Abstract
The existence of dark matter in the Universe has been solidly established in the last decades, after the arrival of accurate cosmological and astrophysical observations, and some consider it the most challenging problem in modern physics. Given the magnitude of the problem, one cannot discard the existence of new particles with properties that may look exotic in comparison with our current understanding of ordinary matter. This is the case for the so-called scalar field dark matter model, which assumes the existence of a (probably fundamental) scalar field with a very tiny mass that can have observable consequences in the formation of cosmological structure. We present here a brief account of the main properties of an ultra-light scalar field (with masses of the order of $10^{-22} \, \mathrm{eV}/c^2$) and how different observations have been used in the last two decades to put constraints on its physical parameters. Among other topics, we review the cosmological solutions of the model, discuss the features of its self-gravitating equilibrium configurations, revisit the gravitational collapse for the formation of galaxies, and revise the possibility to find a soliton structure in the center of dark matter halos.
Highlights
It is without doubt that the existence of dark matter (DM) in the universe is one of the most intriguing mysteries of modern cosmology (Bertone and Hooper, 2018), especially because of the good agreement between observations and the theoretical framework of the so-called concordance model CDM
Different observations seem to indicate that most likely the boson mass is of the order of 10−22eV, which at the same time allows the model to comprise the totality of the DM budget and to explain the seemingly cored density profile in the central parts of the galaxies
It is not yet clear whether the Scalar field dark matter (SFDM) model is to survive further tests, especially those at small scales that are most sensitive to the value of the boson mass and that are currently inconclusive about the preferred value of the boson mass
Summary
It is without doubt that the existence of dark matter (DM) in the universe is one of the most intriguing mysteries of modern cosmology (Bertone and Hooper, 2018), especially because of the good agreement between observations and the theoretical framework of the so-called concordance model CDM. The phenomenological description of DM has been under an intense experimental search, which so far has put strong limits on the interactions between DM and ordinary matter This is the reason why the WIMP (Weakly Interacting Massive Particle) hypothesis (Queiroz, 2017), which has so far been the best option to explain that DM is under extreme pressure, and the study of alternative models seems to be the way to go in the near future (Hooper, 2017). For the purposes of this paper, we shall refer here to the parabolic potential and how the boson mass ma determines the properties of the model at cosmological and astrophysical scales, so that different observations could be used together to constraint its value. More details about the model can be found in a series of interesting reviews of SFDM, such as Ureña-López (2007), Magaña et al (2012b), Suárez et al (2013), Marsh (2015b), Hui et al (2017), and Lee (2018)
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