Article

# Structure Formation with Scalar Field Dark Matter: The Fluid Approach

(Impact Factor: 5.81). 09/2011; 416(1):87. DOI: 10.1111/j.1365-2966.2011.19012.x
Source: arXiv

ABSTRACT

The properties of nearby galaxies that can be observed in great detail
suggest that a better theory rather than cold dark matter (CDM) would describe
in a better way a mechanism by which matter is more rapidly gathered into
large-scale structure such as galaxies and groups of galaxies. In this work we
develop and simulate a hydrodynamical approach for the early formation of
structure in the Universe, this approach is based on the fact that dark matter
is on the form of some kind of scalar field (SF) with a potential that goes as
$\mu^2\Phi^2/2+\lambda\Phi^4/4$, we expect that the fluctuations coming from
the SF will give us some information about the matter distribution we observe
these days.

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Available from: Tonatiuh Matos, Mar 16, 2015
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• "The general aspects of this model concerning the background evolution and the linear perturbations are already very well understood [10] [11] [12] [13] [14]. But, in order to fully understand the final clustering patterns of the BEC dark matter model high resolution hydrodynamical/Nbody simulations are still needed. "
##### Article: Non-linear clustering during the BEC dark matter phase transition
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ABSTRACT: Spherical collapse of the Bose-Einstein Condensate (BEC) dark matter model is studied. The evolution of perturbed quantities like the density of the collapsed region and its expansion rate are calculated for two scenarios. Firstly, we consider the case of a sharp phase transition (which happens when the critical temperature is reached) from the normal dark matter state to the condensate one. In the second case studied we consider a smooth first order phase transition where there is a continuous conversion of "normal" dark matter to the BEC phase. We calculate in detail the perturbative quantities at nonlinear level presenting numerical results for the physics of the collapse for a wide range of the model's space parameter. The model is properly compared to the standard dark matter scenario.
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• "The recent concern in this kind of exotic non-standard field as a good candidate to DE or DM is due to the fact that the scalar part of ELKO spinors has a much richer structure than the standard scalar field when applied to cosmology [8] [9] [10]. The coupled system of equations involving the interaction of DE and DM plus the Friedmann equations are much involved, even for a standard scalar field [10]. Such system is much more involved when dealing with ELKO fields. "
##### Article: A new approach on the stability analysis in ELKO cosmology
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ABSTRACT: In this work it has been developed a new approach to study the stability of a system composed by an ELKO field interacting with dark matter, which could give some contribution in order to alleviate the cosmic coincidence problem. It is assumed that the potential that characterizes the ELKO field is not specified, but it is related to a constant parameter $\delta$. The strength of the interaction between the matter and the ELKO field is characterized by a constant parameter $\beta$ and it is also assumed that both the ELKO field as the matter energy density are related to their pressures by equations of state parameters $\omega_\phi$ and $\omega_m$, respectively. The system of equations is analysed by a dynamical system approach. It was found out the conditions of stability between the parameters $\delta$ and $\beta$ in order to have stable fixed points for the system for different values of the equation of state parameters $\omega_\phi$ and $\omega_m$, and the results are presented in form of tables. The possibility of decay of Elko field into dark matter or vice verse can be read directly from the tables, since the parameters $\delta$ and $\beta$ satisfy some inequalities. This opens the possibility to constrain the potential in order to have a stable system for different interactions terms between the Elko field and dark matter. The cosmic coincidence problem can be alleviated for some specific relations between the parameters of the model.
European Physical Journal C 07/2014; 75(1). DOI:10.1140/epjc/s10052-015-3260-9 · 5.08 Impact Factor
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• "Once the scalar field reaches the minimum (T T c ), and if the mass of the boson associated to the scalar field Φ is greater than the expansion rate of the Universe (m φ H), then the scalar field has a fast oscillation phase [18]. At this regime, if the boson mass is in the range m φ ∼ 10 −23 − 10 −21 – 1 – eV, the SFDM behaves as CDM and their linear perturbations evolve as those in the standard CDM model [19] [20] [21] [22]. Moreover, due to the fact that the effective Jeans length for a scalar field depends on the boson mass as λ J ∼ m −1 φ , the mass power spectrum has a natural cut-off and the overpopulation of substructures is avoided in a natural way. "
##### Article: Is Sextans dwarf galaxy in a scalar field dark matter halo?
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ABSTRACT: The Bose-Einstein condensate/scalar field dark matter model, considers that the dark matter is composed by spinless-ultra-light particles which can be described by a scalar field. This model is an alternative model to the $\Lambda$-cold dark matter paradigm, and therefore should be studied at galactic and cosmological scales. Dwarf spheroidal galaxies have been very useful when studying any dark matter theory, because the dark matter dominates their dynamics. In this paper we study the Sextans dwarf spheroidal galaxy, embedded in a scalar field dark matter halo. We explore how the dissolution time-scale of the stellar substructures in Sextans, constrain the mass, and the self-interacting parameter of the scalar field dark matter boson. We find that for masses in the range $(0.12< m_{\phi}<8) \times10^{-22}$~eV, scalar field dark halos without self-interaction would have cores large enough to explain the longevity of the stellar substructures in Sextans, and small enough mass to be compatible with dynamical limits. If the self-interacting parameter is distinct to zero, then the mass of the boson could be as high as $m_{\phi}\approx2\times10^{-21}$~eV, but it would correspond to an unrealistic low mass fot the Sextans dark matter halo . Therefore, the Sextans dwarf galaxy could be embedded in a scalar field/BEC dark matter halo with a preferred self-interacting parameter equal to zero.
Journal of Cosmology and Astroparticle Physics 06/2014; 2014(09). DOI:10.1088/1475-7516/2014/09/011 · 5.81 Impact Factor