General Relativity and Quantum Cosmology (gr-qc)

Abstract: In this work, we study the rotating wormhole geometries supported by a three-form field. We demonstrate for particular choices of parameters that it is possible for the matter fields threading the wormhole to satisfy the null and weak energy conditions throughout the spacetime, when the three-form field is present. In this case, the form field is interpreted as supporting the wormhole and all the exoticity is confined to it. Thus, the three-form curvature terms, which may be interpreted as a gravitational fluid, sustain these wormhole geometries. Additionally, we also address the ergoregion of the solutions.

Abstract: We numerically construct the asymptotically flat solutions of hairy black holes supported by a symmetric inverted Mexican hat potential with a local minimum and two degenerate global maxima of a real scalar field that contains a quartic self-interaction term. The solutions of hairy black holes emerge from the Schwarzschild black hole when the non-trivial scalar field exists outside the event horizon. Therefore, we perform a comprehensive study on the properties of the hairy black holes such as the area of horizon, the Hawking temperature, the innermost stable circular orbit, the photon sphere, etc. We also numerically study their linear stability in the mode analysis, hence finding that they are unstable against the linear perturbation.

Abstract: Understanding the light ring, one kind fundamental orbit, shall provide us with novel insight into the astronomical phenomena, such as the ringdown of binary merger and shadow of black holes. Recently, topological approach has preliminarily demonstrated its potential advantages on the properties of the light rings. However, for the black holes without $\mathbb{Z}_2$ symmetry and extremal spinning black holes are remained to be tested. In this paper, we aim at these two issues. Due to the NUT charge, the Kerr-Newman Taub-NUT solution has no $\mathbb{Z}_2$ symmetry. By constructing the corresponding topology for the non-extremal spinning black holes, we find the topological number keeps unchanged. This indicates that $\mathbb{Z}_2$ symmetry has no influence on the topological number, while it indeed affects the locations of the light rings and deviates them off the equatorial plane. For the extremal spinning black holes, we find its topology is critically dependent of the leading term of the vector's radial component at the zero point of its angular component on the black hole horizon. The findings state that there exists a topological phase transition, where the topological number changes, for the prograde light rings. While no phase transition occurs for the retrograde light rings. Our study uncovers some universal topological properties for the extremal and non-extremal spinning black holes with or without $\mathbb{Z}_2$ symmetry. It also has enlightening significance on understanding the light rings in a more general black hole background.

Abstract: Binary black-hole mergers up to the third observing run with the minimum false alarm rate smaller than $10^{-5}\,{\rm yr}^{-1}$ tell us that the mass ratio of two black holes follows $m_2/m_1=0.723$ with the chance probability of 0.00301% for $M_{chirp} > 18 M_{\odot}$ where $M_{chirp}$ ($= (m_1m_2)^{3/5}/(m_1+m_2)^{1/5}$) is called the chirp mass of binary with masses $m_1$ and $m_2$ ($ < m_1$). We show that the relation of $m_2/m_1=0.723$ is consistent if the binaries consist of population III stars which are the first stars in the universe. On the other hand, it is found for $M_{chirp} < 18 M_{\odot}$ that the mass ratio follows $m_2/m_1=0.601$ with the chance probability of 0.117% if we ignore GW190412 with $m_2/m_1\sim 0.32$. This suggests the different origin from that for $M_{chirp }> 18 M_{\odot}$.

Abstract: We present an estimation of the noise induced by scattered light inside the main arms of the Einstein Telescope (ET) gravitational wave detector. Both ET configurations for high- and low-frequency interferometers are considered, for which we propose baffle layouts. The level of scattered light and the ET laser beam clipping losses are intimately related to the baffle inner aperture. We discuss how this translates into minimum requirements on the vacuum pipe radius, a critical parameter in the ET design. The noise estimations are computed using analytical calculations complemented with numerical tools, and depend on a number of baseline parameters we use as input in the calculations. We conclude that the scattered light noise can be maintained at acceptable levels such that does not compromise the ET performance, provided some requirements are met.

Abstract: In this study, we investigate the real-time dynamics during the spontaneous deformation of an unstable spherical black hole in asymptotically anti-de Sitter (AdS) spacetime. For the initial value, the static solutions with spherical symmetry are obtained numerically, revealing the presence of a spinodal region in the phase diagram. From the linear stability analysis, we find that only the central part of such a thermodynamically unstable spinodal region leads to the emergence of a type of axial instability. To trigger the dynamical instability, an axial perturbation is imposed on the scalar field. As a result, by the fully nonlinear dynamical simulation, the spherical symmetry of the gravitational system is broken spontaneously, leading to the formation of an axisymmetric black hole.

Abstract: An analytical model of a parabolic screen illuminating a black hole is constructed. This makes it possible to naturally avoid the occurrence of edge effects associated with photons moving along the plane of the screen. The temperature distribution along the radius of the screen corresponds to that for a relativistic disk (Novikov-Thorne disk). It is shown that the structure of the emerging black hole shadow differs significantly from the case when the photon source is a remote screen, since in the model considered, the photons subjected to strong gravitational lensing of the black hole are emitted by the "back side" of the screen, which would not be visible in the absence of a black hole. In the thin screen approximation, the shadow of a Schwarzschild black hole has been constructed in cases when the angle between the axis of symmetry of the illuminating screen and the direction towards the observer is 5, 30, 60, and 80 degrees. For the Kerr black hole, images are shown for angles of 60 and 80 degrees.