arXiv subjects

Qin Fei

Publications and source records attributed to Qin Fei.

6 recordsLinked to original sources

arXiv2023

Constraints on the Primordial Curvature Power Spectrum by Pulsar Timing Array Data: A Polynomial Parameterization Approach

The recent stochastic signal observed jointly by NANOGrav, PPTA, EPTA, and CPTA can be accounted for by scalar-induced gravitational waves (SIGWs). The source of the SIGWs is from the primordial curvature perturbations, and the main contribution to the SIGWs is from the peak of the primordial curvature power spectrum. To effectively model this peak, we apply the Taylor expansion to parameterize it. With the Taylor expansion parameterization, we apply Bayesian methods to constrain the primordial curvature power spectrum based on the NANOGrav 15-year data set. The constraint on the primordial curvature power spectrum possesses a degree of generality, as the Taylor expansion can effectively approximate a wide range of function profiles.

gr-qc↗

arXiv2023

Constraints on primordial curvature spectrum from primordial black holes and scalar-induced gravitational waves

The observational data of primordial black holes and scalar-induced gravitational waves can constrain the primordial curvature perturbation at small scales. We parameterize the primordial curvature perturbation by a broken power law form and find that it is consistent with many inflation models that can produce primordial black holes, such as nonminimal derivative coupling inflation, scalar-tensor inflation, Gauss-Bonnet inflation, and K/G inflation. The constraints from primordial black holes on the primordial curvature power spectrum with the broken power law form are obtained, where the fraction of primordial black holes in dark matter is calculated by the peak theory. Both the real-space top-hat and the Gauss window functions are considered. The constraints on the amplitude of primordial curvature perturbation with Gauss window function are around three times larger than those with real-space top-hat window function. The constraints on the primordial curvature perturbation from the NANOGrav 12.5yrs data sets are displayed, where the NANOGrav signals are assumed as the scalar-induced gravitational waves, and only the first five frequency bins are used.

astro-ph.CO↗

arXiv2020

The Reconstruction of Non-Minimal Derivative Coupling Inflationary Potentials

We derive the reconstruction formulae for the inflation model with the non-minimal derivative coupling term. If reconstructing the potential from the tensor-to-scalar ratio, we could obtain the potential without using the high friction limit. As an example, we reconstruct the potential from the parametrization $r=8α/(N+β)^γ$, which is a general form of the $α$-attractor. The reconstructed potential has the same asymptotic behavior as the T- and E-model if we choose $γ=2$ and $α\ll1$. We also discuss the constraints from the reheating phase preceding the radiation domination by assuming the parameter $w_{re}$ of state equation during reheating is a constant. The scale of big-bang nucleosynthesis could put a up limit on $n_s$ if $w_{re}=2/3$ and a low limit on $n_s$ if $w_{re}=1/6$.

gr-qc↗

arXiv2018

Constant-roll tachyon inflation and observational constraints

For the constant-roll tachyon inflation, we derive the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts and the tensor to scalar ratio up to the first order by using the method of Bessel function approximation. The derived $n_s-r$ results for the constant-roll inflation are also compared with the observations, we find that only one constant-roll inflation is consistent with the observations and observations constrain the constant-roll inflation to be slow-roll inflation. The tachyon potential is also reconstructed for the constant-roll inflation which is consistent with the observations.

gr-qc↗

arXiv2017

The reconstruction of tachyon inflationary potentials

We derive a lower bound on the field excursion for the tachyon inflation, which is determined by the amplitude of the scalar perturbation and the number of $e$-folds before the end of inflation. Using the relation between the observables like $n_s$ and $r$ with the slow-roll parameters, we reconstruct three classes of tachyon potentials. The model parameters are determined from the observations before the potentials are reconstructed, and the observations prefer the concave potential. We also discuss the constraints from the reheating phase preceding the radiation domination for the three classes of models by assuming the equation of state parameter $w_{re}$ during reheating is a constant. Depending on the model parameters and the value of $w_{re}$, the constraints on $N_{re}$ and $T_{re}$ are different. As $n_s$ increases, the allowed reheating epoch becomes longer for $w_{re}=-1/3$, 0 and $1/6$ while the allowed reheating epoch becomes shorter for $w_{re}=2/3$.

gr-qc↗

arXiv2016

Inflationary models with non-minimally derivative coupling

We derive the general formulae for the the scalar and tensor spectral tilts to the second order for the inflationary models with non-minimally derivative coupling without taking the high friction limit. The non-minimally kinetic coupling to Einstein tensor brings the energy scale in the inflationary models down to be sub-Planckian. In the high friction limit, the Lyth bound is modified with an extra suppression factor, so that the field excursion of the inflaton is sub-Planckian. The inflationary models with non-minimally derivative coupling are more consistent with observations in the high friction limit. In particular, with the help of the non-minimally derivative coupling, the quartic power law potential is consistent with the observational constraint at 95\% CL.

gr-qc↗