arXiv subjects

Suvodip Mukherjee

Publications and source records attributed to Suvodip Mukherjee.

113 records · Page 7Linked to original sources

arXiv2015

Statistical Anisotropic Gaussian Simulations of the CMB Temperature Field

Although theoretically expected to be Statistically Isotropic (SI), the observed Cosmic Microwave Background (CMB) temperature \& polarization field would exhibit SI violation due to various inevitable effects like weak lensing, Doppler boost and practical limitations of observations like non-circular beam, masking etc. However, presence of any SI violation beyond these effects may lead to a discovery of inherent cosmic SI violation in the CMB temperature \& polarization field. Recently, Planck presented strong evidence of SI violation as a dipolar power asymmetry of the CMB temperature field in two hemispheres. Statistical studies of SI violation effect require non-SI (nSI) Gaussian realizations of CMB temperature field. The nSI Gaussian temperature field leads to non-zero off-diagonal terms in the Spherical Harmonics (SH) space covariance matrix encoded in the coefficients of the Bipolar Spherical Harmonics (BipoSH) representation. We discuss an effective numerical algorithm, Code for Non-Isotropic Gaussian Sky (CoNIGS) to generate nSI realizations of Gaussian CMB temperature field of Planck like resolution with specific cases of SI violation. Realizations of nSI CMB temperature field are obtained for non-zero quadrupolar $(L=2)$ BipoSH measurements by WMAP, dipolar asymmetry (resembles $L=1$ BipoSH coefficients) with a \emph{scale dependent} modulation field as measured by Planck and for Doppler boosted CMB temperature field which also leads to $L=1$ BipoSH spectra. Our method, CoNIGS can incorporate any kind of SI violation and can produce nSI realizations efficiently.

astro-ph.CO↗

arXiv2015

Statistical Isotropy violation of CMB polarization sky due to Lorentz boost

In the frame of a moving observer, the Cosmic Microwave Background (CMB) fluctuation exhibits violation of Statistical Isotropy (SI). The SI violation effect from our local motion on CMB temperature fluctuation has been measured in the recent Planck results. We calculate the effect of our local motion with velocity $(β\equiv |\boldsymbol v|/c= 1.23 \times 10^{-3})$ on CMB polarization field. The Lorentz transformation of the polarization field leads to aberration in the direction of incoming photons and also modulation of the Stokes parameters, which results in mixing of power between different CMB multipoles. We show that for small values of $β$, the effect on the angular power spectra that corresponds to the diagonal terms in the spherical harmonic space is at $O(β^2)$. But non-zero off-diagonal terms at the linear order in $β$ could provide a measurable signature of SI violation in the Bipolar Spherical Harmonic (BipoSH) representation. We also calculate the measurability of $β$ from polarization maps from experiments like Planck and PRISM. It is possible to measure $β$ from the ideal, cosmic variance limited BipoSH spectra of $EE$, $TE$, $BB$, but not in $EB$ and $TB$. With the instrumental noise of and angular resolution of Planck, it is not possible to measure $β$ with high statistical significance from BipoSH spectra of polarization. PRISM can measure $β$ with high significance in both $EE$ and $TE$ BipoSH spectra, but not in $BB$, $EB$ and $TB$ BipoSH spectra.

astro-ph.CO↗

arXiv2015

Hemispherical asymmetry from an isotropy violating stochastic gravitational wave background

Measurement of Cosmic Microwave Background (CMB) temperature by Planck has resulted in extremely tight constraints on the $Λ$CDM model. However the data indicates a evidence of dipole modulated temperature fluctuations at large angular scale which is beyond the standard Statistically Isotropic (SI) $Λ$CDM model. The signal measured by Planck requires a scale dependent modulation amplitude that is beyond the scope of the phenomenological model considered by Planck. We propose a phenomenological model with mixed modulation field for scalar and tensor perturbations which affect the temperature fluctuations at large angular scales. Hence this model is a possible route to explain the scale dependent nature of the modulation field. The salient prediction of this model is the direction dependent tensor to scalar ratio which results in anisotropic Stochastic Gravitational Wave Background (SGWB). This feature is potentially measurable from the $B$-mode polarization map of Planck and BICEP-2 and leads to determination of the modulation strength. Measurability of SI violated polarization field due to this model is estimated for Planck and PRISM. Absence of the signal in the polarization field can restrict the viability of the model.

astro-ph.CO↗

arXiv2015

Revised cosmological parameters after BICEP 2 and BOSS

Estimation of parameters of the \lq standard\rq \,model of cosmology have dramatically improved over past few decades due to increasingly exquisite measurements made by Cosmic Microwave Background (CMB) experiments. Recent data from Planck matches well with the minimal $Λ$CDM model. A likelihood analysis using Planck, WMAP and a selection of high resolution experiments (highL), tensor to scalar ratio $r_{0.002}$ is found to be $<0.11$ when $dn_{s}/d\ln k = 0$. Planck also imposes an upper bound on neutrino mass $\sum m_ν<0.23\,$eV using Planck+WMAP+highL+BAO likelihood. However, recently results from BICEP 2 claims the detection of $r= 0.2^{+0.07}_{-0.05}$ from polarization spectra. Further, results from SDSS-III BOSS large scale galaxy survey constrains the total neutrino mass to $\sum m_ν=0.36 \pm 0.10$ eV. It is important to study the consequences of these new measurements on other cosmological parameters. In this paper we assess the revised constraints on cosmological parameters in light of these two measurements that are in some tension with the constraints from Planck. Using the prior on $\sum m_ν$ as measured by SDSS-III BOSS and BICEP 2 likelihood, we find that the model with running spectral index ($dn_{s}/d\ln k \neq 0$) leads to a value of $A_L>1$ at $3.1 σ$. But, the model with $dn_{s}/d\ln k =0$ makes $A_L$ consistent with $1$, at $2.1σ$ and also shows that $N_{\rm eff}$ is consistent with its theoretical value of $3.046$ at around $2σ$. Therefore, the analysis in this paper shows that the model with $dn_{s}/d\ln k =0$ gives consistency with other cosmological parameters ($N_{\rm eff}$ and $A_L$ ) when the current limits on $\sum m_ν$ and $r_{0.05}$ are considered. However, on reducing the value of $r_{0.05}$, the model with non-zero $dn_{s}/d\ln k$ gives consistent result of $A_L =1$ [abridged].

astro-ph.CO↗

arXiv2015

Estimation of Inflation parameters for Perturbed Power Law model using recent CMB measurements

Cosmic Microwave Background (CMB) is an important probe for understanding the inflationary era of the Universe. We consider the Perturbed Power Law (PPL) model of inflation which is a soft deviation from Power Law (PL) inflationary model. This model captures the effect of higher order derivative of Hubble parameter during inflation, which in turn leads to a non-zero effective mass $m_{\rm eff}$ for the inflaton field. The higher order derivatives of Hubble parameter at leading order sources constant difference in the spectral index for scalar and tensor perturbation going beyond PL model of inflation. PPL model have two observable independent parameters, namely spectral index for tensor perturbation $ν_t$ and change in spectral index for scalar perturbation $ν_{st}$ to explain the observed features in the scalar and tensor power spectrum of perturbation. From the recent measurements of CMB power spectra by WMAP, Planck and BICEP-2 for temperature and polarization, we estimate the feasibility of PPL model with standard $Λ$CDM model. Although BICEP-2 claimed a detection of $r=0.2$, estimates of dust contamination provided by Planck have left open the possibility that only upper bound on $r$ will be expected in a joint analysis. As a result we consider different upper bounds on the value of $r$ and show that PPL model can explain a lower value of tensor to scalar ratio ($r<0.1$ or $r<0.01$) for a scalar spectral index of $n_s=0.96$ by having a non-zero value of effective mass of the inflaton field $\frac{m^2_{\rm eff}}{H^2}$. The analysis with WP+ Planck likelihood shows a non-zero detection of $\frac{m^2_{\rm eff}}{H^2}$ with $5.7\,σ$ and $8.1\,σ$ respectively for $r<0.1$ and $r<0.01$. Whereas, with BICEP-2 likelihood $\frac{m^2_{\rm eff}}{H^2} = -0.0237 \pm 0.0135$ which is consistent with zero.

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