Late Universe

We are making predictions for the signals expected in dark matter detection experiments and developing techniques for measuring the WIMP properties from upcoming data.

A wide range of astronomical and cosmological observations suggest that the majority of the matter in the Universe is in the form of non-baryonic cold dark matter (CDM). Particle physics provides a number of well motivated CDM candidates, in particular Weakly Interacting Massive Particles (WIMPs). WIMPs arise in several extensions of the Standard Model and are generically produced in the early Universe with the required abundance. WIMPs can be detected directly in the lab, via their interactions with target nuclei, or indirectly, via the products of their annihilation. Numerous experiments are underway, and there are good prospects for detection in the near future. We are making predictions for the signals expected in these experiments and developing techniques for extracting maximum information on the WIMP properties from upcoming data. We are especially interested in the astrophysical input and how the signals depend on the dark matter distribution.

We are trying to understand the nature of the Dark Energy which is driving the acceleration of the Universe, using physics from atom interferometry, to particle colliders through to clusters of galaxies.

Gravity sucks, meaning that the Universe should be decelerating as it expands under the influence of the gravitational attraction from all the sources of matter present. Instead it looks like it is currently accelerating. Something is causing this to happen, a late Universe version of Inflation but at a much lower energy scale. We don't know the origin of the energy density that dominates today and causes the acceleration, so we refer to it as Dark Energy. It could be a variant of Einstein's famous Cosmological Constant, but if it is why does it have the energy density it has? Perhaps it is a scalar field, a low energy equivalent of the inflaton field. Such a field is known either as Quintessence or K-essence depending on the precise way the acceleration occurs. We work on understanding the nature of dark energy and how to determine it observationally.

Einstein's General Relativity works. But there are a few mysteries, such as dark matter and dark energy, which are still not well understood. One possible way to deal with these phenomena is to modify the gravitational theory.

Einstein's theory of General Relativity does a fantastic job of describing the gravitational force over a wide range of scales. Having said that, we know for certain that Einstein's theory will break down at short distances because it's not compatible with quantum mechanics, and there are some suggestions that it also cannot describe the behaviour of the universe over very long distances. One possibility is to replace general relativity at short distance scales is string theory. String theory predicts that our Universe has ten spacetime dimensions. Six of those dimensions are currently hidden from view, perhaps because they are very small and compact, or because physical particles are stuck to a four dimensional surface, or 'brane'. At the other end of the spectrum - large astrophysical scales - eneral relativity cannot explain the accelerating expansion of the universe without the introduction of some very peculiar substance, known as 'dark energy'. This leads us also to consider that an alternative theory of gravity describes how the universe behaves on the largest scales. On both large and small distance scales we are actively involved in developing new models of modified gravity and testing existing models against cosmological, astrophysical and laboratory observations.