Calculation of the axion mass based on high-temperature lattice quantum chromodynamics
Calculation of the axion mass based on high-temperature lattice quantum chromodynamics
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DOI：
10.1038/nature20115
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发表时间：
2016-11-03
期刊：
影响因子：
64.8
通讯作者：
Szabo, K. K.
中科院分区：
文献类型：
--
作者：
Borsanyi, S.;Fodor, Z.;Szabo, K. K.
与粒子物理学标准模型的电弱部分不同，量子色动力学（QCD）在时间反演下具有惊人的对称性。由于QCD如此对称并没有明显的原因，这种现象构成了一个理论问题，通常被称为强CP问题。对此最有吸引力的解决方案（1）需要存在一种新粒子——轴子（2,3），它是一种很有希望的暗物质候选者。在这里，我们利用格点QCD确定轴子质量，假设这些粒子是暗物质的主要成分。计算的关键量是宇宙的状态方程以及QCD拓扑磁化率的温度依赖性，这个量是出了名的难以计算（4 - 8），特别是在最相关的高温区域（高达几个吉电子伏特）。但是通过将真空划分为不同的部分并重新定义费米子行列式，对它进行可控计算变得可行。因此，我们的双重预测有助于大多数宇宙学计算（9）利用状态方程描述早期宇宙的演化，并且可能对指导寻找暗物质轴子的实验起决定性作用。在接下来的几年里，应该有可能通过实验确认或排除暴胀后轴子，这取决于轴子质量是否如这里所预测的那样。或者，在暴胀前的情景中，我们的计算确定了与我们宇宙初始条件相对应的通用轴子角。
Unlike the electroweak sector of the standard model of particle physics, quantum chromodynamics (QCD) is surprisingly symmetric under time reversal. As there is no obvious reason for QCD being so symmetric, this phenomenon poses a theoretical problem, often referred to as the strong CP problem. The most attractive solution for this(1) requires the existence of a new particle, the axion(2,3)-a promising dark-matter candidate. Here we determine the axion mass using lattice QCD, assuming that these particles are the dominant component of dark matter. The key quantities of the calculation are the equation of state of the Universe and the temperature dependence of the topological susceptibility of QCD, a quantity that is notoriously difficult to calculate4-8, especially in the most relevant high-temperature region (up to several gigaelectronvolts). But by splitting the vacuum into different sectors and re-defining the fermionic determinants, its controlled calculation becomes feasible. Thus, our twofold prediction helps most cosmological calculations(9) to describe the evolution of the early Universe by using the equation of state, and may be decisive for guiding experiments looking for dark-matter axions. In the next couple of years, it should be possible to confirm or rule out post-inflation axions experimentally, depending on whether the axion mass is found to be as predicted here. Alternatively, in a pre-inflation scenario, our calculation determines the universal axionic angle that corresponds to the initial condition of our Universe.