Sharif Digital Repository

In low energy limit, some string theory models are described with an effective lagrangian which consist of two term. first is Eistein-Hilbert term and second is chern-simons. Adding the chern-simons term to Eistein-Hilbert lagrangian leads to the new modified field equations which schuwarzshild, Reissner-Nordstrom and FRW metrics satisfy these new modified equations while kerr metric is not a solution for these new fields. Since the gravitational field of spinning objects are similar to electromagnetic field, we expect to observe the chern-simons effects in gravitomagnetic component of the gravitational field. Here, in order to better understanding of subject, we investigate the Maxwell... 

“Sustainable development” is a frequently used phrase, but the idiom has been experienced little since it was coined by the Brundtland, due to its intrinsic complications. The issue is going to compromise two key components; economy and ecology. One of the solutions based on concept of sustainable development that has been proposed for maintaining water quality at acceptable levels is to cap pollutant emissions at a sustainable level, then establish an economic market in which the right to discharge pollutants is traded according to market supply and demand mechanisms. Water quality trading or pollution trading is one such kind of market-based program that has also been described using names... 

Acceleration of the universe is one of the most challenging conundrum of contemporary physics. One of the leading approach to this conundrum is introducing a new component in Einstein’s equations which is called the dark energy. Dark energy models which their’s dynamics are dictated by holographic principle, are called holographic dark energy. Essentially,the constraint implied by the holographic principle is a macroscopic constraint. In consequence, the constraint gives no informations about microscopic aspects of dark energy. To understand the nature of the holographic dark energy, we need a microscopic theory from which we can extract the behaviors of holographic dark energy. It can be...