**AAS 195th Meeting, January 2000**

*Session 125. Cosmology and Large-Scale Structure*

Oral, Saturday, January 15, 2000, 2:00-3:30pm, Centennial I and II
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## [125.03] Using Perturbative Least Action to Recover Cosmological Initial Conditions

*D.M. Goldberg (Princeton University Observatory)*

One of the great challenges in cosmology is interpreting the
observations of large scale structure. On the largest
scales, this frequently means estimating the power spectrum
at present and from that, using linear theory to determine
the power spectrum at high redshift, and consequently, the
corresponding cosmological parameters.

The problem of determining initial conditions becomes much
more complex for fields which are highly non-linear. Due to
mode-mode coupling in the evolution equations, the problem
of finding the time-reversal operator becomes fundamentally
ill-posed; that is, many different sets of initial
conditions can give rise to the same final density field.

In this talk, I will discuss a new technique for
time-reversing dynamics observations. Perturbative Least
Action (PLA) is a variant of Least Action variational method
which develops particle trajectories as perturbations from
known, randomly realized paths, and can be used to generate
many different sets of initial conditions, each of which
will satisfy given highly nonlinear constraints at z=0.

This research was supported through a NSF graduate research
fellowship.

The author(s) of this abstract have provided an email address
for comments about the abstract:
goldberg@astro.princeton.edu

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