@article{10550, abstract = {The global existence of renormalised solutions and convergence to equilibrium for reaction-diffusion systems with non-linear diffusion are investigated. The system is assumed to have quasi-positive non-linearities and to satisfy an entropy inequality. The difficulties in establishing global renormalised solutions caused by possibly degenerate diffusion are overcome by introducing a new class of weighted truncation functions. By means of the obtained global renormalised solutions, we study the large-time behaviour of complex balanced systems arising from chemical reaction network theory with non-linear diffusion. When the reaction network does not admit boundary equilibria, the complex balanced equilibrium is shown, by using the entropy method, to exponentially attract all renormalised solutions in the same compatibility class. This convergence extends even to a range of non-linear diffusion, where global existence is an open problem, yet we are able to show that solutions to approximate systems converge exponentially to equilibrium uniformly in the regularisation parameter.}, author = {Fellner, Klemens and Fischer, Julian L and Kniely, Michael and Tang, Bao Quoc}, issn = {1432-1467}, journal = {Journal of Nonlinear Science}, publisher = {Springer Nature}, title = {{Global renormalised solutions and equilibration of reaction-diffusion systems with non-linear diffusion}}, doi = {10.1007/s00332-023-09926-w}, volume = {33}, year = {2023}, } @article{10551, abstract = {The Dean–Kawasaki equation—a strongly singular SPDE—is a basic equation of fluctuating hydrodynamics; it has been proposed in the physics literature to describe the fluctuations of the density of N independent diffusing particles in the regime of large particle numbers N≫1. The singular nature of the Dean–Kawasaki equation presents a substantial challenge for both its analysis and its rigorous mathematical justification. Besides being non-renormalisable by the theory of regularity structures by Hairer et al., it has recently been shown to not even admit nontrivial martingale solutions. In the present work, we give a rigorous and fully quantitative justification of the Dean–Kawasaki equation by considering the natural regularisation provided by standard numerical discretisations: We show that structure-preserving discretisations of the Dean–Kawasaki equation may approximate the density fluctuations of N non-interacting diffusing particles to arbitrary order in N−1 (in suitable weak metrics). In other words, the Dean–Kawasaki equation may be interpreted as a “recipe” for accurate and efficient numerical simulations of the density fluctuations of independent diffusing particles.}, author = {Cornalba, Federico and Fischer, Julian L}, issn = {1432-0673}, journal = {Archive for Rational Mechanics and Analysis}, number = {5}, publisher = {Springer Nature}, title = {{The Dean-Kawasaki equation and the structure of density fluctuations in systems of diffusing particles}}, doi = {10.1007/s00205-023-01903-7}, volume = {247}, year = {2023}, } @article{10770, abstract = {Mathematical models often aim to describe a complicated mechanism in a cohesive and simple manner. However, reaching perfect balance between being simple enough or overly simplistic is a challenging task. Frequently, game-theoretic models have an underlying assumption that players, whenever they choose to execute a specific action, do so perfectly. In fact, it is rare that action execution perfectly coincides with intentions of individuals, giving rise to behavioural mistakes. The concept of incompetence of players was suggested to address this issue in game-theoretic settings. Under the assumption of incompetence, players have non-zero probabilities of executing a different strategy from the one they chose, leading to stochastic outcomes of the interactions. In this article, we survey results related to the concept of incompetence in classic as well as evolutionary game theory and provide several new results. We also suggest future extensions of the model and argue why it is important to take into account behavioural mistakes when analysing interactions among players in both economic and biological settings.}, author = {Graham, Thomas and Kleshnina, Maria and Filar, Jerzy A.}, issn = {2153-0793}, journal = {Dynamic Games and Applications}, pages = {231--264}, publisher = {Springer Nature}, title = {{Where do mistakes lead? A survey of games with incompetent players}}, doi = {10.1007/s13235-022-00425-3}, volume = {13}, year = {2023}, } @unpublished{17351, abstract = {Contractive coupling rates have been recently introduced by Conforti as a tool to establish convex Sobolev inequalities (including modified log-Sobolev and Poincar\'{e} inequality) for some classes of Markov chains. In this work, we show how contractive coupling rates can also be used to prove stronger inequalities, in the form of curvature lower bounds for Markov chains and geodesic convexity of entropic functionals. We illustrate this in several examples discussed by Conforti, where in particular, after appropriately choosing a parameter function, we establish positive curvature in the entropic and (discrete) Bakry--\'{E}mery sense. In addition, we recall and give straightforward generalizations of some notions of coarse Ricci curvature, and we discuss some of their properties and relations with the concepts of couplings and coupling rates: as an application, we show exponential contraction of the $p$-Wasserstein distance for the heat flow in the aforementioned examples.}, author = {Pedrotti, Francesco}, booktitle = {arXiv}, title = {{Contractive coupling rates and curvature lower bounds for Markov chains}}, doi = {10.48550/arXiv.2308.00516}, year = {2023}, } @inproceedings{17378, abstract = {Generative Pre-trained Transformer models, known as GPT or OPT, set themselves apart through breakthrough performance across complex language modelling tasks, but also by their extremely high computational and storage costs. Specifically, due to their massive size, even inference for large, highly-accurate GPT models may require multiple performant GPUs, which limits the usability of such models. While there is emerging work on relieving this pressure via model compression, the applicability and performance of existing compression techniques is limited by the scale and complexity of GPT models. In this paper, we address this challenge, and propose OPTQ, a new one-shot weight quantization method based on approximate second-order information, that is both highly-accurate and highly-efficient. Specifically, OPTQ can quantize GPT models with 175 billion parameters in approximately four GPU hours, reducing the bitwidth down to 3 or 4 bits per weight, with negligible accuracy degradation relative to the uncompressed baseline. Our method more than doubles the compression gains relative to previously-proposed one-shot quantization methods, preserving accuracy, allowing us for the first time to execute an 175 billion-parameter model inside a single GPU for generative inference. Moreover, we also show that our method can still provide reasonable accuracy in the extreme quantization regime, in which weights are quantized to 2-bit or even ternary quantization levels. We show experimentally that these improvements can be leveraged for end-to-end inference speedups over FP16, of around 3.25x when using high-end GPUs (NVIDIA A100) and 4.5x when using more cost-effective ones (NVIDIA A6000). The implementation is available at https://github.com/IST-DASLab/gptq.}, author = {Frantar, Elias and Ashkboos, Saleh and Hoefler, Torsten and Alistarh, Dan-Adrian}, booktitle = {11th International Conference on Learning Representations }, location = {Kigali, Rwanda}, publisher = {International Conference on Learning Representations}, title = {{OPTQ: Accurate post-training quantization for generative pre-trained transformers}}, year = {2023}, } @article{17379, abstract = {We introduce a computational pipeline for simulating and designing C-shells, a new class of planar-to-spatial deployable linkage structures. A C-shell is composed of curved flexible beams connected at rotational joints that can be assembled in a stress-free planar configuration. When actuated, the elastic beams deform and the assembly deploys towards the target 3D shape. We propose two alternative computational design approaches for C-shells: (i) Forward exploration simulates the deployed shape from a planar beam layout provided by the user. Once a satisfactory overall shape is found, a subsequent design optimization adapts the beam geometry to reduce the elastic energy of the linkage while preserving the target shape. (ii) Inverse design is facilitated by a new geometric flattening method that takes a design surface as input and computes an initial layout of piecewise straight linkage beams. Our design optimization algorithm then calculates the smooth curved beams to best reproduce the target shape at minimal elastic energy. We find that C-shells offer a rich space for design and show several studies that highlight new shape topologies that cannot be achieved with existing deployable linkage structures.}, author = {Becker, Quentin and Suzuki, Seiichi and Ren, Yingying and Pellis, Davide and Panetta, Julian and Pauly, Mark}, issn = {1557-7368}, journal = {ACM Transactions on Graphics}, number = {6}, publisher = {Association for Computing Machinery}, title = {{C-shells: Deployable gridshells with curved beams}}, doi = {10.1145/3618366}, volume = {42}, year = {2023}, } @inbook{17380, abstract = {Deployable gridshells are a class of planar-to-spatial structures that achievea 3D curved geometry by inducing bending on a flat grid of elastic beams. However, theslender nature of these beams often conflicts with the structure’s load-bearing capacity.To address this issue, multiple layers are typically stacked to enhance out-of-planestiffness and prevent stability issues. The primary challenge then lies in deploying suchmulti-layered systems globally, as it requires significant shaping forces for actuation.This paper presents an alternative design approach that involves strategically connect-ing compact-to-volumetric gridshell components using weaving principles to shape athick segmented shell. This innovative approach allows for an incremental construc-tion process based entirely on deployable modules with volumetric configurations thatlocally provide the necessary structural depth for the entire system. To demonstrate thisprinciple, we present the realization of BamX, a research pavilion constructed usingdeployable cylindrical components made from raw bamboo slats. These componentsare interconnected at carefully optimized interlocking woven nodes, resulting in abending-active structural frame that is both strong and exceptionally lightweight. Todetermine the optimal topology and geometry of the pavilion, we employ an integrativecomputational approach that leverages advanced numerical optimization techniques.Our method incorporates a physics-based simulation of the bending and twisting be-havior of the bamboo ribbons. By finding the ideal locations for ribbon crossings, weensure that all external and internal forces are in global equilibrium while minimizingthe mechanical stress experienced by each ribbon. BamX exemplifies how a symbiosisof refined weaving craft and advanced computational modeling enables fascinatingnew opportunities for rethinking deployability in architecture.}, author = {Suzuki, Seiichi and Martin, Alison and Ren, Yingying and Chen, Tzu-Ying and Parascho, Stefana and Pauly, Mark}, booktitle = {Advances in Architectural Geometry 2023}, editor = {Dörfler, Kathrin and Knippers, Jan and Menges, Achim and Parascho, Stefana and Pottmann, Helmut and Wortmann, Thomas}, isbn = {9783111160115}, publisher = {De Gruyter}, title = {{BamX: Rethinking Deployability in Architecture through Weaving}}, doi = {10.1515/9783111162683-016}, year = {2023}, } @article{17381, abstract = {We present an algorithmic approach to discover, study, and design multistable elastic knots. Elastic knots are physical realizations of closed curves embedded in 3-space. When endowed with the material thickness and bending resistance of a physical wire, these knots settle into equilibrium states that balance the forces induced by elastic deformation and self-contacts of the wire. In general, elastic knots can have many distinct equilibrium states, i.e. they are multistable mechanical systems. We propose a computational pipeline that combines randomized spatial sampling and physics simulation to efficiently find stable equilibrium states of elastic knots. Leveraging results from knot theory, we run our pipeline on thousands of different topological knot types to create an extensive data set of multistable knots. By applying a series of filters to this data, we discover new transformable knots with interesting geometric and physical properties. A further analysis across knot types reveals geometric and topological patterns, yielding constructive principles that generalize beyond the currently tabulated knot types. We show how multistable elastic knots can be used to design novel deployable structures and engaging recreational puzzles. Several physical prototypes at different scales highlight these applications and validate our simulation.}, author = {Vidulis, Michele and Ren, Yingying and Panetta, Julian and Grinspun, Eitan and Pauly, Mark}, issn = {1557-7368}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {Association for Computing Machinery}, title = {{Computational exploration of multistable elastic knots}}, doi = {10.1145/3592399}, volume = {42}, year = {2023}, } @article{17382, abstract = {Elastic surfaces that morph between multiple geometrical configurations are of significant engineering value, with applications ranging from the deployment of space-based photovoltaic arrays, the erection of temporary shelters, and the realization of flexible display systems, to understanding the encapsulation and release of viral RNAs. In general, ensuring that a shape with a planar rest configuration can deploy into a target three-dimensional (3D) shape is a nontrivial problem. Moreover, it is difficult to physically realize the local deformations necessary to achieve such global transformation. Here, we give a tutorial on applying conformal mapping to rationalize the geometrical deformation of several microstructure designs. A conformal map is a function that locally preserves angles and shapes but not lengths: some regions are scaled (enlarged or shrunk) more than others. To transform a planar surface to 3D, we implement uniform local scalings as mechanical deformations. Numerous natural and architected material systems exhibit such behavior, including kirigami, origami, hydrogel, linkage mechanisms, and fabric membranes. The design and fabrication of conformally transformable surfaces is a transdisciplinary challenge involving insights from advanced manufacturing, computational design, material science, and mechanics. By recognizing that many material systems exhibit isotropic deformation, we hope to inspire researchers to adopt conformal mapping in designing next-generation surface-based engineering systems.}, author = {Wang, Yue and Ren, Yingying and Chen, Tian}, issn = {1528-9036}, journal = {Journal of Applied Mechanics}, number = {4}, publisher = {American Society of Mechanical Engineers}, title = {{From kirigami to hydrogels: A tutorial on designing conformally transformable surfaces}}, doi = {10.1115/1.4056350}, volume = {90}, year = {2023}, } @article{17498, abstract = {In recent years, there has been tremendous progress on developing program logics for verifying the correctness of programs in a rich and diverse array of languages. Thus far, however, such logics have assumed that programs are written entirely in a single programming language. In practice, this assumption rarely holds since programs are often composed of components written in different programming languages, which interact with one another via some kind of foreign function interface (FFI). In this paper, we take the first steps towards the goal of developing program logics for multi-language verification. Specifically, we present Melocoton, a multi-language program verification system for reasoning about OCaml, C, and their interactions through the OCaml FFI. Melocoton consists of the first formal semantics of (a large subset of) the OCaml FFI—previously only described in prose in the OCaml manual—as well as the first program logic to reason about the interactions of program components written in OCaml and C. Melocoton is fully mechanized in Coq on top of the Iris separation logic framework.}, author = {Guéneau, Armaël and Hostert, Johannes and Spies, Simon and Sammler, Michael Joachim and Birkedal, Lars and Dreyer, Derek}, issn = {2475-1421}, journal = {Proceedings of the ACM on Programming Languages}, number = {OOPSLA2}, pages = {716--744}, publisher = {Association for Computing Machinery}, title = {{Melocoton: A program logic for verified interoperability between OCaml and C}}, doi = {10.1145/3622823}, volume = {7}, year = {2023}, } @article{17499, abstract = {Much work in formal verification of low-level systems is based on one of two approaches: refinement or separation logic. These two approaches have complementary benefits: refinement supports the use of programs as specifications, as well as transitive composition of proofs, whereas separation logic supports conditional specifications, as well as modular ownership reasoning about shared state. A number of verification frameworks employ these techniques in tandem, but in all such cases the benefits of the two techniques remain separate. For example, in frameworks that use relational separation logic to prove contextual refinement, the relational separation logic judgment does not support transitive composition of proofs, while the contextual refinement judgment does not support conditional specifications. In this paper, we propose Conditional Contextual Refinement (or CCR, for short), the first verification system to not only combine refinement and separation logic in a single framework but also to truly marry them together into a unified mechanism enjoying all the benefits of refinement and separation logic simultaneously. Specifically, unlike in prior work, CCR’s refinement specifications are both conditional (with separation logic pre- and post-conditions) and transitively composable. We implement CCR in Coq and evaluate its effectiveness on a range of interesting examples.}, author = {Song, Youngju and Cho, Minki and Lee, Dongjae and Hur, Chung-Kil and Sammler, Michael Joachim and Dreyer, Derek}, issn = {2475-1421}, journal = {Proceedings of the ACM on Programming Languages}, number = {POPL}, pages = {1121--1151}, publisher = {Association for Computing Machinery}, title = {{Conditional contextual refinement}}, doi = {10.1145/3571232}, volume = {7}, year = {2023}, } @article{17500, abstract = {Prior work on multi-language program verification has achieved impressive results, including the compositional verification of complex compilers. But the existing approaches to this problem impose a variety of restrictions on the overall structure of multi-language programs (e.g. fixing the source language, fixing the set of involved languages, fixing the memory model, or fixing the semantics of interoperation). In this paper, we explore the problem of how to avoid such global restrictions. Concretely, we present DimSum: a new, decentralized approach to multi-language semantics and verification, which we have implemented in the Coq proof assistant. Decentralization means that we can define and reason about languages independently from each other (as independent modules communicating via events), but also combine and translate between them when necessary (via a library of combinators). We apply DimSum to a high-level imperative language Rec (with an abstract memory model and function calls), a low-level assembly language Asm (with a concrete memory model, arbitrary jumps, and syscalls), and a mathematical specification language Spec. We evaluate DimSum on two case studies: an Asm library extending Rec with support for pointer comparison, and a coroutine library for Rec written in Asm. In both cases, we show how DimSum allows the Asm libraries to be abstracted to Rec-level specifications, despite the behavior of the Asm libraries not being syntactically expressible in Rec itself. We also verify an optimizing multi-pass compiler from Rec to Asm, showing that it is compatible with these Asm libraries.}, author = {Sammler, Michael Joachim and Spies, Simon and Song, Youngju and D'Osualdo, Emanuele and Krebbers, Robbert and Garg, Deepak and Dreyer, Derek}, issn = {2475-1421}, journal = {Proceedings of the ACM on Programming Languages}, number = {POPL}, pages = {775--805}, publisher = {Association for Computing Machinery}, title = {{DimSum: A decentralized approach to multi-language semantics and verification}}, doi = {10.1145/3571220}, volume = {7}, year = {2023}, } @article{17507, abstract = {Stellar-mass black holes (BHs) are predicted to be embedded in the disks of active galactic nuclei (AGNs) due to gravitational drag and in situ star formation. However, clear evidence for AGN disk-embedded BHs is currently lacking. Here, as possible electromagnetic signatures of these BHs, we investigate breakout emission from shocks emerging around Blandford–Znajek jets launched from accreting BHs in AGN disks. We assume that most of the highly super-Eddington flow reaches the BH and produces a strong jet, and the jet produces feedback that shuts off accretion and thus leads to episodic flaring. These assumptions, while poorly understood at present, yield observable consequences that can probe the presence of AGN-embedded BHs as well as the accretion process itself. They predict a breakout emission characterized by luminous thermal emission in the X-ray bands and bright broadband nonthermal emission from the infrared to the gamma-ray bands. The flare duration depends on the BH's distance r from the central supermassive BH, varying between 103–106 s for r ∼ 0.01–1 pc. This emission can be discovered by current and future infrared, optical, and X-ray wide-field surveys and monitoring campaigns of nearby AGNs.}, author = {Tagawa, Hiromichi and Kimura, Shigeo S. and Haiman, Zoltán and Perna, Rosalba and Bartos, Imre}, issn = {2041-8205}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {American Astronomical Society}, title = {{Observable signatures of stellar-mass black holes in active galactic nuclei}}, doi = {10.3847/2041-8213/acc103}, volume = {946}, year = {2023}, } @article{17513, abstract = {The astrophysical origin of over 90 compact binary mergers discovered by the LIGO and Virgo gravitational wave observatories is an open question. While the unusual mass and spin of some of the discovered objects constrain progenitor scenarios, the observed mergers are consistent with multiple interpretations. A promising approach to solve this question is to consider the observed distributions of binary properties and compare them to expectations from different origin scenarios. Here we describe a new hierarchical population analysis framework to assess the relative contribution of different formation channels simultaneously. For this study we considered binary formation in active galactic nucleus (AGN) disks along with phenomenological models, but the same framework can be extended to other models. We find that high-mass and high-mass-ratio binaries appear more likely to have an AGN origin compared to having the same origin as lower-mass events. Future observations of high-mass black hole mergers could further disentangle the AGN component from other channels.}, author = {Gayathri, V. and Wysocki, Daniel and Yang, Y. and Delfavero, Vera and O’Shaughnessy, R. and Haiman, Zoltán and Tagawa, H. and Bartos, I.}, issn = {2041-8205}, journal = {The Astrophysical Journal Letters}, number = {2}, publisher = {American Astronomical Society}, title = {{Gravitational wave source populations: Disentangling an AGN component}}, doi = {10.3847/2041-8213/acbfb8}, volume = {945}, year = {2023}, } @article{17514, abstract = {Extreme mass-ratio inspirals (EMRIs) take place when a stellar-mass black hole (BH) merges with a supermassive BH (SMBH). The gravitational-wave emission from such an event is expected to be detectable by the future Laser Interferometer Space Antenna (LISA) and other millihertz detectors. It was recently suggested that the EMRI rate in SMBH binary systems is orders of magnitude higher than the EMRI rate around a single SMBH with the same total mass. Here we show that this high rate can produce thousands of SMBH–BH sources at a redshift of unity. We predict that LISA may detect a few hundred of these EMRIs with signal-to-noise ratio above S/N ≥8 within a 4 yr mission lifetime. The remaining subthreshold sources will contribute to a large confusion noise, which is approximately an order of magnitude above LISA’s sensitivity level. Finally, we suggest that the individually detectable systems, as well as the background noise from the subthreshold EMRIs, can be used to constrain the SMBH binary fraction in the low-redshift Universe.}, author = {Naoz, Smadar and Haiman, Zoltán}, issn = {2041-8205}, journal = {The Astrophysical Journal Letters}, number = {2}, publisher = {American Astronomical Society}, title = {{The enhanced population of extreme mass-ratio inspirals in the LISA band from supermassive black hole binaries}}, doi = {10.3847/2041-8213/acf8c9}, volume = {955}, year = {2023}, } @article{17521, abstract = {The upcoming Laser Interferometer Space Antenna (LISA) is expected to detect gravitational waves (GWs) from massive black hole binaries (MBHB). Finding the electromagnetic (EM) counterparts for these GW events will be crucial for understanding how and where MBHBs merge, measuring their redshifts, constraining the Hubble constant and the graviton mass, and for other novel science applications. However, due to poor GW sky localization, multiwavelength, time-dependent EM models are needed to identify the right host galaxy. We studied merging MBHBs embedded in a circumbinary disc (CBD) using high-resolution two-dimensional simulations, with a Γ-law equation of state, incorporating viscous heating, shock heating, and radiative cooling. We simulate the binary from large separation until after merger, allowing us to model the decoupling of the binary from the CBD. We compute the EM signatures and identify distinct features before, during, and after the merger. Our main result is a multiband EM signature: we find that the MBHB produces strong thermal X-ray emission until 1–2 d prior to the merger. However, as the binary decouples from the CBD, the X-ray-bright minidiscs rapidly shrink in size, become disrupted, and the accretion rate drops precipitously. As a result, the thermal X-ray luminosity drops by orders of magnitude, and the source remains X-ray dark for several days, regardless of any post-merger effects such as GW recoil or mass-loss. Looking for the abrupt spectral change where the thermal X-ray disappears is a tell-tale EM signature of LISA mergers that does not require extensive pre-merger monitoring.}, author = {Krauth, Luke Major and Davelaar, Jordy and Westernacher-Schneider, John Ryan and Haiman, Zoltán and Zrake, Jonathan and MacFadyen, Andrew}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, pages = {5441--5454}, publisher = {Oxford University Press}, title = {{Disappearing thermal X-ray emission as a tell-tale signature of merging massive black hole binaries}}, doi = {10.1093/mnras/stad3095}, volume = {526}, year = {2023}, } @article{17522, abstract = {The early growth of black holes (BHs) in high-redshift galaxies is likely feedback regulated. While radiative feedback has been extensively studied, the role of mechanical feedback has received less scrutiny to date. Here, we use high-resolution parsec-scale hydrodynamical simulations to study jet propagation and its effect on 100 M⊙ BH accretion in the dense, low-metallicity gas expected in early protogalaxies. As the jet propagates, it shocks the surrounding gas forming a jet cocoon. The cocoon consists of a rapidly cooling cold phase at the interface with the background gas and an overpressured subsonic phase of reverse shock-heated gas filling the interior. We vary the background gas density and temperature, BH feedback efficiency, and the jet model. We found that the width of the jet cocoon roughly follows a scaling derived by assuming momentum conservation in the jet-propagation direction and energy conservation in the lateral directions. Depending on the assumed gas and jet properties, the cocoon either stays elongated to large radii or isotropizes before reaching the Bondi radius, forming a nearly spherical bubble. Lower jet velocities and higher background gas densities result in self-regulation to higher momentum fluxes and elongated cocoons. In all cases, the outward cocoon momentum flux balances the inward inflowing gas momentum flux near the Bondi radius, which ultimately regulates BH accretion. The time-averaged accretion rate always remains below the Bondi rate, and exceeds the Eddington rate only if the ambient medium is dense and cold, and/or the jet is weak (low velocity and mass loading).}, author = {Su, Kung-Yi and Bryan, Greg L and Haiman, Zoltán and Somerville, Rachel S and Hayward, Christopher C and Faucher-Giguère, Claude-André}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, pages = {4258--4275}, publisher = {Oxford University Press}, title = {{Self-regulation of black hole accretion via jets in early protogalaxies}}, doi = {10.1093/mnras/stad252}, volume = {520}, year = {2023}, } @article{17527, abstract = {The origin of the recently discovered new class of transients, X-ray quasi-periodic eruptions (QPEs), remains a puzzle. Due to their periodicity and association with active galactic nuclei (AGNs), it is natural to relate these eruptions to stars or compact objects in tight orbits around supermassive black holes (SMBHs). In this paper, we predict the properties of emission from bow shocks produced by stars crossing AGN discs, and compare them to the observed properties of QPEs. We find that when a star’s orbit is retrograde and has a low inclination (≲40°) with respect to the AGN disc and the star is massive (≳10 M⊙), the breakout emission from the bow shock can explain the observed duration (∼hours) and X-ray luminosity (∼few × 1042 erg s−1) of QPEs. This model can further explain various observed features of QPEs, such as their complex luminosity evolution, the gradual decline of luminosity of the flares over several years, the evolution of the hardness ratio, the modulation of the luminosity during quiescent phases, and the preference of the central SMBHs to have low masses.}, author = {Tagawa, Hiromichi and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {69--79}, publisher = {Oxford University Press}, title = {{Flares from stars crossing active galactic nucleus discs on low-inclination orbits}}, doi = {10.1093/mnras/stad2616}, volume = {526}, year = {2023}, } @article{17539, abstract = {In this paper, we study how gaseous dynamical friction (DF) affects the motion of fly-by stellar-mass black holes (sBHs) embedded in active galactic nucleus (AGN) discs. We perform three-body integrations of the interaction of two co-planar sBHs in nearby, initially circular orbits around the supermassive black hole. We find that DF can facilitate the formation of gravitationally bound near-Keplerian binaries in AGN discs, and we delineate the discrete ranges of impact parameters and AGN disc parameters for which such captures occur. We also report trends in the bound binaries’ eccentricity and sense of rotation (prograde or retrograde with respect to the background AGN disc) as a function of the impact parameter of the initial encounter. While based on an approximate description of gaseous friction, our results suggest that binary formation in AGN discs should be common and may produce both prograde and retrograde, as well as both circular and eccentric binaries.}, author = {DeLaurentiis, Stanislav and Epstein-Martin, Marguerite and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {1126--1139}, publisher = {Oxford University Press}, title = {{Gas dynamical friction as a binary formation mechanism in AGN discs}}, doi = {10.1093/mnras/stad1412}, volume = {523}, year = {2023}, } @article{17548, abstract = {The shrinking of a binary orbit driven by the interaction with a gaseous circumbinary disc, initially advocated as a potential way to catalyse the binary merger, has recently been debated in the case of geometrically thick (i.e. with H/R ≳ 0.1) discs. However, a clear consensus is still missing mainly owing to numerical limitations, such as fixed orbit binaries or lack of resolution inside the cavity carved by the binary in its circumbinary disc. In this work, we assess the importance of evolving the binary orbit by means of hydrodynamic simulations performed with the code gizmo in meshless finite mass mode. In order to model the interaction between equal mass circular binaries and their locally isothermal circumbinary discs, we enforce hyper-Lagrangian resolution inside the cavity. We find that fixing the binary orbit ultimately leads to an overestimate of the gravitational torque that the gas exerts on the binary and an underestimate of the torque due to the accretion of material on to the binary components. Furthermore, we find that the modulation of the accretion rate on the binary orbital period is strongly suppressed in the fixed orbit simulation, while it is clearly present in the live binary simulations. This has potential implications for the prediction of the observable periodicities in massive black hole binary candidates.}, author = {Franchini, Alessia and Lupi, Alessandro and Sesana, Alberto and Haiman, Zoltán}, issn = {0035-8711}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {1}, pages = {1569--1574}, publisher = {Oxford University Press}, title = {{The importance of live binary evolution in numerical simulations of binaries embedded in circumbinary discs}}, doi = {10.1093/mnras/stad1070}, volume = {522}, year = {2023}, }