Running Kinetic Inflation

TL;DR

Introducing running kinetic inflation, the authors show that a field-dependent kinetic term flattening the potential enables chaotic inflation in supergravity. The canonical inflaton dynamics yield a power-law potential during inflation and a steeper form afterwards, with a kination epoch that can enhance gravity waves while suppressing gravitino problems due to light inflaton masses post-SUSY breaking. The framework naturally links to the nMSSM, allowing Higgs-mediated reheating and inflatino dark matter, and it makes testable predictions for the spectral index and tensor modes, as well as potential collider signals. Overall, the model provides a coherent, testable picture that connects high-scale inflation to SUSY phenomenology and gravitational-wave observables.

Abstract

We study a recently proposed running kinetic inflation model in which the inflaton potential becomes flat due to rapid growth of the kinetic term at large inflaton field values. As concrete examples, we build a variety of chaotic inflation models in supergravity with e.g. quadratic, linear, and fractional-power potentials. The power of the potential generically increases after inflation, and the inflaton is often massless at the potential minimum in the supersymmetric limit, which leads to many interesting phenomena. First, the light inflaton mass greatly relaxes severe thermal and non-thermal gravitino problems. Secondly, the kination epoch is naturally present after inflation, which may enhance the gravity waves. Thirdly, since the inflaton is light, it is likely coupled to the Higgs sector for successful reheating. The inflaton and its superpartner, inflatino, may be produced at the LHC. Interestingly, the inflatino can be dark matter, if it is the lightest supersymmetric particle.

Figures (7)

• Figure 1: The trajectories generated by the symmetry transformation (\ref{['sym']}) for $n=2$ (left) and $n=3$ (right). They correspond to the contours of ${\rm Im}[\phi^n-\phi^{\dag n}] = 0$, $0.2$, $1$, and $2$, respectively. In the region of $|\phi| \gtrsim 1$, each contour corresponds to an inflationary trajectory. It depends on the interactions in the Kähler potential which trajectory is chosen. See the text for details.
• Figure 2: The bird's-eye view of the scalar potential $V(\phi)$ given by Eq. (\ref{['V']}) with $n=m=2$ and $c_1=i$. The flat direction corresponding to the inflationary trajectory is indicated by the red arrow.
• Figure 3: The coupling ${\hat{\lambda}}$, which accounts for the observed density perturbtion, as a function of $2m/n$ for the e-foldings $N = 50$ and $60$.
• Figure 4: The scalar potential near the origin for $m\geq 2$ with respect to the canonically normalized fields $\tilde{\phi}$ and $\hat{\phi}$. The mass term about the origin represents the soft SUSY breaking mass. We define $\tilde{\phi}_{\rm b} = \kappa^{n/(2n-2)}$ and $\tilde{\phi}_{\rm e} = (m_{3/2}\kappa^{m/2}/\lambda)^{1/(m-1)}$.
• Figure 5: The inflationary trajectory for $n=m$ and $c_1 = -i$ in the ${\hat{\phi}} = \phi^2$ plane. During inflation with $|{\hat{\phi}}| > 1$, $Im[\hat{\phi}]$ is stabilized at $1$. After inflation the inflaton acquires a large angular momentum.