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L. Sriramkumar
Research Summary:
My recent and current research work has been been focused on understanding
the possible effects of trans-Planckian modes in:
(a) the early universe (in particular, in the
context of the inflationary scenario) and (b) very high-energy
astrophysical processes. (A related aspect
that I have also been studying is the effect of the trans-
Planckian modes on entropy bounds.) I have briefly
described below the work I have been involved in in investigating
the possible modifications to the inflationary density perturbation
spectrum due to trans-Planckian effects.
It was long believed that quantum gravitational effects will be
important only at very high energies of the order of the Planck
energy. But, over the past few years, it has been realized that,
due to the tremendous red-shift that occurs during the inflationary
epoch in the early universe, trans-Planckian physics can manifest
itself even at energies much lower than the Planck energy.
The presence of a fundamental scale (viz. the Planck scale) points
to the fact that Lorentz invariance may be violated at sufficiently
high energies. In order to take into account such a possible trans-Planckian
effect, recently, models wherein Lorentz invariance is violated
locally, but which nevertheless possess a generally covariant metric
theory of gravity have been constructed by introducing high frequency
dispersion. Also, such models have been used to evaluate the modifications
to the density perturbation spectrum in the inflationary scenario.
However, certain astrophysical observations seem to indicate that
Lorentz invariance may be preserved to extremely high energies.
In such a situation, to study the trans-Planckian effects, it becomes
imperative to construct models that preserve Lorentz invariance
even as they contain a fundamental scale. In this work, we attempt
to construct such a model, evaluate the leading order corrections
to the standard, scale invariant, inflationary density perturbation
spectrum in the model and also study the possible signatures of
the modified spectrum on the cosmic microwave background radiation.
Publications:
L. Sriramkumar, Odd statistics in odd dimensions
for odd couplings, Mod. Phys. Lett. A 17, 1059-1066 (2002).
Preprints:
L. Sriramkumar, Interpolating between the Bose-Einstein
and the Fermi-Dirac distributions in odd dimensions, gr-qc/0212084,
To appear in General Relativity and Gravitation.
Conference/Workshops Attended:
- Recent Advances in Loop Quantum Gravity, Raman Research
Institute, Bangalore, November 28-December 9, 2002.
- Field Theory Aspects of Gravity III, Cochin University
for Science and Technology, Kochi, January 23-29, 2003.
Visits to other Institutes:
- Department of Physics, Indian Institute of Technology,
Kanpur, June 2-7, 2002.
- Raman Research Institute, Bangalore, July 22-26, 2002.
- The Institute of Mathematical Sciences, Chennai, August
5-9, 2002.
Invited Lectures/Seminars:
- Detecting thermal effects in spacetimes with horizons,
Seminar at Department of Physics, Indian Institute of Technology,
Kanpur, June 5, 2002.
- Cavity with a moving boundary and the Bekenstein's bound
on specific entropy, Seminars at Raman Research Institute,
Bangalore, July 22, 2002 and The Institute of Mathematical
Sciences, Chennai, August 7, 2002.
- Semiclassical gravity--Issues, resolutions and prospects,
Colloquium at Raman Research Institute, Bangalore, July 24,
2002.
- Density perturbations from inflation--A cosmological magnifying
glass for physics beyond the Planck scale, Invited talk in
the Meeting on Recent Advances in Loop Quantum Gravity, Raman
Research Institute, Bangalore, November 28-December 9, 2002.
- Modified dispersion relations and the Bekenstein's bound
on specific entropy, Invited Talk in the Third Workshop on
Field Theoretic Aspects of Gravity, Cochin University for Science
and Technology, Kochi, January 23-29, 2003.
- A brief history of the universe, Talk at Department of
Physics, P. S. G. Krishnammal College, Coimbatore,
January 30, 2003.
- The expanding universe, Talk at The National Academy
of Sciences, Allahabad, National Science Day, February 2003.
Other Activities:
- Conducted (the Physics part of) the HRI Science Talent Search
Test 2002.
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