New light physics beyond the Standard Model

该项目将涉及研究粒子物理标准模型以外的可能新的轻粒子的性质，以及它们的天体物理和宇宙学特征和约束，目的是做出与高能理论(如弦理论)相关的预测，以及即将进行的实验搜索。最初的目标将是可靠地计算由于观测到来自超新星1987A的中微子爆发而对Kaluza Klein引力子的限制，通过考虑等离子体混合效应(这可能会将由此产生的对这种引力子与可见扇形物质的耦合常数的限制改变一个数量级)来修正以前的计算。弦理论模型一直(有争议地)预测这种粒子是宇宙常数的必然结果，而加强的约束可能会排除这种情况，或者打开一条发现的道路。等离子体混合效应以前被考虑为标量(自旋0)和矢量(自旋1)，但这将是第一次对自旋2粒子进行计算。该方法将涉及到使用有限温度场论的技术来解释介质中对生产率的影响，特别是在低自旋情况下建立在先前工作基础上的共振生产的可能性。根据结果，研究这种有限的温度效应对Kaluza Klein引力子宇宙学历史的影响也可能是有趣的；由于宇宙在早期非常热，这种影响可能会再次导致与之前的预测相比发生巨大变化。这将使对这些粒子的暗物质遗迹丰度的准确预测成为可能(之前只估计了这些粒子的丰度)，并可能导致可以提供给实验性搜索计划的预测。随后，范围将扩大，以考虑对其他类别的新粒子的限制，包括动机特别好的轴子，以及可能在获取暗能量方面发挥作用的新的光标量。同样，在这种情况下，有限的温度和密度效应并没有被一致地考虑在内。该项目的总体影响将是1。对超越标准模型的物理学和天体粒子物理学研究人员的直接领域。2.在弦理论现象学领域，(部分)预言了这种新的轻粒子的存在。3.通过提供预测、目标和补充约束，在英国和世界范围内寻找新的轻粒子的实验方案。

The project will involve studying the properties of possible new light particles beyond the Standard Model of particle physics and their astrophysical and cosmological signatures and constraints, with the aim to make predictions relevant to high energy theories, such as string theory, as well as upcoming experimental searches. The initial aim will be to reliably calculate the constraints on Kaluza Klein gravitons coming from the observation of a neutrino burst from supernoava 1987a, correcting previous calculations by taking into account plasma mixing effects (which might change the resulting limits on the coupling constants of such gravitons to visible sector matter by orders of magnitude). Such particles have been (controversially) predicted by string theory models as an inevitable consequence of the cosmological constant, and a strengthened constraint could rule out this scenario or open an avenue to a discovery. Plasma mixing effects have previously been considered for scalars (spin 0) and vectors (spin 1) but this would be the first ever computation for a spin 2 particle. The methodology will involve using techniques from finite temperature field theory to account for the in-medium effects on the production rate, and in particular the possibility of resonant production building on the previous work for the lower spin case. Depending on the results, it might also be interesting to investigate the impact of such finite temperature effects on the cosmological history of Kaluza Klein gravitons; since the Universe was extremely hot at early times such effects could again lead to dramatic changes compared to the previous prediction. This will enable a precise prediction of the Dark Matter relic abundance of such particles (which has previously been only estimated) and it might lead to predictions that can be feed into an experimental search programme. Subsequently, the scope will be widened to consider the constraints on other classes of new particles including axions, which are especially well motivated, as well as possible new light scalars that might play a role in sourcing Dark Energy. Again in this case, finite temperature and density effects have not been consistently accounted for. The overall impact of the project will be 1. On the immediate field of researchers in physics beyond the Standard Model and astroparticle physics. 2. On the field of string theory phenomenology, (part of which) has predicted such new light particles exist. 3. The experimental programme searching for new light particles in the UK and world-wide, by providing predictions and targets and complementary constraints.