Phase transitions of boson stars in scalar-tensor theories

Abstract

In scalar-tensor theories, compact objects may experience spontaneous scalarization. Recently, it was shown that matter-induced spontaneous scalarization of neutron stars is predominantly associated with a first-order phase transition. Here we consider matter-induced spontaneous scalarization of boson stars. Employing a repulsive quartic potential for the bosonic matter, we find only first-order phase transitions.

Figures (7)

• Figure 1: Non-rotating boson stars ($n=0$): (a) The scaled ADM mass $M_\text{ADM}/M_0$ versus the scaled boson frequency $\omega/\omega_0$ is shown for non-scalarized (GR) boson stars (solid) with self-interaction coupling constant $\Lambda=300$, and for scalarized boson stars for a massless ($\beta=-4.7$ and $\beta=-10$, dotted), resp. a massive ($m_\phi/m_b=10^{-3}$, $\beta=-10$, dashed) gravitational scalar field; (b) analogous to (a) for the scaled boson mass $M_b/M_0$ versus the central value $\psi_c$ of the boson field.
• Figure 2: Non-rotating boson stars ($n=0$): (a) The relative binding energy $E_\text{bind}$ versus the scaled boson mass $M_b/M_0$ for the same sets of solutions as in Fig. \ref{['fig1']}. (b) Enlargement of the region close to the bifurcation for $\beta=-10$, $m_\phi/m_b=0$.
• Figure 3: Non-rotating boson stars ($n=0$): (a) The scaled boson mass $M_b/M_0$ versus the central value $\psi_c$ of the boson field is shown for the non-scalarized (GR) boson stars, and for the scalarized boson stars for a massless gravitational scalar field and a set of values of the SST parameter $\beta$ for fixed self-coupling constant $\Lambda=300$. (b) The relative binding energy $E_\text{bind}$ versus the scaled boson mass $M_b/M_0$ for the same sets of solutions as in (a). (c) Analogous to (a) for a set of values of $\Lambda$ and fixed $\beta=-10$. (d) Analogous to (b) for the solutions in (c) restricted to the bifurcation regions.
• Figure 4: Rotating boson stars ($n=1$): (a) The scaled ADM mass $M_\text{ADM}/M_0$ versus the scaled boson frequency $\omega/\omega_0$ is shown for non-scalarized (GR) boson stars (solid) with self-interaction coupling constant $\Lambda=300$, and for scalarized boson stars for a massless ($\beta=-4.7$ and $\beta=-10$, dotted) gravitational scalar field; (b) analogous to (a) for the scaled boson mass $M_b/M_0$ versus the maximal value $\psi_\text{max}$ of the boson field.
• Figure 5: Rotating boson stars ($n=1$): (a) The relative binding energy $E_\text{bind}$ versus the scaled boson mass $M_b/M_0$ for the same sets of solutions as in Fig. \ref{['fig4']}. (b) Enlargement of the region close to the bifurcation for $\beta=-10$, $m_\phi/m_b=0$.