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arXiv · 2605.25671

Onset of spontaneous scalarization in dark matter stars

Junya Tanaka
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Abstract

We investigated the onset of spontaneous scalarization in dark matter stars. In scalar-tensor theories, the coupling between matter and a scalar field generates an effective mass, which is known to trigger the growth of the scalar field around stars and black holes (spontaneous scalarization). On the other hand, models in which the scalar field couples not only to baryonic matter but also to dark matter have been discussed in the literature. Moreover, in models with self-interacting dark matter, it is known that dark matter can form compact objects, dark stars (DS). Within the framework of scalar-tensor theories, we studied the parameter ranges in which the growth of the scalar field occurs in dark stars. As a result, we found that the tachyonic instability associated with spontaneous scalarization occurs in some parameter regions with a negative coupling parameter $\beta_d$. We also investigated double-degenerate stars (DDSs), which consist of baryonic matter and dark matter, and found that the baryonic component weakens the tachyonic instability. As a result, dark stars containing baryons can still exhibit the tachyonic instability, whereas neutron stars containing a dark matter component do not develop tachyonic instability induced by the dark matter.

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Junya Tanaka. 2026-05-25. Onset of spontaneous scalarization in dark matter stars. https://arxiv.org/abs/2605.25671

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