arXiv subjects

Leihua Liu

Publications and source records attributed to Leihua Liu.

3 recordsLinked to original sources

arXiv2024

Appearances are deceptive: Can graviton have a mass?

We study the dynamics of linear gravitational perturbations on cosmological backgrounds of massive fermionic fields. We observe that, when gravitational and matter action are expanded to quadratic order in gravitational perturbations on cosmological backgrounds, the graviton appears to have an off-shell mass. We derive a consistent set of two equations for the evolution of linear classical and quantum gravitational perturbations on general cosmological backgrounds, and demonstrate that the graviton mass disappears at the level of equations of motion (on-shell). In the case we consider the expansion of the Universe is driven by the one-loop backreaction of fermions, and the dynamical gravitons evolve on the same background. These equations govern the evolution of linear gravitational perturbations on general cosmological matter backgrounds. A concrete one-loop calculation is performed for the simple case of massive Dirac fermions when the temperature of the cosmological fluid changes adiabatically when compared with the expansion rate of the Universe.

hep-th↗

arXiv2015

Emergent observable deSitter space from an Equation of Motion

We propose that de-Sitter space-time originates from Gaussian distribution in a quantum harmonic oscillator system. This equation associates with a massless Klein-Gordon equation. We discover that every excited states of quantum oscillator also contributes for the de-Sitter space-time. The observable part of metric is related to energy scale and excited quantum number $n$. As for off-diagonal elements, it comes from the superposition of quantum mechanics. These elements can cause in-homogeneous at the very beginning of universe.

hep-th↗

arXiv2015

The Helicity Amplitude for $1/2$ and $3/2^+$ Baryon in the Pseudo-Meson Photoproduction in the Quark Model

We derive the separate helicity amplitudes involving the partial wave analysis in the process of pseudo-scalar meson photon productions with $J^P=3/2^+$, which is independent on model. According to parity, the general amplitude in the case of $J^P=1/2^-$ is given out. We prove this general amplitude is corresponding to the situation of $λ=-1$ as adopting the circular polarization. Finally, the formulas of scattering amplitudes involving the photon-meson production with $J^P=3/2^+$ are obtained from the chiral quark model.

hep-ph↗