Emergently Thermalized Islands in the Landscape

In this note, we point out that in the eternal inflation driven by the metastable vacua of the landscape, it might be possible that some large and local quantum fluctuations with the null energy condition violation can stride over the barriers between different vacua and straightly create some islands with radiation and matter in new vacua. Then these thermalized islands will evolve with the standard cosmology. We show that such islands may be consistent with our observable universe, while has some distinctly observable signals, which may be tested in coming observations.Comment: 4 pages, 1 eps figure, contents added and discussions extended, publish in PL

On Primordial Density Perturbation and Decaying Speed of Sound

The decaying speed of sound can lead to the emergence of the primordial density perturbation in any expanding phase, even if the expansion is decelerated. Recently, some proposals have been given to implement this mechanism, in which it was found that the primordial spectrum of scalar perturbation can be scale invariant. In this note, we will give more insights for the details of this seeding mechanism.Comment: 3 pages, 2 eps figure, contents extended, refs. added, published version

Seeding of Primordial Perturbations During a Decelerated Expansion

A scalar field with a modified dispersion relation may seed, under certain conditions, the primordial perturbations during a decelerated expansion. In this note we examine whether and how these perturbations can be responsible for the structure formation of observable universe. We discuss relevant difficulties and possible solutions.Comment: 5 pages, 3 figures, more details and clarifications added, refs. added, new version with 6 pages has been splitted into various sections, to be published in PRD, v3, matched to published versio

Preheating in Bubble Collisions

In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that during the bubbles collide, due to the dramatically oscillating of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles. In this sense, the collision of bubbles is actually highly inelastic. The cosmological implications of this result are discussed.Comment: 5 pages, 4 figs, discussion improved, refs. added, and Fig.3 revised, to publish in PR