Search for Topological Dark Matter with Atomic Clocks and GPS Constellation

这个项目试图回答“暗物质的本质是什么”这个问题？暗物质是看不见的，但众所周知，它存在于宇宙中的丰度大约是我们所能看到的普通物质(如恒星)的五倍。尽管暗物质的天文证据是压倒性的，但到目前为止，还没有人在实验室中探测到它，我们对它几乎一无所知。到目前为止，许多寻找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的暗物质类型，即所谓的拓扑缺陷，这是通过一些宇宙形成模型预测的。我们检测拓扑缺陷的方法是观察它们对原子钟的预测效果，原子钟是有史以来设计的最精确的仪器。具体地说，我们将使用全球定位系统(GPS)的现有数据，并通过连接到GPS仪器的原子钟来寻找暗物质对时间的微小影响。由于GPS系统和原子钟已经存在并已付费，这是一个预算相对较低、潜在回报较高的项目。如果拓扑缺陷确实存在并被我们发现，这将有助于我们对宇宙的理解建立在更坚实的基础上。同样，能够在误差较小的情况下排除这种可能性也是有价值的，以帮助科学专注于更可能的解释。通过这种方式，这样的调查促进了科学的进步。社会还受益于新技术，只有随着科学进步而来的不可预测的知识才能使这些技术成为可能。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的形式是光场的稳定配置，即拓扑缺陷(TD)。TDS的存在可能会导致粒子质量和耦合常数的偶尔瞬时变化，从而给出一个明显的特征，可以用灵敏的原子钟网络来寻找。该项目将使用现有GPS卫星星座和地面站网络的原子钟作为50,000公里口径的传感器阵列。该探测器的数据已经积累了15年，并已公开提供。PI是精确定位和计时方面的专家，他将通过定制NASA/JPL软件GIMPSY/OASIS来进行GPS数据处理，他是该软件的共同作者之一。输出将是所有GPS卫星和地面站的时钟相位时间序列，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TDS的形式存在，那么就有机会通过这个宏观实验来发现这一点。假设TDS的存在足够丰富，那么地球偶尔会经过这些TDS。对于以30 0公里/秒的银河速度通过GPS系统的TDS，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瞬变序列，从而产生时钟相的阶跃函数，对于GPS星座，约为2 0 0 S，对于地面站约为4 0 S。由于常规的GPS载波相位数据是以几毫米精度的间隔1 S获取的，因此很容易在200-S口径上探测到原子钟相位的~1 ns信号。观察这样的签名将以高置信度提供TDS存在的决定性证据，因为没有已知的背景事件机制可以模仿这样的签名。非观测性会对某些新的物理耦合造成限制。

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.