Non-thermal Dark Matter and the Moduli Problem in String Frameworks

TL;DR

This work analyzes the cosmological moduli and gravitino problems within the G2-MSSM arising from M theory on G2 manifolds. It shows that late decays of moduli rehear the universe in a way that dilutes gravitino production and yields non-thermal Wino dark matter with the observed relic density, largely determined by the light moduli decays. A careful accounting of moduli masses, decay widths, and entropy production demonstrates that BBN is preserved and the gravitino problem is avoided, while the LSP relic density lies near the observed value for natural choices of microscopic parameters. The results provide a concrete, predictive string/M theory framework in which non-thermal production dominates DM and moduli dynamics address longstanding cosmological issues.

Abstract

We address the cosmological moduli/gravitino problems and the issue of too little thermal but excessive non-thermal dark matter from the decays of moduli. The main examples we study are the G2-MSSM models arising from M theory compactifications, which allow for a precise calculation of moduli decay rates and widths. We find that the late decaying moduli satisfy both BBN constraints and avoid the gravitino problem. The non-thermal production of wino LSPs, which is a prediction of G2-MSSM models, gives a relic density of about the right order of magnitude.

Figures (5)

• Figure 1: The contour plot of the relic density in the $G_2$-MSSM in the $D_{X_i}-m_{3/2}$ plane for two (large and small) values of $|\delta|$ which correspond to two (large and small) values of $\gamma$. The solid lines are for $\delta=-3$ (a correction to $\alpha^{-1}_{unif}$ of order $3/26$), and the dashed lines for $\delta=-4.5$.
• Figure 2: The LSP relic density for the $G_2$-MSSM plotted as a function of the reheat temperature of the light moduli. The solid line assumes no coannihilation with charged Winos; the dashed line includes coannihilation with charged Winos.
• Figure 3: The LSP relic density in the $G_2$-framework plotted as a function of the mixing angle of Bino and Wino for $M_2=100$GeV.
• Figure 4: Left: distribution of the average of ${\cal B}^{-2}(\vec{X}_N'\cdot \vec{X}_i)^2$. Right: distribution of the average of the weighted dot product $(\vec{X}_N"'\cdot \vec{X}_i)^2$.
• Figure 5: Left: distribution of $D_{X_i}$. Right: distribution of moduli branching ratio to LSP.