Speaker
Description
As electromagnetic and gravitational-wave observations expand our ability to study compact objects such as black holes and neutron stars, considerable effort has been devoted to testing general relativity and its alternatives in the strong-field regime that characterizes their vicinities. A paradigmatic phenomenon in this context is the scalarization effect, in which the scalar field present in a modified theory of gravity is activated after a critical point. Scalarization occurs for isolated compact objects when a critical configuration is reached within a sequence of equilibrium solutions. In binary systems, this effect is known as dynamical scalarization. Since its discovery, it has been clear that this effect can be understood in many cases as a continuous phase transition, well described by the phenomenological Landau model. Recently, it has been pointed out that spontaneous scalarization can also manifest as a first-order phase transition.
In this work, we take a closer look at the nature of spontaneous scalarization as a phase transition, analyzing in detail cases where it occurs as either a second- or first-order transition, as well as a more unconventional scenario characterized by a negative scalar susceptibility. Critical exponents are explicitly computed, and implications for dynamical scalarization are discussed. In a case where scalarization is accurately described as a continuous phase transition we confirm that the critical exponents align with the standard predictions of the Landau theory, and that a Landau ansatz provides a good fit for defining free energy near the critical point. Additionally, we carry out fully nonlinear numerical simulations that reveal both scalarization and descalarization processes within the first-order regime.
