In Memorium Professor George Leibbrandt of the University of Guelph

                   The Canadian Physics and Mathematics communities suffered a great loss recently
                   when Professor George Leibbrandt of the University of Guelph suddenly passed away last April 3, 2001.

                   George began his career in Theoretical Physics at McMaster University, obtaining a B.Sc. there in 1961.
                   He then went on to carry out graduate work at McGill University, getting an M.Sc. and then a Ph.D.
                   there, completing his studies in 1967. Shortly before the defense of his thesis, he took up a position in
                   the Department of Mathematics and Statistics at the University of Guelph in 1966, a position he retained
                   until his death in 2001.

                   George enjoyed a long, productive and stimulating career in theoretical physics. He actively participated
                   in the life of both the mathematics and physics departments at the University of Guelph, and was a
                   well-known and much admired figure in each. Throughout his career, he supervised 10 postdoctoral
                   fellows and 8 graduate students. He enjoyed the collegiality of his fellow researchers in theoretical
                   physics throughout Southern Ontario, and participated regularly in the activities of the Guelph-Waterloo
                   Physics Institute and in special events held at Toronto, Western, and McMaster. His expertise in
                   theoretical physics took him to some of the most prestigious institutions around the world, including
                   Imperial College, Cambridge University, CERN, Harvard, and the ICTP in Trieste. He won two Humboldt
                   Fellowships and was twice a Bye Fellow at Cambridge.

                   George's expertise was in gauge field theories. He was one of the first people to apply dimensional
                   regularization to perturbative loop corrections in quantum gravity. The technique -- which involves
                   calculating divergent integrals by analytically continuing in the number of spacetime dimensions -- was
                   still quite new at the time, and George became one of the first experts on its application to quantum field
                   theory.

                   In the 1980s George moved on to study field theories in non-covariant gauges. All standard model
                   interactions respect the principle of gauge invariance, which allows for a redefinition of the 4-vector
                   potential associate with a force according to a certain prescription. The simplest example is the
                   modification of the vector potential in electromagnetism by the addition of the gradient of an arbitrary
                   function; if you add such a gradient to the vector potential, both the electric and magnetic fields remain
                   unchanged. In order to calculate in a quantum gauge field theory, it is necessary to "fix the gauge" ie
                   choose a particular form of constraint on the gauge field (eg the photon or gluon) which eliminates the
                   redundant gradient terms. In the 1970s this was almost always done covariantly, ie. in a manner that
                   manifestly respected Lorentz invariance. However, while physical observations cannot depend on this
                   choice of constraint, little was known about how to carry out calculations when the constaint was
                   chosen non-covariantly.

                   George was one of the pioneers in demonstrating how to carry out quantum field theoretic corrections for
                   this case, in a context which came to be referred to as a "non-covariant gauge" choice. His prescription
                   for treating these cases came to be known as the "Mandlestam-Leibbrandt" prescription, named after
                   both George and Stanly Mandlestam, who also worked on this subject. The techniques they developed
                   became essential in demonstrating the finiteness of certain field theories such as N=4 Supersymmetric
                   Yang-Mills theories.

                   In 1999 George was asked to become a founding member of the Perimeter Institute for Theoretical
                   Physics, a task to which he dedicated himself wholeheartedly. He worked closely with the principal
                   donor, Mike Lazaridis, and with Howard Burton, its executive director. George was very concerned that
                   the Institute fulfil its mandate to be a premier place for research in theoretical physics, and he spent
                   many volunteer hours attending board meetings, going through architectural plans, and participating in
                   discussions concerning its scientific merit.

                   George will always be remembered for his kindness and patience. Always ready to help out a student or
                   colleague in need, he had a way of providing encouragement just when you needed it most. His modesty
                   concerning his own accomplishments in physics did not do justice to their importance. He will be sorely
                   missed.