Jae Hyeok Chang

Abstract Recent studies reveal that more than a dozen of white dwarfs displaying near-perfect blackbody spectra in the optical range have been lurking in the Sloan Digital Sky Survey catalog. We point out that, in a way analogous to the cosmic microwave background, these stars serve as excellent test beds for new physics. Specifically, we show how their observed lack of spectral distortions translates into limits on the parameter space of axions with electromagnetic coupling.

Abstract We initiate a study of the gravitational-wave signatures of a phase transition that occurs as the Universe’s temperature increases during reheating. The gravitational-wave signatures of such a heating phase transition are different from those of a cooling phase transition, and their detection could allow us to probe reheating.

Abstract Future gamma-ray experiments, such as the e-ASTROGAM and AMEGO telescopes, can detect the Hawking radiation of photons from primordial black holes (PBHs) if they make up a fraction or all of dark matter. PBHs can analogously also Hawking radiate new particles, which is especially interesting if these particles are mostly secluded from the Standard Model sector, since they might therefore be less accessible otherwise.