We investigate the idea that the universe before the Big Bang is the $CPT$ reflection of the universe after the bang, both classically and quantum mechanically, so that the universe does {\it not} spontaneously violate $CPT$. We show how $CPT$ symmetry selects a preferred vacuum state for quantum fields on a $CPT$-invariant cosmological background spacetime. The universe before the bang and the universe after the bang may be viewed as a universe/anti-universe pair, emerging directly into the hot, radiation-dominated era we observe in our past. This, in turn, leads to a remarkably economical explanation of the cosmological dark matter. With no additional fields beyond Einstein gravity and the standard model of particle physics (including right-handed neutrinos), a $\mathbb{Z}_{2}$ symmetry stabilizes one of the right-handed neutrinos. We calculate its abundance in detail and show that, in order to match the observed dark matter density, its mass must be $4.8\times10^{8}~{\rm GeV}$. We obtain several further predictions, including: (i) that the three light neutrinos are majorana; (ii) that one of these is exactly massless; and (iii) that, in the absence of an epoch of cosmic inflation, there should be no primordial, long-wavelength gravitational waves. We also briefly discuss the natural origin of the matter-antimatter asymmetry within this picture and possibilities for explaining the cosmological perturbations.
Temperature-Dependent CPT Violation: Constraints from Big Bang Nucleosynthesis
Instituto de Física Corpuscular, CSIC-Universitat de València（瓦伦西亚大学CSIC粒子物理研究所）；Departament de Física Teòrica, Universitat de València（瓦伦西亚大学理论物理系）；Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB)（巴塞罗那大学量子物理与天体物理学系）；Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB)（巴塞罗那宇宙科学研究所）
Generating Ekpyrotic Curvature Perturbations Before the Big Bang
我们分析了在大爆炸前的收缩阶段产生几乎尺度不变的宇宙学曲率扰动谱的一般机制，它可以完全用4d有效场论来描述。该机制基于首先产生熵扰动，然后将其转换为曲率扰动，可以自然地纳入循环和ekpyrotic模型，其中大爆炸被建模为膜碰撞，以及其他类型的宇宙学模型与前大爆炸阶段。我们证明了可以获得正确的扰动振幅，并且标量光谱倾斜n的范围往往从略蓝到红色，对于最简单的模型，0.97 < n < 1.02，这个范围与当前的观测结果相一致，但与最简单的大场暴胀模型的预测相比，向蓝色移动了百分之几。
Chaotic Amplification of Neutrino Chemical Potentials by Neutrino Oscillations in Big Bang Nucleosynthesis
我们详细研究了在大爆炸核合成时期放大中微子化学势的活动无菌中微子振荡的参数空间。我们计算了放大的幅度，并显示在放大过程中的混沌的证据。我们还讨论了中微子化学势放大在大爆炸核合成中的意义。它表明，与$\sim 1$ eV $\nue$，其化学势的放大，由活跃的无菌中微子振荡可以降低中微子物种在大爆炸核合成的有效数量显着低于3。
