Search for Topological Dark Matter with Atomic Clocks and GPS Constellation

该项目旨在回答“暗物质的本质是什么”的问题。 暗物质是不可见的，但它在宇宙中的丰度是我们所能看到的普通物质（如恒星）的五倍。 虽然暗物质存在的天文学证据是压倒性的，但到目前为止，还没有人在实验室中检测到它，我们对它几乎一无所知。许多试图将暗物质作为自然界基本粒子的尝试都失败了。 我们的项目将寻找一种不同的可能类型的暗物质，称为拓扑缺陷，由一些宇宙如何形成的模型预测。 我们检测拓扑缺陷的方法是通过观察它们对原子钟的预测影响，原子钟是有史以来最精确的仪器。 具体来说，我们将使用来自全球定位系统（GPS）的现有数据，并寻求暗物质对连接到GPS仪器的原子钟所保持的时间的微小影响。由于全球定位系统和原子钟已经存在，并支付，这是一个相对低预算的项目，具有高潜在回报。 如果拓扑缺陷确实存在，并且我们发现了它们，这将有助于我们对宇宙的理解建立在一个更可靠的基础上。 同样，能够以较小的误差范围排除这种可能性，以帮助科学专注于更可能的解释，这也是有价值的。这样，这种研究促进了科学的进步。 社会也受益于新技术，这些新技术只能通过科学进步带来的不可预测的知识来实现。理解暗物质的本质仍然是当今物理学中最突出的问题之一。 一些模型预测暗物质是以光场的稳定配置的形式存在的，即拓扑缺陷（TD）。 TD的存在可能会导致粒子质量和耦合常数的偶尔瞬态变化，从而给出一个独特的签名，可以用敏感的原子钟网络搜索。该项目将利用现有全球定位系统卫星群和地面站网络的原子钟作为50 000公里孔径传感器阵列。 该探测器的数据已经积累了15年，并公开提供。PI是精确定位和定时方面的专家，他将通过定制NASA/JPL软件GIPSY/OASIS进行GPS数据处理，他是该软件的合著者。输出将是所有GPS卫星和地面站的时钟相位的时间序列，我们已经证明可以以~0.1 ns的精度进行监测。 如果DM以宏观TD的形式存在，那么有机会通过这个宏观实验发现这一点。假设TDs存在足够的丰度，那么地球将偶尔通过这些TDs。对于以~300 km/sec的星系速度通过GPS系统的TD，TDM-SM耦合将导致基本物理常数的瞬变，这将导致原子钟频率的一系列瞬变，从而在GPS星座的~200 s孔径和地面站的~40 s孔径上产生时钟相位的阶跃函数。由于GPS载波相位数据通常以1秒的间隔以几毫米的精度采集，因此可以很容易地在200秒的孔径上检测原子钟相位中的~1 ns信号。观察这样的特征将提供具有高置信水平的TD存在的决定性证据，因为没有已知的机制用于模仿这样的特征的背景事件。非观测将对某些新物理学耦合施加限制。

This project seeks to answer the question "what is the nature of dark matter"? Dark matter is invisible, yet it is known to exist with about five times more abundance in the universe than the ordinary matter (like stars) we can see. Although the astronomical evidence of dark matter is overwhelming, so far nobody has detected it in the laboratory, and we know almost nothing about it. Many attempts to seek dark matter as fundamental particles of nature have so far failed. Our project will search for a different possible type of dark matter known as topological defects, predicted by some models of how the universe formed. Our approach to detect topological defects is by observing their predicted effect on atomic clocks, the most precise instruments ever devised. Specifically, we will use existing data from the Global Positioning System (GPS) and seek the tiny effects of dark matter on time kept by atomic clocks connected to GPS instruments. Since the GPS system and the atomic clocks already exist and are paid for, this is a relatively low-budget project with high potential payoff. If topological defects do exist and we find them, this would help set our understanding of the universe on a more sure footing. Likewise, it would also be valuable to be able to rule out this possibility with a small margin of error, to help science focus on more likely explanations. In this way, such investigations promote the progress of science. Society also benefits in terms of new technologies that can only be made possible with the unpredictable knowledge that comes with scientific progress.Understanding the nature of dark matter remains one of top outstanding problems in physics today. Some models predict dark matter in a form of stable configurations of light fields, the topological defects (TD). The presence of TDs may lead to occasional transient changes of particle masses and coupling constants, thus giving a distinct signature that can be searched for with the network of sensitive atomic clocks. This project will use atomic clocks of the existing GPS satellite constellation and ground station network as a 50,000 km-aperture sensor array. Data from this detector have been accumulated over 15 years and are publicly available. The PI, an expert in precision positioning and timing, will conduct the GPS data processing by customizing the NASA/JPL software GIPSY/OASIS of which he is a co-author. The output will be a time series of clock phase for all GPS satellites and ground stations, which we have demonstrated can be monitored with a precision of ~0.1 ns. If DM exists in the form of macroscopic TDs, then there is a chance to discover this with this macroscopic experiment. Assuming TDs exist in sufficient abundance, then the Earth would pass through these TDs occasionally. For TDs that pass through the GPS system at galactic speeds ~300 km/sec, TDM-SM coupling would lead to transients in fundamental physical constants, which would cause a sequence of transients in atomic clock frequency, hence producing step-like functions in clock phase across an aperture of ~200 s for the GPS constellation, and ~40 s for ground stations. Since GPS carrier phase data is routinely acquired with few-mm precision at intervals of 1 s, detecting ~1 ns signals in the atomic clock phase over a 200-s aperture is easily achievable. Observing such a signature would provide decisive evidence of the existence of TDs with a high confidence level, as there is no known mechanism for background events that would mimic such a signature. Non-observation will place constraints on certain new-physics couplings.