Dear All,

Joel Weller - Wednesday 24/11/10 4.30pm - Maths 103 QMUL

This week in our Wednesday seminar series, Joel Weller from the
University of Sheffield will be speaking about "Coupled DBI
Cosmology". The abstract is below. The seminar will start at 4.30pm in
Room 103 of the Maths Building on the Mile End Campus. The discussion
group meeting will be held as usual at 3.15pm in Room 513.

As always, for directions to the building and a list of upcoming
seminars please go to our wiki site at http://cosrel.maths.qmul.ac.uk
.

The School of Mathematical Sciences is undertaking a major
refurbishment programme that will radically change the design to our
building both externally and internally. During the reconstruction, we
regret that access to the building will be limited. If this could
impact upon your intention to attend a seminar, please contact Bill
White on 0207 882 5514 or email to [log in to unmask] to discuss your
particular requirements.

Best wishes,

Ian

---------------------------------------------
Dr Ian Huston

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

[log in to unmask]
http://www.maths.qmul.ac.uk/~ith
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Coupled DBI Cosmology

Joel Weller - University of Sheffield

The availability of high precision observational data in cosmology
means that it is possible to go beyond simple descriptions of cosmic
inflation in which the expansion is driven by a single scalar field.
One set of models of particular interest involve the Dirac-Born-Infeld
(DBI) action, arising in string cosmology, in which the dynamics of
the field are affected by a speed limit in a manner akin to special
relativity. In this talk, I will introduce a scalar-tensor theory in
which the matter component is a field with a DBI action. Transforming
to the Einstein frame, I will explore the effect of the resulting
coupling on the background dynamics of the fields and the first-order
perturbations. The coupling forces the scalar field into the minimum
of its effective potential, so the dynamics are determined by the DBI
field, which has the interesting effect of increasing the number of
efolds of inflation and decreasing the boost factor of the DBI field.
Focusing on this case, I will show that the power spectrum of the
primordial perturbations is determined by the behaviour of the
perturbations of the modified DBI field and calculate the effect of
varying the model parameters on the inflationary observables