Using Dark Matter Microhalos to Probe the Universe's First Second

该奖项资助了北卡罗来纳大学教堂山分校的Adrienne Erickcek教授的研究活动。宇宙在第一秒的演化是未知的。虽然有强有力的证据表明，宇宙的第一秒包含了一段被称为暴胀的加速膨胀时期，但我们确实知道暴胀为什么会发生，为什么会结束。我们也不知道宇宙是如何在暴胀后转变成一个热的、辐射主导的状态的。此外，我们对早期宇宙动力学的无知严重限制了我们对暗物质起源的理解，暗物质是一种知之甚少的质量来源，目前占宇宙能量密度的25%左右。许多关于暗物质的解释都假设暗物质起源于宇宙第一秒充满的热等离子体。因此，宇宙在这段时间内的演化影响了暗物质粒子的性质与宇宙中暗物质数量之间的关系。这个项目将通过伽马射线观测来限制暗物质最小引力束缚结构的丰度，从而增强我们对暴胀、辐射支配的开始以及暗物质起源的理解。PI将让本科生、高中生和公众参与到暗物质微晕的研究中来。本科生将分析微晕形成的模拟，从而学习数据分析技术和科学编程。他们还将获得第一手的研究经验，这将使他们接触到STEM职业的兴奋。将为高中学生开发一个暗物质模块，让他们有机会分析矮球状星系和螺旋星系的公开运动学数据。然后，PI将在教师会议上领导四次专业发展讲习班，培训高中教师在其物理课程中使用该模块。最后，私家侦探将在莫尔黑德大学展示她的研究成果。“卡罗莱纳科学咖啡馆”每月举办一次，它为公众提供了在非正式环境中与科学研究人员互动的机会。这些小的暗物质结构，被称为微晕，是由膨胀过程中产生的密度扰动产生的，其尺度是其他宇宙学观测无法达到的。它们也在宇宙的第一秒开始进化，在核合成开始之前。该项目将扩展PI早期对微晕能力的分析，以探测早期宇宙的演化，并将使用高红移小体积的n体模拟来测试这些对微晕丰度的分析预测。这些模拟还将确定小尺度密度扰动的性质如何影响微光晕的内部结构。然后PI将计算这些微晕中暗物质湮灭的预期伽马射线发射。对小尺度原始密度波动和辐射支配开始的约束将决定哪种暴胀模型与热遗迹暗物质兼容，并可能打破暗物质遗迹密度与早期宇宙演化之间的简并。

This award funds the research activities of Professor Adrienne Erickcek at the University of North Carolina at Chapel Hill. The evolution of the Universe during its first second is unknown. While there is strong evidence that the Universe's first second included a period of accelerated expansion called inflation, we do know why inflation happened or why it ended. We also do not know how the Universe transitioned to a hot, radiation-dominated state after inflation. Furthermore, our ignorance of the dynamics of the early Universe severely limits our understanding of the origins of dark matter, which is a poorly understood source of mass that currently makes up about 25% of the Universe's energy density. Many proposed explanations for dark matter postulate that dark matter originated from the hot plasma that filled the Universe during its first second. Consequently, the evolution of the Universe during that time affects the relationship between the properties of the dark matter particle and amount of dark matter in the Universe. This project will enhance our understanding of inflation, the onset of radiation domination, and the origins of dark matter by using gamma-ray observations to constrain the abundance of the smallest gravitationally bound structures of dark matter. The PI will engage undergraduate students, high school students, and the general public in the proposed investigation of dark matter microhalos. Undergraduate students will analyze simulations of microhalo formation, thereby learning data analysis techniques and scientific programming. They will also gain first-hand research experience, which will expose them to the excitement of STEM careers. A module on dark matter will be developed for high school students to give them the opportunity to analyze publically available kinematic data for dwarf spheroidal and spiral galaxies. The PI will then lead four professional development workshops at teacher conferences to train high school teachers to use this module in their physics courses. Finally, the PI will present her research at Morehead?s monthly Carolina Science Cafe, which provides the general public the opportunity to interact with a scientific researcher in an informal setting.These small dark matter structures, called microhalos, grow from density perturbations that were generated during inflation on scales that are inaccessible by other cosmological observations. They also began to evolve during the Universe's first second, prior to the onset of nucleosynthesis. This project will extend the PI's earlier analyses of microhalos' capacity to probe the evolution of the early Universe to a wider range of dark matter particles and will use N-body simulations of small volumes at high redshifts to test these analytical predictions for the microhalo abundance. These simulations will also determine how the properties of the small-scale density perturbations affect the microhalos' internal structures. The PI will then calculate the expected gamma-ray emission from dark matter annihilation within these microhalos. The resulting constraints on the small-scale primordial density fluctuations and the onset of radiation domination will determine which inflationary models are compatible with thermal-relic dark matter and may break the degeneracy between the relic density of dark matter and the evolution of the early Universe.