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    Quantum Gravity, Hydrodynamics and Emergent Cosmology: A Collection of Perspectives

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    International audienceThis collection of perspective pieces captures recent advancements and reflections from a dynamic research community dedicated to bridging quantum gravity, hydrodynamics, and emergent cosmology. It explores four key research areas: (a) the interplay between hydrodynamics and cosmology, including analog gravity systems; (b) phase transitions, continuum limits and emergent geometry in quantum gravity; (c) relational perspectives in gravity and quantum gravity; and (d) the emergence of cosmological models rooted in quantum gravity frameworks. Each contribution presents the distinct perspectives of its respective authors. Additionally, the introduction by the editors proposes an integrative view, suggesting how these thematic units could serve as foundational pillars for a novel theoretical cosmology framework termed "hydrodynamics on superspace"

    The Nobel “Pride” Phenomenon: An analysis of Nobel Prize discoveries and their recognition

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    International audienceThe Nobel Prize is considered one of the highest forms of recognition of scientific accomplishment, conferring immense prestige upon its recipients. Given the significant time lag between the award and the discovery, Nobel Prizes are bestowed to individuals associated with institutions and countries other than the original place of the discovery. Contextualizing our research in status-seeking literature, we define the imprecise and sometimes excessive appropriation of Nobel Prizes by institutions and even countries as the “Nobel ‘Pride’ Phenomenon”. Our empirical analysis focuses on the time and location of the 653 discoveries underlying each of the 350 Nobel Prizes in medicine, physics, and chemistry until 2024. About one-third of all Nobel laureates came from another institution or country. Furthermore, Nobel Prize creativity is highly concentrated, with more than 80 % of discoveries made in just five countries. These findings cast new light on the Nobel laureates' demographics, geographic and historical movements, and institutional affiliations, and have implications for research policy at institutions and national levels

    Refined Analysis of Federated Averaging's Bias and Federated Richardson-Romberg Extrapolation

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    International audienceIn this paper, we present a novel analysis of FedAvg with constant step size, relying on the Markov property of the underlying process. We demonstrate that the global iterates of the algorithm converge to a stationary distribution and analyze its resulting bias and variance relative to the problem's solution. We provide a first-order bias expansion in both homogeneous and heterogeneous settings. Interestingly, this bias decomposes into two distinct components: one that depends solely on stochastic gradient noise and another on client heterogeneity. Finally, we introduce a new algorithm based on the Richardson-Romberg extrapolation technique to mitigate this bias

    Pseudorapidity distributions of charged hadrons in lead-lead collisions at sNN\sqrt{s_\mathrm{NN}} = 5.36 TeV

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    International audienceThe pseudorapidity (η\eta) distributions of charged hadrons are measured using data collected at the highest ever nucleon-nucleon center-of-mass energy of sNN\sqrt{s_\mathrm{NN}} = 5.36 TeV for collisions of lead-lead ions. The data were recorded by the CMS experiment at the LHC in 2022 and correspond to an integrated luminosity of 0.30 ±\pm 0.03 μ\mub1^{-1}. Using the CMS silicon pixel detector, the yields of primary charged hadrons produced in the range η\vert\eta\vert<\lt 2.6 are reported. The evolution of the midrapidity particle density as a function of collision centrality is also reported. In the 5% most central collisions, the charged-hadron η\eta density in the range η\vert\eta\vert <\lt 0.5 is found to be 2032 ±\pm 91 (syst), with negligible statistical uncertainty. This result is consistent with an extrapolation from nucleus-nucleus collision data at lower center-of-mass energies. Comparisons are made to various Monte Carlo event generators and to previous measurements of lead-lead and xenon-xenon collisions at similar collision energies. These new data detail the dependence of particle production on the collision energy, initial collision geometry, and the size of the colliding nuclei

    Technical Status Report on Plasma Components and Systems in the context of EuPRAXIA

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    International audienceThe EuPRAXIA project aims to construct two state-of-the-art accelerator facilities based on plasma accelerator technology. Plasma-based accelerators offer the possibility of a significant reduction in facility size and cost savings over current radio frequency (RF) accelerators. The two facilities - one laser-driven one a beam-driven - are envisioned to provide electron beams with an energy in the range of 1-5 GeV and beam quality comparable to existing RF machines. This will enable a versatile portfolio of applications from compact free-electron laser (FEL) drivers to sources for medical and industrial imaging. At the heart of both facilities is the use of plasma-based accelerator components and systems which encompass not only the accelerating medium itself, but also a range of auxiliary systems such as plasma-based electron beam optics and plasma-based mirrors for high-intensity lasers. From a technical standpoint, a high-degree of control over these plasma devices will be essential for EuPRAXIA to achieve its target performance goals. The ability to diagnose and characterize these plasma devices and to simulate their operation will be further essential success factors. Additionally, compatibility with extended operation at high-repetition rates and integration into the accelerator beamline will also prove crucial. In this work, we aim to review the current status of plasma components and related systems for both laser-driven and beam-driven plasma accelerators and to assess challenges to be addressed regarding implementation at future EuPRAXIA facilities

    Bridging multifluid and drift-diffusion models for bounded plasmas

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    International audienceFluid models represent a valid alternative to kinetic approaches in simulating low-temperature discharges: a well-designed strategy must be able to combine the ability to predict a smooth transition from the quasineutral bulk to the sheath, where a space charge is built at a reasonable computational cost. These approaches belong to two families: multifluid models, where momenta of each species are modeled separately, and drift-diffusion models, where the dynamics of particles is dependent only on the gradient of particle concentration and on the electric force. It is shown that an equivalence between the two models exists and that it corresponds to a threshold Knudsen number, in the order of the square root of the electron-to-ion mass ratio; for an argon isothermal discharge, this value is given by a neutral background pressure Pn≳1000 Pa. This equivalence allows us to derive two analytical formulas for a priori estimation of the sheath width: the first one does not need any additional hypothesis but relies only on the natural transition from the quasineutral bulk to the sheath; the second approach improves the prediction by imposing a threshold value for the charge separation. The new analytical expressions provide better estimations of the floating sheath dimension in collisions-dominated regimes when tested against two models from the literature

    Tail Modulo Cons, OCaml, and Relational Separation Logic

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    International audienceCommon functional languages incentivize tail-recursive functions, as opposed to general recursive functions that consume stack space and may not scale to large inputs. This distinction occasionally requires writing functions in a tail-recursive style that may be more complex and slower than the natural, non-tail-recursive definition. This work describes our implementation of the tail modulo constructor (TMC) transformation in the OCaml compiler, an optimization that provides stack-efficiency for a larger class of functions --- tail-recursive modulo constructors --- which includes in particular the natural definition of 'List.map' and many similar recursive data-constructing functions. We prove the correctness of this program transformation in a simplified setting --- a small untyped calculus --- that captures the salient aspects of the OCaml implementation. Our proof is mechanized in the Coq proof assistant, using the Iris base logic. An independent contribution of our work is an extension of the Simuliris approach to define simulation relations that support different calling conventions. To our knowledge, this is the first use of Simuliris to prove the correctness of a compiler transformation

    Nucleon tensor form factors at large NcN_{c}

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    International audienceWe investigate nucleon tensor form factors in the large-NcN_{c} limit. In this picture, the nucleon emerges as a state of the NcN_c valence quarks, which were bound by pion mean fields that were created by the presence of the valence quarks self-consistently. We find that the tensor charge (gTud=0.99g^{u-d}_{T}=0.99) and the anomalous tensor magnetic moment (κTu+d=7.61\kappa^{u+d}_{T}=7.61) are dominated by valence quarks, while the tensor quadrupole moment (QTud=7.02Q^{u-d}_{T}=-7.02) shows significant sea quark effects. We examine how these quantities vary as the average size of the pion mean field is changed, showing interpolation between non-relativistic quark and Skyrme limits. We also observe that gTudg^{u-d}_{T} and κTu+d\kappa^{u+d}_{T} depend weakly on the pion mass. In contrast, QTudQ^{u-d}_{T} exhibits strong enhancement near the chiral limit. The numerical results are in good agreement with available lattice QCD data and provide predictions for unmeasured quantities

    Mars Without the Southern Perennial CO 2 Cover

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    International audienceThe Martian South Polar Layered Deposits (SPLD) are composed mostly of ice and dust with a thin perennial CO 2 cover and some internal CO 2 ice layers. In the North, the seasonal CO 2 cap is lost during summer, allowing H 2 O ice to sublimate into the atmosphere. In the South, the perennial CO 2 cover prevents H 2 O ice sublimation. This work uses the Mars Planetary Climate Model to investigate how the H 2 O and CO 2 cycles are affected if the thin perennial CO 2 SPLD cover is lost. We find that during southern summer, the atmospheric water content will more than double in the south polar region. However, on a global scale, the NPLD is still the dominant source of humidity because of its larger surface area. When exposing some of the South Polar Cap buried water ice, the south polar cap becomes the dominant source of atmospheric humidity due to Mars's spin-orbital alignment.</div

    Efficient (3,3)(3,3)-isogenies on fast Kummer surfaces

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    International audienceWe give an alternative derivation of (N,N)(N,N)-isogenies between fast Kummer surfaces which complements existing works based on the theory oftheta functions. We use this framework to produce explicit formulae for the case of N=3N = 3, and show that the resulting algorithms are more efficient than all prior (3,3)(3, 3)-isogeny algorithms

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