499 research outputs found

    Is dark matter a BEC or scalar field?

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    This is a brief review on the history of the Bose-Einstein condensate (BEC) or boson star model of galactic dark matter halos, where ultra-light scalar dark matter particles condense in a single BEC quantum state. The halos can be described as a self-gravitating, possibly self-interacting, coherent scalar field. On a scale larger than galaxies, dark matter behaves like cold dark matter while below that scale the quantum mechanical nature suppresses the dark matter structure formation due to the minimum length scale determined by the mass m\st{>}{\sim}10^{-24} eV and the self-interaction of the particles. This property could alleviate the cusp problem and missing satellite problems of the Λ\LambdaCDM model. Furthermore, this model well reproduces the observed rotation curves of spiral and dwarf galaxies, which makes the model promising.Comment: published versio

    Characteristic Size and Mass of Galaxies in the Bose-Einstein Condensate Dark Matter Model

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    We study the characteristic length scale of galactic halos in the Bose-Einstein condensate (or scalar field) dark matter model. Considering the evolution of the density perturbation we show that the average background matter density determines the quantum Jeans mass and hence the spatial size of galaxies at a given epoch. In this model the minimum size of galaxies increases while the minimum mass of the galaxies decreases as the universe expands. The observed values of the mass and the size of the dwarf galaxies are successfully reproduced with the dark matter particle mass m≃5×10−22eVm\simeq 5\times 10^{-22}eV. The minimum size is about 6×10−3m/Hλc6\times 10^{-3}\sqrt{m/H}\lambda_c and the typical rotation velocity of the dwarf galaxies is O(H/mO(\sqrt{H/m}) c, where HH is the Hubble parameter and λc\lambda_c is the Compton wave length of the particle. We also suggest that ultra compact dwarf galaxies are the remnants of the dwarf galaxies formed in the early universe.Comment: Accepted for publication in Physics letters

    Brief History of Ultra-light Scalar Dark Matter Models

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    This is a review on the brief history of the scalar field dark matter model also known as fuzzy dark matter, BEC dark matter, wave dark matter, or ultra-light axion. In this model ultra-light scalar dark matter particles with mass m=O(10−22)eVm = O(10^{-22})eV condense in a single Bose-Einstein condensate state and behave collectively like a classical wave. Galactic dark matter halos can be described as a self-gravitating coherent scalar field configuration called boson stars. At the scale larger than galaxies the dark matter acts like cold dark matter, while below the scale quantum pressure from the uncertainty principle suppresses the smaller structure formation so that it can resolve the small scale crisis of the conventional cold dark matter model.Comment: 5 page

    Fermion Scattering at a Phase Wave

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    We study fermion reflection at a phase wave which is formed during a bubble collision in a first order phase transition. We calculate the reflection and the transmission coefficients by solving the Dirac equation with the phase wave background. Using the results we analyze the damping and the velocity of the wave.Comment: 19 pages. Standard Latex file with 2 tex figure
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