Coleman-de Luccia Bubble Research Articles

Higher-dimensional view on quantum cosmology

We argue that the choice of boundary condition for the wave function in quantum cosmology depends on the UV completion of general relativity. We provide an explicit example using a braneworld scenario in which a de Sitter cosmology is induced on the surface of a Coleman-de Luccia bubble in a 5-dimensional AdS space. The corresponding boundary conditions are unambigously fixed by demanding consistency with the known physics of bubble nucleation and this selects the Vilenkin weighting for the amplitude from a 4D viewpoint.

Vacuum decay in the presence of a cosmic string

We study the false vacuum decay and bubble nucleation in the presence of a cosmic string in dS spacetime. A cosmic string induces a deficit angle in spacetime around itself so the nucleated bubble has the shape of a rugby ball. Working in thin wall approximation and using the junction conditions we study the dynamics of the bubble wall and calculate the Euclidean action. An interesting feature in our analysis is that the tension of the string is screened by the bubble such that an observer inside the bubble measures a different value of the tension than an outside observer. We show that the string can act as a catalyzer in which the nucleation rate is enhanced compared to the Coleman-de Luccia instanton. However, in general, the nucleation rate is not a monotonic function of the difference between the two tensions so in some regions of the parameters space the nucleation rate may be smaller than the Coleman-de Luccia bubble.

Vacuum decay and bubble nucleation in f(R) gravity

In this work we study vacuum decay and bubble nucleation in models of $f(R)$ higher curvature gravity. Building upon the analysis of Coleman-De Luccia (CDL), we present the formalism to calculate the Euclidean action and the bounce solution for a general $f(R)$ gravity in the thin wall approximation. We calculate the size of the nucleated bubble and the decay exponent for the Starobinsky model and its higher power extensions. We have shown that in the Starobinsky model with a typical potential the nucleated bubble has a larger size in comparison to the CDL bubble and with a lower tunneling rate. However, for higher power extension of the Starobinsky model the size of the bubble and the tunneling exponent can be larger or smaller than the CDL bubble depending on the model parameters. As a counterintuitive example, we have shown that a bubble with a larger size than the CDL bubble but with a higher nucleation rate can be formed in $f(R)$ gravity.

On big crunch solutions in Prokushkin-Vasiliev theory

We construct simple solutions of three-dimensional higher spin gravity interacting with matter in which only the scalar and spin-two fields are excited. They preserve Lorentz symmetry and are similar to the four-dimensional solutions constructed by Sezgin and Sundell, with the difference that the additional twisted sectors of the three-dimensional theory are excited. Furthermore, the three-dimensional system contains an extra parameter $\lambda$ which allows us to vary the mass of the scalar. Among other reasons, the resulting solutions are interesting for the holographic study of cosmological singularities: they describe the growth of a Coleman-De Luccia bubble in anti-de Sitter space, ending in a big crunch singularity. We initiate the holographic study of these solutions, finding evidence for their interpretation within a multi-trace deformation which renders the dual field theory unstable. The limit $\lambda \to 0$ is particularly interesting as it captures effects of a running coupling in a large-$N$ interacting fermion model. We also propose a generalization of our solutions, consisting of a dressing with Lorentz-invariant projectors. This additional sector remains non-trivial when the scalar field is turned off.

Observers in an accelerated universe

If the current acceleration of our Universe is due to a cosmological constant, then a Coleman-De Luccia bubble will nucleate in our Universe. In this work, we consider that our observations could be likely in this framework, consisting in two infinite spaces, if a foliation by constant mean curvature hypersurfaces is taken to count the events in the spacetime. Thus, we obtain and study a particular foliation, which covers the existence of most observers in our part of spacetime.

Watching worlds collide: effects on the CMB from cosmological bubble collisions

We extend our previous work on the cosmology of Coleman-de Luccia bubble collisions. Within a set of approximations we calculate the effects on the cosmic microwave background (CMB) as seen from inside a bubble which has undergone such a collision. We find that the effects are always qualitatively similar—an anisotropy that depends only on the angle to the collision direction—but can produce a cold or hot spot of varying size, as well as power asymmetries along the axis determined by the collision. With other parameters held fixed the effects weaken as the amount of inflation which took place inside our bubble grows, but generically survive order 10 efolds past what is required to solve the horizon and flatness problems. In some regions of parameter space the effects can survive arbitrarily long inflation.

When Worlds Collide

We analyze the cosmological signatures visible to an observer in a Coleman–de Lucciabubble when another such bubble collides with it. We use a gluing procedure to generalizethe results of Freivogel, Horowitz and Shenker to the case of a general cosmologicalconstant in each bubble and study the resulting spacetimes. The collision breaks theisotropy and homogeneity of the bubble universe and provides a cosmological‘axis of evil’ which can affect the cosmic microwave background in several uniqueand potentially detectable ways. Unlike more conventional perturbations to theinflationary initial state, these signatures can survive even relatively long periods ofinflation. In addition, we find that for a given collision the observers in the bubblewith smaller cosmological constant are safest from collisions with domain walls,possibly providing another anthropic selection principle for small positive vacuumenergy.

Holographic framework for eternal inflation

In this paper we provide some circumstantial evidence for a holographic duality between bubble nucleation in an eternally inflating universe and a Euclidean conformal field theory (CFT). The holographic correspondence (which is different than Strominger's de Sitter (dS)/CFT duality) relates the decay of ($3+1$)-dimensional de Sitter space to a two-dimensional CFT. It is not associated with pure de Sitter space, but rather with Coleman-De Luccia bubble nucleation. Alternatively, it can be thought of as a holographic description of the open, infinite, Friedmann-Robertson-Walker (FRW) cosmology that results from such a bubble. The conjectured holographic representation is of a new type that combines holography with the Wheeler-DeWitt formalism to produce a Wheeler-DeWitt theory that lives on the spatial boundary of a $k=\ensuremath{-}1$ FRW cosmology. We also argue for a more ambitious interpretation of the Wheeler-DeWitt CFT as a holographic dual of the entire Landscape.