Debashis Ghoshal

Research Summary:

A model of hybrid inflation, inspired by string theory in the context of a brane-antibrane system is studied in detail. The branes are taken to be partially compactified on a six-dimensional compact space. The interbrane distance acts as the inflaton, whereas the end of the inflationary epoch is brought about by the onset of the tachyon which rapidly rolls to the minimum of its potential. The number of e-foldings is controlled by the initial conditions and can be sufficiently large. The slow roll parameters turn out to be determined by the geometry and allow for little parametric dependence. We show that the primordial density fluctuations can be made consistent with current data, but this requires a low string scale. (Work in collaboration with D. Choudhury, D.P. Jatkar and S. Panda.)

The condensation of tachyon in the presence of a nonzero Neveu-Schwarz field-strength H=dB is investigated. An operator valued gauge field configuration is proposed to describe an NS-5-brane as well as an intersecting system of a semi-infinite D6-brane with its boundary on a NS5-brane. It is shown that operator valued gauge fields are better thought of as mathematical objects known as gerbes. (Work in collaboration with D.P. Jatkar and M. Kreuzer.)

The nonlocal effective field theory of the tachyonic scalar of the p-adic string theory is deformed by a noncommutative parameter. A soliton with gaussian profile was obtained for all values of the noncommutative parameter. It is shown to interpolate smoothly between the p-adic solitons of the original (commutative) theory and the noncommutative soliton at infinite noncommutativity.

Publications:

• Hybrid inflation and the brane-antibrane system
  J. Cosmology & Astrophys. 0307: 009 (2003)
  (in collaboration with D. Choudhury, D.P. Jatkar and S. Panda)

Preprints:

• Noncommutative p-tachyon
  HRI-P/031101 (To be published in the proceedings of p-Adic MathPhys 2003)

• NS fivebrane and tachyon condensation
  HRI-P-0312001, hep-th/0312245
  (in collaboration with D.P. Jatkar and M. Kreuzer)

Conference/Workshops Attended:

• p-Adic MathPhys 2003 at the Steklov Institute, Moscow, Russia (Oct 2003).

• National Workshop on String Theory at the Indian Institute of Technology (Kanpur), Kanpur, India (Dec 2003).

• VIII Winter School of APCTP/KIAS on String Theory at Korea Institute of Advanced Study, Seoul, South Korea (Feb 2004).

Visits to other Institutes:

• Harvard University, Cambridge, USA (one month during Apr--May, 2003).

• LPTHE, Université Pierre & Marie Curie Paris VI, Paris, France.

• Institute of Mathematical Sciences, Chennai, India.

• Tata Institute of Fundamental Research, Mumbai, India (on sabbatical leave from Jan--Mar, 2004).

Invited Lectures/Seminars:

• NS fivebrane and tachyon condensation, a seminar at the Centre for Theoretical Physics, MIT, Cambridge, USA.

• Hybrid inflation and brane-antibrane system, Paris area joint string theory seminar.

• Noncommutative p-tachyon, invited seminar in p-Adic MathPhys 2003 at the Steklov Institute, Moscow, Russia; also in the National Workshop on String Theory at the Indian Institute of Technology (Kanpur), Kanpur, India.

• Recent progress in p-adic string theory, seminar at the Institute of Nuclear Research, Moscow, Russia.

• Noncommutative solitons in a nonlocal field theory, a seminar at the Institute of Mathematical Sciences, Chennai, India.

• Supersymmetric gauge theories I, a course of five invited lectures in the VIII Winter School of APCTP/KIAS on String Theory at Korea Institute of Advanced Study, Seoul, South Korea.

Academic Recognition and Awards:

Awarded the Invitation Fellowship (long-term) of the Japan Society for the Promotion of Science for the year 2004--05.

Other Activities:

Taught part of the graduate course Mathematical Physics -I during the semester Aug--Dec, 2003.