Semiclassical vacuum decay

【Advertisement】The occurrence of semiclassical vacuum decay arXiv:1909.11196 Phys.Rev.D100 (2019) 096019

【广告】半经典真空衰变的发生 arXiv:1909.11196 Phys.Rev.D100 (2019) 096019

Quantum tunnelling in non-relativistic quantum mechanics of a single particle is a distinguishing feature from the classical mechanics where surmounting a potential barrier requires large enough energy instead of quantum mechanically penetrating the potential barrier with lower energy.

单粒子的非相对论量子力学里的量子隧穿是其有别于经典力学的显著特征:在经典力学中逾越一个势垒需要足够大的能量,而在量子力学中即使以较低的能量也能量子地隧穿势垒。

This feature persists when generalized into the case of relativistic field theory with multiple potential minimums, one of which is absolute minimum in both classical and (perturbative) quantum sense, while the rest of which is still classically stable but metastable by barrier penetration in quantum field theory.

这个特征在推广到拥有多个势能极小值的相对论性场论的时候依然得以保持。这些极小值中有一个是全局最小值,无论在经典抑或微扰量子论意义上。其它极小值在经典意义上可以是稳定的,但在量子场论的势垒隧穿的意义下却是亚稳的。

Vacuum decay in field theory proceeds via sudden nucleations of true vacuum bubbles in the false vacuum environment, which is essentially a quantum phenomenon without classical analog. The decay rate is estimated by Euclidean instanton as an analog to the WKB approximation in nonrelativistic quantum mechanics.

场论中的真空隧穿是通过假真空环境下真真空泡泡的突然成核的方式进行的,这在本质上是一个没有经典对应的量子现象。作为非相对论量子力学的WKB近似的对应,该衰变率由欧几里得瞬子估计得到。

Recently, semiclassical vacuum decay was found in Phys. Rev. Lett. 123 no. 3, (2019) that vacuum decay in field theory could proceed via classical evolution of the equation of motion for some initial configurations of false vacuum fluctuations. In particular, flyover vacuum decay was suggested in arXiv:1906.09657 that, a sufficiently large local initial fluctuation in field velocity could carry the field value directly flying over the potential barrier.

最近, Phys. Rev. Lett. 123 no. 3, (2019)  发现了半经典的真空衰变,即场论中的真空衰变可以从一些初始的假真空扰动经由经典运动方程进行。特别地, arXiv:1906.09657  发现了所谓飞掠式的真空衰变,即一个足够大的场速度的局部初始扰动可以提携场值飞掠势垒。

In our paper, we found that condition for semiclassical vacuum decay is rather loose, even allowing for the dubbed pop-up vacuum decay, where the semiclassical vacuum decay could still occur even if the initial energy density is everywhere insufficient to classically overcome the potential barrier.

在我们的文章中,我们发现半经典真空衰变的发生条件十分宽松,甚至允许所谓冒泡式的真空衰变,即半经典真空衰变甚至可以在初始能量密度处处不足以经典地克服势垒的情况下发生。

 

polar

gif : The time evolution of field profile for the last example of Fig.4 in the mentioned paper. The initial profile for field velocity is everywhere below the threshold for a classical surmounting over the potential barrier, however, after gathering energy through the gradient term in the equation of motion, a true vacuum bubble (red) is eventually formed out of the false vacuum background (blue), and then expands as usual but with oscillating feature inside the bubble.

动图:所提及文章的图4的最后一个例子的场构型的时间演化。场速度的初始构型处处低于经典翻越势垒的阈值,然而,在通过运动方程中的梯度项收集能量后,一个真空空泡泡(红色)最终从假真空背景(蓝色)中形成,并随后膨胀如常却伴随着泡泡内部的振荡。

It is worth noting that, the semiclassical vacuum decay is not only entirely motivated from the numerical simulations [ Phys.Rev. D100 (2019) 065016 , JHEP 1910 (2019) 174 , Phys.Rev.Lett. 123 (2019) 031601 ], but also from some theoretical considerations [ JHEP 1807 (2018) 014 , Phys.Rev. D100 (2019) 016011 ] and even experimential (cold atom) interest [ EPL 110 (2015) 56001 , J.Phys. B50 (2017) 024003].

值得注意的是,半经典真空衰变不只全出于数值模拟 [ Phys.Rev. D100 (2019) 065016 , JHEP 1910 (2019) 174 , Phys.Rev.Lett. 123 (2019) 031601 ] 的动机,还有来自理论上的考量 [ JHEP 1807 (2018) 014 , Phys.Rev. D100 (2019) 016011 ],甚至是实验(冷原子)上的兴趣[ EPL 110 (2015) 56001 , J.Phys. B50 (2017) 024003]。

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