arXiv subjects

Chenhuan Wang

Publications and source records attributed to Chenhuan Wang.

5 recordsLinked to original sources

arXiv2026

Ultra-slow-roll Inflation with Non-perturbative Non-Gaussianity and Scalar Induced Gravitational Waves

An ultra-slow-roll phase during inflation could potentially produce the right abundance of primordial black holes (PBHs) for them to form all of dark matter (DM). We consider such a scenario, carefully treating the transitions from slow to ultra slow roll inflation and back, using a parametrisation of the inflaton potential that can describe inflation from the time when CMB scales crossed out of the horizon until its end. A $δN$ analysis shows that this model can possess $O(1)$ non-Gaussianity. When computing the primordial black hole abundance, we keep the full non-linear relation between curvature perturbations and the density contrast and consider the non-Gaussianity to all orders. We find that $O(1)$ non-Gaussianity is sufficient to enhance the PBH abundance by orders of magnitude, leading to reduced gravitational wave (GW) signals for fixed PBH abundance. The signal to noise ratio is computed for future gravitational wave observatories. We find that, in spite of the reduced strength, the GW signal is well above the sensitivity of LISA if PBHs form a significant component of DM.

astro-ph.CO↗

arXiv2026

Graviton Production from Inflaton Condensate: Boltzmann vs Bogoliubov

We study graviton production from an oscillating inflaton condensate during reheating by systematically comparing Boltzmann and Bogoliubov descriptions for inflaton potentials of the form $V(ϕ)\proptoϕ^n$ around the minimum. The Bogoliubov framework provides a unified description of graviton production, capturing both perturbative and non-perturbative effects across short and long wavelengths, whereas the Boltzmann approach is restricted to perturbative production at short wavelengths. For the quadratic case ($n=2$), we find that the two approaches yield identical graviton spectra at short wavelengths, indicating that the Boltzmann treatments fully captures perturbative gravitational production in this regime. For steeper potentials ($n>2$), however, we identify a sizable contribution arising from the non-adiabatic transition between inflation and reheating. This component is naturally incorporated in the Bogoliubov formalism but absent in the Boltzmann description, and we show that it is important over a broad range of momenta. We derive analytic approximations within both frameworks that clarify the physical origin and scaling behavior of the spectrum. Our results delineate the regime of validity of Boltzmann approaches and show that, for steeper inflaton potentials, graviton production is governed by non-adiabatic transition dynamics for which the Bogoliubov formalism provides the most appropriate description.

hep-ph↗

arXiv2026

Accretion Effects on Primordial Black Hole Reheating Constraints

In this work, we study the effects of accretion on the primordial black hole (PBH) reheating scenario. PBHs could form from primordial fluctuations. If they have the right mass and abundance, they could dominate the Universe and complete the reheating entirely through Hawking radiation. We find accretion effects on the BH can not only increase the BH mass, but also prolong such early matter domination. The consequence of the accretion is further investigated using isocurvature induced gravitational waves (GWs), which are generated right after the sudden evaporation of the BHs from the oscillation of the gravitational potential. Big Bang nucleosynthesis limits on the energy density of the GWs put important constraints on the PBH domination scenario. Inclusion of accretion shifts such constraints significantly towards smaller formation mass and smaller initial abundance. Furthermore, the PBH could undergo mergers leading to extended mass functions. We find similar shifts in the allowed parameters with the inclusion of accretion for the merger constraint. We find the constraints from isocurvature GWs typically stronger than the constraints from mergers.

astro-ph.CO↗

arXiv2025

Inflaton Self Resonance, Oscillons, and Gravitational Waves in Small Field Polynomial Inflation

In this work, we investigate the post-inflationary dynamics of a simple single-field model with a renormalizable inflaton potential featuring a near-inflection point at a field value $ϕ_0$. Due to the concave shape of the scalar potential, the effective mass of the inflaton becomes imaginary during as well as for some period after slow-roll inflation. As a result, in the initial reheating phase, where the inflaton oscillates around its minimum with a large amplitude, some field fluctuations grow exponentially; this effect becomes stronger at smaller $ϕ_0$. This aspect can be analyzed using the Floquet theorem. We also analytically estimate the backreaction time after which the perturbations affect the evolution of the average inflaton field. In order to fully analyze this non-perturbative regime, we perform a (classical) lattice simulation, which reveals that the exponential growth of field fluctuations can fragment the system. This leads to a large amount of non-Gaussianity at very small scales, but the equation of state remains close to matter-like. The evolution of the background field throughout the fragmentation phase can be understood using the Hartree approximation. For sufficiently small $ϕ_0$ soliton-like objects, called oscillons in the literature, are formed. This leads to areas with high local over-density, $δρ\gg \barρ$ where $\barρ$ is the average energy density. We speculate that this could lead to the formation of light primordial black holes, with lifetime $\gtrsim 10^{-19} \text{sec}$. Other possibly observational consequences, in particular gravitational waves in the $\text{MHz} - \text{GHz}$ range, are discussed as well. Although a complete analytical study is difficult in our case, we obtain a power law scaling for the potential observables on $ϕ_0$.

astro-ph.CO↗

arXiv2024

Gravitational Dark Matter Production in Supergravity $α$-Attractor Inflation

We consider gravitational particle production (GPP) of dark matter (DM) under a supergravity framework, where the $α$-attractor inflation model is used. The particle spectrum is computed numerically and the DM number density is obtained. We show how the DM mass, gravitino mass and inflation model parameters modify the results, and find the reheating temperature which leads to sufficient DM production. In our setup, supergravity corrections suppress the efficiency of GPP, and make the isocurvature constraint much weaker compared with the normal case. With tensor-to-scalar ratio ranging from $10^{-3}-10^{-4}$ and DM mass from $10^{-2} m_ϕ- m_ϕ$, the required reheating temperature should be around $10^3 \textrm{GeV} - 10^7 \textrm{GeV}$.

hep-ph↗