arXiv subjects

Karim Trabelsi

Publications and source records attributed to Karim Trabelsi.

9 recordsLinked to original sources

arXiv2025

Prescribed exponential stabilization of scalar neutral differential equations: Application to neural control

This paper presents a control-oriented delay-based modeling approach for the exponential stabilization of a scalar neutral functional differential equation, which is then applied to the local exponential stabilization of a one-layer neural network of Hopfield type with delayed feedback. The proposed approach utilizes a recently developed partial pole placement method for linear functional differential equations, leveraging the coexistence of real spectral values to explicitly prescribe the exponential decay of the closed-loop solution. While a delayed proportional (P) feedback control may achieve stabilization, it requires higher gains and only allows for a shorter maximum delay compared to the proportional-derivative (PD) feedback control presented in this work. The framework provides a practical illustration of the stabilization strategy, improving upon previous literature results that characterize the solution's exponential decay for simple real spectral values. This approach enhances neural stability in cases where the inherent dynamics are stable and offers a method to achieve local exponential stabilization with a prescribed decay rate when the inherent dynamics are unstable.

math.SP↗

arXiv2022

Snowmass White Paper: Belle II physics reach and plans for the next decade and beyond

Belle II is an experiment operating at the intensity frontier. Over the next decades, it will record the decay of billions of bottom mesons, charm hadrons, and tau leptons produced in 10 GeV electron-positron collisions at the SuperKEKB high-luminosity collider at KEK. These data, collected in low-background and kinematically known conditions, will allow us to measure hundreds of parameters that test the standard model (SM) and probe for the existence of new particles, at mass scales orders of magnitudes higher than those studied at the energy frontier. We project our sensitivities for measurements that are of primary relevance and where Belle II will be unique or world leading for data corresponding to 1 to 50 ab$^{-1}$. Belle II will uniquely probe non-SM contributions in sensitive $b \to q\bar q s$ decays and charmless $b \to q\bar q d(u)$ decays, semileptonic $b \to s ν\barν$ and $s τ^+ τ^-$ decays, fully leptonic $b \to \ell ν$ decays, and select $c \to u$ processes. Belle II will lead exploration of non-SM physics in $b \to c τν$ and $b \to s γ$ decays and will most precisely determine the quark-mixing parameters $|V_{ub}|$ and $|V_{cb}|$. Belle II will measure many parameters in $τ$ physics to precisions that will be world leading for the foreseeable future, including the electric and magnetic dipole moments, branching fractions for charged-lepton-flavor-violating decays, and quantities that test lepton-flavor universality. Belle II will perform unique searches for dark-sector particles with masses in the MeV-GeV range. We will also pursue a broad spectroscopy program for conventional and multiquark $c \bar c$ and $b \bar b$ states and provide essential inputs to sharpen the interpretation of muon magnetic-anomaly results. Our exploration of uncharted regions of non-SM parameter space with high precision will reveal non-SM particles or set stringent constraints on their existence, guiding future endeavors.

hep-ex↗

arXiv2022

A new approach to semi-leptonic tags in $B$-meson semi-invisible decays

Kinematic variables designed for pairwise decays to partly undetected final states -- a prominent example being $M_{T2}$ and its Lorentz-invariant version $M_2$ -- have been extensively deployed in high-$p_T$ collider searches. A new range of potential applications at flavour facilities -- where $B$ mesons or $τ$ leptons are also pairwise produced -- was recently proposed. One general challenge in these decays arises if both the signal parent and the 'other' parent, often used as a tag, decay semi-invisibly. In such cases, which notably include semi-leptonic tags, signal identification is generally hindered by the ensuing lack of knowledge of the signal-parent boost. $M_2$ helps precisely to overcome this challenge, and allows to leverage the otherwise superior efficiency of semi-leptonic decays. Our strategy rests on two novel constraints that can be imposed on $M_2$. The first is that of the known mass of the decaying-parent mass squared which, in connection with other constraints, gives rise to $M_{2sB}$. The second is on the flight direction of the signal parent, often well reconstructed at facilities with high vertexing capabilities such as Belle II and LHCb. This constraint gives rise to the $M_{2V}$ variable, that can be used even at facilities where the collision energy is not known. We test these ideas in a decay of great current interest in the context of the persistent discrepancies in $B$ decays, namely $B \to K τμ$. We find that a bare-bones application of $M_{2sB}$ leads, alone, to an improvement that is already halfway between the current approach and the "truth-level" semi-leptonic case. Ceteris paribus -- in particular statistics -- our approach thus makes semi-leptonic tags competitive with fully reconstructed hadronic tags.

hep-ph↗

arXiv2022

Physics reach of a long-lived particle detector at Belle II

We have studied three realistic benchmark geometries for a new far detector GAZELLE to search for long-lived particles at the \superkekb accelerator in Tsukuba, Japan. The new detector would be housed in the same building as Belle II and observe the same $e^+e^-$ collisions. To assess the discovery reach of GAZELLE, we have investigated three new physics models that predict long-lived particles: heavy neutral leptons produced in tau lepton decays, axion-like particles produced in $B$ meson decays, and new scalars produced in association with a dark photon, as motivated by inelastic dark matter. We do not find significant gains in the new physics discovery reach of GAZELLE compared to the Belle II projections for the same final states. The main reasons are the practical limitations on the angular acceptance and size of GAZELLE, effectively making it at most comparable to Belle II, even though backgrounds in the far detector could be reduced to low rates. A far detector for long-lived particles would be well motivated in the case of a discovery by Belle II, since decays inside GAZELLE would facilitate studies of the decay products. Depending on the placement of GAZELLE, searches for light long-lived particles produced in the forward direction or signals of a confining hidden force could also benefit from such a far detector. Our general findings could help guide the design of far detectors at future electron-positron colliders such as the ILC, FCC-ee or CEPC.

hep-ph↗

arXiv2019

Using an amplitude analysis to measure the photon polarisation in $B \to Kππγ$ decays

A method is proposed to measure the photon polarisation parameter $λ_γ$ in $b\to sγ$ transitions using an amplitude analysis of $B\to Kππγ$ decays. Simplified models of the $Kππ$ i system are used to simulate $B^+ \to K^+π^-π^+γ$ and $B^0\to K^+π^-π^0$ decays, validate the amplitude analysis method, and demonstrate the feasibility of a measurement of the $λ_γ$ parameter irrespective of the model parameters. Similar sensitivities to $λ_γ$ are obtained with both the charged and neutral hadronic systems. In the absence of any background and distortion due to experimental effects, the statistical uncertainty expected from an analysis of $B^+ \to K^+π^-π^+γ$ decays in an LHCb data set corresponding to an integrated luminosity of $9\,$fb$^{-1}$ is estimated to be $0.009$. A similar measurement using $B^0\to K^+π^-π^0$ decays in a Belle II data sample corresponding to an integrated luminosity of $5\,$ab$^{-1}$ would lead to a statistical uncertainty of $0.018$

hep-ph↗

arXiv2017

Volumetric expressions of the shape gradient of the compliance in structural shape optimization

In this article, we consider the problem of optimal design of a compliant structure under a volume constraint, within the framework of linear elasticity. We introduce the pure displacement and the dual mixed formulations of the linear elasticity problem and we compute the volumetric expressions of the shape gradient of the compliance by means of the velocity method. A preliminary qualitative comparison of the two expressions of the shape gradient is performed through some numerical simulations using the Boundary Variation Algorithm.

math.OC↗

arXiv2016

Certified Descent Algorithm for shape optimization driven by fully-computable a posteriori error estimators

In this paper we introduce a novel certified shape optimization strategy - named Certified Descent Algorithm (CDA) - to account for the numerical error introduced by the Finite Element approximation of the shape gradient. We present a goal-oriented procedure to derive a certified upper bound of the error in the shape gradient and we construct a fully-computable, constant-free a posteriori error estimator inspired by the complementary energy principle. The resulting CDA is able to identify a genuine descent direction at each iteration and features a reliable stopping criterion. After validating the error estimator, some numerical simulations of the resulting certified shape optimization strategy are presented for the well-known inverse identification problem of Electrical Impedance Tomography.

math.NA↗

arXiv2014

Future sensitivity to new physics in B_d, B_s and K mixings

We estimate, in a large class of scenarios, the sensitivity to new physics in B_d and B_s mixings achievable with 50 ab-1 of Belle II and 50 fb-1 of LHCb data. We find that current limits on new physics contributions in both B_{d,s} systems can be improved by a factor of ~5 for all values of the CP violating phases, corresponding to over a factor of 2 increase in the scale of new physics probed. Assuming the same suppressions by CKM matrix elements as those of the standard model box diagrams, the scale probed will be about 20 TeV for tree-level new physics contributions, and about 2 TeV for new physics arising at one-loop. We also explore the future sensitivity to new physics in K mixing. Implications for generic new physics and for various specific scenarios, such as minimal flavor violation, light third-generation dominated flavor violation, or U(2) flavor models are studied.

hep-ph↗

arXiv2012

Physics Achievements from the Belle Experiment

The Belle experiment, running at the KEKB e+e- asymmetric energy collider during the first decade of the century, achieved its original objective of measuring precisely differences between particles and anti-particles in the B system. After collecting 1000 fb-1 of data at various Upsilon resonances, Belle also obtained the many other physics results described in this article.

hep-ex↗