标题： 热和非热情景下从重子生成得到的中微子质量界限 显示英文标题

标题： Bounds on neutrino masses from baryogenesis in thermal and non-thermal scenarios

摘要： 通过轻子生成的重子生成是一个有吸引力的场景，它将右手中微子领域的物理与低能中微子数据联系起来。 在当前中微子振荡数据的基础上，我们研究了最轻右手中微子（$N_1$）的质量尺度（$M_1$）以及它们的质量层次（$M_2/M_1$和$M_3/M_1$）的限制，这些限制来自我们将在论文的两个不同部分讨论的轻子生成约束。 在第一部分中，我们在一个{\it 热力的}的情景下研究了典型的轻子生成，因此得出了对$M_1$的限制。 可以看出，$N_1$的质量尺度必须满足约束$M_1\geq 10^8$GeV，以产生足够的轻子不对称性。 我们随后提出一个模型，其中该限制可以放宽到 TeV 尺度。 在第二部分中，我们研究了拓扑缺陷的形成和演化，这些非热物体预计会在早期宇宙相变过程中形成。 特别是，我们考虑了$B-L$宇宙弦及其对轻子生成的影响，从而对$N_1$的质量尺度进行了限制。 可以看出，对于$B-L$对称性破缺尺度$\eta_{B-L}>10^{11}$GeV，在某些参数空间中，宇宙弦的贡献比热轻子生成更为显著。 显示英文摘要

摘要： Baryogenesis via leptogenesis is an attractive scenario that links the physics of right handed neutrino sector with the low energy neutrino data. In the light of current neutrino oscillation data we studied the bound on the mass scale ($M_1$) of lightest right handed neutrino ($N_1$) as well as their mass hierarchy ($M_2/M_1$ and $M_3/M_1$) from the leptogenesis constraint which we discussed in two different parts of the thesis. In part-I, we studied the canonical leptogenesis in a {\it thermal} scenario and hence the bound on $M_1$. It is shown that the mass scale of $N_1$ must satisfy the constraint $M_1\geq 10^8$ GeV in order to produce the adequate lepton asymmetry. We then led to propose a model where this bound can be relaxed to TeV scale. In part-II, we studied the formation and evolution of topological defects which are non-thermal objects and are expected to be formed during the early Universe phase transitions. In particular, we considered $B-L$ cosmic strings and their effect on leptogenesis and hence the bound on the mass scale of $N_1$. It is shown that for the $B-L$ symmetry breaking scale $\eta_{B-L}>10^{11}$GeV, in certain parameter space, the cosmic strings make a more dominant contribution than thermal leptogenesis.