Dynamical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo>ℓ</mml:mo></mml:math>-boson stars: Generic stability and evidence for nonspherical solutions
Víctor Jaramillo, N. Sanchis-Gual, Juan Barranco, Argelia Bernal, Juan Carlos Degollado, Carlos Herdeiro, Darío Núñez
Abstract
$\ensuremath{\ell}$-boson stars are static, spherical, multifield self-gravitating solitons. They are asymptotically flat, finite energy solutions of Einstein's gravity minimally coupled to an odd number of massive, complex scalar fields. A previous study assessed the stability of $\ensuremath{\ell}$-boson stars under spherical perturbations, finding that there are both stable and unstable branches of solutions, as for single-field boson stars ($\ensuremath{\ell}=0$). In this work we probe the stability of $\ensuremath{\ell}$-boson stars against nonspherical perturbations by performing numerical evolutions of the Einstein-Klein-Gordon system, with a 3D code. For the timescales explored, the $\ensuremath{\ell}$-boson stars belonging to the spherical stable branch do not exhibit measurable growing modes. We find, however, evidence of zero modes; that is, nonspherical perturbations that neither grow nor decay. This suggests the branching off toward a larger family of equilibrium solutions: we conjecture that $\ensuremath{\ell}$-boson stars are the enhanced isometry point of a larger family of static (and possibly stationary), nonspherical multifield self-gravitating solitons.