Non-Thermal Production of Dangerous Relics in the Early Universe

TL;DR

The paper demonstrates that non-thermal production of TeV-scale gravitational relics in the early Universe can be competitive with or exceed thermal production. It shows that scalar moduli can be produced by the expansion of spacetime, with a mass term $M_X^2 \approx m_X^2 + C_H H^2$, yielding a potentially large abundance unless $\xi$ is near 1/6 or $C_H$ is large, which can push the reheating bound down to around $100$ GeV. It also analyzes gravitino production, revealing that helicity-1/2 gravitinos can be efficiently generated after inflation, with yields that can exceed thermal expectations by several orders of magnitude in realistic inflation models. Collectively, these results indicate that non-thermal cosmological production of gravitational relics must be incorporated into viable SUSY and string-inspired cosmologies, significantly impacting reheating and early-Universe constraints.

Abstract

Many models of supersymmetry breaking, in the context of either supergravity or superstring theories, predict the presence of particles with weak scale masses and Planck-suppressed couplings. Typical examples are the scalar moduli and the gravitino. Excessive production of such particles in the early Universe destroys the successful predictions of nucleosynthesis. In particular, the thermal production of these relics after inflation leads to a bound on the reheating temperature, T_{RH} < 10^9 GeV. In this paper we show that the non-thermal generation of these dangerous relics may be much more efficient than the thermal production after inflation. Scalar moduli fields may be copiously created by the classical gravitational effects on the vacuum state. Consequently, the new upper bound on the reheating temperature is shown to be, in some cases, as low as 100 GeV. We also study the non-thermal production of gravitinos in the early Universe, which can be extremely efficient and overcome the thermal production by several orders of magnitude, in realistic supersymmetric inflationary models.

Figures (4)

• Figure 1: The ratio $n_X/s$ as a function of $C_H$ for scalar moduli particles $X$ minimally coupled to gravity and with squared masses $M_X^2=m_X^2+C_HH^2$. In the figure $m_X$ is expressed in units of the inflaton mass $m_I$, and $T_{RH}=10^9$ GeV, $m_I=10^{13}$ GeV.
• Figure 2: Ratio of the energy density in scalar moduli particles minimally coupled to gravity to the critical density, as a function of $C_H$. Conventions are the same as in fig. 1.
• Figure 3: The ratio $n_X/s$ of scalar moduli particles as a function of the parameter $\xi$, for $C_H=0$. The solid, long-dashed and short-dashed lines correspond to $m_X/m_I=0.001$, $m_X/m_I=0.01$ and $m_X/m_I=0.1$, respectively.
• Figure 4: Ratio of the energy density in scalar moduli particles to the critical density as a function of $\xi$, for $C_H=0$. The solid, long-dashed and short-dashed lines correspond to $m_X/m_I=0.001$, $m_X/m_I=0.01$ and $m_X/m_I=0.1$, respectively.