Li K, Arif M, Cory D G, Haun R, Heacock B, Huber M G, Nsofini J, Pushin D A, Saggu P, Sarenac D, Shahi C B, Skavysh V, Snow W M, Young A R
Department of Physics, Indiana University, Bloomington, Indiana 47408, USA.
Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA.
Phys Rev D. 2016 Mar;93(6). doi: 10.1103/physrevd.93.062001.
The physical origin of the dark energy that causes the accelerated expansion rate of the Universe is one of the major open questions of cosmology. One set of theories postulates the existence of a self-interacting scalar field for dark energy coupling to matter. In the chameleon dark energy theory, this coupling induces a screening mechanism such that the field amplitude is nonzero in empty space but is greatly suppressed in regions of terrestrial matter density. However measurements performed under appropriate vacuum conditions can enable the chameleon field to appear in the apparatus, where it can be subjected to laboratory experiments. Here we report the most stringent upper bound on the free neutron-chameleon coupling in the strongly coupled limit of the chameleon theory using neutron interferometric techniques. Our experiment sought the chameleon field through the relative phase shift it would induce along one of the neutron paths inside a perfect crystal neutron interferometer. The amplitude of the chameleon field was actively modulated by varying the millibar pressures inside a dual-chamber aluminum cell. We report a 95% confidence level upper bound on the neutron-chameleon coupling ranging from < 4.7 × 10 for a Ratra-Peebles index of = 1 in the nonlinear scalar field potential to < 2.4 × 10 for = 6, one order of magnitude more sensitive than the most recent free neutron limit for intermediate . Similar experiments can explore the full parameter range for chameleon dark energy in the foreseeable future.
导致宇宙加速膨胀率的暗能量的物理起源是宇宙学的主要开放性问题之一。一组理论假定存在一种与物质耦合的自相互作用标量场作为暗能量。在变色龙暗能量理论中，这种耦合引发了一种屏蔽机制，使得该场在空旷空间中的振幅非零，但在地球物质密度区域会被大幅抑制。然而，在适当的真空条件下进行的测量可以使变色龙场出现在仪器中，从而可以对其进行实验室实验。在此，我们使用中子干涉技术报告了在变色龙理论的强耦合极限下自由中子与变色龙耦合的最严格上限。我们的实验通过完美晶体中子干涉仪内中子路径之一上它所诱导的相对相移来寻找变色龙场。通过改变双腔铝制单元内的毫巴压力来主动调制变色龙场的振幅。我们报告了中子 - 变色龙耦合的95%置信水平上限，对于非线性标量场势中拉特拉 - 皮布尔斯指数(n = 1)的情况，上限为(< 4.7×10^{-4})；对于(n = 6)的情况，上限为(< 2.4×10^{-5})，比最近针对中间(n)值的自由中子极限灵敏度高一个数量级。在可预见的未来，类似实验可以探索变色龙暗能量的完整参数范围。
