August 25th, 2020

лошадь, диаграмма, Фейнман

Немножко КХД. Немножко механики

Another Unorthodox Introduction to QCD and now Machine Learning:
Andrew J. Larkoski
These are lecture notes presented at the online 2020 Hadron Collider Physics Summer School hosted by Fermilab. These are an extension of lectures presented at the 2017 and 2018 CTEQ summer schools in arXiv:1709.06195 and still introduces perturbative QCD and its application to jet substructure from a bottom-up perspective based on the approximation of QCD as a weakly-coupled, conformal field theory. With machine learning becoming an increasingly important tool of particle physics, I discuss its utility exclusively from the biased view for increasing human knowledge. A simple argument that the likelihood for quark versus gluon discrimination is infrared and collinear safe is presented as an example of this approach. End-of-lecture exercises are also provided.
Comments: 18 pages, 17 figures scattered throughout, 4 exercises. Comments welcome!

Particle sliding on a turntable in the presence of frictional forces:
Akshat Agha, Sahil Gupta, Toby Joseph
Motion of a point particle sliding on a turntable is studied. The equations of motion are derived assuming that the table exerts frictional force on the particle, which is of constant magnitude and directed opposite to the direction of motion of the particle relative to the turntable. After expressing the equations in terms of dimensionless variables, some of the general properties of the solutions are discussed. Approximate analytic solutions are found for the cases in which (i) the particle is released from rest with respect to the lab frame and, (ii) the particle is released from rest with respect to the turntable. The equations are then solved numerically to get a more complete understanding of the motion. It is found that one can define an escape speed for the particle which is the minimum speed required to get the particle to move off to infinity. The escape speed is a function of the distance from the center of the turntable and for a given distance from the center, it depends on the direction of initial velocity. A qualitative explanation of this behavior is given in terms of the fictitious forces. Numerical study also indicates an alternative way for measuring the coefficient of friction between the particle and the turntable.
Comments: 8 pages, 8 figures

О сколько нам открытий чудных...

Внезапно вычитал, что По историческим причинам в оптике принята противоположная терминология: вращение вектора E в направлении правого винта называют левым, а противоположное вращение - правым. [Батыгин-Топтыгин, Современная электродинамика. Часть 1. С 207].

Как говорит один уважаемый человек, ааааааасукасукасука!!! То-то я всегда на какую-то фигню наталкивался: то система координат оказывается левой, то знак не тот, то еще какая фигня!.. Надо посмотреть, как во 2 томе Ландавшица это все определяется...