Jayanti Prasad

Research Summary:

I have been working on a problems related to formation of large scale structure in the Universe. This work is mainly done numerically, for which we are using N-body codes. Under this study I have done following short projects.

• PM code : I wrote a particle mesh (PM) code and checked it for various power law models.

• Adhesion approximation : Adhesion approximation gives a way to prevent the thickening of pancake in the Zeldovich approximation by invoking an artificial viscosity. In this approximation particles stick together when they come close to each other in place of crossing, due to viscosity and pancake remains thin. Mathematically this leads to the Burger's equation. In the small viscosity limit it exactly matches with the the Zeldovich approximation. In N body simulation whenever pancake is formed there are some particles which have the same Eulerian positions but they have reached there from different Lagrangian positions, as a result they have different velocities and multi-stream regions are formed. In the early stage (linear) of simulation when the strength of perturbations is small we have single stream regions, then it becomes three stream and so on. This artifical viscosity works mainly in the dense multi-stream regions. Outside the multi-streams regions Zeldovich approximation keeps giving the right results. We are studying the viscosity in the multi-stream regions with a series of numerical experiments. We have found that N-body curve for the mass inside pancake jumps from one value of &nu to another when the number of streams in multi-stream region are increased. In this experiments we have studied the collapse of a plane wave in n-Body simulations and the Adhesion approximation.

• Effect of large scale fluctuation on small scales and vice versa : In one of the studies we are looking at the effect of small scale density fluctuations on large scales and effect of large scales on small scales. A single plane wave of a long wave length is taken for the large scales and a rectangular box power spectrum centered at a wavelength of eight grid lengths for small scales. What we have found is that the presence of small scale fluctuations does changes the size of the multi-stream flow if the amplitude of these fluctuations is large. Presence of large scales does make a big difference to perturbations at small scales.

Conference/Workshops Attended:

• An advanced school on the physics of galaxy formation
  Harish-Chandra Research Institute, Allahabad ,India
  (Dec.16-30, 2003)

• International Conference on Gravitation and cosmology
  January5 -10, 2004
  Department of Physics
  Cochin University of Science and Technology
  Kochi - 682022, INDIA.

Other Activities:

I was tutor for a course on Astrophysics given by Jasjeet Bagla in HRI