Brief History of Ultra-light Scalar Dark Matter Models

Abstract

Abstract. 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 )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.Despite long efforts dark matter (DM) remains a great mystery in physics and astronomy [1]. While numerical results of the cold dark matter (CDM) model are remarkably successful in explaining the large scale structure of the universe, it encounters some problems at the scale of galactic or sub-galactic structures. For example, the numerical simulations usually predict cusped central halo density and too many sub-halos and small galaxies, which seem to be in contradiction with observations [2][3][4][5].Recently, there is a growing interest in the idea that DM particles are ultra-light scalars in Bose-Einstein condensate (BEC). (For a review, see Refs. 6-13) In this model, due to the tiny DM particle mass m = O(10 −22 )eV, the DM particle number density is very high and hence the inter-particle distance is much smaller than the de Broglie wave length of the DM particles. Therefore, the particles are in BEC and move collectively as a wave rather than incoherent particles. At the scale larger than galaxies the DM perturbation behaves like that of CDM, while below the scale quantum pressure from the uncertainty principle suppresses the small structure formation, which makes it a viable alternative to CDM. This property helps us to resolve the small scale problems of the CDM model such as the missing satellite problem or the cusp/core problem [14].Before 2000 there were only a few groups of scientists working on this topic, without much communication even between them. Being unaware of precedent works, many researchers in this field independently proposed similar ideas with various names such as BEC DM, scalar field DM (SFDM), fuzzy DM, ultra-light axion (ULA), ultralight axion like particle (ALP), wave DM, ψ DM, repulsive DM or (super)fluid DM among many, although the basic physics of these models is quite similar. (Henceforth, I will use the term 'SFDM' for the model.) This unfortunate ⋆ e-mail: scikid@jwu.ac.kr situation has brought some confusions among researchers in this field. Therefore, at this point, it is desirable to summarize what have already attempted in this exciting field. 1The hypothesis that galactic DMs are ultra-light scalar particles in BEC has a long history. In Ref.[15] Baldeschi et al. considered the galactic halo model of self-gravitating bosons wit...

Core mass-halo mass relation of bosonic and fermionic dark matter halos harboring a supermassive black hole

“…Accordingly, for the DM halos considered by Davies and Mocz [44], with mass M v = 10 12 M (Milky Way) and M v = 2×10 14 M (elliptical galaxy in the Virgo cluster), the presence of the SMBH is expected to change the value of the core mass (especially in the second case), except if it forms after the quantum core as assumed by these authors. 13 The same conclusion is reached in the case of fermions for which (M h ) * ,F = 2.31 × 10 12 M . By contrast, for self-interacting bosons in the TF limit, we find that the effect of the BH becomes important for DM halos of mass (M h ) * ,TF = 6.92 × 10 14 M .…”

Spin precession experiments for light axionic dark matter

“…This fuzzy dark matter has a Compton wavelength on the order of the size of dwarf galaxies, which circumvents potential problems associated with structure formation from standard cold dark matter [52][53][54][55][56][57][58][59]. In addition, recent measurements suggest there are slight excesses in the cooling of white dwarfs that could be explained by the addition of ultralight axions [60].…”

Binary pulsars as probes for spin-2 ultralight dark matter

“…The traditional fields that follow this pattern are axion-like particles and dilatons [1][2][3][4][5][6][7]. However, with these same assumptions, nearly the same late Universe cosmological evolution and phenomenology can be obtained from a massive vector or spin-2 tensor field, as shown respectively in [8][9][10][11][12][13][14] and [15,16] 2 .…”