Observational Signatures of Cosmic Strings

这个奖项资助了塔夫茨大学Ken D.Olum教授的一些研究活动。宇宙弦是微观上很细的物体，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。对宇宙弦的探测将提供一扇了解基本物理的窗口，其能量超出任何加速器所能及的范围。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观测引力波。北美纳赫兹引力波天文台(NANOGrav)探测到一个信号，这很可能是宇宙中许多来源形成的引力波背景的第一个迹象。这些源可能是星系中心的几对巨型黑洞，但也可能是宇宙弦环。奥勒姆教授将研究宇宙弦发出的引力波，并将它们与目前和即将进行的NANOGrav观测进行比较。奥勒姆教授还将让研究生参与这项工作，从而培养未来几代研究物理学家-这是一项符合国家利益的活动。这项工作将进一步将对宇宙的研究与对自然基本定律的研究联系起来。更技术上，奥勒姆教授将模拟宇宙弦环在引力自相互作用的影响下的演化，以了解它们的形状和引力波谱如何随着时间的变化而变化。他将使用从他之前的宇宙弦网络模拟中获得的现实的宇宙弦环路。通过组合来自这些环路的光谱，他将产生预计来自宇宙弦的引力波背景光谱，并将其与他是NANOGrav合作组织成员的脉冲星计时观测进行比较。他还将研究环圈对各向异性引力波发射的反应速度，即所谓的“火箭效应”，这对确定星系中宇宙弦环的聚集程度非常重要，从而研究它们的潜在可观测性。这一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优势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.