Scientific Series

We study the implications of precision measurements of light-element abundances, in combination with the Cosmic Microwave Background, for scenarios of physics beyond the Standard Model that generate large inhomogeneities in the baryon-to-photon ratio. We show that precision Big Bang Nucleosynthesis (BBN) places strong constraints on any mechanism that produces large-scale inhomogeneities at temperatures around or below the TeV scale. In particular, we find that fluctuations of order 25% on comoving length scales larger than the horizon at T ~ 3 TeV are incompatible with the observed light-element abundances. This sensitivity to early-universe physics arises because baryon-number inhomogeneities homogenize primarily through diffusion, a slow process. As a result, BBN serves as a novel probe of baryogenesis below the TeV scale, readily ruling out some proposed scenarios in the literature. We discuss the implications for electroweak baryogenesis, and further show that precision BBN provides a new probe of first-order phase transitions that generate gravitational waves in the pHz–mHz frequency range. This yields constraints on the electroweak phase transition, as well as first-order phase transitions that have been suggested as an explanation of the pulsar timing array signal. Finally, we comment on the future prospects for improving this probe

In this session, members of Perimeter’s Training and Educational Outreach teams will share resources for developing a teaching statement and introduce evidence-based strategies for effective teaching. Participants will be guided to reflect on their own teaching philosophy and will receive practical tips for preparing statements for academic job applications. The session will also highlight approaches for creating engaging lectures and tutorials, with opportunities to try out selected strategies and discuss how to incorporate them into current and future teaching.

We formulate the holomorphic twists of the 6d N=(0,1) and (0,2) abelian tensor multiplets as moduli spaces in derived geometry, using Deligne cohomology as a key tool. This description allows one to mimic the Beilinson-Drinfeld construction of lattice chiral algebras to quantize these 6d theories; their factorization homology on closed 3-folds relates to Witten's construction of line bundles on intermediate Jacobians. This is work in progress with Chris Elliott, Ingmar Saberi, and Brian Williams.

We are now in the era of multi-messenger astronomy, where neutron stars and black holes—the most extreme objects in the Universe—can be studied through both electromagnetic signals and gravitational waves. These compact remnants of massive stars provide unique windows into the short lives and deaths of their progenitors and the history of star formation across cosmic time. In this talk, I will show how we can apply cutting-edge computational models to uncover the origins of black holes and neutron stars and to address outstanding puzzles, including how and where the gravitational wave mergers detected by LIGO/Virgo/KAGRA are formed.

The QCD axion is not only a leading contender as a solution to the Strong CP problem, it is also a natural dark matter candidate. In particular, the post-inflationary axion is particularly attractive because of the possibility of a unique prediction of the axion mass if axion makes up all of dark matter. On the other hand, QCD axion models often suffers from the so-called axion quality problem, where the axion shift symmetry is unprotected from quantum gravity effects. In this talk I will discuss the tension between solutions to the quality problem and viable cosmology for post-inflationary QCD axions. I will start with a simple Z_N solution as an illustrative example of the close connection between the quality problem and the domain wall problem. I will then analyze proposals in the literature that involve more complex symmetry structure and show that they share a set of cosmological issues. Our study suggests that a viable post-inflationary QCD axion model is likely to have a non-standard cosmological history which could significantly impact the prediction of the "correct" axion mass.

  Supermassive black holes (SMBHs) exist in many galaxies. Their growth is accompanied by strong energy output, which is capable of regulating host galaxy evolution. Understanding SMBH growth is thus critical for studying galaxy formation and evolution. However, it has been difficult to quantify SMBH growth in different galaxies and cosmic epochs. In this talk, I will present Trinity, an empirical technique to determine the typical SMBH mass and growth rate in different galaxies and dark matter halos from z=0-10. I will discuss how the galaxy—SMBH connection from Trinity will help observational astronomers extract more information from data, as well as theoretical astronomers create better simulations of galaxy evolution. In addition, I will give an overview of the Trinity predictions that match latest JWST data, as well as those that do not match observations. Finally, I will talk about how observations with next-generation telescopes will enable a better understanding of the galaxy—SMBH connection, and how Trinity will be helpful for quantifying the constraining power of future observations.

The moduli space of quasimaps gives a partial compactification of maps from an algebraic curve to a variety. In physics, the cohomology of this moduli space can be viewed as the state space of a (twisted) supersymmetric gauge theory. It is shown by Bullimore-Dimofte-Gaiotto-Hilburn-Kim that when the target space is a flag variety, this cohomology admits an action of the Lie algebra gl_n and can be identified with the Verma module for generic parameters. I will describe a further compactification of these moduli spaces called relative quasimaps, first introduced by Ciocan-Fontanine-Kim-Maulik, and explain how their cohomology is related to the tilting module of gl_n.

With increasingly precise measurements of the small-scale cosmic microwave background (CMB), the kinetic Sunyaev–Zel’dovich (kSZ) effect has emerged as a powerful probe of cosmology and astrophysics through cross-correlations with galaxy surveys. In this talk, I will review established applications, focusing on large-scale velocity reconstruction and its ability to test signatures of the early universe, such as primordial non-Gaussianity and compensated isocurvature perturbations. I will then introduce a new way to combine these data sets, which provides unique constraints on the distribution of ‘missing baryons’ at low redshifts, thereby opening a new window on baryonic feedback and cosmological inferences from the small-scale distribution of matter. Finally, I will explore the sensitivity of this statistic to the epoch of helium reionization, and compare its prospects to other proposed probes such as optical-depth fluctuations in the observed CMB.