May 31st, 2021

лошадь, диаграмма, Фейнман

Тормозное излучение в нерелятивистских столкновениях

Симпатичная статейка, с хорошим обзором в начале.

Non-relativistic electron-ion bremsstrahlung: an approximate formula for all parameters:
Josef Pradler, Lukas Semmelrock
The evaluation of the electron-ion bremsstrahlung cross section exact to all orders in the Coulomb potential is computationally expensive due to the appearance of hypergeometric functions. Therefore tabulations are widely used. Here, we provide an approximate formula for the non-relativistic dipole process valid for all applicable relative velocities and photon energies. Its validity spans from the Born- to the classical regime and from soft-photon emission to the kinematic endpoint. The error remains below 3% (and widely below 1%) except at an isolated region of hard-photon emission at the quantum-to-classical crossover. We use the formula to obtain the thermally averaged emission spectrum and cooling function in a Maxwellian plasma and demonstrate that they are accurate to better than 2%.
Comments: 7 pages, 3 figures
лошадь, диаграмма, Фейнман

Черенок в вакууме?.. - Все возможно, если Лоренц-инвариантность нарушается!

Если бога нет, то всё дозволено.
Ф.М. Достоевский

Бразильцы продолжают нарушать лоренцеву инвариантность:

Vacuum Radiation in z=2 Lifshitz QED:
R. Bufalo, T. Cardoso e Bufalo
We discuss in this paper the vacuum Cherenkov radiation in the z=2 Lifshitz electrodynamics. The improved ultraviolet behavior, in terms of higher spatial derivatives, and the renormalizable couplings, due to the time-space anisotropic scaling, present in the Lifshitz setting are extremely important in fulfilling the physical constraints in order to this vacuum process to happen. We evaluate in details the instantaneous rate of energy loss for a charge, and also analyze the emission of very soft photons in this framework.
Comments: 16 pages, 1 figure, accepted for publication PRD

Мне здесь понравилась чеканная формулировка:

It is well known that ordinary Cherenkov radiation can only occur for particles propagating
in a medium, since a Lorentz-invariant vacuum prevents it by energy-momentum conservation [ ].

Нужно будет использовать, а то я до сих пор вместо английского формулирую мысли по-русски английскими словами:/
лошадь, диаграмма, Фейнман

Валера Бирюков продолжает изгибать

Double-lens technique for efficient capture of short-lived particles by a crystal:
V.M. Biryukov
For the experiments to measure the dipole moments of short-lived particles via crystal channeling, we propose a beam-optics system of two crystal lenses that increases the number of channeled short-lived particles per one incident primary proton by a factor of about 1000 at LHC.
Comments: 8 pages, 3 figures
лошадь, диаграмма, Фейнман

Уже радиочастотные резонаторы на 3D-принтере предлагают печатать!

Ну це вже зовсiм! До чего техника дошла!

First 3D Printed IH-Type Linac Structure -- Proof-of-Concept for Additive Manufacturing of Linac rf Cavities:
Hendrik Hähnel, Ulrich Ratzinger
Additive manufacturing (or "3D printing") has become a powerful tool for rapid prototyping and manufacturing of complex geometries. As technology is evolving, the quality and accuracy of parts manufactured this way is ever improving. Especially interesting for the world of particle accelerators is the process of 3D printing of stainless steel (and copper) parts. We present the first fully functional IH-type drift tube structure manufactured by metal 3D printing. A 433 MHz prototype cavity has been constructed to act as a proof-of-concept for the technology. The cavity is designed to be UHV capable and includes cooling channels reaching into the stems of the DTL structure. We present the first experimental results for this prototype.
Comments: Submitted to JACow, presented at the 12th International Particle Accelerator Conference - IPAC21
лошадь, диаграмма, Фейнман

Дальнейший обсчет эффекта Комптона в свежем PRL

Оказывается, со времен Фейнмана и Брауна там еще есть, что обсчитывать! Статья в открытом доступе.

Compton Scattering Total Cross Section at Next-to-Leading Order
Roman N. Lee, Matthew D. Schwartz, and Xiaoyuan Zhang
Phys. Rev. Lett. 126, 211801 – Published 24 May 2021

An analytic formula is given for the total scattering cross section of an electron and a photon at order α^3 in QED. This includes both the double-Compton scattering real-emission contribution as well as the virtual Compton scattering part. When combined with the recent analytic result for the pair-production cross section, the complete α^3 cross section is now known. Both the next-to-leading order calculation as well as the pair-production cross section are computed using modern multiloop calculation techniques, where cut diagrams are decomposed into a set of master integrals that are then computed using differential equations.