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Undesignable motifs in structural RNAs and combinatorial consequences
No full textInternational audienceRNA design aims at constructing RiboNucleic Acids (RNA) sequences that perform a predefined biological function, usually modeled by multiple constraints on the sequence and structure level. In its most popular setting, called the inverse folding problem, designed RNAs should adopt a predefined target secondary structure, preferentially to any alternative structure. It was previously observed that some secondary structures are undesignable, i.e. no RNA sequence can fold uniquely into the target structure while satisfying some criterion measuring how preferential this folding is compared to alternative conformations.We show that the proportion of designable secondary structures decreases exponentially with the size of the target secondary structure, for various popular combinations of energy models and design objectives. This exponential decay is, at least in part, due to the existence of undesignable motifs, which can be generically constructed, and jointly analyzed to yield asymptotic upper-bounds on the number of designable structures. Finally, we define a lower bound of the minimal ensemble defect of a secondary structure. We show that, across uniformly distributed secondary structures, such lower bound admits a normal limiting distribution whose two parameters, the expected value and the variance, both grow linearly with the size of secondary structure.</div
Search for lepton-number-violating decays
No full textInternational audienceA search is performed for lepton-number-violating decays, using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb. No significant signal is observed, and upper limits are set on the branching fractions, and , at the 95% confidence level
Non-Linear Counterfactual Aggregate Optimization
No full textRecsys '25, CONSEQUENCES WorkshopInternational audienceWe consider the problem of directly optimizing a non-linear function of an outcome, where this outcome itself is the sum of many small contributions. The non-linearity of the function means that the problem is not equivalent to the maximization of the expectation of the individual contribution. By leveraging the concentration properties of the sum of individual outcomes, we derive a scalable descent algorithm that directly optimizes for our stated objective. This allows for instance to maximize the probability of successful A/B test, for which it can be wiser to target a success criterion—such as exceeding a given uplift—rather than chasing the highest expected payoff
Many-body Quantum Score: a scalable benchmark for digital and analog quantum processors and first test on a commercial neutral atom device
No full textWe propose the Many-body Quantum Score (MBQS), a practical and scalable application level benchmark protocol designed to evaluate the capabilities of quantum processing units (QPUs)—both gate-based and analog—for simulating many-body quantum dynamics. MBQS quantifies performance by identifying the maximum number of qubits with which a QPU can reliably reproduce correlation functions of the transverse-field Ising model following a specific quantum quench. This paper presents the MBQS protocol and highlights its design principles, supported by analytical insights, classical simulations, and experimental data. It also displays results obtained with Ruby, an analogQPU based on Rydberg atoms developed by the Pasqal company. These findings demonstrateMBQS’s potential as a robust and informative tool for benchmarking near-term quantum devices for many-body physics
A functional inequalities approach for the field-road diffusion model with (symmetric) nonlinear exchanges
No full textIn this note, we consider the so-called field-road diffusion model in a bounded domain, consisting of two parabolic PDEs posed on sets of different dimensions and coupled through (symmetric) nonlinear exchange terms. We propose a new and rather direct functional inequalities approach to prove the exponential decay of a relative entropy, and thus the convergence of the solution towards the stationary state selected by the total mass of the initial datum
Quantum Mechanics on Lie Groups: I. Noncommutative Fourier Transforms
No full textInternational audienceStarting from square-integrable wave functions on a Lie group, we build an invertible Fourier transform mapping them on wave functions on the dual of the Lie algebra. This is a group-theoretic version of the map from position space to momentum space, with generally noncommuting momenta owing to the group structure. As a result, the multiplication of momentum-dependent functions involves star products, which makes the construction of noncommutative Fourier series much more involved than that of their commutative cousin. We show that our formalism provides an isometry of Hilbert spaces, and use it to derive a noncommutative Poisson summation formula for any compact Lie group. This is a key preliminary for the computation of Wigner functions and path integrals for quantum systems on group manifolds
Ordres de charge et de spin dans le modèle t-U-V-J : une approche de particule esclave de spin 1
No full textStrongly-correlated fermion systems on a lattice have been a subject of intense focus in the field of condensed-matter physics. These systems are notoriously difficult to solve, even with state-of-theart numerical methods, especially in regimes of parameters where degrees of freedom compete or cooperate at similar energy and length scales. Here, we introduce a spin-1 slave-particle technique to approximately treat the t-U -V -J fermionic model at arbitrary electron dopings in a simple manner. This formalism relies on a self-consistent cluster mean-field method, and it couples effective pseudo-spin and pseudo-fermion sectors, representing the original electron charge and spin degrees, respectively. We study the phase diagram of the model under various conditions and report the appearance of charge and spin stripes within this formalism. These stripes are a consequence of the cluster mean-field treatment of the pseudo-particle sectors and have not been detected in previous slave-particle studies.Les systèmes de fermions fortement corrélés sur un réseau ont fait l'objet d'une attention particulière dans le domaine de la physique de la matière condensée. Ces systèmes sont réputés difficiles à résoudre, même avec les méthodes numériques les plus avancées, en particulier dans les régimes de paramètres où les degrés de liberté entrent en concurrence ou coopèrent à des échelles d'énergie et de longueur similaires. Nous présentons ici une technique de particule esclave de spin 1 permettant de traiter de manière simple et approximative le modèle fermionique t-U-V-J à des dopages électroniques arbitraires. Ce formalisme repose sur une méthode de champ moyen de cluster auto-cohérente et couple les secteurs pseudo-spin et pseudo-fermion effectifs, représentant respectivement les degrés de charge et de spin électroniques d'origine. Nous étudions le diagramme de phase du modèle dans diverses conditions et signalons l'apparition de bandes de charge et de spin dans ce formalisme. Ces bandes sont une conséquence du traitement par champ moyen sur cluster des secteurs de pseudo-particules et n'ont pas été détectées dans les études précédentes de particules esclaves
Search for heavy neutral leptons in B-meson decays
No full textInternational audienceA search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of . The results are interpreted in both lepton-number-conserving and lepton-number-violating scenarios. No significant excess is observed. Constraints are placed on the squared mixing element to the active muon neutrino, under the assumption that couplings to other lepton flavours are negligible, in the mass range of - GeV
Homogenizing elastic lattices with mechanisms
No full textInternational audienceWe propose an asymptotic method for homogenizing periodic elastic latticesthat works in the presence of mechanisms, both of the macroscopic type(strain-producing modes) and of the microscopic type (internal modes). When amicroscopic mechanism is present, the unit-cell problem produced by classicalhomogenization is singular. It can be fixed by including the amplitude~ of the mechanism as an additional macroscopic degree offreedom (enrichment variable) contributing to the effective energy via itsgradient . When a macroscopic mechanism ispresent, homogenization delivers a degenerate effective energy at leadingorder, which can be regularized by accounting for the strain gradient. Weintroduce an asymptotic second-order homogenization scheme that integratesthese two features: it delivers an effective energy capturing both thestrain-gradient effect relevantto macroscopic mechanisms, and the regularization relevant to microscopic mechanisms, if any is present. Theversatility of the approach is illustrated with a selection of latticesdisplaying a variety of effective behaviors. It follows a unified pattern thatleads to a classification of these effective behaviors. Whereas the proceduredelivers known effective models for elastic lattices without mechanisms, itcan generate novel effective models for lattices possessing mechanisms
