## Early Universe Relics:

Inflation and Reheating

Very recently I became interested in issues of gravitational
and matter field instabilities during preheating after inflation.
Together with **Karsten Jedamzik** from the
**Early Universe Gang** at the
Max Planck Institut
für Astrophysik, Garching bei München I started to
study these phenomena consistently by trying to take backreaction
into account. This is important in order to reliably describe
the resonance phenomena, and especially their termination and
thus the resulting field and metric fluctuations. Our goal is to
determine observational consequences and in turn constrain models
of inflation.

The figure on the left shows first results for the
evolution of the matter field fluctuations and the metric
perturbations, for the simple case of a massive inflaton
with quadratic coupling to another scalar field. From
these calculations, presented in detail in
**this paper**,
we conclude that, contrary to some other claims in the literature, metric
perturbations at least on scales relevant for structure
formation, are not strongly modified during preheating
and certainly do not grow non-linear.

We began to investigate preheating in the context of more
general inflaton and matter field potentials. To this end
a numerical code should be developed which takes into
account as many nonlinear effects during preheating and
reheating as possible. Preliminary results seem to indicate
that significant increase of large scale metric fluctuations
is possible in certain cases but typically requires
considerable fine tuning of parameters. In the farther
future this numerical tool should probably also be extended
to fermions, gauge bosons, gravitinos etc.

Processes during reheating after inflation may also be important
for the creation of superheavy
particles and/or topological defects at the end of inflation
which today may constitute non-thermal
dark matter and whose decay may contribute
to the **ultrahigh energy cosmic ray flux**.

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