117743186
Statistical isotropy violation in WMAP CMB maps due to non-circular beams
We simulate CMB maps using actual WMAP non-circular beams and scanning strategy. Our estimated BipoSH spectra from these maps match the WMAP-7 results very well. This is the first explicit and conclusive demonstration that the SI violation reported in WMAP-7 maps is due to the non-circularity of the beams. It is also evident that only a very careful and adequately detailed modeling, as carried out here, can conclusively establish that the entire signal arises from non-circular beam effect. This is important since cosmic SI violation signals are expected to be subtle and and dismissing a large SI violation signal as observational artefact based on simplistic `plausibility' arguments run the serious risk of throwing the `baby with the bathwater'.
53357358
Astrophysical motivation for directed searches for a stochastic gravitational wave background
The nearby Universe is expected to create an anisotropic stochastic gravitational-wave background (SGWB). Different algorithms have been developed and implemented to search for isotropic and anisotropic SGWBs. The aim of this paper is to quantify the advantage of an optimal anisotropic search, specifically comparing a point source with an isotropic background. Clusters of galaxies appear as point sources to a network of ground-based laser-interferometric detectors. The optimal search strategy for these sources is a ``directed radiometer search.'' We show that the flux of SGWBs created by the millisecond pulsars in the Virgo cluster produces a significantly stronger signal than the nearly isotropic background of unresolved sources of the same kind. We compute their strain power spectra for different cosmologies and the distribution of populations over redshifts. We conclude that a localized source, like the Virgo cluster, can be resolved from the isotropic background with very high significance using the directed-search algorithm. For backgrounds dominated by nearby sources, up to a redshift of about 3, we show that the directed search for a localized source can have a signal-to-noise ratio that is greater than that for the all-sky integrated isotropic search.
55736791
CMB polarization TE power spectrum estimation with non-circular beam
Precise measurements of the Cosmic Microwave Background (CMB) anisotropy have been one of the foremost concerns in modern cosmology as it provides valuable information on the cosmology of the universe. However, an accurate estimation of the CMB power spectrum faces many challenges as the CMB experiments sensitivity increases. Furthermore, for polarization experiments the precision of measurement is complicated by the fact that the polarisation signal is very faint compared to the measured total intensity, and could be impossible to detect in the presence of high level of systematics. One of the most important source of errors in CMB polarization experiment is the beam asymmetry. For large data set the estimation of the CMB polarization power spectrum with standard optimal Maximum Likelihood (ML) is prohibitive for high resolution CMB experiments due to the enormous required computation time. In this paper, we present a semi-analytical framework using the pseudo-$C_{l}$ estimator to compute the power spectrum TE of the temperature anisotropy and the E-component of the polarization radiation field using non-circular beams. We adopt a model of beams obtained from a perturbative expansion of the beam around a circular (axisymmetric) one in harmonic space, and compute the resulting bias matrix which relates the true power spectrum with the observed one using an efficient algorithm for rapid computation. We show that for a multipole up to $l_{max}=500$, the bias matrix can be computed in less than one second with a single CPU processor at 2.53 GHz. We find that the uncertainties induced by the beam asymmetry in the polarization power spectrum at the peak of the bias matrix for WMAP and Planck experiments can be as large as a few 10 to 20% (upper limit for Planck LFI 30 GHz)
62838156
Revealing Non-circular beam effect in WMAP-7 CMB maps with BipoSH measures of Statistical Isotropy
Mild, unavoidable deviations from circular-symmetry of instrumental beams in current Cosmic Microwave Background (CMB) experiments now pose a significant challenge to deriving high precision inferences from the high sensitivity and resolution of CMB measurements. We present analytic results, verified by numerical simulations, that CMB maps of cosmological signal that respect underlying statistical isotropy (SI) symmetry, measured with an instrument that has mildly non-circular (NC) beam would, nevertheless, exhibit SI violation. Further, we show that appropriate observable measures constructed within the Bipolar spherical harmonic (BipoSH) representation of SI violation capture subtle NC-beam effects coupled with the scan strategy of the instrument. 
Accompanying their latest 7-year data release, the WMAP team published very high significance measurements of non-zero BipoSH spectra, A^{20}_{l l} and A^{20}_{l-2 l}, in the "W" and "V" band of the experiment. We present a strong case that the BipoSH measurement are primarily explained by the quadrupolar (m=2) component of the NC-beams, b_{l2}, of the respective channels. The fact that subtle levels of non-circularity, e.g., WMAP beams |b_{l2}|/b_{l0} < 0.01, lead to measurable BipoSH spectra points to the immense promise and potential of the BipoSH representation. The key result of this work is that using BipoSH measurements it is possible to estimate an equivalent single hit,'parallel transported' effective NC-beam that matches both the angular power spectrum and the non-zero BipoSH measurements of the observed maps. Hence, BipoSH analysis provides a very simple and effective characterization of CMB maps made with NC-beam. (Abridged)
14880786
Non-circular beam correction to the CMB power spectrum
Abstract In the era of high precision CMB measurements, systematic effects are beginning to limit the ability to extract subtler cosmological information. The non-circularity of the experimental beam has become progressively important as CMB experiments strive to attain higher angular resolution and sensitivity. The effect of non-circular beam on the power spectrum is important at multipoles larger than the beam-width. For recent experiments with high angular resolution, optimal methods of power spectrum estimation are computationally prohibitive and sub-optimal approaches, such as the Pseudo- C l method are used. We provide an analytic framework for correcting the power spectrum for the effect of beam non-circularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. We advocate that when the non-circular beams are important, it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transforms die down fast with m .
16042899
On a boundary-localized Higgs boson in 5D theories
In the context of a simple five-dimensional (5D) model with bulk matter coupled to a brane-localized Higgs boson, we point out a non-commutativity in the 4D calculation of the mass spectrum for excited fermion towers: the obtained expression depends on the choice in ordering the limits, $$N \rightarrow \infty $$N→∞ (infinite Kaluza–Klein tower) and $$\epsilon \rightarrow 0$$ϵ→0 ($$\epsilon $$ϵ being the parameter introduced for regularizing the Higgs Dirac peak). This introduces the question of which one is the correct order; we then show that the two possible orders of regularization (called I and II) are experimentally equivalent, as both can typically reproduce the measured observables, but that the one with less degrees of freedom (I) could be uniquely excluded by future experimental constraints. This conclusion is based on the exact matching between the 4D and 5D analytical calculations of the mass spectrum – via regularizations of type I and II. Beyond a deeper insight into the Higgs peak regularizations, this matching brings another confirmation of the validity of the 5D mixed formalism. All the conclusions, deduced from regularizing the Higgs peak through a brane shift or a smoothed square profile, are expected to remain similar in realistic models with a warped extra-dimension. The complementary result of the study is that the non-commutativity disappears, both in the 4D and the 5D calculations, in the presence of higher order derivative operators. For clarity, the 4D and 5D analytical calculations, matching with each other, are presented in the first part of the paper, while the second part is devoted to the interpretation of the results.
119239891
Vector meson fragmentation using a model with broken SU(3) at the next-to-leading order
A detailed study of fragmentation of vector mesons at the next-to-leading order (NLO) in QCD is given for e+e- scattering. A model with broken SU(3) symmetry using three input fragmentation functions α(x, Q2), β(x, Q2) and γ(x, Q2) and a strangeness suppression parameter λ describes all the light quark fragmentation functions for the entire vector meson octet. At a starting low energy scale of for three light quarks (u, d, s) along with initial parametrization, the fragmentation functions are evolved through DGLAP evolution equations at NLO and the cross-section is calculated. The heavy quarks contribution are added in appropriate thresholds during evolution. The results obtained are fitted at the momentum scale of for LEP and SLD data. Good-quality fits are obtained for ρ, K*, ω and ϕ mesons, implying the consistency and efficiency of this model. Strangeness suppression in this model is understood both in terms of ratios of quark fragmentation functions alone as well as in terms of observables; the latter yield a suppression through the K*/ρ multiplicity ratio of about 0.23 while the x dependence of this suppression is also parametrized through the cross-section ratios.
53636995
LHC signatures of warped-space vectorlike quarks
A bstractWe study the LHC signatures of TeV scale vectorlike quarks b′, t′ and χ with electromagnetic charges −1/3, 2/3 and 5/3 that appear in many beyond the standard model (BSM) extensions. We consider warped extra-dimensional models and analyze the phenomenology of such vectorlike quarks that are the custodial partners of third generation quarks. In addition to the usually studied pair-production channels which depend on the strong coupling, we put equal emphasis on single production channels that depend on electroweak couplings and on electroweak symmetry breaking induced mixing effects between the heavy vectorlike quarks and standard model quarks. We identify new promising gg-initiated pair and single production channels and find the luminosity required for discovering these states at the LHC. For these channels, we propose a cut that allows one to extract the relevant electroweak couplings. Although the motivation is from warped models, we present many of our results model-independently.
118559327
Constraining large‐scale H i bias using redshifted 21‐cm signal from the post‐reionization epoch
In the absence of complex astrophysical processes that characterize the reionization era, the 21-cm emission from neutral hydrogen (H i) in the post-reionization epoch is believed to be an excellent tracer of the underlying dark matter distribution. Assuming a background cosmology, it is modelled through (i) a bias function b(k, z), which relates H i to the dark matter distribution and (ii) a mean neutral fraction () which sets its amplitude. In this paper, we investigate the nature of large-scale H i bias. The post-reionization H i is modelled using gravity only N-body simulations and a suitable prescription for assigning gas to the dark matter haloes. Using the simulated bias as the fiducial model for H i distribution at z≤ 4, we have generated a hypothetical data set for the 21-cm angular power spectrum (Cl) using a noise model based on parameters of an extended version of the Giant Metrewave Radio Telescope (GMRT). The binned Cl is assumed to be measured with S/N ≳ 4 in the range 400 ≤l≤ 8000 at a fiducial redshift z= 2.5. We explore the possibility of constraining b(k) using the principal component analysis on these simulated data. Our analysis shows that in the range 0.2 < k < 2 Mpc−1, the simulated data set cannot distinguish between models exhibiting different k-dependences, provided 1 ≲b(k) ≲ 2 which sets the 2σ limits. This justifies the use of linear bias model on large scales. The largely uncertain is treated as a free parameter resulting in degradation of the bias reconstruction. The given simulated data are found to constrain the fiducial with an accuracy of ∼4 per cent (2σ error). The method outlined here could be successfully implemented on future observational data sets to constrain b(k, z) and and thereby enhance our understanding of the low-redshift Universe.
85536545
Formation rates of Dark Matter Haloes
We derive an estimate of the rate of formation of dark matter halos per unit volume as a function of the halo mass and redshift of formation. Analytical estimates of the number density of dark matter halos are useful in modeling several cosmological phenomena. We use the excursion set formalism for computing the formation rate of dark matter halos. We use an approach that allows us to differentiate between major and minor mergers, as this is a pertinent issue for semi-analytic models of galaxy formation. We compute the formation rate for the Press-Schechter and the Sheth-Tormen mass function. We show that the formation rate computed in this manner is positive at all scales. We comment on the Sasaki formalism where negative halo formation rates are obtained. Our estimates compare very well with N-Body simulations for a variety of models. We also discuss the halo survival probability and the formation redshift distributions using our method.