phase space for the dual set via an asymptotic notion of T-duality. The resulting asymptotic symmetry algebras can be very different. For our particular example, we find a large algebra of symmetries for the black string phase space which includes as subalgebras \mathfrak{bms}_2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mstyle mathvariant="fraktur"> <mml:mi>𝔟</mml:mi> <mml:mi>𝔪</mml:mi> <mml:mi>𝔰</mml:mi> </mml:mstyle> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , \mathfrak{bms}_3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mstyle mathvariant="fraktur"> <mml:mi>𝔟</mml:mi> <mml:mi>𝔪</mml:mi> <mml:mi>𝔰</mml:mi> </mml:mstyle> <mml:mn>3</mml:mn> </mml:msub> </mml:math> , and a twisted warped conformal algebra. On the way, we show that a chiral half of the Brown-Henneaux boundary conditions are dual to the Compère-Song-Strominger ones.

We determine 1/N corrections to a notion of generalized entanglement entropy known as entwinement dual to the length of a winding geodesic in asymptotically AdS3 geometries. We explain how 1/N corrections can be computed formally via the FLM formula by relating entwinement to an ordinary entanglement entropy in a fictitious covering space. Moreover, we explicitly compute 1/N corrections to entwinement for thermal states and small winding numbers using a monodromy method to determine the corrections to the dominant conformal block for the replica partition function. We also determine a set of universal corrections at finite temperature for large winding numbers. Finally, we discuss the implications of our results for the “entanglement builds geometry” proposal.

We discover a first-order phase transition in the canonical ensemble of random unlabeled networks with a prescribed average number of links. The transition is caused by the nonconcavity of microcanonical entropy. Above the critical point coinciding with the graph symmetry phase transition, the canonical and microcanonical ensembles are equivalent and have a well-behaved thermodynamic limit. Below the critical point, the ensemble equivalence is broken, and the canonical ensemble is a mixture of phases: empty networks and networks with average degrees diverging logarithmically with the network size. As a consequence, networks with bounded average degrees do not survive in the thermodynamic limit, decaying into the empty phase. The celebrated percolation transition in labeled networks is thus absent in unlabeled networks. In view of these differences between labeled and unlabeled ensembles, the question of which one should be used as a null model of different real-world networks cannot be ignored.

Individuals' decisions to promote or limit diversity in the workplace are ambivalent and may be influenced by their cognitive focus. Drawing from construal level theory, we test across five studies whether individuals are more supportive of diversity when diversity is thought of more abstractly versus concretely. Furthermore, we examined the salience of diversity pros and cons as the underlying mechanisms, as well as the role of egalitarian beliefs as a boundary condition for this discrepancy. We tested these hypotheses in five studies, which varied in samples, cognitive focus manipulation, and measures. Dutch and American individuals indicated more positive attitudes toward diversity (Studies 1 and 2) and made more choices that enhanced diversity (Studies 2 and 5) when they considered diversity abstractly (for most companies and teams) rather than concretely (for their own company and teams). Furthermore, the discrepancy in diversity attitudes by construal level was more pronounced among individuals with egalitarian beliefs (Study 3) and was driven by the heightened salience of diversity pros at more abstract versus concrete levels of construal (Study 4). This research contributes to further understanding the ambivalent view of diversity and provides concrete recommendations for diversity management in organizations.

5d Superconformal Field Theories (SCFTs) are intrinsically strongly-coupled UV fixed points, whose realization hinges on string theoretic methods: they can be constructed by compactifying M-theory on local Calabi-Yau threefold singularities or alternatively from the world-volume of 5-brane-webs in type IIB string theory. There is a correspondence between 5-brane-webs and toric Calabi-Yau threefolds, however this breaks down when multiple 5-branes are allowed to end on a single 7-brane. In this paper, we extend this connection and provide a geometric realization of brane configurations including 7-branes. A web with 7-branes defines a so-called generalized toric polygon (GTP), which corresponds to combinatorial data that is obtained by removing vertices along external edges of a toric polygon. We identify the geometries associated to GTPs as non-toric deformations of toric Calabi-Yau threefolds and provide a precise, algebraic description of the geometry, when 7-branes are introduced along a single edge. The key ingredients in our analysis are T-branes in a type IIA frame, which includes D6-branes. We show that performing Hanany-Witten moves for the 7-branes on the type IIB side corresponds to switching on semisimple vacuum expectation values on the worldvolume of D6-branes, which in turn uplifts to complex structure deformations of the Calabi-Yau geometries. We test the proposal by computing the crepant resolutions of the deformed geometries, thereby checking consistency with the expected properties of the SCFTs.

The Coherent Backscattering (CBS) peak is a well-known interferential signature of weak localization in disordered or chaotic systems. More recently, a second interference feature -- the Coherent Forward Scattering (CFS) peak -- was predicted to emerge in the regime of strong localization. However, it has never been directly observed. Here we report the first direct observation of the CFS peak and demonstrate its dual role as a signature of non-ergodicity and as a probe of symmetries in quantum chaotic systems. Using a shaken rotor model realized with a Bose-Einstein condensate (BEC) of ultracold atoms in a modulated optical lattice, we investigate dynamical localization in momentum space. The CFS peak emerges in the position distribution as a consequence of non-ergodic dynamics, while its growth timescale reveals the underlying localization length. By finely tuning the modulation, we control time-reversal and parity symmetries and measure their distinct effects on both CBS and CFS peaks. Our results highlight the strong link of both the temporal growth and contrast of the CFS with symmetry and localization, making it a robust probe of these properties. This work opens new directions for characterizing non-ergodicity and symmetries in quantum chaotic or disordered systems, with possible applications in many-body localization and chaos.