Tufts/CfA/MIT Cosmology Seminar, at CfA:

                     Tuesday October 8, 1996
                             2:30 pm
                         Phillips Auditorium

              "The Structure of Cosmic String Wakes"

                          Andrew Sornborger
                    DAMTP, Cambridge University

Abstract: 
The clustering of baryons and cold dark matter induced by a single
moving string is analyzed numerically making use of a new
three-dimensional Eulerian cosmological hydro code$^{1)}$ which is
based on the PPM method to track the baryons and the PIC method to
evolve the dark matter particles.

A long straight string moving with a speed comparable to $c$ induces a
planar overdensity (a``wake").  Since the initial perturbation is a
velocity kick towards the plane behind the string and there is no
initial Newtonian gravitational line source, the baryons are trapped
in the center of the wake, leading to an enhanced baryon to dark
matter ratio. The cold coherent flow leads to very low post--shock
temperatures of the baryonic fluid.

In contrast, long strings with a lot of small-scale
structure (which can be described by adding a Newtonian gravitational
line source) move slowly and form filamentary objects.  The large
central pressure due to the gravitational potential causes the baryons
to be expelled from the central regions and leads to a relative
deficit in the baryon to dark matter ratio. In this case, the velocity of
the baryons is larger, leading to high post-shock temperatures.

Note: mpeg simulations may be found at
http://www.damtp.cam.ac.uk/user/ats25/