[论文解读] Inflation in Supergravity with a Single Superfield

Takahiro Terada|arXiv (Cornell University)|Aug 21, 2015

Cosmology and Gravitation Theories参考文献 10被引用 4

一句话总结

本文提出了一种新颖的超引力框架，仅使用一个超多重态即可实现大场暴胀，避免了对额外稳定子超多重态的依赖。通过在凯勒势中引入高阶项，该模型稳定了暴胀子超多重态的标量伴子，并确保势能平坦且为正，从而在无需微调的情况下实现自然暴胀。

ABSTRACT

Supergravity is a well-motivated theory beyond the standard model of particle physics, and a suitable arena to study high-energy physics at the early universe including inflation, whose observational evidences are growing more and more. Inflation in supergravity, however, cannot be easily described because of restrictions from supersymmetry (SUSY). The scalar potential has an exponential factor and a large negative term whereas a flat and positive potential is needed to realize inflation. The standard method to obtain such an inflationary scalar potential requires an additional superfield to the one containing inflaton. In this thesis, we propose and develop an alternative method which does not require the additional superfield and thus reduces the necessary degrees of freedom by half. That is, we study inflation in supergravity with only a single chiral superfield which contains inflaton. We accomplish it by introducing a higher dimensional term in the inflaton Kahler potential, which plays an important dual role: fixing the value of the scalar superpartner of the inflaton resulting in effective single field models, and ensuring the positivity of the inflaton potential at the large field region. Our proposal is not just particular models but rather a new framework to realize various inflationary models in supergravity. In particular, large field inflation in supergravity using one superfield without tuning has become possible for the first time. In our generic models, SUSY breaking at the inflationary scale by inflaton is not completely restored after inflation, so null results for SUSY search at the LHC are predicted for the simplest cases. Remarkably, however, it is possible with tuning to embed arbitrary positive semidefinite scalar potentials into supergravity preserving SUSY at the vacuum. Our discovery opens up an entirely new branch of model building of inflation in supergravity.

研究动机与目标

• 解决在超引力中构建可行暴胀模型的挑战，而无需引入辅助稳定子超多重态。
• 解决超引力中固有的张力：标量势通常包含指数项和负项，与暴胀期间所需的平坦且正的势能相冲突。
• 开发一种通用框架，实现在单超多重态模型中无需微调的大场暴胀。
• 探讨该单超多重态框架中暴胀期间的规范对称性自发破缺及其现象学后果，包括大型强子对撞机（LHC）的约束。
• 通过莫比乌斯变换和对偶对称性，建立对凯勒势修改的几何与对称性理解。

提出的方法

• 在单个复超多重态的凯勒势中引入高阶项，以动态方式固定暴胀子超多重态标量分量的超伴子。
• 利用暴胀子超多重态虚部的平移对称性，在大场值区域稳定标量势。
• 采用一种修改后的凯勒势，使其在缩放对称性和平移对称性下保持必要的对偶结构（莫比乌斯群）。
• 通过调节凯勒势的高阶项，构建出在大场值区域具有平坦区域的标量势。
• 证明该模型自然支持大场暴胀，无需额外超多重态或参数的微调。
• 利用由修改后的凯勒势导出的暴胀势，分析慢滚参数及观测预测（ns, r, As）。

实验结果

研究问题

• RQ1 能否仅使用一个复超多重态在超引力中实现大场暴胀，而无需引入辅助稳定子超多重态？
• RQ2 在凯勒势中引入高阶项如何稳定暴胀子的标量伴子并确保势能平坦？
• RQ3 在此单超多重态框架中，暴胀期间的规范对称性自发破缺有何影响？
• RQ4 该模型的观测预测（ns, r, As）与普朗克2015年数据相比如何？
• RQ5 所提出的凯勒势结构是否与凯勒几何中的已知对称性（如缩放对称性或平移对称性）相关？

主要发现

• 该模型仅使用一个复超多重态即实现了超引力中的大场暴胀，消除了对额外稳定子超多重态的需求。
• 凯勒势中的高阶项固定了暴胀子的标量伴子，有效将模型简化为单场有效理论。
• 由于凯勒势的特定结构，标量势在大场值区域变得平坦且为正，从而支持成功的慢滚暴胀。
• 该模型预测暴胀期间的规范对称性自发破缺由暴胀子超多重态驱动，而非稳定子，这与双超多重态模型形成鲜明对比。
• 在最简情况下，由于弱能标处不存在轻量级超伴子，该模型预测大型强子对撞机（LHC）的超对称搜索将得到零结果。
• 该框架可通过调节凯勒势，将任意正半定标量势嵌入超引力，同时在真空处保持规范对称性。