Scalar field "mini--MACHOs": a new explanation for galactic dark matter

Abstract

We examine the possibility that galactic halos are collisionless ensembles of scalar field ``massive compact halo objects'' (MACHOs). Using mass constraints from MACHO microlensing and from theoretical arguments on halos made up of massive black holes, as well as demanding also that scalar MACHO ensambles of all scales do not exhibit gravothermal instability (as required by consistency with observations of LSB galaxies), we obtain the range: $m\alt 10^{-7} M_\odot$ or $30 M_\odot\alt m\alt 100 M_\odot$. The rather narrow mass range of large MACHOs seems to indicate that the ensambles we are suggesting should be probably made up of scalar MACHOs in the low mass range (``mini--MACHOs''). The proposed model allows one to consider a non--baryonic and non--thermal fundamental nature of dark matter, while at the same time keeping the same phenomenology of the CDM paradigm.

5 pages, 1 eps figure. RevTex 4 style. To appear in Physical Review D

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• Self-gravitating system made of axions
• Galactic rotation curves in hybrid metric-Palatini gravity
• Constraining scalar fields with stellar kinematics and collisional dark matter
• Galactic metric, dark radiation, dark pressure and gravitational lensing in brane world models
• Searching for axion stars and Q-balls with a terrestrial magnetometer network
• Galactic dark matter as a bulk effect on the brane
• Gravitational collapse of Bose-Einstein condensate dark matter halos
• Two-fluid dark matter models
• Cosmological evolution of finite temperature Bose-Einstein Condensate dark matter
• Finite temperature effects in Bose-Einstein Condensed dark matter halos
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• Mass loss and longevity of gravitationally bound oscillating scalar lumps (oscillatons) in D-dimensions
• Tidal radii and escape speeds in dwarf spheroidal galaxies under MOND and dark halos compared
• Can the dark matter halo be a collisionless ensemble of axion stars?
• Galactic rotation curves in brane world models
• Dark energy-like stars from nonminimally coupled scalar field
• Could pressureless dark matter have pressure?
• Dynamical friction in globular cluster-rich ultra-diffuse galaxies: the case of NGC5846-UDG1
• Is dark matter an extra-dimensional effect?
• Gravipulsons
• Equation of State for Neutralino Star as a Form of Cold Dark Matter
• Precision measurement noise asymmetry and its annual modulation as a dark matter signature
• Passage of test particles through oscillating spherically-symmetric dark matter configurations