arXiv subjects

Pavan Kumar Aluri

Publications and source records attributed to Pavan Kumar Aluri.

6 recordsLinked to original sources

arXiv2026

Examination of frequency and scale dependence of CMB hemispherical power asymmetry

In this study, we revisit the well-known cosmic microwave background (CMB) anomaly referred to as Hemispherical Power Asymmetry (HPA), using CMB temperature maps from the Planck mission public release 4 (PR4) and the WMAP nine-year data release. Employing the Local Variance Estimator (LVE) method, we systematically reexamine the properties of HPA to investigate possible frequency dependence as well as scale dependence in its amplitude and direction. We model the HPA as a scale-dependent dipole modulation following a power-law form, rather than assuming a scale-invariant case. Our analysis incorporates seven cleaned frequency-specific CMB temperature maps from both the Planck and WMAP missions to test the robustness of the observed asymmetry across instruments and frequency channels. We find that the dipolar modulation characteristic of HPA is present in all cases examined, with consistent estimates of the preferred direction and scale-dependent variation in dipole amplitudes. These results support the conclusion that the observed asymmetry is unlikely to arise from instrumental artifacts or data-processing effects, and instead points toward a persistent large-scale feature of the CMB sky with a possible cosmological origin.

astro-ph.CO↗

arXiv2025

Examining statistical isotropy of CMB low multipoles from Planck PR4 data

Low multipoles ($l$) in cosmic microwave background (CMB) temperature anisotropies have shown some `peculiarities' when examined since the release of the full sky CMB maps, using a variety of tests. In this paper, we concern ourselves with the very first peculiarities seen in CMB data viz., a breakdown of statistical isotropy in the form of axiality and planarity of these low-$l$ modes, and preferred alignments among them. We scrutinize the latest CMB data from ESA's Planck mission, PR4, to evaluate the current status of these deviations. We employ the Power tensor method which allows an invariant characterization of the distribution of power in a given multipole, and apply it to probe the first sixty multipoles i.e., $l=2$ to 61. We find that there are significant number of modes that are intrinsically anisotropic with a cumulative probability of $0.3\%$. However since the planarity study reveals that those modes that are unusually planar are subset of these anisotropic modes, we conclude that they may not be intrinsically planar. The quadrupole is still well aligned with the octopole. Besides, $l=3$, higher multipoles aligned with quadrupole are found to be insignificant. Interestingly, the collective alignment axis of the first sixty multipoles is found to be broadly closer to the axis of dipole, quadrupole, octopole and other modes aligned with $l=2$.

astro-ph.CO↗

arXiv2024

CMB low multipole alignments across WMAP and \emph{Planck} data releases

The first observations of the cosmic microwave background (CMB) from NASA's \emph{Wilkinson Microwave Anisotropy Probe} (WMAP) led to finding `alignment' anomalies not expected from fluctuations in the isotropic cosmological model. We study the data of all 8 full-sky public releases since then to test for anomalous alignments and shapes of the first 60 multipoles, i.e., over the range $2\leq l \leq 61$. We use rotationally invariant and covariant statistics to test isotropy of all subsequent WMAP data releases, along with those from the ESA's \emph{Planck} mission. Anomalous alignments among the multipoles $l=1, 2, 3$ are very consistent and robust. More alignments are detected, some of them new, while significance is diluted by the large range of the search. Power entropy, a measure of the randomness of the multipoles, is consistently anomalous at about $2\sigma$ level or better across all data releases. It appears that the CMB is not as random as the cosmological principle predicts on large angular scales

astro-ph.CO↗

arXiv2022

Is the Observable Universe Consistent with the Cosmological Principle?

The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.

astro-ph.CO↗

arXiv2015

A Perturbative Analysis of Synchrotron Spectral Index Variation over Microwave Sky

In this paper, we implement a perturbative approach, first proposed by Bouchet & Gispert (1999), to estimate variation of spectral index of galactic polarized synchrotron emission, using linear combination of simulated Stokes Q polarization maps of selected frequency bands from WMAP and Planck observations on a region of sky dominated by the synchrotron Stokes Q signal. We find that, a first order perturbative analysis recovers input spectral index map well. Along with the spectral index variation map our method provides a fixed reference index, \hat β_{0s}, over the sky portion being analyzed. Using Monte Carlo simulations we find that, <\hat β_{0s}> = -2.84 \pm 0.01, which matches very closely with position of a peak at β_s(p) = -2.85, of empirical probability density function of input synchrotron indices, obtained from the same sky region. For thermal dust, mean recovered spectral index, <\hat β_d> = 2.00 \pm 0.004, from simulations, matches very well with spatially fixed input thermal dust spectral index β_d = 2.00. As accompanying results of the method we also reconstruct CMB, thermal dust and a synchrotron template component with fixed spectral indices over the {\it entire} sky region. We use full pixel-pixel noise covariance matrices of all frequency bands, estimated from the sky region being analyzed, to obtain reference spectral indices for synchrotron and thermal dust, spectral index variation map, CMB map, thermal dust and synchrotron template components. The perturbative technique as implemented in this work has the interesting property that it can build a model to describe the data with an arbitrary but enough degree of accuracy (and precession) as allowed by the data. We argue that, our method of reference spectral index determination, CMB map, thermal dust and synchrotron template component reconstruction is a maximum likelihood method.

astro-ph.CO↗

arXiv2008

Dark Energy and Dark Matter in General Relativity with local scale invariance

We consider a generalization of Einstein's general theory of relativity such that it respects local scale invariance. This requires the introduction of a scalar and a vector field in the action. We show that the theory naturally displays both dark energy and dark matter. We solve the resulting equations of motion assuming an FRW metric. The solutions are found to be almost identical to those corresponding to the standard $Λ$CDM model

hep-ph↗