Smoothed Particles Hydrodynamics – the implementations of the incompressibility

The Smoothed Particle Hydrodynamics (SPH) is a fully Lagrangian, grid-free technique for fluid-flow simulations. An important and open issue in the SPH is a proper implementation of the incompressibility constraint. Generally there are two ways to deal with this problem. The first Weakly Compressible SPH (WCSPH) is the most widespread technique. It involves governing equations closed by a suitably-chosen equation of state. The second, Truly Incompressible SPH (ISPH), utilizes Projection Method – the technique known from the grid methods. The purpose of the present study is quantitative comparison of both techniques. The Smoothed Particle Hydrodynamics (SPH) is a fully Lagrangian, grid-free technique for fluid-flow simulations. An important and open issue in the SPH is a proper implementation of the incompressibility constraint. Generally there are two ways to deal with this problem. The first Weakly Compressible SPH (WCSPH) is the most widespread technique. It involves governing equations closed by a suitably-chosen equation of state. The second, Truly Incompressible SPH (ISPH), utilizes Projection Method – the technique known from the grid methods. The purpose of the present study is quantitative comparison of both techniques.

Accessing CKM suppressed top decays at the LHC

We present an strategy for measuring the off-diagonal elements of the third row of CKM matrix $|V_{tq}|$ through the branching fractions of top quark decays $t\to q W$, where $q$ is a light quark jet. This strategy is an extension of existing measurements, with the improvement rooted in the use of orthogonal $b$- and $q$-taggers that add a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding a null $|V_{td}|^2+|V_{ts}|^2$ at $95\%$ C.L. at the HL-LHC.Comment: Talk at the 16th International Workshop on Top Quark Physics (Top2023), 24-29 September 202

Theory of scanning gate microscopy

A systematic theory of the conductance measurements of non-invasive (weak probe) scanning gate microscopy is presented that provides an interpretation of what precisely is being measured. A scattering approach is used to derive explicit expressions for the first and second order conductance changes due to the perturbation by the tip potential in terms of the scattering states of the unperturbed structure. In the case of a quantum point contact, the first order correction dominates at the conductance steps and vanishes on the plateaus where the second order term dominates. Both corrections are non-local for a generic structure. Only in special cases, such as that of a centrally symmetric quantum point contact in the conductance quantization regime, can the second order correction be unambiguously related with the local current density. In the case of an abrupt quantum point contact we are able to obtain analytic expressions for the scattering eigenfunctions and thus evaluate the resulting conductance corrections.Comment: 19 pages, 7 figure

Nonresonant leptoquark with multigeneration couplings for μμjj and μνjj at the LHC

CMS has recently reported [A. M. Sirunyan (CMS Collaboration), Search for pair production of second-generation leptoquarks at s=13 TeV, Phys. Rev. D 99, 032014 (2019).] a moderate excess in the μνjj final state in a second-generation leptoquark search, but they have disregarded it because the excess is not present in the μμjj final state and because they do not observe the expected resonant peak in the distributions. As a proof of concept, we show that a simple leptoquark model including second- and third-generation couplings with non-negligible single- and nonresonant production in addition to usual pair production could explain the data - excess (μνjj), lack of excess (μμjj), and missing peak in the distributions - while being in agreement with collider constraints. We take this result and analysis as a starting point of a reconsideration of the ATLAS and CMS second-generation leptoquark searches. We also discuss which consequences and modifications should be performed in the searches to test if this deviation would correspond to a new physics signal. We observe that low-energy flavor constraints can be avoided by adding heavier particles to the model.Fil: Alvarez, Ezequiel. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología. Centro Internacional de Estudios Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Szewc, Manuel. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología. Centro Internacional de Estudios Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Topic Model for four-top at the LHC

We study the implementation of a Topic Model algorithm in four-top searches at the LHC as a test-probe of a not ideal system for applying this technique. We study this Topic Model behavior as its different hypotheses such as mutual reducibility and equal distribution in all samples shift from true. The four-top final state at the LHC is not only relevant because it does not fulfill these conditions, but also because it is a difficult and inefficient system to reconstruct and current Monte Carlo modeling of signal and backgrounds suffers from non-negligible uncertainties. We implement this Topic Model algorithm in the Same-Sign lepton channel where S/B is of order one and all backgrounds cannot have more than two b-jets at parton level. We define different mixtures according to the number of b-jets and we use the total number of jets to demix. Since only the background has an anchor bin, we find that we can reconstruct the background in the signal region independently of Monte Carlo. We propose to use this information to tune the Monte Carlo in the signal region and then compare signal prediction with data. We also explore Machine Learning techniques applied to this Topic Model algorithm and find slight improvements as well as potential roads to investigate. Although our findings indicate that still with the full LHC run 3 data the implementation would be challenging, we pursue through this work to find ways to reduce the impact of Monte Carlo simulations in four-top searches at the LHC.Comment: 26 pages, 10 figures, appendix included. Minor corrections to match JHEP version. As suggested by Referee, all the code needed to reproduce the results in the paper is uploaded to https://github.com/ManuelSzewc/Topic-Model-for-four-top-at-the-LHC/. Comments welcom