Astrophysics

If a black hole horizon has its microscopic structure as is conjectured by the candidates of quantum gravity, the dispersion relation of gravitational waves (GWs) near the horizon may be drastically modified since its wavelength can be comparable to the size of the microscopic structure because of its infinite gravitational blue-shift near the horizon.  We investigate ringdown-GWs from a perturbed black hole with such a modified dispersion relation and found that the change of modified dispersion relation near the horizon would lead to the partial reflection of infalling GWs at the horizon and echo-signals may appear in the late-time of ringdown-GWs. This implies that the echoes can be a supporting evidence of the existence of microscopic degrees of freedom on black hole horizons.

Cosmic microwave background (CMB) experiments, which currently provide some of the most powerful cosmological data sets, will become much more constraining in the near future. While these measurements promise to teach us more about the nature of dark energy, inflation and neutrino physics, increased precision will require special attention dedicated to the data analysis. In this talk I will focus on the gravitational lensing of the CMB and some of its implications. By introducing a novel analysis technique, applying it to the Planck satellite data and commenting on improvements which will be possible with a CMB Stage 4 experiment, I will first show how we can utilize CMB gravitational lensing to probe self-consistency of the CMB data sets. Then I will overview how gravitational lensing induces non-Gaussian covariances between the CMB data and how these covariances affect constraints on the cosmological parameters.