The Early Mirror Universe: Inflation, Baryogenesis, Nucleosynthesis and Dark Matter

TL;DR

The paper investigates a parity-mally mirrored universe where a copy of the Standard Model exists and interacts with the visible sector mainly through gravity. By positing a lower reheating temperature in the mirror sector, it derives independent thermal histories and explores how GUT and electroweak baryogenesis can yield a larger mirror baryon asymmetry, potentially making mirror baryons the dominant dark matter component. It further shows that primordial nucleosynthesis in the mirror world predicts a much higher mirror helium abundance, Y'_4, than in the ordinary world. The authors discuss consequences for structure formation, including self-interacting mirror baryons, and outline observational signatures in the CMB, large-scale structure, and microlensing that could test the scenario.

Abstract

There can exist a parallel `mirror' world which has the same particle physics as the observable world and couples the latter only gravitationally. The nucleosynthesis bounds demand that the mirror sector should have a smaller temperature than the ordinary one. By this reason its evolution should be substantially deviated from the standard cosmology as far as the crucial epochs like baryogenesis, nucleosynthesis etc. are concerned. Starting from an inflationary scenario which could explain the different initial temperatures of the two sectors, we study the time history of the early mirror universe. In particular, we show that in the context of the GUT or electroweak baryogenesis scenarios, the baryon asymmetry in the mirror world should be larger than in the observable one and in fact the mirror baryons could provide the dominant dark matter component of the universe. In addition, analyzing the nucleosynthesis epoch, we show that the mirror helium abundance should be much larger than that of ordinary helium. The implications of the mirror baryons representing a kind of self-interacting dark matter for the large scale structure formation, the CMB anysotropy, the galactic halo structures, microlensing, etc. are briefly discussed.

Figures (4)

• Figure 1: Panel A. The combination $x^3F(kx^2,k_c)$ as a function of $k$ for $k_c=10^4$ and $x=0.6,\;0.1,\;0.01$ (dash). The solid curve corresponding to $x=1$ in fact measures the possible BA in the ordinary world, $F(k,k_c)=(g_s/\epsilon)B(k)$. Panel B. The curves confining the parameter region in which $\beta=\Omega'_B/\Omega_B$ varies from 1 to 100, for $x=0.6$ (solid) and for $x=0.01$ (dash). The parameter area above thick solid curve corresponds to $F(k,k_c) < 10^{-6}$ and it is excluded by the observable value of $\eta$.
• Figure 2: The contours of $\beta =\Omega_B'/\Omega_B$ in the plane of the parameters $x$ and $D$, corresponding to $\beta =1,10$ and 100 from top to bottom.
• Figure 3: The primordial mirror $^4$He mass fraction as a function of $x$. The dashed curve represents the approximate result of eq. (\ref{['helium']}). The solid curves obtained via exact numerical calculation correspond, from bottom to top, to $\eta'$ varying from $10^{-10}$ to $10^{-6}$.
• Figure 4: The M-photon decoupling redshift $1+z_{dec}'$ as a function of $x$ (solid). The long-dash line marks the ordinary decoupling redshift $1+z_{\rm dec} = 1100$. We also show the matter-radiation equality redshift $1+z_{\rm eq}$ and the mirror Jeans-horizon mass equality redshift $1+z'_c$, for the cases $\Omega_m h^2 =0.2$ (respectively lower dash and lower dott) and $\Omega_m h^2=0.6$ (upper dash and dott).