Quintessence and scalar dark matter in the Universe

Abstract

Continuing with previous works, we present a cosmological model in which dark matter and dark energy are modeled by scalar fields Φ and Ψ, respectively, endowed with the scalar potentials V (Φ) = Vo [cosh (λ √ κoΦ) − 1] andṼ (Ψ) =Ṽo [sinh (α √ κoΨ)] β . This model contains 95% of scalar field. We obtain that the scalar dark matter mass is mΦ ∼ 10 −26 eV. The solution obtained allows us to recover the success of the standard CDM. The implications on the formation of structure are reviewed. We obtain that the minimal cutoff radio for this model is rc ∼ 1.2 kpc.PACS numbers: 98.80.-k, 95.35.+d For years, there has been a lot of evidence about the missing matter in the Universe. It is known that the components of the Universe are radiation, baryons, neutrinos, etc. but observations show that their contribution is less than 5 % of the total mass of the Cosmos, in agreement with Big Bang Nucleosynthesis predictions. This suggests that there must exist a non-baryonic type of matter in galaxies and clusters of galaxies [1,2]. Recently, the observations of Ia-type supernovae [3,4] showed that there must exist another component that accelerates the expansion of the Universe. This new component must have a negative equation of state ω < −1/3, where p = ωρ [5]. The observations point out into a flat Universe filled with radiation, plus baryons, plus neutrinos, etc. contributing with ∼ 5%, a dark matter component with ∼ 25% and the so called dark energy contributing with ∼ 70% to the total mass of the Cosmos [6]. One of the most successful models until now is the Λ Cold Dark Matter (ΛCDM) model, where the dark energy is a cosmological constant [7]. However, some problems of this model has not been solved yet. First of all, if a cosmological constant exists, why is its contribution to the total matter of the same order of magnitude as baryons and cold dark matter?. This is the cosmic coincidence problem. Also, the suggested value for the cosmological constant appears well below the values predicted by particle physics. On the other hand, the existence of a cosmological constant leads to a strong fine tuning problem over the initial conditions of the Universe.These last facts open the possibility for the scalar fields as strong candidates to be the missing matter of the Universe [8][9][10][11]. A reliable model for dark energy is a fluctuating, inhomogeneous scalar field, rolling down a scalar potential, called Quintessence (Q) [15]. For this case, great effort has been done to determine the appropriate scalar potential that could explain current cosmological observations [9,10,13]. One example, is the pure exponential potential [9,13]. It has the advantages that it mimics the dominant density background and it appears naturally as a solution for a completely scalar dominated Universe [14]. But nucleosynthesis constraints require that the scalar field contribution be Ω Φ ≤ 0.2, which indicates that the scalar field would never dominate the Universe [9]. However, a special group of scalar potentials has been proposed in orde...

Scalar field dark matter: Head-on interaction between two structures

“…Because the excited states are unstable and decay in a short time scale we collide in the present task only ground state configurations. Once we account with these ground state data: i) we interpolated the wave function of such configuration centered at (0, z 0 ), ii) we place another of these equilibrium configuration at the point (0, −z 0 ), iii) we choose z 0 so that the two configurations are far enough one from the other (see below) and iv) resolved Poisson equation (2). Then we have initial data for two ground state equilibrium configurations in our axially symmetric domain.…”

“…An alternative to ameliorate these two problems consists in assuming that the dark matter is made of an ultralight spinless particle, the so called Scalar Field Dark Matter Model (SFDM). In the cosmological frame, the analysis of such hypothesis indicated that the power of structures could be controlled through a parameter in the model, that is, the mass of the scalar field representing the spinless particle [1,2,3,4]. Once the mass m of the boson is fixed the power spectrum suffers a cutt-off according to the mass of the smallest structure desired.…”

Scalar Field Dark Matter and Galaxy Formation

“…The SFDM model [6][7][8][9][10][11][12][13] assumes that both the dark matter and the dark energy are of scalar field nature. A particular model we have considered in the last years is the following: For the dark energy we adopt a quintessence field Ψ with a scalar potential of the formṼ (Ψ ) =Ṽ 0 sinh (α √ κ 0 Ψ ) β .…”

“…It has been shown that this quintessence potential is a reliable model for the dark energy, because of its asymptotic behavior [14]. Nevertheless, the main point of the SFDM model is to assume that the dark matter is also a scalar field Φ endowed with a self-interacting potential (see [11])…”

Brief History of Ultra-light Scalar Dark Matter Models

“…This interesting behavior of the SFDM is confirmed by the precise numerical studies [58] and makes the SFDM an ideal alternative for the CDM. This property alleviates the small scale problems of the CDM model [32,35,56,59]. Equating c 2 q k 2 with 4πGρ gives the quantum Jeans length scale [31,60,61] at the redshift z,…”