Theoretical High Energy Group

The High Energy/Cosmology/Astrophysics/Nuclear Physics group has seven permanent and two visiting
faculty members,

Sreerup Raychaudhuri
Gautam Sengupta
S. D. Joglekar
V. Ravishankar
V. Sreedhar
Deshdeep Sahdev
Pankaj Jain

along with five graduate students,

Sukanta Panda
Santosh K. Rai
S. Sarala
Moninder S. Modgil
Akhilesh Ranjan

The group has a wide range of research interests which include Collider Physics, Supersymmetry, Quantum Chromodynamics, Quark Gluon Plasma, Gauge Field Theories, Quantum Gravity, String Theory, D-Brane Physics, Non-Commutative Field Theories, Cosmology, Neutrino Astrophysics, Cosmic Rays and Axions. The group is very active in both phenomenological and formal aspects of high energy physics. The faculty members in the group have considerable interaction with one another and have written many joint research papers. The group organizes weekly seminars in which speakers are invited from all over the country. Several of the faculty members have also served as members of Organization and Advisory committees of many
National/International conferences. The group recently organized an international   WORKSHOP ON QCD (QCD 2002) Nov 18-22, 2002.
  It is planning to organize a Strings workshop in December 2003.

Recent Research Work of High Energy Theory Group

The work of Dr. Sreerup Raychaudhuri   is concerned with the production and detection of elementary particles at high energy particle accelerators. These `atom-smasher' machines, converting their enormous energy to matter, produce some thousands of particles per millisecond, and the particle detectors fitted with these accelerators then produce extremely complicated signals. Using the techniques of relativistic quantum field theory, statistical analysis and extensive numerical simulations on the computer, Dr. Raychaudhuri compares these signal patterns with the predictions of various theoretical models, especially focussing on the possibility that new, hitherto undiscovered, particles may have left indications somewhere in the mass of data. Such studies are intended to form a bridge between mathematical physicists developing new theories and experimentalists actually involved in the fabrication and use of accelerator machines. Among the theories in which Dr. Raychaudhuri is interested are supersymmetry and low-scale quantum gravity . The last is a new suggestion that has come up since 1998 and envisages a world of more than three dimensions, with the new dimension(s) being curled up into tiny circles too small to be observed.

The adjacent picture shows a schematic diagram of a popular model of low-scale quantum gravity  due to L. Randall and R. Sundrum (1999). In this model, the world is envisaged as a four-dimensional hyperspace embedded in a five-dimensional space, the fifth dimension being indicated by the red line. Our observable Universe lies at one end of this dimension. Another such `world' lies at the other end of the fifth dimension and is the home of strong gravitational fields causing severe warping of the spacetime. The gravitational force propagates across the fifth dimension, weakening on the way, until it reaches our world with a feeble strength measured by Newton's gravitational constant  G. However, it should still be possible, if this model is true, to detect minuscule effects of quantum gravity in particle scattering experiments conducted at very high energies. The prediction and isolation of such delicate effects is one of the major ends to which Dr. Raychaudhuri's research work is currently directed.  He is being assisted in this work by his graduate student Mr. Santosh K. Rai and numerous collaborators in other institutions.

Dr. S. D. Joglekar is interested in a wide range of topics which include
Gauge Theories, Renormalization Theory including cohomological problems in Gauge Theories,
Anomalies, Renormalization of theories with Scalar fields, energy-momentum
tensor, Anomalies and Path Integral Formulations, Superspace Formulations of
Gauge Theories, Nonlocal Theories; Noncovariant gauges.

He presently works on (1) Non-covariant gauges (2) Non-local field theories.
(1)         A formulation for giving a careful constructive definition of
path-integrals in Noncovariant gauges (that requires no "prescription") has
been given. It is consistent intrinsically with the well-defined
path-integrals for Lorentz gauges.
(2)         It has been applied to the axial pole prescription and the
energy integral convergence problem in the Coulomb gauges.
(3)         These results have suggested a re-examination of interpolating
gauges; which has brought out unexpected sensitivity of boundary conditions
on the variation of the gauge parameter in interpolating gauges to maintain
gauge-invariance, making it of doubtful value in definition of non-covariant
(4)         A general rigorous framework for embedding the formal apparatus
of noncovariant gauges has been constructed and this has brought into focus
the necessity for additional restrictions that have to be dealt with in
these gauges during renormalization.
(5)         Several issues regarding non-local field theory/ non-local
regularization such as (i) violation of causality in non-local field theory
(ii) renormalizability to all orders (iii) Phenomenological bounds on the
mass parameter are/will be under study.

Dr. Joglekar has recently served on the national organizing committee of  the Conference: Asymptotic Domains
of Theoretical Physics-2002" held at IIT Mumbai

V. Ravishankar is a theoretical physicist who has two main interests. They are Quark Gluon Plasma (QGP),
and Quantum Hall Effect (QHE). In QGP, he is interested in studying mechanism(s) that
describe its prduction and equilibration  in ultra relativistic heavy ion collisions. Although
there is a general consensus that the QGP has already been produced and "seen" in the laboratory, a
full(er) understanding of this unique phase of hadronic matter will emerge only after the above mentioned
aspects are  studied carefully and the dynamical response functions are evaluated and compared with
the experiments. The current investigations include setting up appropriate transport equations and
finding a suitable source term in the extended phase space that also includes the compact SU(3) group
space correspomding to the color as a dynamical variable.

In QHE, he has been interested in understanding the physics of partially polarised
fractional quantum hall systems, and the nature of their excitations - in particular,
the Skyrmionic excitations. He has worked on the signatures for the composite fermion model.
He has also been interested in QHE at finite temperature and in the presence of disorder.
Currently, he is working on the so called generalised exclusion statistics with applications to
quantum Hall systems in mind.

Earlier, Ravishankar has worked on the density matrix formalism of N-level systems
and used it to determine set(s) of complete polarisation observables. He has applied the results
to study nuclear and atomic systems. He has also worked on spin structure functions of high spin
targets and their quark parton interpretation.

The research interests of Dr. Gautam Sengupta are principaly centered on modern aspects of
quantum field theory namely string theory and its applications to quantum
gravity. Specific interests in String Theory includes D-brane physics,
Matrix String Theories, AdS-CFT Correspondence, quantum
gravity in de-Sitter spaces, black holes in string theory and related
brane world gravity.

Current activities over the last couple of years have been the study of
black holes in brane world models. In this context we have provided a
construction of rotating black holes described by a Kerr metric in a
brane world model. Subsequently this construction was generalised for
brane world in arbitrary dimensions providing a construction of a
Myers-Perry rotating black hole in a brane world.

Past research interests have ranged over matrix string theories, D-brane
physics, duality symmetries, conformal field theory and topological field
theories. In this context we had outlined a construction of a D-string
BPS solution in a type IIB string theory in the frameowrk of the IKKT
matrix theory. We had also constructed a classical solution in type IIB
string theory describing a plane wave in a stringy space-time. Furthermore
we had obtained the first construction of a conformal field theory
for a classical string solution which described a space-time with extended
singularity in four dimensions. Past activities in topological field
theories have led to the discovery of a twisted version of the
Krichever-Novikov Algebra related to global operator formalisms for
conformal field theories on compact Riemann surfaces.

Dr. Sengupta has acted as a chair for one of the sessions in the annual international conference in
String Theory, STRINGS 2001 at TIFR, Mumbai (January 5-10, 2001), the Millenium Meeting on
String Theory  ( MMST) at J N Center for Advanced Scientific Research, Bangalore (January 2-7, 2000)
and  in the International Winter Workshop on String Theory, Field
Theory and Gravity at Puri (Dec 1998).

He has also been a member of the National Organizing Committee
for STRINGS 2001.

Dr Pankaj Jain has wide range of interests in High Energy Physics/Astrophysics. He has been interested in understanding the structure of fundamental particles such as the proton. These particles are bound states of elementary particles called quarks but their precise bound state structure remains poorly understood. The fundamental theory describing the interactions of quarks is called Quantum Chromodynamics or QCD. The theory has turned out to be extremely complicated and notoriously hard to solve. A fundamental problem associated with this theory is that quarks have never been seen in a free state. Furthermore so far it has not been possible to theoretically calculate the  scattering processes involving protons except in some very special circumstances such that all the momenta involved in the process are very large. Dr. Jain is interested in understanding the electromagnetic structure of these particles. Since proton is not a point particle its interaction with photons is described in terms of a form factor. These form factors show a very simple structure experimentally, essentially obeying a simple power law as a function of the momentum. However even this basic power dependence is so far not understood theoretically. In collaboration with John Ralston from University of Kansas, USA, Dr. Jain is working towards a solution to this basic problem.

Dr. Jain has also been interested in the polarized radiation from cosmologically distant sources. Recent
observations have indicated that optical polarizations from distant quasars tend to be aligned with one another.
This effect is very surprising since the alignment is seen for quasars which are very far away from one another and
are not expected to have any correlation over such large distances. The effect is particularly pronounced in the
direction of the Virgo supercluster of galaxies. The Virgo supercluster has been observed to have a magnetic field
of order 1 microgauss over very large length scales of order 10 Mpc. Dr. Jain along with graduate students Sukanta
Panda and S. Sarala recently proposed that the alignment effect can be explained if we assume that the quasars
are also emitting axions. Axions are a hypothetical pseudoscalar particle which is predicted by many extensions of the
Standard Model of particle physics but has not been observed so far. In the presence of a background magnetic field
it decays into photons whose polarizations are aligned along the background magnetic field. Hence we can explain the
alignment effect if the quasars emit axions which decay while propagation through the Virgo supercluster. The
polarizations of photons produced in this manner will be aligned along the direction of the background magnetic field
and hence will explain the alignment effect. This is the only known explanation of this puzzling effect


Schematic illustration of how the axion-photon mixing explains the  observed alignment of optical polarization alignment in the direction of the Virgo Supercluster. Axions (shown by the brown arrow) emitted by distant quasars decay into photons (shown by the blue wave line) in the presence of the background supercluster magnetic field (B). The photon produced in this process is polarized parallel to the background magnetic field and hence leads to an alignment of the observed polarizations.

Dr. Jain has also been working on the fascinating subject of ultra high energy cosmic rays. The origin of cosmic rays at energies greater than 10 20 eV is very poorly understood. Particles such as protons at energies greater than 1020 eV
are not able to propagate distances larger than roughly 50 Mpc through intergalactic space since they are attenuated by Cosmic Microwave Background Radiation. Since it is believed that astrophysical sources capable of accelerating particle to these energies exist mostly at distances larger than 50 Mpc the observation of large number of events with energies in excess of 1020  eV is very puzzling. Cosmic rays at such high energies are observed through the giant air showers that they generate when the incident cosmic rays hits an air nucleus. The elementary particle Neutrino can travel farthest distance in intergalactic space and could be responsible for these events if its interaction with matter at ultra high energies was strong enough. Within the standard model of particle physics its interaction with matter is so weak that it will have very small probability to interact with the air particles and hence will have very little probability to generate the observed giant air showers. Dr. Jain and collaborators recently proposed that at energies relevant for these cosmic rays neutrino interaction with matter is very strong within the recently proposed models which involve extra spatial dimension. Hence these models provide an elegant solution to the problem of the origin of ultra high energy cosmic rays.

Recent Research Publications

By Gautam Sengupta,  Archive: hep-th/0205087

ROTATING BRANE WORLD BLACK HOLES, By Moninder Singh Modgil, Sukanta Panda, Gautam Sengupta, (To appear in Modern Physics Letters A), e-Print Archive: hep-th/0104122


OSCILLATING COLOR TRANSPARENCY IN PI A ---> PI P(A - 1) AND GAMMA A ---> PI N(A - 1), Pankaj Jain, Bijoy Kundu, John P. Ralston,   Phys. Rev. D65, 094027 (2002)

By Supriya Kar and Sudhakar Panda, hep-th/0205078

Pankaj Jain, Supriya Kar, Douglas W. McKay, Sukanta Panda and John P. Ralston,  hep-ph/0205052

By Prasanta Das, Santosh Kumar Rai and Sreerup Raychaudhuri, hep-ph/0102242

By Dilip Kumar Ghosh, Sreerup Raychaudhuri,  Phys. Lett. B495, 114 (2000),  hep-ph/0007354

By Satish D. Joglekar, hep-th/0205045

By Satish D. Joglekar,  Eur. Phys. J. direct C12, 1 (2001),  hep-th/0106264

PREEQUILIBRIUM EVOLUTION OF QUARK - GLUON PLASMA, Gouranga C. Nayak, V. Ravishankar, Phys. Rev. C58, 356 (1998), hep-ph/9710406

L. O'Raifeartaigh, V.V. Sreedhar, Annals Phys. 293, 215 (2001),  hep-th/0007199

THE TWO EXPONENTIAL LIOUVILLE THEORY AND THE UNIQUENESS OF THE THREE POINT FUNCTION, L. O'Raifeartaigh, J. M. Pawlowski, V.V. Sreedhar, Phys. Lett. B481, 436 (2000),  hep-th/0003247

Moninder Singh Modgil, Deshdeep Sahdev,  gr-qc/0107055

Subir Mukhopadhyay, Koushik Ray, JHEP 0107, 007 (2001),  hep-th/0102146

Subir Mukhopadhyay, Koushik Ray,  Nucl. Phys. B576,  152,2000,  hep-th/9909107


The theory group operates a Computation Facility, which houses several computers using LINUX operating system. The facility is heavily used for large scale numerical simulations.

Computer Room