Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
New low frequency radio telescopes currently being built open up the possibility of observing the 21 cm radiation before the Epoch of Reionization in the future, in particular at redshifts 200 ≥ z ≥ 30, also known as the dark ages. At these high redshifts, Cosmic Microwave Back-ground (CMB) radiation is absorbed by neutral hydrogen at its 21 cm hyperfine transition. This redshifted 21 cm signal thus carries information about the state of the early Universe and can be used to test fundamental physics.
Precision tests of Local Position Invariance (LPI) involve many different methods in atomic, nuclear and gravitational physics, astrophysics and cosmology, and many different epochs and environments. We present some methods for comparing or combining different methods, either in a model-independent way or within simple scalar field models of variation. We focus on which methods are most sensitive to cosmologically recent time variation, and also on tests of spatial variation within the Solar System.
I will describe a method of understanding how the nuclear binding energies depend on the masses of the light quarks. This is useful in applications ranging from anthropic constraints to equivalence principle tests and bounds on the time variation on the quark masses.
To date, optical clocks based on singly trapped ions1) and ultracold neutral atoms trapped in the Stark-shift-free optical lattices2) are regarded as promising candidates for future atomic clocks. So far “optical lattice clocks” have been evaluated with uncertainty of 1×10-15 (ref. 3)) limited by that of Cs atomic clocks. Frequency comparison between highly-stable and accurate optical lattice clocks is, therefore, crucial for their further evaluation.
We propose new experiments with high sensitivity to a possible variation of the electron-to-proton mass ratio µ me/mp. We consider a nearly degenerate pair of molecular vibrational levels, each associated with a different electronic potential. With respect to a change in µ, the change in the splitting between such levels can be large both on an absolute scale and relative to the splitting. We demonstrate the existence of such pairs of states in Cs2, where the narrow spectral lines achievable with ultracold molecules make the system promising for future searches for small variations in µ.
We have used molecular hydrogen transitions in high quality spectra of quasars Q0403-443, Q0347-383 and Q0528-250, to search for a change in the proton-to-electron mass ratio, mu. Our improvement on previous works is twofold. Firstly, we use an improved technique to calibrate the wavelength scale of the VLT/UVES data, which reduces systematics. Secondly, we model all the hydrogen Lyman alpha transitions in the vicinity of each molecular hydrogen transition.
High precision measurements in atomic and molecular systems have reached unprecedented accuracy owing to the state-of-the-art quantum control of both light and matter. We have recently completed an evaluation of the uncertainty of our 87Sr optical lattice clock at the 1x10e-16 fractional level, surpassing the best current evaluations of Cs primary standards. By analyzing worldwide measurements of the absolute frequency of the clock transitions in Sr, we constrain temporal variations of fundamental physical constants as well as their possible couplings to the gravitational potential.