Observational Signatures of Cosmic Strings

该奖项资助塔夫茨大学 Ken D. Olum 教授的一些研究活动。 宇宙弦是微观上很薄的物体，甚至是宇宙学长度的基本物体，它可能存在于我们的宇宙中，也可能不存在。宇宙弦的探测将为了解任何加速器无法达到的能量下的基础物理学提供一个窗口。对宇宙超弦网络的观测可以证实弦理论的正确性，弦理论是我们目前将引力物理学与支配亚原子世界的物理学统一起来的最佳理论。 发现宇宙弦网络的最大希望是通过引力波的观测。 北美纳赫兹引力波天文台（NANOGrav）检测到一个信号，这可能是整个宇宙中许多来源形成的引力波背景的第一个迹象。 这些来源可能是星系中心的成对巨大黑洞，但它们也可能是宇宙弦环。 奥卢姆教授将研究宇宙弦发射的引力波，并将其与当前和即将到来的 NANOGrav 观测结果进行比较。 奥卢姆教授还将让研究生参与这项工作，从而培养下一代研究物理学家——这是一项符合国家利益的活动。 这项工作将进一步将宇宙研究与自然基本规律研究联系起来。从技术上讲，奥卢姆教授将模拟宇宙弦环在引力自相互作用作用下的演化，以观察它们的形状和引力波谱如何随时间变化。 他将使用取自他之前的宇宙弦网络模拟的现实宇宙弦环群。 通过结合这些环的光谱，他将生成宇宙弦中预期的引力波背景光谱，并将其与 NANOGrav 合作组织（他是该合作组织的成员）的脉冲星计时观测结果进行比较。 他还将研究环对各向异性引力波发射的反应所获得的速度，即所谓的“火箭效应”，这对于确定星系中宇宙弦环的聚集程度及其潜在的可观测性非常重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award funds some of the research activities of Professor Ken D. Olum at Tufts University.Cosmic strings are microscopically thin or even fundamental objects of cosmological length, which may or may not exist in our universe. Detection of cosmic strings would provide a window into fundamental physics at energies beyond the reach of any accelerator. Observation of a cosmic superstring network could provide a confirmation of the correctness of string theory, which is our current best theory for unifying the physics of gravity with the physics that governs the subatomic world. The best hope for discovering a cosmic string network is through observation of gravitational waves. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has detected a signal that is likely be the first sign of a gravitational wave background formed by many sources throughout the universe. These sources could be pairs of giant black holes in the centers of galaxies, but they could also be cosmic string loops. Professor Olum will study the gravitational waves that would be emitted by cosmic strings and compare them with current and forthcoming NANOGrav observations. Professor Olum will also involve graduate students in this work and thereby train future generations of research physicists --- an activity which is in the national interest. The work will further connect studies of the universe with studies of the fundamental laws of nature.More technically, Professor Olum will simulate the evolution of cosmic string loops under the effects of gravitational self-interaction to see how their shapes and their gravitational wave spectra change over time. He will use a realistic population of cosmic string loops taken from his previous cosmic string network simulations. By combining the spectra from these loops, he will generate a gravitational wave background spectrum to be expected from cosmic strings and compare it with pulsar timing observations from the NANOGrav collaboration, of which he is a member. He will also study the velocities acquired by loops in reaction to anisotropic gravitational wave emission, the so-called "rocket effect", which is important for determining the degree of clustering of cosmic string loops in galaxies, and thus their potential observability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.