Bharat Ratra


Mail Address:

Department of Physics
116 Cardwell Hall
Kansas State University
Manhattan, KS 66506-2601, U.S.A.

Phone:  (785) 532 6265 (Work)   or   (785) 532 6786 (Msgs)

    Fax:  (785) 532 6787  or  (785) 532 6806

E-Mail: ratra@phys.ksu.edu

                                                                                                                                                        Sachin


Research Interests:


My current research  focuses on developing and testing cosmological models for the large-scale matter
and radiation distributions in the universe.

A primary goal is to test Einstein's general relativity on extremely large spatial- and  temporal-scales,
inaccessible to any other method. More immediate goals include determining the geometry and contents
of the universe and how large-scale structure in the universe was formed. The cosmological models
studied include currently popular ones that are spatially open, or spatially flat and dominated by
quintessence, a time-variable cosmological `constant' (both developed  in  collaboration with
Jim Peebles). Of particular interest are the predictions these models make for the cosmic microwave
background radiation (CMBR) anisotropy.

The anisotropy in the CMBR, i.e., the variation in the CMBR temperature from point to point in the
sky, contains information about the geometry and contents of the universe. Hence the current flood of
CMBR observational data enable inter-comparison of a broad range of cosmological models, and thus
provides a powerful probe of the large-scale parameters of the universe. For the past few years we have
been analyzing CMBR anisotropy data sets from the NASA COBE satellite and other ground-based and
balloon-borne experiments. We should soon be able to significantly constrain large-scale parameters of
the universe by combining data from a  large number of CMBR anisotropy experiments.

 KSU CMBR webpage

Other interests include inflation,, dark matter, the classical cosmological tests, cosmological simulations
of low- and intermediate-redshift large-scale structure, and cosmological magnetic fields.

We collaborate with the Kansas State University High Energy Physics Group and the
University of Kansas Cosmology Group and do some of our numerical computations on the  HP Convex
Exemplars at the Kansas State University Center for Scientific Supercomputing.
 


Papers:

 Search SPIRES

B. Ratra, "Restoration of Spontaneously Broken Continuous Symmetries in de Sitter Spacetime",
Phys. Rev. D 31, 1931 (1985).  PRD Online

W. Fischler, B. Ratra, and L. Susskind, "Quantum Mechanics of Inflation",
Nucl. Phys. B 259, 730 (1985).   Scanned JPEG pg 1   pg 2   pg 3   pg 4   pg 5   pg 6   pg 7   pg 8
 pg 9   pg 10   pg 11   pg 12   pg 13   pg 14   pg 15

J. Atick, A. Dhar, and B. Ratra, "Superstring Propagation in Curved Superspace in the Presence of
Background Super Yang-Mills Fields", Phys. Lett. B 169, 54 (1986).
 Scanned JPEG pg 1   pg 2   pg 3   pg 4   pg 5

J. Atick, A. Dhar, and B. Ratra, "Superspace Formulation of Ten Dimensional N = 1 Supergravity
Coupled to N = 1 Super Yang-Mills Theory", Phys. Rev. D 33, 2824 (1986). PRD Online

B. Ratra and L. Yaffe, "Spherically Symmetric Classical Solutions in SU(2) Gauge Theory with a
Higgs Field", Phys. Lett. B 205, 57 (1988).   Scanned JPEG pg 1   pg 2   pg 3   pg 4   pg 5

P.J.E. Peebles and B. Ratra, "Cosmology with a Time-Variable Cosmological `Constant'",
Astrophys. J. Lett. 325, L17 (1988).    ADS

B. Ratra and P.J.E. Peebles, "Cosmological Consequences of a Rolling Homogeneous Scalar Field",
Phys. Rev. D 37, 3406 (1988).   PRD Online

B. Ratra, "Expressions for Linearized Perturbations in Ideal Fluid Cosmological Models",
Phys. Rev. D 38, 2399 (1988).    PRD Online

B. Ratra, "Joining Conditions for Cosmological Perturbations at an Equation of State Transition",
Phys. Rev. D 43, 3802 (1991).    PRD Online

B. Ratra, "Inflation in an Exponential Potential Scalar Field Model", Phys. Rev. D 45, 1913 (1992).
PRD Online

B. Ratra, "Quantum Mechanics of Exponential Potential Inflation", Phys. Rev. D 40, 3939 (1989).
PRD Online

B. Ratra, "Some Observational Constraints on Scalar Field Inflation Models of the Very Early
Universe", Princeton preprint PUPT-1132 (1989).   Postscript

B. Ratra, "Inflation in a Quartic Potential Scalar Field Model",
Caltech preprint GRP-217/CALT-68-1594 (1989).   Postscript

B. Ratra, "Expressions for Linearized Perturbations in a Massive Scalar Field Dominated
Cosmological Model", Phys. Rev. D 44, 352 (1991).   PRD Online

B. Ratra, "Inflation and `Reheating' in a Scalar Field Dominated Cosmological Model",
Caltech preprint GRP-229/CALT-68-1666 (1990).   Postscript

B. Ratra, "Effect of `Reheating' on Inflation Epoch Spatial Irregularities",
Caltech preprint GRP-230/CALT-68-1667 (1990).   Postscript

B. Ratra, "Dependence of Cosmological Energy Density Irregularities on the Shape of the Scalar Field
Potential During Inflation and `Reheating'", Phys. Rev. D 44, 365 (1991). PRD Online

B. Ratra, "Observationally Constrainable Free Parameters of Scalar Field Inflation Models",
Phys. Lett. B 260, 21 (1991).   Scanned JPEG pg 1   pg 2   pg 3   pg 4   pg 5   pg 6

B. Ratra, "Is Inflation Observationally `Fine-Tuned'?", in Trends in Astroparticle Physics, eds. D. Cline
and  R. Peccei (World Scientific 1992), p. 143.   Postscript

B. Ratra, "Cosmological `Seed' Magnetic Field From Inflation", Astrophys. J. Lett. 391, L1 (1992).  ADS

B. Ratra, "Inflation Generated Cosmological Magnetic Field",
Caltech preprint GRP-287/CALT-68-1751 (1991).   Postscript

B. Ratra and A. Quillen, "Gravitational Lensing Effects in a Time-Variable Cosmological `Constant'
Cosmology", Mon. Not. Roy. Astr. Soc. 259, 738 (1992).  ADS

B. Ratra, "Comments on `Dependence of Density Perturbations on the Coupling Constant in a Simple
Model of Inflation'", Princeton preprint PUPT-1345 (1992).  Postscript

B. Ratra, "Spontaneously Broken Continuous Symmetries in Hyperbolic (or Open) de Sitter
Spacetime", Phys. Rev. D 50, 5252 (1994).    PRD Online

B. Ratra and P.J.E. Peebles, "Inflation in an Open Universe", Phys. Rev. D 52, 1837 (1995).
PRD Online

B. Ratra and P.J.E. Peebles, "Cold Dark Matter Cosmogony in an Open Universe",
Astrophys. J. Lett. 432, L5 (1994).    ADS

M. Kamionkowski, B. Ratra, D.N. Spergel, and N. Sugiyama, "Cosmic Background Radiation
Anisotropy in an Open Inflation, Cold Dark Matter Cosmogony",
Astrophys. J. Lett. 434, L1 (1994).    ADS

B. Ratra, "CDM Cosmogony in an Open Universe", in CMB Anisotropies Two Years After COBE:
Observations, Theory, and the Future, ed. L.M. Krauss (World Scientific 1994), p. 158.   Postscript

K.M. Górski, B. Ratra, N. Sugiyama, and A.J. Banday, "COBE DMR-Normalized Open
Inflation, Cold Dark Matter Cosmogony", Astrophys. J. Lett. 444, L65 (1995).   ADS

B. Ratra, R.M. Kulsrud, and A.C. Quillen, "`Cosmological' Magnetic Braking and the Formation of
`Primordial' Stars and Black Holes", Princeton preprint PUPT-1535 (1995). Postscript

B. Ratra, N. Sugiyama, A.J. Banday, and K.M. Górski, "Cosmic Microwave Background Anisotropy
in COBE-DMR-Normalized Open and Flat- Cold Dark Matter Cosmogonies",
Astrophys. J. 481, 22 (1997).   ADS

K. Ganga, B. Ratra, and N. Sugiyama, "Tentative Appraisal of Compatibility of Small-Scale Cosmic
Microwave Background Anisotropy Detections in the Context of COBE-DMR-Normalized Open and
Flat-Lambda Cold Dark Matter Cosmogonies", Astrophys. J. Lett. 461, L61 (1996).   ADS

K. Ganga, B. Ratra, J.O. Gundersen, and N. Sugiyama, "UCSB South Pole 1994 Cosmic Microwave
Background Anisotropy Measurement Constraints on Open and Flat-Lambda Cold Dark Matter
Cosmogonies", Astrophys. J. 484, 7 (1997).   ADS

K.M. Górski, B. Ratra, R. Stompor, N. Sugiyama, and A.J. Banday, "COBE-DMR-Normalized Open
Cold Dark Matter Cosmogonies", Astrophys. J. Supp. 114, 1 (1998). ADS

K. Ganga, B. Ratra, S.E. Church, N. Sugiyama, P.A.R. Ade, W.L. Holzapfel, P.D. Mauskopf, and
A.E. Lange, "Using Sunyaev-Zel'dovich Infrared Experiment (SuZIE) Arcminute-Scale Cosmic
Microwave Background Anisotropy Data to Probe Open and Flat-Lambda Cold Dark Matter
Cosmogonies", Astrophys. J. 484, 517 (1997).   ADS

S. Cole, D.H. Weinberg, C.S. Frenk, and B. Ratra, "Large-Scale Structure in COBE-Normalized Cold
Dark Matter Cosmogonies", Mon. Not. Roy. Astron. Soc. 289, 37 (1997). ADS

K. Ganga, B. Ratra, M.A. Lim, N. Sugiyama, and S.T. Tanaka, "MAX 4 and MAX 5 Cosmic
Microwave Background Anisotropy Measurement Constraints on Open and Flat- Lambda Cold Dark
Matter Cosmogonies", Astrophys. J. Supp. 114, 165 (1998).  ADS

B. Ratra, K. Ganga, N. Sugiyama, G.S. Tucker, G.S. Griffin, H.T. Nguyên, and J.B. Peterson, "Using
White Dish CMB Anisotropy Data to Probe Open and Flat-Lambda CDM Cosmogonies",
Astrophys. J. 505, 8 (1998).   ADS

C. Park, W.N. Colley, J.R. Gott III, B. Ratra, D.N. Spergel, and N. Sugiyama, "Cosmic Microwave
Background Anisotropy Correlation Function and Topology from Simulated Maps for MAP",
Astrophys. J. 506, 473 (1998).   ADS

B. Ratra, K. Ganga, R. Stompor, N. Sugiyama, P. de Bernardis, and K.M. Górski, "ARGO CMB
Anisotropy Measurement Constraints on Open and Flat-Lambda Cold Dark Matter Cosmogonies",
Astrophys. J. 510, 11 (1999).   ADS

B. Ratra, R. Stompor, K. Ganga, G. Rocha, N. Sugiyama, and K.M. Górski, "Cosmic Microwave
Background Anisotropy Constraints on Open and Flat-Lambda Cold Dark Matter Cosmogonies from
UCSB South Pole, ARGO, MAX, White Dish, and SuZIE Data", Astrophys. J. 517, 549 (1999).   ADS

G. Rocha, R. Stompor, K. Ganga, B. Ratra, S.R. Platt, N. Sugiyama, and K.M. Górski, "Python I, II
and III Cosmic Microwave Background Anisotropy Measurement Constraints on Open and
Flat-Lambda Cold Dark Matter Cosmogonies", Astrophys. J. 525, 1 (1999). ADS

S. Podariu and B. Ratra, "Supernova Ia Constraints on a Time-Variable Cosmological "Constant" ",
Astrophys. J. 532, 109 (2000).   ADS

J.R. Gott, M.S. Vogeley, S. Podariu, and B. Ratra, "Median Statistics,  H_0, and the Accelerating
Universe", Astrophys. J., submitted (2000).   astro-ph

S. Podariu, P. Nugent, and B. Ratra, "Cosmological-Model-Parameter Determination from
Satellite-Acquired Type Ia and IIP Supernova Data",
Astrophys. J., submitted (2000).    astro-ph


Postdoctoral Research Associates:

 Dr. Pia Mukherjee
 Dr Tarun Souradeep
 Dr. Graca Rocha, now at University of Oxford

Graduate Students:


Silviu Podariu
 


KSU Physics
 

Last updated 28 August 2000.