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1. Search for CP violation in t$$ \overline{\textrm{t}} $$H and tH production in multilepton channels in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP07(2023)092  

   Tumasyan, A. ; Adam, W. ; Andrejkovic, J. W. ; Bergauer, T. ; Chatterjee, S. ; Damanakis, K. ; Dragicevic, M. ; Escalante Del Valle, A. ; Hussain, P. S. ; Jeitler, M. ; et al ( July 2023 , Journal of High Energy Physics)

   The charge-parity (CP) structure of the Yukawa interaction between the Higgs (H) boson and the top quark is measured in a data sample enriched in the t$$ \overline{\textrm{t}} $$$\overline{t}$H and tH associated production, using 138 fb⁻¹of data collected in proton-proton collisions at$$ \sqrt{s} $$$\sqrt{s}$= 13 TeV by the CMS experiment at the CERN LHC. The study targets events where the H boson decays via H → WW or H →ττand the top quarks decay via t → Wb: the W bosons decay either leptonically or hadronically, and final states characterized by the presence of at least two leptons are studied. Machine learning techniques are applied to these final states to enhance the separation ofCP-even fromCP-odd scenarios. Two-dimensional confidence regions are set onκ_tand$$ \overset{\sim }{\kappa } $$$\tilde{\kappa }$_t, which are respectively defined as theCP-even andCP-odd top-Higgs Yukawa coupling modifiers. No significant fractionalCP-odd contributions, parameterized by the quantity|$$ {f}_{CP}^{\textrm{Htt}} $$$f_{\mathrm{CP}}^{\mathrm{Htt}}$|are observed; the parameter is determined to be|$$ {f}_{CP}^{\textrm{Htt}} $$$f_{\mathrm{CP}}^{\mathrm{Htt}}$|= 0.59 with an interval of (0.24,0.81) at 68% confidence level. The results are combined with previous results covering the H→ZZ and H→ γγdecay modes, yielding two- and one-dimensional confidence regions onκ_tand$$ \overset{\sim }{\kappa } $$$\tilde{\kappa }$_t, while|$$ {f}_{CP}^{\textrm{Htt}} $$$f_{\mathrm{CP}}^{\mathrm{Htt}}$|is determined to be|$$ {f}_{CP}^{\textrm{Htt}} $$$f_{\mathrm{CP}}^{\mathrm{Htt}}$|= 0.28 with an interval of|$$ {f}_{CP}^{\textrm{Htt}} $$$f_{\mathrm{CP}}^{\mathrm{Htt}}$| <0.55 at 68% confidence level, in agreement with the standard modelCP-even prediction of|$$ {f}_{CP}^{\textrm{Htt}} $$$f_{\mathrm{CP}}^{\mathrm{Htt}}$|= 0.

    

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2. Operational prediction of solar flares using a transformer-based framework

   https://doi.org/10.1038/s41598-023-40884-1  

   Abduallah, Yasser ; Wang, Jason T. L. ; Wang, Haimin ; Xu, Yan ( August 2023 , Scientific Reports)

   Solar flares are explosions on the Sun. They happen when energy stored in magnetic fields around solar active regions (ARs) is suddenly released. Solar flares and accompanied coronal mass ejections are sources of space weather, which negatively affects a variety of technologies at or near Earth, ranging from blocking high-frequency radio waves used for radio communication to degrading power grid operations. Monitoring and providing early and accurate prediction of solar flares is therefore crucial for preparedness and disaster risk management. In this article, we present a transformer-based framework, named SolarFlareNet, for predicting whether an AR would produce a$$\gamma$$$\gamma$-class flare within the next 24 to 72 h. We consider three$$\gamma$$$\gamma$classes, namely the$$\ge$$$\ge$M5.0 class, the$$\ge$$$\ge$M class and the$$\ge$$$\ge$C class, and build three transformers separately, each corresponding to a$$\gamma$$$\gamma$class. Each transformer is used to make predictions of its corresponding$$\gamma$$$\gamma$-class flares. The crux of our approach is to model data samples in an AR as time series and to use transformers to capture the temporal dynamics of the data samples. Each data sample consists of magnetic parameters taken from Space-weather HMI Active Region Patches (SHARP) and related data products. We survey flare events that occurred from May 2010 to December 2022 using the Geostationary Operational Environmental Satellite X-ray flare catalogs provided by the National Centers for Environmental Information (NCEI), and build a database of flares with identified ARs in the NCEI flare catalogs. This flare database is used to construct labels of the data samples suitable for machine learning. We further extend the deterministic approach to a calibration-based probabilistic forecasting method. The SolarFlareNet system is fully operational and is capable of making near real-time predictions of solar flares on the Web.

    

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3. Tail-dependence, exceedance sets, and metric embeddings

   https://doi.org/10.1007/s10687-023-00471-z  

   Janßen, Anja ; Neblung, Sebastian ; Stoev, Stilian ( May 2023 , Extremes)

   There are many ways of measuring and modeling tail-dependence in random vectors: from the general framework of multivariate regular variation and the flexible class of max-stable vectors down to simple and concise summary measures like the matrix of bivariate tail-dependence coefficients. This paper starts by providing a review of existing results from a unifying perspective, which highlights connections between extreme value theory and the theory of cuts and metrics. Our approach leads to some new findings in both areas with some applications to current topics in risk management.

   We begin by using the framework of multivariate regular variation to show that extremal coefficients, or equivalently, the higher-order tail-dependence coefficients of a random vector can simply be understood in terms of random exceedance sets, which allows us to extend the notion of Bernoulli compatibility. In the special but important case of bivariate tail-dependence, we establish a correspondence between tail-dependence matrices and$$L^1$$$L^1$- and$$\ell _1$$${\ell }_1$-embeddable finite metric spaces via the spectral distance, which is a metric on the space of jointly 1-Fréchet random variables. Namely, the coefficients of the cut-decomposition of the spectral distance and of the Tawn-Molchanov max-stable model realizing the corresponding bivariate extremal dependence coincide. We show that line metrics are rigid and if the spectral distance corresponds to a line metric, the higher order tail-dependence is determined by the bivariate tail-dependence matrix.

   Finally, the correspondence between$$\ell _1$$${\ell }_1$-embeddable metric spaces and tail-dependence matrices allows us to revisit the realizability problem, i.e. checking whether a given matrix is a valid tail-dependence matrix. We confirm a conjecture of Shyamalkumar and Tao (2020) that this problem is NP-complete.

    

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4. Locality-sensitive bucketing functions for the edit distance

   https://doi.org/10.1186/s13015-023-00234-2  

   Chen, Ke ; Shao, Mingfu ( July 2023 , Algorithms for Molecular Biology)

   Many bioinformatics applications involve bucketing a set of sequences where each sequence is allowed to be assigned into multiple buckets. To achieve both high sensitivity and precision, bucketing methods are desired to assign similar sequences into the same bucket while assigning dissimilar sequences into distinct buckets. Existingk-mer-based bucketing methods have been efficient in processing sequencing data with low error rates, but encounter much reduced sensitivity on data with high error rates. Locality-sensitive hashing (LSH) schemes are able to mitigate this issue through tolerating the edits in similar sequences, but state-of-the-art methods still have large gaps.

   In this paper, we generalize the LSH function by allowing it to hash one sequence into multiple buckets. Formally, a bucketing function, which maps a sequence (of fixed length) into a subset of buckets, is defined to be$$(d_1, d_2)$$$(d_1,d_2)$-sensitive if any two sequences within an edit distance of$$d_1$$$d_1$are mapped into at least one shared bucket, and any two sequences with distance at least$$d_2$$$d_2$are mapped into disjoint subsets of buckets. We construct locality-sensitive bucketing (LSB) functions with a variety of values of$$(d_1,d_2)$$$(d_1,d_2)$and analyze their efficiency with respect to the total number of buckets needed as well as the number of buckets that a specific sequence is mapped to. We also prove lower bounds of these two parameters in different settings and show that some of our constructed LSB functions are optimal.

   These results lay the theoretical foundations for their practical use in analyzing sequences with high error rates while also providing insights for the hardness of designing ungapped LSH functions.

    

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5. Stationary Structures Near the Kolmogorov and Poiseuille Flows in the 2d Euler Equations

   https://doi.org/10.1007/s00205-023-01842-3  

   Coti Zelati, Michele ; Elgindi, Tarek M. ; Widmayer, Klaus ( February 2023 , Archive for Rational Mechanics and Analysis)

   We study the behavior of solutions to the incompressible 2dEuler equations near two canonical shear flows with critical points, the Kolmogorov and Poiseuille flows, with consequences for the associated Navier–Stokes problems. We exhibit a large family of new, non-trivial stationary states that are arbitrarily close to the Kolmogorov flow on the square torus$$\mathbb {T}^2$$$T^2$in analytic regularity. This situation contrasts strongly with the setting of some monotone shear flows, such as the Couette flow: there the linearized problem exhibits an “inviscid damping” mechanism that leads to relaxation of perturbations of the base flows back to nearby shear flows. Our results show that such a simple description of the long-time behavior is not possible for solutions near the Kolmogorov flow on$$\mathbb {T}^2$$$T^2$. Our construction of the new stationary states builds on a degeneracy in the global structure of the Kolmogorov flow on$$\mathbb {T}^2$$$T^2$, and we also show a lack of correspondence between the linearized description of the set of steady states and its true nonlinear structure. Both the Kolmogorov flow on a rectangular torus and the Poiseuille flow in a channel are very different. We show that the only stationary states near them must indeed be shears, even in relatively low regularity. In addition, we show that this behavior is mirrored closely in the related Navier–Stokes settings: the linearized problems near the Poiseuille and Kolmogorov flows both exhibit an enhanced rate of dissipation. Previous work by us and others shows that this effect survives in the full, nonlinear problem near the Poiseuille flow and near the Kolmogorov flow on rectangular tori, provided that the perturbations lie below a certain threshold. However, we show here that the corresponding result cannot hold near the Kolmogorov flow on$${\mathbb T}^2$$$T^2$.

    

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