Accelerated expansion of the Universe in the Presence of Dark Matter Pressure

TL;DR

This paper investigates whether dark matter pressure can influence the expansion history of the Universe. It uses the DM EOS $P_{DM}=P_{DM}( ho_{DM})$ inferred from galaxy rotation curves (Barranco), derives the DM density evolution via $d(\rho_{DM} a^3)/da = -(3/c^2) P_{DM} a^2$ and solves for $\rho_{DM}(a)$, then computes $H(a)$ from $H^2(a) = (8πG/3)(\rho_{DM}(a) + \rho_{DE})$ in a flat FRW model. Nonzero DM pressure raises $H(a)$ at all redshifts, increases the growth rate of the scale factor, and makes the deceleration parameter more negative for $a>1$, while luminosity-distance observables $d_L(z)$ remain largely unaffected. Including DM pressure in cosmological modeling could help explain part of the observed acceleration without conflicting with distance measurements, underscoring the need to consider DM pressure in fits to cosmological data.

Abstract

Expansion dynamics of the Universe is one of the important subjects in modern cosmology. The dark energy equation of state determines this dynamics so that the Universe is in an accelerating phase. However, the dark matter can also affect the accelerated expansion of the Universe through its equation of state. In the present work, we explore the expansion dynamics of the Universe in the presence of dark matter pressure. In this regard, applying the dark matter equation of state from the observational data related to the rotational curves of galaxies, we calculate the evolution of dark matter density. Moreover, the Hubble parameter, history of scale factor, luminosity distance, and deceleration parameter are studied while the dark matter pressure is taken into account. Our results verify that the dark matter pressure leads to the higher values of the Hubble parameter at each redshift and the expansion of the Universe grows due to the DM pressure.

Figures (12)

• Figure 1: Dark matter EOS related to the galaxy U5750 with the parameters ${\rho}_0=0.31\ GeV/cm^3$ and $p_0=1.1\times 10^{-8} \ GeV/cm^3$ and $\chi^2_{min}/d.o.f.=0.01$, Barranco. $\rho_c$ denotes the critical density of the Universe.
• Figure 2: Evolution of DM density, $\rho_{DM}(a)$, versus the cosmological scale factor, $a$, for two cases of zero pressure DM (ZPDM) and non zero pressure DM (NZPDM).
• Figure 3: Hubble parameter versus the cosmological scale factor, $a$, for two cases of ZPDM and NZPDM. Besides, $H_0$ denotes the present day value of the Hubble parameter.
• Figure 4: Hubble parameter versus the redshift, z, in two cases of ZPDM and NZPDM and the observational data from the median $D4000_n - z$ relations Moresco.
• Figure 5: Same as Fig. \ref{['fig3']} but for the observational data from the upper envelope Moresco.