Rapid Tunneling and Percolation in the Landscape

Abstract

Motivated by the possibility of a string landscape, we reexamine tunneling of a scalar field across single/multiple barriers. Recent investigations have suggested modifications to the usual picture of false vacuum decay that lead to efficient and rapid tunneling in the landscape when certain conditions are met. This can be due to stringy effects (e.g. tunneling via the DBI action), or by effects arising due to the presence of multiple vacua (e.g. resonance tunneling). In this paper we discuss both DBI tunneling and resonance tunneling. We provide a QFT treatment of resonance tunneling using the Schrödinger functional approach. We also show how DBI tunneling for supercritical barriers can naturally lead to conditions suitable for resonance tunneling. We argue using basic ideas from percolation theory that tunneling can be rapid in a landscape where a typical vacuum has multiple decay channels and discuss various cosmological implications. This rapidity vacuum decay can happen even if there are no resonance/DBI tunneling enhancements, solely due to the presence of a large number of decay channels. Finally, we consider various ways of circumventing a recent no-go theorem for resonance tunneling in quantum field theory.

Analyzing multifield tunneling with exact bounce solutions

“…3 Therefore, in the case of multifield potentials, we cannot assume tunneling happens in the direction of the "smallest" barrier. In Sec.…”

“…The string theory landscape motivates the study of multifield potentials with a large number of metastable vacua [1][2][3][4][5][6][7][8][9][10][11]. Since our Universe may have occupied a metastable vacuum in the past or may do so today, it is of cosmological interest to study tunneling out of metastable vacua [12][13][14][15][16][17][18][19][20].…”

Kink Collisions in Curved Field Space

“…Moreover, string theory offers the possibility of an enormous landscape of local minima, making it important to determine if tunneling events and bubble collisions are essential cosmological processes. These considerations have inspired numerous authors to study transitions between collections of metastable vacua, with results of possible importance to key outstanding issues, such as the cosmological constant problem and the search for experimental signatures of a multiverse [6][7][8][9][10][11][12][13][14][15].…”

Cosmological first-order phase transitions beyond the standard inflationary scenario

“…When very rapid tunneling occurs a vacuum bubble can nucleate and find itself on a non-vacuum background that had not enough time to evolve to a de Sitter spacetime. Rapid tunneling occurs for instance in chain inflation [1] where many coupled fields are at work providing a series of catalysed tunneling processes through many minima on the landscape, or in the context of resonance or DBI tunneling [2,3].…”

“…When very rapid tunneling occurs a vacuum bubble can nucleate and find itself on a non-vacuum background that had not enough time to evolve to a de Sitter spacetime. Rapid tunneling occurs for instance in chain inflation [1] where many coupled fields are at work providing a series of catalysed tunneling processes through many minima on the landscape, or in the context of resonance or DBI tunneling [2,3].Here, we will study the nucleation and the classical evolution of vacuum bubbles on nonvacuum backgrounds in the thin-wall approximation; for a more ample treatment see [4]. A background we utilise for both analyses is a flat FRW model that will serve as the setting for ambient phase transitions, like reheating.…”