This series covers all areas of research at Perimeter Institute, as well as those outside of PI's scope.
I present three possible non-standard additions to cosmology. First I show that a very long early period of inflation could exist in which parameters evolve, or 'relax', to seemingly fine-tuned values. Next, I show that even if cosmic inflation existed, a period after inflation with anisotropic stress can dramatically affect super-horizon modes and thus the imprint on the cosmic microwave background. Finally, I show that cosmological singularities can be avoided by a bounce without using exotic matter that violates the Null Energy Condition, but by the addition of vorticity in compact ex
In 1983, Nielsen and Ninomiya predicted that the Adler-Bell-Jakiw (or chiral) anomaly should be observable in a crystal that has protected Dirac states in the bulk (3+1 D). Following recent progress in the field of Topological Quantum Matter, the anomaly has now been observed, most clearly in the two semimetals Na3Bi and GdPtBi. I will discuss the general problem of realizing Weyl Fermions in semimetals, and explain what the chiral anomaly is in condensed matter. I will remark on its historical context, starting with pion decay.
Population expansions are ubiquitous in nature. They control the speed of many important dynamical processes, including multicellular development, biological evolution and epidemic outbreaks. Yet, the theoretical description of spreading behaviors has been limited largely to mean-field models that ignore the randomness inherent to living systems.
It has long been believed that Stradivari and his contemporaries in 18^{th} Century Italy built violins with playing qualities unmatched by later makers. However, a team of researchers led by Claudia Fritz and Joseph Curtin have shown that under double-blind conditions neither professional violinists nor experienced listeners can tell Old Italian violins from new ones at better than chance levels. Moreover, players and listeners tend to prefer the new.
With two confident binary black hole mergers already detected in their first observing run, the advanced LIGO detectors are expected to detect hundreds more in coming years. We are poised to learn more about compact binary (e.g., BNS, NSBH, BBH) formation
In 2015 the LIGO detectors observed gravitational waves from two distinct stellar-mass binary black hole mergers. This long awaited feat now opens avenues to explore astrophysical questions which cannot, or are difficult to, be answered purely by electromagnetic means. Massive stars which end their lives in a pair-instability supernova are not thought to leave a remnant behind, meaning there should exist a gap in the black hole mass spectrum. In this talk I will discuss whether LIGO observations can tell us something about this apparent mass gap.
Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating both continuous gravitational waves and a background of gravitational radiation in the nanohertz to microhertz regime. An array of precisely timed pulsars spread across the sky can form a galactic-scale gravitational wave detector in the nanohertz band.
The spectral action functional of noncommutative geometry provides a model of Euclidean (modified) gravity, possibly coupled to matter. The terms in the large energy asymptotic expansion of the spectral action can be computed via pseudodifferential calculus. In the case of highly symmetric spacetimes, like Robertson-Walker metrics and Bianchi IX gravitational instantons, there is a richer arithmetic structure in the spectral action, and the terms in the asymptotic expansion are expressiblein terms of periods of motives and of modular forms.
By a celebrated theorem of Jacob Lurie, an extended TQFT is entirely determined by what it assigns to a point. It is natural to ask whether this theorem applies to TQFTs of physical interest. And, if yes, what do these theories assign to a point? In this talk, I will propose an answer for the case of 3-dimensional Chern-Simons theory. I will then
explore the relation to line defects in chiral WZW models, and boundary conditions for full WZW models. At last, I will present a conjectural classification of the above mentioned line defects and boundary conditions.