Journal Club

Seminar Room

Friday 19th of September, 2025

Hour: 11:00

Title: What is the source of the PTA GW signal?

Presented by: Mikael Chala

Ref: https://arxiv.org/pdf/2308.08546

Abstract:

The most conservative interpretation of the nHz stochastic gravitational wave background (SGWB) discovered by NANOGrav and other pulsar timing array (PTA) collaborations is astrophysical, namely that it originates from supermassive black hole (SMBH) binaries. However, alternative cosmological models have been proposed, including cosmic strings, phase transitions, domain walls, primordial fluctuations, and “audible” axions. We perform a multimodel analysis (MMA) to compare how well these different hypotheses fit the NANOGrav data, both in isolation and in combination with SMBH binaries, and address the questions: Which interpretations fit the data best, and which are disfavored? We also discuss experimental signatures that can help discriminate between different sources of the PTA GW signal, including fluctuations in the signal strength between frequency bins, individual sources, and how the PTA signal extends to higher frequencies.

Hour: 11:30

Title: Born–Oppenheimer EFT: a unified description of ordinary and exotic quarkonia

Presented by: Andrii Dashko

Ref: https://arxiv.org/pdf/2509.13043

Abstract:

We show how the Born-Oppenheimer effective field theory (BOEFT) provides a unified description of ordinary and exotic quarkonia grounded on the non-relativistic expansions of QCD and supplemented with lattice QCD inputs. We apply BOEFT to tetraquarks, pentaquarks, quarkonium hybrids and to assess threshold effects in the quarkonium spectrum.