Buschmann Malte, Dessert Christopher, Foster Joshua W, Long Andrew J, Safdi Benjamin R
Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
Leinweber Center for Theoretical Physics, Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 USA.
Phys Rev Lett. 2022 Mar 4;128(9):091102. doi: 10.1103/PhysRevLett.128.091102.
The quantum chromodynamics (QCD) axion may modify the cooling rates of neutron stars (NSs). The axions are produced within the NS cores from nucleon bremsstrahlung and, when the nucleons are in superfluid states, Cooper pair breaking and formation processes. We show that four of the nearby isolated magnificent seven NSs along with PSR J0659 are prime candidates for axion cooling studies because they are coeval, with ages of a few hundred thousand years known from kinematic considerations, and they have well-measured surface luminosities. We compare these data to dedicated NS cooling simulations incorporating axions, profiling over uncertainties related to the equation of state, NS masses, surface compositions, and superfluidity. Our calculations of the axion and neutrino emissivities include high-density suppression factors that also affect SN 1987A and previous NS cooling limits on axions. We find no evidence for axions in the isolated NS data, and within the context of the Kim-Shifman-Vainshtein-Zakharov QCD axion model, we constrain m_{a}≲16 meV at 95% confidence level. An improved understanding of NS cooling and nucleon superfluidity could further improve these limits or lead to the discovery of the axion at weaker couplings.
量子色动力学（QCD）轴子可能会改变中子星（NSs）的冷却速率。轴子在中子星核心内由核子轫致辐射产生，并且当核子处于超流态时，通过库珀对的破坏和形成过程产生。我们表明，附近孤立的七个壮丽中子星中的四个以及PSR J0659是轴子冷却研究的主要候选对象，因为它们是同时期的，根据运动学考虑可知年龄为几十万岁，并且它们的表面光度测量得很准确。我们将这些数据与纳入轴子的专门的中子星冷却模拟进行比较，分析与状态方程、中子星质量、表面成分和超流性相关的不确定性。我们对轴子和中微子发射率的计算包括高密度抑制因子，这些因子也会影响1987A超新星以及之前对轴子的中子星冷却限制。我们在孤立中子星数据中没有发现轴子的证据，并且在金 - 希夫曼 - 瓦因施泰因 - 扎哈罗夫QCD轴子模型的框架内，我们在95%置信水平下将轴子质量(m_{a})限制在(m_{a}\lesssim16,\text{meV})。对中子星冷却和核子超流性的进一步理解可能会进一步提高这些限制，或者在较弱耦合下导致轴子的发现。
