Hi all,

Ewan Tarrant - Wednesday 18th January - 4.30pm Maths 103

The first QMUL Relativity and Cosmology seminar of this term will be
on Wednesday 18th January at 4.30pm. Ewan Tarrant of the University of
Nottingham will be speaking about "Coupled Quintessence and the Halo
Mass Function". The abstract is below.
The seminar will be in the usual place, Maths building Room 103.

For further information on this term's seminars and other activities
in the group please visit our wiki at http://cosrel.maths.qmul.ac.uk .

Best wishes,

Ian

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Dr Ian Huston

Postdoctoral Researcher
Cosmology and Relativity Group
Astronomy Unit, School of Physics and Astronomy
Queen Mary, University of London

[log in to unmask]
http://www.maths.qmul.ac.uk/~ith
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Coupled Quintessence and the Halo Mass Function
Ewan Tarrant

A sufficiently light scalar field slowly evolving in a potential can
account for the dark energy density that presently dominates the
universe. This quintessence field is expected to couple directly to
matter components, unless some symmetry of a more fundamental theory
protects or suppresses it. Such a coupling would leave distinctive
signatures in the background expansion history of the universe and on
cosmic structure formation, particularly at galaxy cluster scales.
With the arrival of greatly improved high redshift cluster surveys
such as the Dark Energy Survey (DES) and Planck, the mass distribution
of the most massive objects in the Universe are a powerful tool which
may be used to distinguish between different models of dark energy.

Using semi–analytic expressions for the CDM halo mass function, I will
make predictions for halo abundance in models where the quintessence
scalar field is coupled to cold dark matter, for a variety of
quintessence potentials. How the quintessence field behaves in the
highly non-linear regimes of halo collapse has yet to be understood
and properly modelled. I will present two different methods for
calculating the threshold of collapse parameter and show that the
assumptions made in both calculations strongly affects halo abundance
in the high mass tail of the mass function. In general, depending on
the form of the quintessence potential and the strength of the
coupling, the predicted number of haloes at a given epoch of a given
mass, can lie above or below that of Lambda-CDM.