A5103129535- Cosmology and Gravitation Theories
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Geophysics and Gravity Measurements
- Scientific Research and Discoveries
- Black Holes and Theoretical Physics
- Relativity and Gravitational Theory
- Statistical and numerical algorithms
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Advanced Differential Geometry Research
- Solar and Space Plasma Dynamics
- Particle physics theoretical and experimental studies
- Climate variability and models
- Superconducting and THz Device Technology
- Neutrino Physics Research
- Computational Physics and Python Applications
- Pulsars and Gravitational Waves Research
- Stochastic processes and financial applications
- Geomagnetism and Paleomagnetism Studies
- Complex Systems and Time Series Analysis
- Statistical Mechanics and Entropy
- Astrophysics and Star Formation Studies
- Reservoir Engineering and Simulation Methods
Inter-University Centre for Astronomy and Astrophysics
2014-2023
Indian Institute of Science Education and Research Pune
2020-2023
Raman Research Institute
2022-2023
Savitribai Phule Pune University
2010-2016
International University of the Caribbean
2003-2012
Kansas State University
2000-2003
University of Toronto
1997-2000
Canadian Institute for Theoretical Astrophysics
1998-2000
We discuss a scenario in which extra dimensional effects allow scalar field with steep potential to play the dual role of inflaton as well dark energy (quintessence). The post-inflationary evolution universe this is generically characterized by ``kinetic regime'' during kinetic greatly exceeds its resulting ``stiff'' equation state for matter ${P}_{\ensuremath{\varphi}}\ensuremath{\simeq}{\ensuremath{\rho}}_{\ensuremath{\varphi}}.$ regime precedes radiation dominated epoch and introduces an...
The statistical expectation values of the temperature fluctuations cosmic microwave background (CMB) are assumed to be preserved under rotations sky. This assumption isotropy (SI) CMB anisotropy should observationally verified since detection a violation SI could have profound implications for cosmology. We propose set measures, κℓ (ℓ = 1, 2, 3, ...), detecting in an observed sky map indicated by nonzero κℓ. define estimator spectrum and analytically compute its bias variance. results match...
The observed angular power spectrum of the cosmic microwave background temperature anisotropy, ${C}_{l},$ is a convolution cosmological radiative transport kernel with an assumed primordial inhomogeneities. Exquisite measurements ${C}_{l}$ over wide range multipoles from Wilkinson Microwave Anisotropy Probe (WMAP) has opened up possibility to deconvolve for given set parameters (base model). We implement improved (error sensitive) Richardson-Lucy deconvolution algorithm on measured WMAP...
We investigate inflationary scenarios driven by a class of potentials which are similar in form to those that arise certain minimal supersymmetric extensions the standard model. find these allow brief period departure from inflation sandwiched between two stages slow roll inflation. show such background behavior leads step like feature scalar power spectrum. set scales drop spectrum occurs at length scale corresponds Hubble radius today — seems necessary explain lower observed quadrupole...
Recently, we have shown that scalar spectra with lower power on large scales and certain other features naturally occur in {\it punctuated inflation}, i.e. the scenario wherein a brief period of rapid roll is sandwiched between two stages slow inflation. Such gain importance due to fact they can lead better fit observed Cosmic Microwave Background (CMB) anisotropies, when compared conventional, featureless, law spectrum. In this paper, examples from canonical field as well tachyonic models,...
Certain oscillatory features in the primordial scalar power spectrum are known to provide a better fit outliers cosmic microwave background data near multipole moments of ℓ = 22 and 40. These usually generated by introducing step popular, quadratic potential describing canonical field. Such model will be ruled out, if tensors remain undetected at level corresponding tensor-to-scalar ratio of, say, r ≃ 0.1. In this work, addition popular potential, we investigate effects small field tachyon...
Measurement of the CMB bispectrum, or three-point correlation function, has now become one principle efforts in early-Universe cosmology. Here we show that there is an odd-parity component bispectrum been hitherto unexplored. We argue temperature-polarization bispectra can arise, principle, through weak lensing by chiral gravitational waves cosmological birefringence, although signals will be small even best-case scenarios. these requires only modest modifications to usual data-analysis...
Amongst the multitude of inflationary models currently available, that lead to features in primordial scalar spectrum are drawing increasing attention, since certain have been found provide a better fit cosmic microwave background data than conventional, nearly scale invariant, spectrum. In this work, we carry out complete numerical analysis two oscillations over all scales power We consider model described by quadratic potential which is superposed sinusoidal modulation and recently popular...
Using modified Richardson-Lucy algorithm we reconstruct the primordial power spectrum (PPS) from Planck Cosmic Microwave Background (CMB) temperature anisotropy data. In our analysis use different combinations of angular spectra to shape and locate possible features. Performing an extensive error found dip near ℓ ∼ 750–850 represents most prominent feature in Feature 1800–2000 is detectable with high confidence only 217 GHz apparently consequence a small systematic as described revised 2013...
Abstract This paper discusses the science case for a sensitive spectro-polarimetric survey of microwave sky. Such would provide tomographic and dynamic census three-dimensional distribution hot gas, velocity flows, early metals, dust, mass in entire Hubble volume, exploit CMB temperature polarisation anisotropies down to fundamental limits, track energy injection absorption into radiation background across cosmic times by measuring spectral distortions blackbody emission. In addition its...
We analyze the three-year WMAP temperature anisotropy data seeking to confirm power spectrum and likelihoods published by team. apply five independent implementations of four algorithms estimation two parameter estimation. Our single most important result is that we broadly analysis. Still, do find small but potentially discrepancies: On large angular scales there a excess in (5-10% at l~300). Recently, latter discrepancy was explained Huffenberger et al. (2006) terms over-subtraction...
In this paper we implement an improved (error-sensitive) Richardson-Lucy deconvolution algorithm on the measured angular power spectrum from Wilkinson Microwave Anisotropy Probe (WMAP) 3 year data to determine primordial assuming different points in cosmological parameter space for a flat $\ensuremath{\Lambda}\mathrm{CDM}$ model. We also present preliminary results of estimation by free form spectrum, reasonably large volume space. The recovered considerably number has likelihood far better...
Precise measurements of the anisotropies in cosmic microwave background enable us to do an accurate study on form primordial power spectrum for a given set cosmological parameters. In previous paper [A. Shafieloo and T. Souradeep, Phys. Rev. D 70, 043523 (2004).], we implemented improved (error sensitive) Richardson-Lucy deconvolution algorithm measured angular from first year WMAP data determine assuming concordance model. This recovered has likelihood far better than scale invariant, or,...
We examine statistical isotropy of large scale anisotropies the Internal Linear Combination (ILC) map, based on 3 yr WMAP data. Our study reveals no significant deviation from angular scales ILC map. Comparing map and 1 we find a improvement in which can be due to gain model, improved processing, foreground minimization.
We explore a class of primordial power spectra that can fit the observed anisotropies in cosmic microwave background well and predicts value for Hubble parameter consistent with local measurement $H_0 = 74$ km/s/Mpc. This spectrum consists continuous deformation between best-fit law derived from modified Richardson-Lucy deconvolution algorithm applied to $C_\ell$s spectrum. find linear interpolation half-way fits Planck data better than $\Lambda$CDM by $\Delta\log\mathcal{L} 2.5$. In effect,...
We discuss the discordance between estimated values of cosmological parameters from Planck assuming concordance ΛCDM model and low-redshift measurements. In particular, we consider Hubble constant mismatch temperature constraint for Riess et al. [1] local measurements as well value S8 some weak lensing surveys such Kilo Degree Survey (KiDS-450) Dark Energy (DES) observations. The can come a wide range non-standard or astrophysical processes particular systematics this paper, without...
Following the pioneering observations with COBE in early 1990s, studies of cosmic microwave background (CMB) have focused on temperature and polarization anisotropies. CMB spectral distortions - tiny departures energy spectrum from that a perfect blackbody provide second, independent probe fundamental physics, reach deep into primordial Universe. The theoretical foundation has seen major advances recent years, which highlight immense potential this emerging field. Spectral property Universe...
Exploring Cosmic History and Origins (ECHO), popularly known as `CMB-Bh$\overline{a}$rat', is a space mission that has been proposed to the Indian Space Research Organisation (ISRO) for scientific exploitation of Microwave Background (CMB) at next level precision accuracy. The quest CMB polarization $B$-mode signals, generated by inflationary gravitational waves in very early universe, one key goals its experimental design. This work studies potential ECHO instrumental configuration detect...
We present a numerical study of topological descriptors initially Gaussian and scale-free density perturbations evolving via gravitational instability in an expanding Universe. The measured Euler number the excursion set at percolation threshold, ${\ensuremath{\delta}}_{\mathrm{c}}$, is positive nearly equal to isolated components, suggesting that these structures are trees. Our critical point counts reconciles clumpy appearance field ${\ensuremath{\delta}}_{\mathrm{c}}$ with filamentary...
We use weighted-mean and median statistics techniques to combine individual cosmic microwave background (CMB) anisotropy detections determine binned, multipole-space, CMB power spectra. The resultant spectra are peaked. derived spectrum is not a good representation of the measurements in number multipole-space bins, if Gaussian correlations between small. This could mean that some observational error bars underestimated, possibly as consequence undetected systematic effects. Discarding most...
We investigate the behaviour of classical and quantum fields in conical space-time associated with a point mass 2+1 dimensions. show that presence boundary conditions alters electrostatic field charge leading to finite self-force on from direction exactly as if itself were charged. The geometry also affects zero fluctuations scalar existence vacuum polarisation --- $\langle T_\mn \rangle$, dimensional analog Schwarzschild metric. resulting linearised semi-classical Einstein equations $G_\mn...
We calculate the expected angular power spectrum of temperature fluctuations in microwave background radiation (MBR) generated quasi-steady state cosmology (QSSC). The paper begins with a brief description how is produced and thermalized QSSC. then discuss within framework simple model likely sources due to astrophysical cosmological causes. Power peaks at l ≈ 6-10, 180-220, 600-900 are shown be respectively related this curvature effects last minimum scale factor, clusters, groups galaxies....
Bipolar spherical harmonics (BiPoSHs) provide a general formalism for quantifying departures in the cosmic microwave background (CMB) from statistical isotropy and Gaussianity. However, prior work has focused only on BiPoSHs with even parity. Here we show that there is another set of odd parity, explore their cosmological applications. We describe systematic artifacts CMB map could be sought by measurement these odd-parity BiPoSH modes. These modes may also produced cosmologically through...
The statistical expectation values of the temperature fluctuations cosmic microwave background (CMB) are assumed to be preserved under rotations sky. We use bipolar power spectrum (BiPS) proposed in Hajian & Souradeep investigate isotropy (SI) CMB anisotropy maps recently measured by Wilkinson Microwave Anisotropy Probe (WMAP). method can isolate and probe specific regions choice multipole space using appropriate window functions. BiPS is estimated for full-sky based on first-year WMAP data...
The recent Cosmic Microwave Background (CMB) measurements indicate that there is power deficiency of the CMB anisotropies at large scales compared with $\ensuremath{\Lambda}\mathrm{CDM}$ model. We have investigated possibility explaining such effects by a class primordial spectra which infrared cutoffs close to horizon scale. spectrum recovered direct deconvolution observed angular indicates data prefers sharp cutoff localized excess (bump) just above cutoff. been motivated assess plausible...