Boson Star Normal Modes

Understand

Boson stars are gravitationally bound objects that arise in ultralight dark matter models and form in the centers of galactic halos or axion miniclusters.

• We systematically study the excitations of a boson star, taking into account the mixing between positive and negative frequencies introduced by gravity.
• We show that the spectrum contains zero-energy modes in the monopole and dipole sectors resulting from spontaneous symmetry breaking by the boson star background.
• We analyze the general properties of the eigenmodes and derive their orthogonality and completeness conditions which have non-standard form due to the positive-negative frequency mixing.