26 research outputs found
Multi-state Boson Stars
Motivated by the increasing interest in models which consider scalar fields
as viable dark matter candidates, we have constructed a generalization of
relativistic Boson Stars (BS) composed of two coexisting states of the scalar
field, the ground state and the first excited state. We have studied the
dynamical evolution of these Multi-state Boson Stars (MSBS) under radial
perturbations, using numerical techniques. We show that stable MSBS can be
constructed, when the number of particles in the first excited state, N2, is
smaller than the number of particles in the ground state, N1. On the other
hand, when N2 > N1, the configurations are initially unstable. However, they
evolve and settle down into stable configurations. In the stabilization
process, the initially ground state is excited and ends in a first excited
state, whereas the initially first excited state ends in a ground state. During
this process, both states emit scalar field radiation, decreasing their number
of particles. This behavior shows that even though BS in the first excited
state are intrinsically unstable under finite perturbations, the configuration
resulting from the combination of this state with the ground state produces
stable objects. Finally we show in a qualitative way, that stable MSBS could be
realistic models of dark matter galactic halos, as they produce rotation curves
that are flatter at large radii than the rotation curves produced by BS with
only one state.Comment: 14 pages. Extended discussion and new figures added. Conclusions
unchanged. Accepted for publication in Physical Review
Scalar Field Dark Matter: non-spherical collapse and late time behavior
We show the evolution of non-spherically symmetric balls of a
self-gravitating scalar field in the Newtonian regime or equivalently an ideal
self-gravitating condensed Bose gas. In order to do so, we use a finite
differencing approximation of the Shcr\"odinger-Poisson (SP) system of
equations with axial symmetry in cylindrical coordinates. Our results indicate:
1) that spherically symmetric ground state equilibrium configurations are
stable against non-spherical perturbations and 2) that such configurations of
the SP system are late-time attractors for non-spherically symmetric initial
profiles of the scalar field, which is a generalization of such behavior for
spherically symmetric initial profiles. Our system and the boundary conditions
used, work as a model of scalar field dark matter collapse after the turnaround
point. In such case, we have found that the scalar field overdensities tolerate
non-spherical contributions to the profile of the initial fluctuation.Comment: 8 revtex pages, 10 eps figures. Accepted for publication in PR
Bayesian analysis for rotational curves with -boson stars as a dark matter component
Using Low Brightness Surface Galaxies (LBSG) rotational curves we inferred
the free parameters of -boson stars as a dark matter component. The
-boson stars are numerical solutions to the non-relativistic limit of the
Einstein-Klein-Gordon system, the Schr\"odinger-Poisson (SP) system. These
solutions are parametrized by an angular momentum number and
an excitation number . We perform a bayesian analysis by modifying the
SimpleMC code to perform the parameter inference, for the cases with , and multistates of -boson stars. We used the Akaike
information criterion (AIC), Bayesian information criterion and the Bayes
factor to compare the excited state (=1) and the multistate case with the
ground state (=0) as the base model due to its simplicity. We found that
the data in most galaxies in the sample favours the multistates case and that
the scalar field mass tends to be slightly bigger than the ground state case.Comment: 14 pages, 9 Figure
Are black holes a serious threat to scalar field dark matter models?
Classical scalar fields have been proposed as possible candidates for the
dark matter component of the universe. Given the fact that super-massive black
holes seem to exist at the center of most galaxies, in order to be a viable
candidate for the dark matter halo a scalar field configuration should be
stable in the presence of a central black hole, or at least be able to survive
for cosmological time-scales. In the present work we consider a scalar field as
a test field on a Schwarzschild background, and study under which conditions
one can obtain long-lived configurations. We present a detailed study of the
Klein-Gordon equation in the Schwarzschild spacetime, both from an analytical
and numerical point of view, and show that indeed there exist quasi-stationary
solutions that can remain surrounding a black hole for large time-scales.Comment: 34 pages, 13 figure
A further analysis for galactic dark matter halos with pressure
Spherically symmetric and static dark matter halos in hydrostatic equilibrium demand that dark matter should have an effective pressure that compensates the gravitational force of the mass of the halo. An effective equation of state can be obtained for each rotational velocity profile of the stars in galaxies. In this work, we study one of this dark matter equation of state obtained for the Universal Velocity Profile and analyze the properties of the self-gravitating structures that emerges from this equation of state. The resulting configurations explaining the observed rotational speeds are found to be unstable. We conclude that either the halo is not in hydrostatic equilibrium,or it is non spherically symmetric, or it is not static if the Universal Velocity profile should be valid to fit the rotational velocity curve of the galaxies.Fil: Aceña, Andrés Esteban. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Barranco, Juan. Universidad de Guanajuato; MéxicoFil: Bernal, Argelia. Universidad de Guanajuato; MéxicoFil: López, Ericson. Escuela Politécnica Nacional; EcuadorFil: Llerena, Mario. Universidad de La Serena; Chil
Scalar Field Dark Matter: head-on interaction between two structures
In this manuscript we track the evolution of a system consisting of two
self-gravitating virialized objects made of a scalar field in the newtonian
limit. The Schr\"odinger-Poisson system contains a potential with
self-interaction of the Gross-Pitaevskii type for Bose Condensates. Our results
indicate that solitonic behavior is allowed in the scalar field dark matter
model when the total energy of the system is positive, that is, the two blobs
pass through each other as should happen for solitons; on the other hand, there
is a true collision of the two blobs when the total energy is negative.Comment: 8 revtex pages, 11 eps figures. v2 matches the published version.
v2=v1+ref+minor_change
Schwarzschild black holes can wear scalar wigs
We study the evolution of a massive scalar field surrounding a Schwarzschild
black hole and find configurations that can survive for arbitrarily long times,
provided the black hole or the scalar field mass is small enough. In
particular, both ultra-light scalar field dark matter around supermassive black
holes and axion-like scalar fields around primordial black holes can survive
for cosmological times. Moreover, these results are quite generic, in the sense
that fairly arbitrary initial data evolves, at late times, as a combination of
those long-lived configurations.Comment: 5 pages, 3 figures. Accepted for publication in Physical Review
Letter
Dynamical evolutions of â„“-boson stars in spherical symmetry
In previous work, we have found new static, spherically symmetric boson star solutions which generalize the standard boson stars (BSs) by allowing a particular superposition of scalar fields in which each of the fields is characterized by a fixed value of its non-vanishing angular momentum number. We call such solutions 'boson stars'. Here, we perform a series of fully non-linear dynamical simulations of perturbed BSs in order to study their stability, and the final fate of unstable configurations. We show that for each value of, the configuration of maximum mass separates the parameter space into stable and unstable regions. Stable configurations, when perturbed, oscillate around the unperturbed solution and very slowly return to a stationary configuration. Unstable configurations, in contrast, can have three different final states: collapse to a black hole, migration to the stable branch, or explosion (dissipation) to infinity. Just as it happens with BSs, migration to the stable branch or dissipation to infinity depends on the sign of the total binding energy of the star: bound unstable stars collapse to black holes or migrate to the stable branch, whereas unbound unstable stars either collapse to a black hole or explode to infinity. Thus, the parameter allows us to construct a new set of stable configurations. All our simulations are performed in spherical symmetry, leaving a more detailed stability analysis including non-spherical perturbations for future work.Fil: Alcubierre, Miguel. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Barranco, Juan. Universidad de Guanajuato; MéxicoFil: Bernal, Argelia. Universidad de Guanajuato; MéxicoFil: Degollado, Juan Carlos. Universidad Nacional Autónoma de México; MéxicoFil: Diez Tejedor, Alberto. Universidad de Guanajuato; MéxicoFil: Megevand Politano, Miguel Federico. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Córdoba. Instituto de FÃsica Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de FÃsica Enrique Gaviola; ArgentinaFil: Núñez, DarÃo. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Sarbach, Olivier. Universidad Michoacana de San Nicolás de Hidalgo; Méxic