Parity-violation in bouncing cosmology

We investigate the possibility of the enhancement of parity-violation signal in bouncing cosmology. Specifically, we are interested in deciding which phase should generate the most significant parity-violation signals. We find that the dominant contribution comes from the bouncing phase, while the contraction phase has a smaller contribution. Therefore, bouncing cosmology can enhance the parity-violation signals during the bouncing phase. Moreover, since the bouncing phase has the highest energy scale in bouncing cosmology, we can also probe new physics at this scale by studying the parity-violation effect.Comment: 28 pages, 22 figure

Pulsar timing array observations as possible hints for nonsingular cosmology

Recent pulsar timing array (PTA) experiments have reported strong evidence of the stochastic gravitational wave background (SGWB). If interpreted as primordial gravitational waves (GWs), the signal favors a strongly blue-tilted spectrum. Consequently, the nonsingular cosmology, which is able to predict a strongly blue-tilted GW spectrum with $n_T \simeq 2$ on certain scales, offers a potential explanation for the observed SGWB signal. In this paper, we present a Genesis-inflation model capable of explaining the SGWB signal observed by the PTA collaborations while also overcoming the initial singularity problem associated with the inflationary cosmology. Furthermore, our model predicts distinctive features in the SGWB spectrum, which might be examined by forthcoming space-based gravitational wave experiments.Comment: 20 pages, 8 figures; references added, published in EPJ

Microlensing effects of wormholes associated to blackhole spacetimes

In this paper, we investigate the microlensing effects of wormholes associated to black hole spacetimes. Specifically, we work on three typical wormholes (WH): Schwarzschild WH, Kerr WH, and RN WH, as well as their blackhole correspondences. We evaluate the deflection angle upon the second order under weak field approximation using Gauss-Bonnet theorem. Then, we study their magnification with numerics. We find that the prograde case of Kerr-like metric could lead to multi-peaks of magnification when the mass part is compatible with the charge part. Moreover, the first two gentle peaks of Kerr BH are larger than the WH case by one order of magnitude, while the main peak of Kerr BHs and WHs are of the same order. For other cases, the behavior of magnification from wormholes and their corresponding blackholes is similar. Our result may shed new light on exploring compact objects through the microlensing effect.Comment: Figures are improved, discussions are improve

Higher order correction to weak-field lensing of Ellis-Bronnikov wormhole

Gravitational lensing effect at higher order under weak field approximation is believed to be important to distinguish black holes and other compact objects like wormholes. The deflection angle of a generic wormhole is difficult to solve analytically, thus approximation methods are implemented. In this paper, we investigate the weak-field deflection angle of a specific wormhole, the Ellis-Bronnikov wormhole (EBWH), up to the 1/b^4 order. We use different approximation formalism, study their precision at 1/b^4 order by a comparison to a purely numerical result, and finally rank these formalism by their accuracy. Moreover, we find that certain formalism are sensitive to the choice of coordinate system, when the corresponding deflection angle approaches 0 in the negative-mass branch of universe.Comment: Comments are welcome

Microlensing effect of charged spherically symmetric wormhole

We systematically investigate the microlensing effect of charged spherically symmetric wormhole, where the light source is remote from the throat. Remarkably, there will be at most three images by considering the charge part. We study all situations including three images, two images, and one image, respectively. The numerical result shows that the range of total magnification is from $10^5$ to $10^{-2}$ depending on various metrics. In the case of three images, there will be two maximal values of magnification (a peak, and a gentle peak) when the contribution via mass is much less than that of charge. However, we cannot distinguish the case that forms three images or only one image as the total magnification is of order $10^5$. Finally, our theoretical investigation could shed new light on exploring the wormhole with the microlensing effect.Comment: 10 pages, 9 figure