Add to Calendar 2024-05-23T14:00:00 2024-05-23T16:00:00 A study of sporadic pulsars and radio transients with the CHIME telescope Event Information: Lay abstract: Pulsars are the remnants of massive stars. Their rapid and precise rotation allows us to use them as tools to test many theories of physics. Pulsars come in many flavours; some are sporadic and only emit radio waves occasionally. This thesis uses the Canadian Hydrogen Mapping Experiment (CHIME) to study pulsars of all flavours. First, I developed a new processing pipeline so that we can fully utilise the capabilities of CHIME/Pulsar. Then, I create a technique, LuNfit, to characterise the single pulses of pulsars. I then apply LuNfit to 35 pulsars with a 477-hour CHIME/Pulsar observation campaign. Finally, I discovered a new long-period transient, CHIME J0630+25, with a period of 421 seconds.  This marks only the fourth object in this new class. Their nature remains unknown, but we speculate that CHIME J0630+25 is likely a white dwarf or a neutron star. Event Location: Henn 309

Add to Calendar 2024-05-24T10:00:00 2024-05-24T12:00:00 Negative Lambda Quantum Cosmology Event Information: Abstract: We present a model of quantum cosmology based on anti-de Sitter/conformal field theory (AdS/CFT) holography. The spacetimes in our construction are time-symmetric, big-bang/big-crunch cosmologies with a negative cosmological constant $\Lambda$. In the simplest version of our model the cosmology lives inside a spatially finite bubble within an otherwise empty AdS spacetime. By studying the thermodynamic and geometric properties of this spacetime, we provide evidence that the ``bubble of cosmology'' spacetime has a well-defined dual CFT description.   It is also desirable to have a cosmology which is globally homogeneous and isotropic. We present an upgraded model in which this is the case.  Although a homogeneous cosmology is not asymptotically AdS and hence cannot be described directly by AdS/CFT, the time-reflection symmetry of the spacetime allows us to perform an analytic continuation, following which the spacetime is an asymptotically AdS Euclidean wormhole. If we assume that the cosmology is spatially flat a second analytic continuation obtains a Lorentzian traversable AdS wormhole. The AdS wormhole spacetimes can be described using holography: they are dual to a pair of three-dimensional CFTs coupled via a four-dimensional theory.  We explain how an anomalously large amount of negative energy can support the traversable wormhole, and we begin to populate the holographic dictionary relating observables in the wormhole/cosmology to observables in the microscopic theory. Finally we show that time-dependent scalar fields naturally enable these cosmologies to contain a period of accelerated expansion, suggesting that our $\Lambda<0$ models could ultimately provide the framework for a fully microscopic description of our universe.   Event Location: Henn 318