This series covers all areas of research at Perimeter Institute, as well as those outside of PI's scope.
Time poses a fundamental problem in neuroscience, in part, because at its core the brain is a prediction machine: the brain evolved to allow animals to anticipate, adapt, and prepare for future events. To accomplish this function the brain tells time on scales spanning 12 orders of magnitude. In contrast to most man made clocks that share a very simply underlying principle-counting the "tics" of an oscillator-evolution has devised many different solutions to the problem of telling time.
I reexamine the current situation in particle and neutrino physics from a top-down perspective, discussing such underlying issues as uniqueness versus environment, minimality versus remnants, and naturalness versus tuning.
On de
Sitter space, there exists a special value for the mass of a graviton for which
the linear theory propagates 4 rather than 5 degrees of freedom. If a fully non-linear version of the theory
exists and can be coupled to known matter, it would have interesting properties
and could solve the cosmological constant problem. I will describe evidence for and obstructions
to the existence of such a theory.
Exoplanets, planets circling distant stars, are proving to be an extraordinary source of new thinking about the potential for life beyond Earth. Until recently, we have assumed that our Solar System and its planets were probably representative of such systems elsewhere. But the amazing array of very odd exoplanets that are being uncovered have stimulated a renaissance of thought on the subject of potential homes for life in the universe.
It has
recently been realized that some studies of supersymmetric gauge theories, when
properly interpreted, lead to insights whose importance transcends
supersymmetry. I will illustrate the insightful nature of supersymmetry by two
examples having to do with the microscopic description of the thermal
deconfinement transition, in non-supersymmetric pure Yang-Mills theory and in
QCD with adjoint fermions. A host of strange ``topological" molecules will
be seen to be the major players in the confinement-deconfinement dynamics.
Advances in quantum engineering and material science are enabling new approaches for building systems that behave quantum mechanically on long time scales and large length scales. I will discuss how microwave and optical technologies in particular are leading to new domains of many-body physics, both classical and quantum, using photons and phonons as the constituent particles. Furthermore, I will highlight practical consequences of these advances, including improved force and acceleration sensing, efficient signal transduction, and topologically robust photonic circuits.
The success of gauge theory descriptions of Nature follows simply, in hindsight, from Lorentz symmetry, quantum mechanics, and the existence of interacting massless particles with spin. Yet, remarkably, the most generic type of massless particle spin has never been seriously examined: Wigner's so-called "continuous spin" particles (CSPs), which have a tower of polarization states carrying all integer or half-integer helicities that mix under boosts.
A fascinating aspect of the two dimensional
world is the possible existence of anyons, particles which obey 'fractional'
statistics different from fermionic and bosonic statistics. In this colloquium,
following an introduction to fractional particles in the context of quantum
Hall systems, some of the tantalizing experiments for detecting the fractional
charge of these particles will be described.
Probes of fractional statistics in these systems will be discussed,
Despite its feeble in strength, gravity plays a pivotal role in shaping our Universe and the things in it. Ever since Newton formulated his universal law of gravitation the recognition that all things gravitate has been nearly sacrosanct. Repeatedly, apparent gravitational anomalies have either foretold the existence of new physics or a misunderstanding of gravity itself, from the existence of nuclear forces to Einstein's general relativity. Eighty years ago gravity betrayed the existence of dark matter, and fifteen years ago gravity demanded dark energy from reluctant cosmologists.
Ordinary differential equations become much less ordinary
when they are allowed to have singularities.
Solving them naively in formal power series, one often obtains divergent
series, just as in the perturbation series for physical observables in quantum
field theory.