Fractal Dimension as a measure of the scale of Homogeneity (2010)
Yadav, Jaswant K., Bagla, J. S., Khandai, Nishikanta
In the multi-fractal analysis of large scale matter distribution, the scale of transition to homogeneity is defined as the scale above which the fractal dimension of underlying point distribution is...
Bagla, J. S., Khandai, Nishikanta
We model the distribution of neutral Hydrogen (HI hereafter) in the post-reionization universe. This model uses gravity only N-Body simulations and an ansatze to assign HI to dark matter haloes that...
Khandai, Nishikanta, Datta, Kanan K., Bagla, J. S.
Simulated maps of the HI distribution in the post-reionization era are used to study the prospects for detection with existing and upcoming radio telescopes. We consider detection in the redshifted...
Mass function of haloes: scale invariant models (2009)
Bagla, J. S., Khandai, Nishikanta, Kulkarni, Girish
Press-Schechter theory gives a simple, approximate functional form of the mass function of dark matter haloes. Sheth and Tormen (ST) refined this mass function to give an improved analytical fit to...
The hyperfine transition of 3He+ as a probe of the intergalactic medium (2009)
We explore the prospects of using the hyperfine transition of 3He+ as a probe of the intergalactic medium. The emission signal from ionized regions during reionization is expected to be...
Hubble, Hubble's law and the expanding universe (2009)
Hubble's name is associated closely with the idea of an expanding universe as he discovered the relation between the recession velocity and distances of galaxies. Hubble also did a lot of pioneering...
Metal Enrichment and Reionization Constraints on Early Star Formation (2009)
Bagla, J. S., Kulkarni, Girish, Padmanabhan, T.
The epoch of reionization and formation of first stars are inter-linked topics that are of considerable interest. We use a simplified approach for studying formation of stars in collapsed haloes, and...
The Adaptive TreePM: An Adaptive Resolution Code for Cosmological N-body Simulations (2008)
Bagla, J. S., Khandai, Nishikanta
Cosmological N-Body simulations are used for a variety of applications. Indeed progress in the study of large scale structures and galaxy formation would have been very limited without this tool. For...
Effects of the size of cosmological N-Body simulations on physical quantities - III: Skewness (2008)
Bagla, J. S., Prasad, Jayanti, Khandai, Nishikanta
N-Body simulations are an important tool in the study of formation of large scale structures. Much of the progress in understanding the physics of galaxy clustering and comparison with observations...
Khandai, Nishikanta, Bagla, J. S.
We discuss the performance characteristics of using the modification of the tree code suggested by Barnes \cite{1990JCoPh..87..161B} in the context of the TreePM code. The optimisation involves...
We study the interplay of clumping at small scales with the collapse and relaxation of perturbations at larger scales using N-Body simulations. We quantify the effect of collapsed haloes on...
Fractal Dimensions of a Weakly Clustered Distribution and the Scale of Homogeneity (2007)
Bagla, J. S., Yadav, Jaswant, Seshadri, T. R.
Homogeneity and isotropy of the universe at sufficiently large scales is a fundamental premise on which modern cosmology is based. Fractal dimensions of matter distribution is a parameter that can be...
The vanishing phantom menace (2006)
Jassal, H. K., Bagla, J. S., Padmanabhan, T.
We demonstrate that the recently released high redshift supernova data from the SNLS (SuperNova Legacy Survey) project is in better agreement with CMB observations, unlike the earlier data sets which...
N-Body simulations are a very important tool in the study of formation of large scale structures. Much of the progress in understanding the physics of galaxy formation and comparison with...
Jassal, H. K., Bagla, J. S., Padmanabhan, T.
The dark energy component of the universe is often interpreted either in terms of a cosmological constant or as a scalar field. A generic feature of the scalar field models is that the equation of...
Cosmological N-Body Simulations (2004)
In this review we discuss Cosmological N-Body codes with a special emphasis on Particle Mesh codes. We present the mathematical model for each component of N-Body codes. We compare alternative...
Cosmological N-Body simulation: Techniques, Scope and Status (2004)
Cosmological N-Body simulations have become an essential tool for studying formation of large scale structure. These simulations are computationally challenging even though the available computing...
Comments on the size of the simulation box in cosmological N-Body simulations (2004)
N-Body simulations are a very important tool in the study of formation of large scale structures. Much of the progress in understanding the physics of high redshift universe and comparison with...
Ray, S., Bagla, J. S., Padmanabhan, T.
We investigate non-linear scaling relations for two-dimensional gravitational collapse in an expanding background using a 2D TreePM code and study the strongly non-linear regime ($\bar\xi \leq 200$)...
Bagla, J. S., Prasad, Jayanti, Ray, Suryadeep
We study the interplay of clumping at small scales with the collapse and relaxation of perturbations at much larger scales. We present results of our analysis when the large scale perturbation is...
We present an algorithm for parallelising the TreePM code. We use both functional and domain decompositions. Functional decomposition is used to separate the computation of long range and short range...
WMAP constraints on low redshift evolution of dark energy (2004)
Jassal, H. K., Bagla, J. S., Padmanabhan, T.
The conceptual difficulties associated with a cosmological constant have led to the investigation of alternative models in which the equation of state parameter, $w=p/\rho$, of the dark energy...
We estimate the signal from large scale structure at high redshifts in redshifted 21cm line. We focus on z ~ 3 and the LCDM cosmology. We assume that neutral hydrogen is to be found only in galaxies,...
Cosmology with tachyon field as dark energy (2002)
Bagla, J. S., Jassal, H. K., Padmanabhan, T.
We present a detailed study of cosmological effects of homogeneous tachyon matter coexisting with non-relativistic matter and radiation, concentrating on the inverse square potential and the...
Performance Characteristics of TreePM codes (2002)
We present a detailed analysis of the error budget for the TreePM method for doing cosmological N-Body simulations. It is shown that the choice of filter for splitting the inverse square force into...
A Comparison of Simulated and Analytic Major Merger Counts (2000)
Cohn, J. D., Bagla, J. S., White, Martin
We use large volume, high resolution, N-body simulations of 3 different $\Lambda$CDM models, with different clustering strengths, to generate dark matter halo merging histories. Over the reliable...
TreePM: A code for Cosmological N-Body Simulations (1999)
We describe the TreePM method for carrying out large N-Body simulations to study formation and evolution of the large scale structure in the Universe. This method is a combination of Barnes and Hut...
The Observed Evolution of Galaxy Clustering Vs. Epoch-Dependent Biasing Models (1999)
Magliocchetti, M., Bagla, J. S., Maddox, S. J., Lahav, O.
We study the observed evolution of galaxy clustering as a function of redshift. We find that the clustering of galaxies decreases as we go from observations of the local Universe to $z \sim 2$. On...
Neutral hydrogen at high redshift: probing structure formation (1998)
Large inhomogeneities in neutral hydrogen in the universe can be detected at redshifts $z \leq 10$ using the redshifted 21cm line emission from atomic hydrogen. This paper reviews the expected...
Gamma-ray bursts from stellar remnants - Probing the universe at high redshift (1998)
Wijers, R.A.M.J., Bloom, J.S., Bagla, J.S., Natarajan, P.
A gamma-ray burst (GRB) releases an amount of energy similar to that of a supernova explosion, which combined with its rapid variability suggests an origin related to neutron stars or black holes....
Evolution of Galaxy and Quasar Clustering (1997)
We study the evolution of correlation function of dark matter halos in the CDM class of models. We show that the halo correlation function does not evolve in proportion with the correlation function...
Evolution of Galaxy Clustering (1997)
We show that the galaxy correlation function does not evolve in proportion with the correlation function of the underlying mass distribution. Earliest galaxies cluster very strongly and the amplitude...
Scaling Relations for Gravitational Collapse in Two Dimensions (1997)
Bagla, J. S., Engineer, S., Padmanabhan, T.
It is known that radial collapse around density peaks can explain the key features of evolution of correlation function in gravitational clustering in three dimensions. The same model also makes...
Clustering in Redshift Space at High Redshifts (1997)
Recent observations show a large concentration of galaxies at high redshift. At first sight strong clustering of galaxies at high redshifts seems to be in contradiction with the models of structure...
Cosmological N-body simulations (1997)
In this review we discuss Cosmological N-Body codes with a special emphasis on Particle Mesh codes. We present the mathematical model for each component of N-Body codes. We compare alternative...
Bagla, J. S., Nath, Biman, Padmanabhan, T.
Large inhomogeneities in neutral hydrogen in the universe can be detected at redshifts $z \leq 10$ using the redshifted 21 cm line emission. We use cosmological N-Body simulations for dark matter and...
Critical Index and Fixed Point in the Transfer of Power in Nonlinear Gravitational Clustering (1996)
We investigate the transfer of power between different scales and coupling of modes during non-linear evolution of gravitational clustering in an expanding universe. We start with a power spectrum of...
Crisis in Cosmology : Observational Constraints on Omega and H_0 (1995)
Bagla, J. S., Padmanabhan, T., Narlikar, J. V.
Thanks to new technology of observations and fresh inputs from particle physics, cosmology has advanced on both observational and theoretical fronts. It is therefore opportune that we take stock of...
An Indicator of Nonlinear Gravitational Clustering (1995)
Alignment of velocity and acceleration before shell crossing, and later misalignment are used to define velocity contrast, an indicator of dynamical state of matter undergoing gravitational collapse....
In an expanding universe, velocity field and gravitational force field are proportional to each other in the linear regime. Neither of these quantities evolve in time and these can be scaled suitably...
Evolution Of Gravitational Potential In The Quasilinear And Nonlinear Regimes (1995)
We study the evolution of the power spectrum of gravitational potential during the nonlinear clustering in an $\Omega=1$ matter dominated phase. N-body simulations suggest that the potential does not...
Nonlinear Evolution of Density Perturbations (1993)
: From the epoch of recombination $(z\approx 10^3)$ till today, the typical density contrasts have grown by a factor of about $10^6$ in a Friedmann universe with $\Omega=1$. However, during the same...
During the evolution of density inhomogeneties in an $\Omega=1$, matter dominated universe, the typical density contrast changes from $\delta\simeq 10^{-4}$ to $\delta\simeq 10^2$. However, during...