August 13th, 2020

лошадь, диаграмма, Фейнман

Вечерело...

и на высоком мертвом дереве медитировала цапля, ровно как год назад...


DSC_0046_obr.jpg © qedqed.iMGSRC.RU


Отличие, однако, заключалось в том, что в этот раз мне удалось вычислить ее заранее. А поскольку медитирует она очень внимательно, нужно подкрадываться очень осторожно и быть готовым сделать несколько быстрых снимков прежде, чем она покинет свой насест.

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лошадь, диаграмма, Фейнман

Снова о возможности экспериментального наблюдения критического поля

How to access QED at supercritical Coulomb field: https://arxiv.org/abs/2008.05005
R. V. Popov, V. M. Shabaev, D. A. Telnov, I. I. Tupitsyn, I. A. Maltsev, Y. S. Kozhedub, A. I. Bondarev, N. V. Kozin, X. Ma, G. Plunien, T. Stöhlker, D. A. Tumakov, V. A. Zaytsev
In slow collisions of two bare nuclei with the total charge number larger than the critical value, Zcr≈173, the initially neutral vacuum can spontaneously decay into the charged vacuum and two positrons. Detection of the spontaneous emission of positrons would be the direct evidence of this fundamental phenomenon. However, the spontaneous emission is generally masked by the dynamical positron emission, which is induced by a strong time-dependent electric field created by the colliding nuclei. In our recent paper [I.A. Maltsev et al., Phys. Rev. Lett. 123, 113401 (2019)] it has been shown that the spontaneous pair production can be observed via measurements of the pair-production probabilities for a given set of nuclear trajectories. In the present paper, we have significantly advanced this study by exploring additional aspects of the process we are interested in. We calculate the positron energy spectra and find that these spectra can give a clear signature of the transition from the subcritical to the supercritical regime. It is found that focusing on a part of the positron spectrum, which accounts for the energy region where the spontaneously created positrons can contribute, allows to get a much stronger evidence of the transition to the supercritical mode, making it very well pronounced in collisions, for example, of two uranium nuclei. The possibility of extending this study to collisions of bare nuclei with neutral atoms is also considered. The probability of a vacancy in the lowest-energy state of a quasimolecule which is formed in collisions of a bare U nucleus with neutral U and Cm atoms has been calculated. The relatively large values of this probability make such collisions suitable for observing the vacuum decay.
Comments: 18 pages, 22 figures, 1 table
лошадь, диаграмма, Фейнман

Задача многих тел в теории ядра

A Guided Tour of Ab Initio Nuclear Many-Body Theory: https://arxiv.org/abs/2008.05061
H. Hergert
Over the last decade, new developments in Similarity Renormalization Group techniques and nuclear many-body methods have dramatically increased the capabilities of ab initio nuclear structure and reaction theory. Ground and excited-state properties can be computed up to the tin region, and from the proton to the presumptive neutron drip lines, providing unprecedented opportunities to confront two- plus three-nucleon interactions from chiral Effective Field Theory with experimental data. In this contribution, I will give a broad survey of the current status of nuclear many-body approaches, and I will use selected results to discuss both achievements and open issues that need to be addressed in the coming decade.
Comments: 39 pages + references (58 pages total), 15 figures, to be published in Frontiers in Physics as a contribution to the Research Topic "The Future of Nuclear Structure: Challenges and Opportunities in the Microscopic Description of Nuclei"