Debashis Ghoshal

Research Summary:

The time dependent solution to the equation of motion of the tachyonic scalar field on an unstable D-brane system may have cosmological relevance. In collaboration with D. Choudhury, D.P. Jatkar and S. Panda, we analysed the effective action of the tachyon field of both bosonic as well as superstring theory and find that the non-standard kinetic term requires a correction to the Born-Infeld type Lagrangian. The effect of the resulting dynamics in inflation (with the tachyon as the inflaton) is explored numerically. It is found that the resulting inflation is of fast-roll type and unlikely to produce sufficient expansion. We also examine if the time dependent tachyon can provide an effective cosmological constant and contrast its behaviour with quintessence.

An extension of the above model in the context of the annihilation of a brane-antibrane, in which the inter-brane separation and the tachyon realize a hybrid inflationary scenario, is in progress.

Supersymmetric gauge theories can provide an explicit description of string theory in a certain gravitational wave background. In collaboration with R. Gopakumar and D.P. Jatkar, we attempt to write a matrix description of these strings.

Publications:

D. Ghoshal, Normalization of the boundary superstring field theory action in Strings 2001, Edited by A. Dabholkar et al, American Mathematical Society (2002).

D. Choudhury, D. Ghoshal, D. Jatkar and S. Panda, On the cosmological relevance of the tachyon, Phys. Lett. B544 (2002) 231 - 238.

Conference/Workshops Attended:

Workshop on String Theory at the Harish-Chandra Research Institute, Allahabad.

Particles, Strings & Cosmology (PASCOS 03)

at the Tata Institute of Fundamental Research, Mumbai.

International Conference in Theoretical Physics and Workshop on String Theory at the Indian Association for the Cultivation of Science, Kolkata.

XVIII SERC Main School in Theoretical High Energy Physics at the Indian Institute of Technology (Madras), Chennai.

Visits to other Institutes:

Helsinki Institute of Physics, University of Helsinki, Finland.

Niels Bohr Institute, Copenhagen, Denmark.

Centre for Theoretical Studies, Indian Institute of Science, Bangalore, India.

Tata Institute of Fundamental Research, Mumbai, India.

Lectures/Seminars:

PP-Wave and matrix string theory, seminars at the Helsinki Institute of Physics, Finland and Niels Bohr Institute, Copenhagen, Denmark.

Tachyonic inflation, seminars at the Niels Bohr Institute, Copenhagen, Denmark and Centre for Theoretical Studies, Indian Institute of Science, Bangalore, India.

Recent developments in tachyon dynamics, seminar in the Workshop on String Theory, Indian Association for the Cultivation of Science, Kolkata.

Other Activities:

Instructor for the course Mathematical Physics, a part of the Graduate Curriculum in Physics of the Harish-Chandra Research Institute.

Organizer of the Workshop on String Theory held at the Harish-Chandra Research Institute.

Guest Faculty and Tutor for the course Large Field Theories in the XVIII SERC Main School in Theoretical High Energy Physics at the Indian Institute of Technology (Madras), Chennai.