Primordial black hole and wormhole formation by domain walls

Abstract

In theories with a broken discrete symmetry, Hubble sized spherical domain walls may spontaneously nucleate during inflation. These objects are subsequently stretched by the inflationary expansion, resulting in a broad distribution of sizes. The fate of the walls after inflation depends on their radius. Walls smaller than a critical radius fall within the cosmological horizon early on and collapse due to their own tension, forming ordinary black holes. But if a wall is large enough, its repulsive gravitational field becomes dominant much before the wall can fall within the cosmological horizon. In this "supercritical" case, a wormhole throat develops, connecting the ambient exterior FRW universe with an interior baby universe, where the exponential growth of the wall radius takes place. The wormhole pinches off in a time-scale comparable to its light-crossing time, and black holes are formed at its two mouths. As discussed in previous work, the resulting black hole population has a wide distribution of masses and can have significant astrophysical effects. The mechanism of black hole formation has been previously studied for a dust-dominated universe. Here we investigate the case of a radiation-dominated universe, which is more relevant cosmologically, by using numerical simulations in order to find the initial mass of a black hole as a function of the wall size at the end of inflation. For large supercritical domain walls, this mass nearly saturates the upper bound according to which the black hole cannot be larger than the cosmological horizon. We also find that the subsequent accretion of radiation satisfies a scaling relation, resulting in a mass increase by about a factor of 2.

Gravitational decoupling and the Picard-Lefschetz approach

“…Naively one might think that the first term in (21), coming from the first order variation with respect to the metric, should be identical to (10). After all, (10) was supposed to be a general result.…”

“…10 We also rescale N such that the time interval for which this path integral is defined is simply t ∈ ½0; 1. In this gauge a physical time interval can be read off from the metric…”

“…If we keep a 1 ¼ a 2 ¼ const in this limit, then the physical time interval Δτ generically goes to 0. Instead, we choose to hold the 10 This corresponds to computing a propagator, i.e., a Green's function of the Wheeler-DeWitt equation [46]. Choosing the entire real line C R ¼ R would instead give a solution to the Wheeler-DeWitt equation.…”

“…This is the kind of potential relevant for tunneling in axion monodromy models of inflation [3][4][5][6][7][8][9] and is also of interest for recent discussion of bubble wall nucleation in the early Universe [10,11]. In [12], three of the current authors studied field-theoretic tunneling in this potential using the Euclidean prescription.…”

Mass bound for primordial black hole from trans-Planckian censorship conjecture

“…We conclude in the last section. It is worth noting that, the derived PBH mass bounds would not be applicable to other scenarios of PBH production from curvaton [25,26], scalar lumps [27,28], cosmic strings [29,30], domain walls [31,32], primordial bubbles [33], bubble collisions [34,35], and preheating instability [36], to name just a few.…”