Medina Reus, ElenaMartínez Alonso, Luis2023-06-172023-06-172020-11-132470-001010.1103/PhysRevD.102.103517https://hdl.handle.net/20.500.14352/7615© 2020 American Physical Society. The financial support of the Spanish Ministerio de Ciencia, Innovacion y Universidades under Projects No. FIS2015-63966-P and No. PGC2018-094898-B-I00 is gratefully acknowledged. We thank Professor Gabriel Alvarez Galindo for fruitful discussions.Single-field inflaton models in the kinetic dominance period admit formal solutions given by generalized asymptotic expansions called psi series. We present a method for computing psi series for the Hubble parameter as a function of the inflaton field in the Hamilton-Jacobi formulation of inflaton models. Similar psi series for the scale factor, the conformal time, and the Hubble radius are also derived. They are applied to determine the value of the inflaton field when the inflation period starts and to estimate the contribution of the kinetic dominance period to calculate the duration of inflation. These psi series are also used to obtain explicit two-term truncated psi series near the singularity for the potentials of the Mukhanov-Sasaki equation for curvature and tensor perturbations. The method is illustrated with wide families of inflaton models determined by potential functions combining polynomial and exponential functions, as well as with generalized Starobinsky models.engjournal articlehttp://dx.doi.org/10.1103/PhysRevD.102.103517https://journals.aps.orgopen access51-73Inflationary universeAnalytic structureSpectrumFlatnessHorizon.Física-Modelos matemáticosFísica matemática