arXiv subjects

Jun-Ru Chen

Publications and source records attributed to Jun-Ru Chen.

4 recordsLinked to original sources

arXiv2026

Tidal Love numbers of multi-state Boson stars

In this paper, we calculate the tidal Love numbers of multi-state boson stars (MSBSs) composed of ground state and first excited state complex scalar fields. Under synchronized and nonsynchronized frequency conditions, the background solutions of MSBSs are classified into single-branch and double-branch types. The field functions, ADM mass, and binding energy of different solutions are discussed. We then calculate the quadrupolar ($\ell=2$) electric and magnetic tidal Love numbers for branches containing stable solutions. Our results show that the electric tidal Love numbers are initially positive and then suddenly transition to negative values. This phenomenon occurs when the parameters satisfy $\tilde{\mu}_1 > 0.891$ or $\tilde{\omega}_0 > 0.777$; for smaller values of these parameters, the electric Love numbers remain positive. The magnetic tidal Love numbers are always negative, with absolute values smaller than those of the electric tidal Love numbers.

gr-qc↗

arXiv2025

Proca stars and their frozen states in an infinite tower of higher-derivative gravity

In this work, we investigate the five-dimensional Proca star under gravity with the infinite tower of higher curvature corrections. We find that when the coupling constant exceeds a critical value, solutions with a frequency approaching zero appear. In the finite-order corrections case $n=2$ (Gauss-Bonnet gravity), the matter field and energy density diverge near the origin as $\omega\to 0$. In contrast, for $n\geq 3$, the divergence is efficiently suppressed, both the field and the energy density remain finite everywhere, and both the matter field and energy density remain finite everywhere. In the limit $\omega \to 0$, a class of horizonless frozen star solutions emerges, which are referred to ``frozen stars". Importantly, frozen stars contain neither curvature singularities nor event horizons. These frozen stars develop a critical horizon at a finite radius $r_c$, where $-g_{tt}$ and $1/g_{rr}$ approach zero. The frozen star is indistinguishable from that of an extremal black hole outside $r_c$, and its compactness can reach the extremal black hole value.

gr-qc↗

arXiv2024

Hayward spacetime with axion scalar field

In this work, we investigate a static spherically symmetric system in which Einstein gravity is minimally coupled with a self-interacting complex scalar field and a nonlinear electromagnetic field, referred to as Hayward axion stars. Employing numerical methods, we find that it essentially describes axion stars with the magnetic charge. In the absence of magnetic charge and with only the scalar field present, the system reduces to axion stars. We discover that when the magnetic charge $q$ exceeds a critical value, extreme solutions with frequencies $\omega$ approaching zero can be found and the critical horizon emerges. Within this horizon, the scalar field and energy density are highly concentrated and decrease precipitously at its boundary. The time component of the metric function approaches zero within this region, indicating that gravity is extremely intense, and time nearly ceases to flow. To an observer at infinity, the star appears to be frozen, hence we refer to these extreme solutions exhibiting a critical horizon as Hayward axion frozen stars. Furthermore, it is important to note that as $\omega \rightarrow 0$, the mass of the Hayward axion frozen star becomes independent of the decay constant and is only determined by the magnetic charge. Additionally, we find that the frozen star solutions possess two light rings. With an increase in the magnetic charge, these light rings move outward, while changes in the decay constant have little effect on their positions.

hep-th↗

arXiv2023

Tidal Love numbers of Axion stars

We investigate the tidal deformability of spherically symmetric axion stars on the stable branches, including the Newtonian and relativistic branches. The results suggest that on the stable branch, the electric Love numbers of axion star are positive, while the magnetic Love numbers are negative. On the Newtonian stable branch, the electric tidal Love numbers are much larger than the magnetic ones, while on the relativistic stable branch, they are slightly larger. Furthermore, the relativistic stable branch has much smaller tidal Love numbers than the Newtonian stable branch, indicating weaker deformability of axion stars on the relativistic stable branch. This could be attributed to the fact that on the relativistic branch, axion stars are more compact, resulting hardly distorted by tidal forces.

gr-qc↗