学术文献库

In a model of spontaneous scalarization of neutron stars proposed by Damour and Esposite-Farese, a general relativistic branch becomes unstable to trigger tachyonic growth of a scalar field $ϕ$ toward a scalarized branch. Applying this scenario to cosmology, there is fatal tachyonic instability of $ϕ$ during inflation and matter dominance being incompatible with solar-system constraints on today's field value $ϕ_0$. In the presence of a four-point coupling $g^2 ϕ^2 χ^2/2$ between $ϕ$ and an inflaton field $χ$, it was argued by Anson et al. that a positive mass squared heavier than the square of a Hubble expansion rate leads to the exponential suppression of $ϕ$ during inflation and that $ϕ_0$ can remain small even with the growth of $ϕ$ after the radiation-dominated epoch. For several inflaton potentials approximated as $V(χ)=m^2 χ^2/2$ about the potential minimum, we study the dynamics of $ϕ$ during reheating as well as other cosmological epochs in detail. For certain ranges of the coupling $g$, the homogeneous field $ϕ$ can be amplified by parametric resonance during a coherent oscillation of the inflaton. Incorporating the backreaction of created particles under a Hartree approximation, the maximum values of $ϕ$ reached during preheating are significantly smaller than those obtained without the backreaction. We also find that the minimum values of $g$ consistent with solar system bounds on $ϕ$ at the end of reheating are of order $10^{-5}$ and hence there is a wide range of acceptable values of $g$. Thus, the scenario proposed by Anson et al. naturally leads to the viable cosmological evolution of $ϕ$ consistent with local gravity constraints, without modifying the property of scalarized neutron stars.