arXiv subjects

Hua-Kai Deng

Publications and source records attributed to Hua-Kai Deng.

6 recordsLinked to original sources

arXiv2020

Neutron Star as a Mirror for Gravitational Waves

Gravitational wave (GW) has become one of the most active fields in physics and astronomy since the first direct detection of GW event in 2015. As is well known, multiple images of GW events are possible through the gravitational lenses. Here, we propose a novel mirror imaging mechanism for GW events different from the gravitational lens. In the literature, the superconductor was predicted to be highly reflective mirror for GWs. It is well known that neutron stars exhibit superconductivity and superfluidity. In this work, we predict that there are two types of GW mirror imaging phenomena caused by the neutron star located in Milky Way or the same host galaxy of GW source, which might be detected within a life period of man (namely the time delay $Δt$ can be a few years to a few tens of years). It is expected to witness this predicted GW mirror imaging phenomenon in the near future. In the long term, the observations of this novel GW mirror imaging phenomenon might help us to find numerous neutron stars unseen by other means, and learn more about the complicated internal structures of neutron stars, as well as their equations of state.

gr-qc↗

arXiv2020

Cosmic Anisotropy and Fast Radio Bursts

In the recent years, the field of fast radio bursts (FRBs) is thriving and growing rapidly. It is of interest to study cosmology by using FRBs with known redshifts. In the present work, we try to test the possible cosmic anisotropy with the simulated FRBs. In particular, we only consider the possible dipole in FRBs, rather than the cosmic anisotropy in general, while the analysis is only concerned with finding the rough number of necessary data points to distinguish a dipole from a monopole structure through simulations. Noting that there is no a large sample of actual data of FRBs with known redshifts by now, simulations are necessary to this end. We find that at least 2800, 190, 100 FRBs are competent to find the cosmic dipole with amplitude 0.01, 0.03, 0.05, respectively. Unfortunately, even 10000 FRBs are not competent to find the tiny cosmic dipole with amplitude of ${\cal O}(10^{-3})$. On the other hand, at least 20 FRBs with known redshifts are competent to find the cosmic dipole with amplitude 0.1. We expect that such a big cosmic dipole could be ruled out by using only a few tens of FRBs with known redshifts in the near future.

astro-ph.CO↗

arXiv2019

${\cal P}-v$ Criticality in Gauged Supergravities

AdS black holes show richer transition behaviors in extended phase space by assuming the cosmological constant and its conjugate quantity to behave like thermodynamic pressure and thermodynamic volume. We study the extended thermodynamics of charged dilatonic AdS black holes in a class of Einstein-Maxwell-dilaton theories that can be embedded in gauged supergravities in various dimensions. We find that the transition behaviors of higher dimensional dilatonic AdS black holes are different from the four dimensional counterparts, and new transition behaviors emerges in higher dimensions. First, there exists standard Van der Waals transition only in a five dimensional dilatonic AdS black hole with two equal charges. Second, there emerge a new phase transition branch in negative pressure region in six and seven dimensional dilatonic black holes with two equal charges. Third, there emerge transition behaviors in higher dimensional black hole with single charge cases, which are absent in four dimensions.

gr-qc↗

arXiv2018

Null Signal for the Cosmic Anisotropy in the Pantheon Supernovae Data

The cosmological principle assumes that the universe is homogeneous and isotropic on cosmic scales. There exist many works testing the cosmic homogeneity and/or the cosmic isotropy of the universe in the literature. In fact, some observational hints of the cosmic anisotropy have been claimed. However, we note that the paucity of the data considered in the literature might be responsible for the `found' cosmic anisotropy. So, it might disappear in a large enough sample. Very recently, the Pantheon sample consisting of 1048 type Ia supernovae (SNIa) has been released, which is the largest spectroscopically confirmed SNIa sample to date. In the present work, we test the cosmic anisotropy in the Pantheon SNIa sample by using three methods, and hence the results from different methods can be cross-checked. All the results obtained by using the hemisphere comparison (HC) method, the dipole fitting (DF) method and HEALPix suggest that no evidence for the cosmic anisotropy is found in the Pantheon SNIa sample.

astro-ph.CO↗

arXiv2018

Testing the Cosmic Anisotropy with Supernovae Data: Hemisphere Comparison and Dipole Fitting

The cosmological principle is one of the cornerstones in modern cosmology. It assumes that the universe is homogeneous and isotropic on cosmic scales. Both the homogeneity and the isotropy of the universe should be tested carefully. In the present work, we are interested in probing the possible preferred direction in the distribution of type Ia supernovae (SNIa). To our best knowledge, two main methods have been used in almost all of the relevant works in the literature, namely the hemisphere comparison (HC) method and the dipole fitting (DF) method. However, the results from these two methods are not always approximately coincident with each other. In this work, we test the cosmic anisotropy by using these two methods with the Joint Light-Curve Analysis (JLA) and simulated SNIa datasets. In many cases, both methods work well, and their results are consistent with each other. However, in the cases with two (or even more) preferred directions, the DF method fails while the HC method still works well. This might shed new light on our understanding of these two methods.

astro-ph.CO↗

arXiv2017

Model-Independent Constraints on Lorentz Invariance Violation via the Cosmographic Approach

Since Lorentz invariance plays an important role in modern physics, it is of interest to test the possible Lorentz invariance violation (LIV). The time-lag (the arrival time delay between light curves in different energy bands) of Gamma-ray bursts (GRBs) has been extensively used to this end. However, to our best knowledge, one or more particular cosmological models were assumed {\it a priori} in (almost) all of the relevant works in the literature. So, this makes the results on LIV in those works model-dependent and hence not so robust in fact. In the present work, we try to avoid this problem by using a model-independent approach. We calculate the time delay induced by LIV with the cosmic expansion history given in terms of cosmography, without assuming any particular cosmological model. Then, we constrain the possible LIV with the observational data, and find weak hints for LIV.

gr-qc↗