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Jasjeet Singh Bagla
Research Summary: My main research interest for the last few years has been Cosmology and the physics of the high redshift Universe. Most of these studies require use of N-Body simulations and developing algorithms for these is also one of my interests. I have developed a parallel algorithm for the TreePM method of cosmological simulations. I am optimising this code further in order to better the efficiency of parallelisation. With the emergence of new instruments, high redshift Universe
is becoming more accessible. It is important to make predictions
for various observable quantities in popular models of structure
formation. These serve as a guide to observers who are planning
these observations, and the models can also be tested against observations.
Martin White (University of California, Berkeley) and I have used
high resolution N-Body simulations that were run using the TreePM
method to predict signal for emission in the redshifted Studies of clustering of galaxies in the non-linear regime are plagued by the issue of bias. It has long been recognised that measurement of higher order correlations and moments allow determination of bias. However in absence of clean analytical formulation in the non-linear regime, there is no clear method of making use of higher order moments for this purpose. Numerical studies carried out with Suryadeep Ray suggest that the dependence of bias on higher moments depends very strongly on the shape of the power spectrum, and hence can be used to deduce bias as well as the dark matter power spectrum. Zel'dovich approximation is a one step mapping in which the entire information about the transformation and the resulting structures can be specified in terms of the initial gravitational potential. All non-linear structures like the caustics can be described as singularities of the Zel'dovich mapping, as defined and classified in catastrophe theory. We have devised algorithms for locating all the singularities for Zel'dovich approximation in two dimensions. Using these algorithms we can generate the network of filaments and pancakes directly from the initial conditions. We find that point caustics correlate very strongly with large halos that form in N-Body simulations, more strongly than density peaks. These caustics cluster very strongly, more so than density peaks. This work has been done in collaboration with Prof.Shandarin (Kansas, USA) and Prof.Sahni (IUCAA). Observations suggest that the dominant constituents of the universe
are dark energy, with
Publications:
Preprints:
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cm line. The expected signal is very weak and will be difficult to
observe with existing instruments like the Giant Meter wave Radio
Telescope that has been set up near Pune. E.g., it will require
observations extending over 
hours to detect neutral hydrogen in emission at a redshift of 
.
, and dark matter, with 
. Together, these make up more than 
of the energy density of the universe. Recently it has been suggested
that string inspired tachyon fields might play the role of both
the components, thereby reducing the problem to some extent. We
have studied the possibility of tachyon fields playing the role
of dark energy and find that it does as well as other possibilities
like Quintessence (Bagla, Jassal and Padmanabhan, 2002). We are
continuing the study to see if it is possible to construct models
where tachyon condensates play the role of dark matter as well.
, To appear in the IAU 8th Asian-Pacific Regional
Meeting, Proceedings volume I, Eds. Satoru Ikeuchi, John Hearnshaw,
and Tomoyuki Hanawa; ASP conference series, vol.289. astro-ph/0212228.
node PC cluster for use by institute members here at HRI. Its usage
in the first year has been about 
. More information on this is available at http://cluster.mri.ernet.in.