(Welcome Seminar) The Dark Matter – Baryon Coincidence: Problem, Solutions, and Signatures

• Yi Chung (IBS CTPU-PTC)

Room: B438 The comparable abundances of dark matter and baryons, known as the Dark Matter – Baryon coincidence, call for an explanation that relates the dark sector to the QCD sector. In Asymmetric Dark Matter models, the number densities in the two sectors are naturally similar due to an underlying symmetry. However, a complete solution should also include a mechanism that accounts for their comparable masses. In this talk, I will present the attempts along this direction, including my contributions in 2411.16860 and 2411.18725. The relevant phenomenology will also be discussed.

(Welcome Seminar) Hints for Baryon Asymmetry and Dark Matter in the PTA Signal

• Sudhakantha Girmohanta (IBS CTPU-PTC)

Room: B438 If the nano-Hz gravitational-wave signal observed by Pulsar Timing Array (PTA) experiments originates from a strongly supercooled first-order phase transition in a dark sector, the associated supercooling at temperatures of order GeV would dilute any pre-existing baryon asymmetry and dark matter abundance. This necessitates new mechanisms for their generation. In this talk, I will outline the motivation for interpreting the PTA signal as arising from a dark-sector phase transition, and sketch two mechanisms capable of producing the baryon asymmetry and dark matter after the transition. The resulting phenomenological consequences will be discussed briefly.

Spectral Bounds in N=(1,0) Supergravity Theories in Various Dimensions

• Sören Kotlewski (IBS CTPU-PTC)

Room: B438 One of the most important implications of the Swampland conjectures is the finiteness of the set of consistent theories of quantum gravity. For theories with a large amount of supersymmetry - those with 32 and 16 supercharges - a full classification of consistent supergravity spectra has been performed and supports the finiteness claim based on the Swampland arguments. For theories with less supersymmetry, there are much weaker constraints which make it more challenging to argue for the boundedness of spectra. A broad class of supergravity theories with 8 supercharges (in various even dimensions) is obtained by compactifications of F-Theory on elliptically fibred Calabi-Yau manifolds. This additional input allows to use tools from algebraic geometry to bound the number of multiplets appearing in the corresponding supergravity theories. Based on the pioneering work 2507.06317 by Birkar and Lee, we aim to give a mathematical proof for a saturated bound for consistent spectra of 6D N=(1,0) supergravity theories as well as a generalization thereof to 4D N=1 supergravity theories.

Gravitational Wave Detections of Environmental Effects by Extreme Mass Ratio Inspirals

• Hong Guo (IBS-CTPU-PTC)

Room: B438 Gravitational-wave astronomy provides an unprecedented observational window into strong gravitational fields and extreme matter environments surrounding compact objects in our universe. Extreme mass-ratio inspirals (EMRIs) refer to binary systems formed when a stellar-mass compact object is captured by a supermassive black hole and undergoes a long-lasting inspiral with a highly precessing orbit. Owing to their long-lived evolution and large number of orbital cycles, these systems are exceptionally sensitive to small perturbations, making them an ideal physical platform for testing general relativity, probing the properties of compact objects, and investigating environmental effects in the vicinity of black holes. In this talk, I will introduce my recent progress on using EMRI GW signals to probe environmental effects around black holes. Such effects include the influence of additional matter or fields on the orbital dynamics and the GW phase evolution, for example, non-vacuum corrections induced by the presence of scalar or electromagnetic fields and their observable imprints on GW signals.