arXiv subjects

Yu-Shi Hao

Publications and source records attributed to Yu-Shi Hao.

5 recordsLinked to original sources

arXiv2026

Primordial black holes spin from cosmological first-order phase transitions

The stochastic bubble nucleation during cosmological first-order phase transitions leads to variations in the phase transition initiation times across different Hubble volumes, thereby generating non-Gaussian density perturbations in regions with delayed transitions. Based on the accumulation mechanism and the false vacuum island model . This paper investigates the spin angular momentum of primordial black holes formed from nonspherical collapse. By introducing the nucleation history integration method, without assuming a Gaussian distribution, we calculate the expectation values and variances of the semi-axis lengths of overdense ellipsoidal regions, combined with the statistical properties of the velocity shear tensor, we derive the quantitative relationship between the Kerr parameter $a_*$ describing black hole spin and the phase transition parameters , latent heat strength $\alpha$ and phase transition rate $\beta$. The study finds that the Kerr parameter increases with $\alpha$ and decreases with $\beta$; estimate the typical the magnitude of $a_*$ can reach $10^{-3}$, which is significantly higher than that of primordial black holes formed in the radiation-dominated era under peak theory, but still lower than that in a matter-dominated era.

astro-ph.CO↗

arXiv2024

Primordial black holes and curvature perturbations from false vacuum islands

Recently, much attention has been focused on the false vacuum islands that are flooded by an expanding ocean of true-vacuum bubbles slightly later than most of the other parts of the world. These delayed decay regions will accumulate locally larger vacuum energy density by staying in the false vacuum longer than those already transited into the true vacuum. A false vacuum island with thus acquired density contrast of a super-horizon size will evolve locally from radiation dominance to vacuum dominance, creating a local baby Universe that can be regarded effectively as a local closed Universe. If such density contrasts of super-horizon sizes can ever grow large enough to exceed the threshold of gravitational collapse, primordial black holes will form similar to those collapsing curvature perturbations on super-horizon scales induced by small-scale enhancements during inflation. If not, such density contrasts can still induce curvature perturbations potentially observable today. In this paper, we revisit and elaborate on the generations of primordial black holes and curvature perturbations from delayed-decayed false vacuum islands during asynchronous first-order phase transitions with fitting formulas convenient for future model-independent studies.

astro-ph.CO↗

arXiv2024

General backreaction force of cosmological bubble expansion

The gravitational-wave energy-density spectra from cosmological first-order phase transitions crucially depend on the terminal wall velocity of asymptotic bubble expansion when the driving force from the effective potential difference is gradually balanced by the backreaction force from the thermal plasma. Much attention has previously focused on the backreaction force acting on the bubble wall alone but overlooked the backreaction forces on the sound shell and shock-wave front, if any, which have been both numerically and analytically accomplished in our previous studies but only for a bag equation of state. In this paper, we will generalize the backreaction force on bubble expansion beyond the simple bag model.

hep-ph↗

arXiv2024

General bubble expansion at strong coupling

The strongly coupled system like the quark-hadron transition (if it is of first order) is becoming an active play yard for the physics of cosmological first-order phase transitions. However, the traditional field theoretic approach to strongly coupled first-order phase transitions is of great challenge, driving recent efforts from holographic dual theories with explicit numerical simulations. These holographic numerical simulations have revealed an intriguing linear correlation between the phase pressure difference (pressure difference away from the wall) to the nonrelativistic terminal velocity of an expanding planar wall, which has been reproduced analytically alongside both cylindrical and spherical walls from perfect-fluid hydrodynamics in our previous study but only for a bag equation of state. We also found, in our previous study, a universal quadratic correlation between the wall pressure difference (pressure difference near the bubble wall) to the nonrelativistic terminal wall velocity regardless of wall geometries. In this paper, we will generalize these analytic relations between the phase/wall pressure difference and terminal wall velocity into a more realistic equation of state beyond the simple bag model, providing the most general predictions so far for future tests from holographic numerical simulations of strongly coupled first-order phase transitions

hep-ph↗

arXiv2022

Cosmic inflation from broken conformal symmetry

A period of rapidly accelerating expansion is expected in the early Universe implemented by a scalar field slowly rolling down along an asymptotically flat potential preferred by the current data. In this paper, we point out that this picture of the cosmic inflation with an asymptotically flat potential could emerge from the Palatini quadratic gravity by adding the matter field in such a way to break the local gauged conformal symmetry in both kinetic and potential terms.

gr-qc↗