Physics Student Conference Program and Information
◎Constraining the Mass Density of Cosmic Strings Piercing Rotating Black Holes
Multiple theories predict the presence of cosmic strings with different mass densities μ. A number of ways to constrain μ have been developed. In this project, the speakers derived an equation governing the perturbation of a rotating black hole pierced by a straight, infinitely long cosmic string along its axis of rotation, from which the quasinormal mode frequencies were calculated. These results were used to put a constraint on μ for a Black-hole-string system through the analysis of its ringdown signals.
●Cheung Ho Yeuk
●Poon Wing Hei
◎Search Pipeline for Targeted Sub-threshold for Strongly-lensed Gravitational-wave Events
Strongly-lensed gravitational waves events can generate multiple signals that are different in amplitude and time separation. We assume the strongly-lensed signals are sub-threshold that are buried in the noise background. A GstLAL-based pipeline is presented to search for the sub-threshold signal using reduced template banks for each targeted specific gravitational events. The pipeline is applied to all the event from Advanced LIGO’s first and second observing run, O1 and O2. It is shown that pipeline can effectively reduce the noise background and hence improve the signifiernce of(near-) sub-threshold triggers.
講者：Chan Chun Lung
◎How neutrino affect on cosmic expansion
Neutrino is fermion that only interacts via gravity and weak interaction. It is electrically neutral and its rest mass is nearly negligible. This greatly increase the difficulty for researchers to detect it. However, it has large abundance so it may still play an important role in universe evolution. Thus, the effect of neutrino on cosmic expansion and structure formation is studied in this project.
講者：KO Yip Choi
◎Directional Dependences of Cosmological Parameters from the Cosmic Microwave Background Anisotropy
The possibilities of directional variation of the cosmological parameters are considered. By using MCMC, the Planck CMB temperature angular power spectrum for twelve different half-skies is fitted, centering on twelve different directions, to search for directional dependences of the standard cosmological parameters. The results show that there are more than 3σ deviations of the parameters between different directions. The directional distributions ofns, H0, and cosmological baryon and dark matter densities Ωbh2, Ωch2 all follow a dipole form Acosθ+B, where θ is the angle to the best-fit dipole axis, with the values of Adeviating by 2-4σ from zero. The best-fit dipole axes forns, Ωch2, H0, and τ all align within 1σ uncertain-ties, pointing to the direction of V≡(b=−48.7±20.4◦, l= 170.8±49.2◦). The dipole axes for Ωbh2 and ln(1010As) are also aligned with each other,but they are perpendicular to V. The results suggest either significant deviation from the standard ΛCDM cosmology, or previously unknown systematic errors in the sky.