M. Sami
Reader

Department of Physics,
Jamia Millia Islamia,
Jamia Nagar,
New Delhi 110025, India

Phone : +91 (11) 6314631 (O)
6835617 (R)
Fax:+91 (11) 6840229
e-mail:

Ph.D. (Moscow)

Research Interests

String Inspired Cosmology and Observational Constraints

The recent advances in observational astrophysics support the inflationary paradigm and confirm the current acceleration of universe. The inflationary scenario not only successfully addresses the problem of initial conditions of the hot big bang but also gives important clues about the origin of structure in the universe. It is puzzling that the realization of cosmological inflation is ad hoc. As inflation is operating around the Planck's scale, the needle of hope points towards string theory, a consistent quantum theory at this scale. The current acceleration of universe implies the existence of an exotic form of energy (dark energy) which constitutes up to 70 percent of the total energy in the universe at present. So far, there is no satisfactory explanation of this phenomenon supported by a fundamental theory. I believe that the answer to the mentioned puzzles would come from string theory. Needless, to say that string theory has its own problems. The process of compactification in string theory which relates the higher dimensional theory to the four dimensional real world, is not yet well understood. Cosmology is expected to play an important role here and it is believed that the synthesis of the two theories will lead to the true picture of nature.
Recently, myself and M. R. Garousi and Shinji Tsujikawa studied the cosmological evolution of the massive DBI ( Dirac-Born-Infeld) scalar field on the ant-D3 brane of KKLT vacua. They have shown that this scenario satisfies the observational constraint coming from the Cosmic Microwave Background anisotropies and other observational data. We have shown that the model can account for observed late time acceleration of universe and may lead to successful reheating. We are investigating the detailed dynamics of this process at present. We are also investigating the possibility of production of primordial magnetic field of cosmological interest in their scenario.
The other area of theoretical cosmology inspired by string theory, I have been working on with collaborators, is related to Brane World cosmology a la Randall-Sundrum (RS). This scenario enhances the prospects of inflation. With collaborators (V. Sahni, N. Dadhich and T. Shiromizu),I have investigated the possibility of unification of inflation with quintessence in the frame work of brane worlds. It was, recently, shown by us (M. Sami and V. Sahni) that these concepts can be synthesized successfully in brane world cosmology provided reheating is implemented by "instant preheating mechanism". However, the recent measurements of CMB anisotropy by WMAP places very strong constraints on the brane world inflation.
The study of perturbations in brane worlds is a challenging problem at present. Recently, with collaborators J. Francis, R. Maartens and J. Lidsey, I have been involved in the study of cosmological perturbations from brane inflation with a Gauss-Bonnet term. I am currently studying the observational constraints on the Gauss-Bonnet brane world inflation. I have also investigated the theoretical models of Phantom energy with N. Dadhich and P. Singh.
Publications