**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
gauges.
(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 10^{20}
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 10^{20} 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**

** ROTATING BLACK HOLES IN HIGHER DIMENSIONAL BRANE WORLDS,
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
**

**ELECTROMAGNETIC POLARIZATION EFFECTS DUE TO AXION PHOTON MIXING, Pankaj
Jain, Sukanta Panda, S. Sarala:
hep-ph/0206046
**

**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)
**

**ELECTROMAGNETIC STRINGS: TIME - LIKE WINDINGS AND HAGEDORN TEMPERATURE,
By Supriya Kar and Sudhakar Panda, hep-th/0205078
**

**ANGULAR DEPENDENCE OF NEUTRINO FLUX IN KM**3 DETECTORS IN LOW SCALE
GRAVITY MODELS.
Pankaj Jain, Supriya Kar, Douglas W. McKay, Sukanta Panda and John
P. Ralston, hep-ph/0205052
**

**ANOMALOUS MAGNETIC MOMENT OF THE MUON IN A COMPOSITE MODEL,
By Prasanta Das, Santosh Kumar Rai and Sreerup Raychaudhuri, hep-ph/0102242
**

**TESTING THE RANDALL-SUNDRUM MODEL AT A HIGH-ENERGY E- E- COLLIDER.
By Dilip Kumar Ghosh, Sreerup Raychaudhuri, Phys. Lett. B495,
114 (2000), hep-ph/0007354
**

**SOME OBSERVATIONS ON NONCOVARIANT GAUGES AND THE EPSILON TERM,
By Satish D. Joglekar, hep-th/0205045
**

**INTERPOLATING GAUGES AND THE IMPORTANCE OF A CAREFUL TREATMENT OF EPSILON
TERM.
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
**

**THE MAXIMAL KINEMATICAL INVARIANCE GROUP OF FLUID DYNAMICS AND EXPLOSION
- IMPLOSION DUALITY,
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
**

**RECURRENCE METRICS AND THE PHYSICS OF CLOSED TIME - LIKE CURVES,
Moninder Singh Modgil, Deshdeep Sahdev, gr-qc/0107055
**

**FRACTIONAL BRANES ON A NONCOMPACT ORBIFOLD.
Subir Mukhopadhyay, Koushik Ray, JHEP 0107, 007 (2001), hep-th/0102146
**

**D-BRANES ON FOURFOLDS WITH DISCRETE TORSION,
Subir Mukhopadhyay, Koushik Ray, Nucl. Phys. B576, 152,2000,
hep-th/9909107
**

**Facilities**

**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.**

**
**