Nature of phase transitions and metastability in scalar-tensor theories

TL;DR

This paper reveals that in scalar-tensor theories, phase transitions leading to spontaneous scalarization in compact stars are predominantly first-order, implying metastability and transitions are more common than previously thought, with significant observational implications.

Contribution

The study demonstrates that first-order phase transitions are the primary mechanism for spontaneous scalarization in scalar-tensor theories, challenging the prior focus on second-order transitions.

Findings

First-order phase transitions are more common than second-order in scalarization.

Metastability and transitions between stable configurations are more likely.

New observational prospects arise from these metastable transitions.

Abstract

Compact stars above a critical stellar mass develop large scalar fields in some scalar-tensor theories. This scenario, called spontaneous scalarization, has been an intense topic of study since it passes weak-field gravity tests naturally while providing clear observables in the strong-field regime. The underlying mechanism for the onset of scalarization is often depicted as a second-order phase transition. Here, we show that a first-order phase transition is in fact the most common mechanism. This means metastability and transitions between locally stable compact object configurations are much more likely than previously believed, opening vast new avenues for observational prospects.