l-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 l-boson stars under spherical perturbations, finding that there are both stable and unstable branches of solutions, as for single-field boson stars (l ¼ 0). In this work we probe the stability of l-boson stars against nonspherical perturbations by performing numerical evolutions of the Einstein-Klein-Gordon system, with a 3D code. For the timescales explored, the l-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 l-boson stars are the enhanced isometry point of a larger family of static (and possibly stationary), nonspherical multifield selfgravitating solitons.

We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solutions in General Relativity which are supported by a family of ghost scalar fields with quartic potential. This family consists of a particular composition of the scalar field modes, in which each mode is characterized by the same value of the angular momentum number , yet the composition yields a spherically symmetric stress-energy-momentum and metric tensor. For = 0 our solutions reduce to wormhole configurations which had been reported previously in the literature. We discuss the effects of the new parameter on the wormhole geometry including the motion of free-falling test particles. 2FIG. 1: Gravitational potential produced by a point mass ∼ −1/r (left panel) and by the exotic distribution presented in this work (right panel), see section V A. In both cases a test particle with vanishing angular momentum is considered.Moreover, under specific circumstances, the bump could be such that it connects two separated regions of spacetime. The resulting configuration is dubbed wormhole, and it offers challenges and opportunities to better understand the relation between matter and geometry, aside from the fact that, being bona fide solutions to Einstein's equations, it could potentially describe an astrophysical scenario if exotic matter turns out to actually being present in our Universe.In cosmology, matter with negative pressure can be used to describe the observed accelerated expansion of the Universe [5,8,14,17] and seems to be favored by several observational constraints [2,12,19]. Additionally, modeling the dark energy with an equation of state of the form p = ωρ, the observations suggest a value of ω close to −1 or even smaller, in which case the existence of astrophysical or cosmological wormholes becomes plausible.The studies of traversable wormholes have their origin with Ellis' work [11], where the author presented a black hole like solution to Einstein's equations, and in order to remove the singularity, used a scalar field and drain the hole. Actually, the same solution, based on a different approach was obtained almost at the same time by Bronnikov [6]. It turned out that the solution represented a bridge between two regions of the spacetime [1]. Over the years, the idea was further developed, and the best known example of a traversable wormhole appeared in 1988, in the work of Morris and Thorne [28]. Since then, a plethora of literature has arisen and the complexity of the models has increased, see for example [25,33] and references therein.In order to obtain a wormhole solution to the Einstein equations, some works use generation procedures, such as the Newman-Janis algorithm, which allows to obtain a Kerr black hole solution starting from a Schwarzschild one; in this way, a rotating (although not asymptotically flat) solution was obtained starting from one of the original Ellis models [27]. There is also a technique which uses the thin shell approach, which assumes that the matter is concentrated in a th...

A new class of complex scalar field objects, which generalize the well known boson stars, was recently found as solutions to the Einstein-Klein-Gordon system. The generalization consists in incorporating some of the effects of angular momentum, while still maintaining the spacetime's spherical symmetry. These new solutions depend on an (integer) angular parameter $\ell$, and hence were named $\ell$-boson stars. Like the standard $\ell=0$ boson stars these configurations admit a stable branch in the solution space; however, contrary to them they have a morphology that presents a shell-like structure with a "hole" in the internal region. In this article we perform a thorough exploration of the parameter space, concentrating particularly on the extreme cases with large values of $\ell$. We show that the shells grow in size with the angular parameter, doing so linearly for large values, with the size growing faster than the thickness. Their mass also increases with $\ell$, but in such a way that their compactness, while also growing monotonically, converges to a finite value corresponding to about one half of the Buchdahl limit. Furthermore, we show that $\ell$-boson stars can be highly anisotropic, with the radial pressure diminishing relative to the tangential pressure for large $\ell$, reducing asymptotically to zero, and with the maximum density also approaching zero. We show that these properties can be understood by analyzing the asymptotic limit $\ell\rightarrow\infty$ of the field equations and their solutions. We also analyze the existence and characteristics of both timelike and null circular orbits, especially for very compact solutions.

In this paper we consider that dark energy could be described solely by a complex scalar field with a Bose-Einstein condensate-like potential (denoted as CSFDE), that is, with a self-interaction and a mass term. In particular, we analyse a solution which in a fast oscillation regime at late-times behaves as a Cosmological Constant. Our proposal adequately describes the standard homogeneous and flat Fridman dynamics, furthermore, in this quintessence–complex scalar field scenario it is possible to mimic the dynamics related to dark energy. However, when the precision cosmological tests are implemented in this landscape, the generic Equation-of-State derived for this model in a restricted regime of ai (which corresponds to the scale factor at which the scalar field turns on), cannot be constrained by late-time current observations, since the analysis constraints solely the scalar field parameters within values ruled out by the theoretical model. This result is a clear hint to consider future CSFDE models with, for instance, two scalar fields in order to study the early-time dynamics of the Universe.

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