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.
In this talk I will discuss a new class of cosmological scalar fields. Similarly to gravity, these theories are described by actions linearly depending on second derivatives. The latter can not be excluded without breaking the generally covariant formulation of the action principle. Despite the presence of these second derivatives the equations of motion are of the second order. Hence there are no new pathological degrees of freedom.
Did you know you could fit the entire human race in the volume of a sugar cube? Or that, if the Sun were made of bananas, it wouldn't make much difference? Or that 98 per cent of the Universe is invisible? Award-winning science writer Marcus Chown invites you to come along and discover how the Universe we live in is far stranger than anything we could possibly have invented.
Usually in quantum field theory one considers two different interpretations:
1: The field is an infinite number of quantum oscillators, giving rise to a wave functional \Psi(\phi).
2: The positive frequency component of a field, \phi_+(x), is a wave function analogous to standard quantum mechanics.
While interpretation 2 is often only mentioned implicitly it is crucial to standard computations of measurable scattering probabilities.
The nature of antimatter is examined in the context of algebraic quantum
field theory. It is shown that the notion of antimatter is more general
than that of antiparticles. Properly speaking, then, antimatter is not
matter made up of antiparticles --- rather, antiparticles are particles
made up of antimatter. We go on to discuss whether the notion of antimatter
is itself completely general in quantum field theory. Does the
matter-antimatter distinction apply to all field theoretic systems? The