Cosmological constraints on cosmic strings

宇宙弦的宇宙学约束

• 批准号: SAPIN-2018-00020
• 负责人: Hernandez, Oscar
• 金额: $ 1.82万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=680407
• 关键词: Cosmological; constraints; cosmic; strings

With data about the universe's structure accumulating at an ever-increasing rate, cosmology can now be used to constrain fundamental physics. I am interested in using galaxy surveys, the cosmic microwave background (CMB), and 21 cm cosmology to search for and constrain new physics beyond the particle physics Standard Model (SM), in particular cosmic strings.******Cosmic strings are linear topological defects that can form in a large class of extensions of the SM. Many inflationary scenarios constructed in the context of supergravity models lead to the formation of gauge theory cosmic strings at the end of the inflationary phase, and in a large class of brane inflation models, inflation ends with the formation of a network of cosmic superstrings which can be stabilized as macroscopic objects. Whereas cosmic strings cannot be the dominant source of the primordial fluctuations they can still be a secondary source. Thus searching for cosmic strings probes particle physics beyond the SM in an energy range complementary to that probed by particle accelerators. ******The gravitational effects of the string can be parametrized by its string tension a dimensionless constant which is predicted to be between 1e-8 and 1e-6 for Grand Unified models, and between 1e-12 and 1e-6 for cosmic superstrings. The best robust experimental limit comes from the Planck collaboration's measurement of the CMB angular power spectrum leading to a string tension less than about 1e-7. ******In recent years much research has been done to find a more sensitive probe of cosmic strings in CMB and 21 cm intensity maps. As long cosmic strings move, they accrete matter into over-dense wakes which perturb the CMB light and the 21 cm line in particular. Edge and shape detection algorithms such as the Canny algorithm, as well as wavelets, and curvelets have been proposed as alternatives to the power spectrum in looking for cosmic strings in these maps. While promising, studies of these proposals on numerically simulated maps have not yet yielded significantly stronger limits than those from Planck. Furthermore, all these proposals involve choices and it remains unclear whether or not different choices would improve detection. Finally, none of the above proposals find the location of strings on sky maps. We recently proposed a Bayesian interpretation of cosmic string detection that improves on these shortcomings. Here we present our program to develop machine learning techniques and neural networks to search for cosmic strings in galaxy surveys, CMB, and 21 cm intensity maps. The neural networks will be developed with numerical simulation involving realistic noise, before being used on actual data. We hope to either find evidence for strings or determine that the string tension is below 1e-12 and thus constrain extensions of the SM. Our program will have a significant impact in the training of the next generation of scientists.

随着有关宇宙结构的数据以不断增长的速度积累，宇宙学现在可以用来约束基础物理学。我对使用星系调查，宇宙微波背景（CMB）和21厘米宇宙学来寻找和约束粒子物理标准模型（SM）之外的新物理，特别是宇宙弦感兴趣。******宇宙弦是线性拓扑缺陷，可以在SM的大量扩展中形成。在超引力模型背景下构建的许多暴胀情景导致在暴胀阶段结束时形成规范理论宇宙弦，而在大类膜暴胀模型中，暴胀以宇宙超弦网络的形成而结束，这些网络可以稳定为宏观物体。虽然宇宙弦不可能是原始波动的主要来源，但它们仍然可以是次要来源。因此，寻找宇宙弦探测的粒子物理超越了SM，其能量范围与粒子加速器探测的能量范围互补。******弦的引力效应可以通过它的弦张力参数化一个无量纲常数，预测在大统一模型中为1e-8和1e-6之间，在宇宙超弦中为1e-12和1e-6之间。最好的鲁棒性实验极限来自普朗克合作对宇宙微波背景角功率谱的测量，导致弦张力小于约1e-7。******近年来，人们进行了大量的研究，以寻找一种更灵敏的宇宙弦探测CMB和21厘米强度图。随着长宇宙弦的移动，它们会将物质吸积成密度过大的尾迹，从而干扰CMB光，尤其是21厘米线。边缘和形状检测算法，如Canny算法，以及小波和曲线被提议作为在这些地图中寻找宇宙弦的功率谱的替代方案。虽然这些建议很有希望，但在数值模拟地图上的研究还没有产生比普朗克更强的限制。此外，所有这些建议都涉及选择，目前尚不清楚不同的选择是否会提高检测。最后，上述建议都没有在天空地图上找到字符串的位置。我们最近提出了宇宙弦探测的贝叶斯解释，改进了这些缺点。在这里，我们展示了我们的计划，开发机器学习技术和神经网络，以搜索宇宙弦在星系调查，CMB和21厘米强度图。在应用于实际数据之前，神经网络将在涉及实际噪声的数值模拟中进行开发。我们希望找到弦的证据，或者确定弦的张力低于1e-12，从而约束SM的扩展。我们的项目将对培养下一代科学家产生重大影响。