arXiv subjects

Meir Shimon

Publications and source records attributed to Meir Shimon.

34 records · Page 2Linked to original sources

arXiv2016

POLARBEAR Constraints on Cosmic Birefringence and Primordial Magnetic Fields

We constrain anisotropic cosmic birefringence using four-point correlations of even-parity $E$-mode and odd-parity $B$-mode polarization in the cosmic microwave background measurements made by the POLARization of the Background Radiation (POLARBEAR) experiment in its first season of observations. We find that the anisotropic cosmic birefringence signal from any parity-violating processes is consistent with zero. The Faraday rotation from anisotropic cosmic birefringence can be compared with the equivalent quantity generated by primordial magnetic fields if they existed. The POLARBEAR nondetection translates into a 95% confidence level (C.L.) upper limit of 93 nanogauss (nG) on the amplitude of an equivalent primordial magnetic field inclusive of systematic uncertainties. This four-point correlation constraint on Faraday rotation is about 15 times tighter than the upper limit of 1380 nG inferred from constraining the contribution of Faraday rotation to two-point correlations of $B$-modes measured by Planck in 2015. Metric perturbations sourced by primordial magnetic fields would also contribute to the $B$-mode power spectrum. Using the POLARBEAR measurements of the $B$-mode power spectrum (two-point correlation), we set a 95% C.L. upper limit of 3.9 nG on primordial magnetic fields assuming a flat prior on the field amplitude. This limit is comparable to what was found in the Planck 2015 two-point correlation analysis with both temperature and polarization. We perform a set of systematic error tests and find no evidence for contamination. This work marks the first time that anisotropic cosmic birefringence or primordial magnetic fields have been constrained from the ground at subdegree scales.

astro-ph.CO↗

arXiv2015

A Globally Unevolving Universe

A scalar-tensor theory of gravity is formulated in which $G$ and particle masses are allowed to vary. The theory yields a globally static cosmological model with no evolutionary timescales, no cosmological coincidences, and no flatness and horizon `problems'. It can be shown that the energy densities of dark energy ($ρ_{DE}$) and non-relativistic baryons and dark matter ($ρ_{M}$) are related by $ρ_{DE}=2ρ_{M}$, in agreement with current observations, if DE is associated with the canonical kinetic and potential energy densities of the scalar fields. Under general assumptions, the model favors light fermionic dark matter candidates (e.g., sterile neutrinos). The main observed features of the CMB are naturally explained in this model, including the spectral flatness of its perturbations on the largest angular scales, and the observed adiabatic and gaussian nature of density perturbations. More generally, we show that many of the cosmological observables, normally attributed to the dynamics of expanding space, could be of kinematic origin. In gravitationally bound systems, the values of G and particle masses spontaneously freeze out by a symmetry breaking of the underlying conformal symmetry, and the theory reduces to standard general relativity (with, e.g., all solar system tests satisfied).

physics.gen-ph↗

arXiv2014

Neutrino Mass from SZ Surveys

The expected sensitivity of cluster SZ number counts to neutrino mass in the sub-eV range is assessed. We find that from the ongoing {\it Planck}/SZ measurements the (total) neutrino mass can be determined at a (1-sigma) precision of 0.06 eV, if the mass is in the range 0.1-0.3 eV, and the survey detection limit is set at the 5-sigma significance level. The mass uncertainty is predicted to be lower by a factor ~2/3, if a similar survey is conducted by a cosmic-variance-limited experiment, a level comparable to that projected if CMB lensing extraction is accomplished with the same experiment. At present, the main uncertainty in modeling cluster statistical measures reflects the difficulty in determining the mass function at the high-mass end.

astro-ph.CO↗

arXiv2013

Temporal Variation of the Fundamental Physical Quantities in a Static Universe

The standard interpretation of the observed redshifted spectra and luminosities towards distant astrophysical objects is that the universe is expanding, an inference which is found to be consistent with other cosmological probes as well. Clearly, only the interpretation of {\it dimensionless} quantities does not depend on the physical unit system as opposed to {\it dimensional} quantities whose dynamics does depend on the arbitrarily chosen system of units. All that redshift or luminosity measurements really indicate is that cosmological scales expand {\it relative} to local scales. An alternative choice of a ruler could be the distance between two remote galaxies, in which case local distances have to decrease with time (with respect to the ruler) for consistency with redshift measurements. In the latter choice, microscopic scales such as the Compton wavelength, or the Planck length, decrease with time, and consequently fundamental `constants' such as the Planck constant, speed of light, Newton gravitational constant, and particle masses, are spacetime-dependent. To illustrate this fundamental indeterminacy we construct an alternative interpretation to the expanding model that is characterized by a static metric with time-dependent fundamental physical quantities. The two alternative descriptions, are referred to as the `expanding' and `static' space perspectives, respectively. Cosmological inflation, recombination, and all other early universe processes are unaltered; the `expanding' and `static' perspectives are associated with exactly the same cosmological model.

physics.gen-ph↗

arXiv2013

Scale Invariant Gravitation and Unambiguous Interpretation of Physical Theories

Our conventional system of physical units is based on local or microscopic {\it dimensional} quantities which are {\it defined}, for convenience or otherwise aesthetic reasons, to be spacetime-independent. A more general choice of units may entail variation of fundamental physical quantities (`constants') in spacetime. The theory of gravitation generally does not satisfy conformal symmetry, i.e. it is not invariant to local changes of the unit of length. Consequently, the {\it dimensionless} action associated with the Einstein-Hilbert action ($S_{EH}$) of gravitation, $ϕ_{EH}=S_{EH}/\hbar$, is not invariant to local changes of the length unit; clearly an unsatisfactory feature for a dimensionless quantity. Here we amend the phase by adding extra terms that account for spacetime variation of the physical `constants' in arbitrary unit systems. In such a unit system, all dimensional quantities are implicitly spacetime-dependent; this is achieved by a conformal transformation of the metric augmented by appropriate metric-dependent rescalings of the dimensional quantities. The resulting modified dimensionless action is scale-invariant, i.e. independent of the unit system, as desired. The deep connection between gravitation, dimensionless physical quantities, and quantum mechanics, is elucidated and the implicit ambiguity in interpretations of dimensional quantities is underlined.

physics.gen-ph↗

arXiv2013

Tangential Velocity of the Dark Matter in the Bullet Cluster from Precise Lensed Image Redshifts

We show that the fast moving component of the "bullet cluster" (1E0657-56) can induce potentially resolvable redshift differences between multiply-lensed images of background galaxies. The moving cluster effect can be expressed as the scalar product of the lensing deflection angle with the tangential velocity of the mass components, and it is maximal for clusters colliding in the plane of the sky with velocities boosted by their mutual gravity. The bullet cluster is likely to be the best candidate for the first measurement of this effect due to the large collision velocity and because the lensing deflection and the cluster fields can be calculated in advance. We derive the deflection field using multiply-lensed background galaxies detected with the Hubble Space Telescope. The velocity field is modeled using self-consistent N-body/hydrodynamical simulations constrained by the observed X-ray and gravitational lensing features of this system. We predict that the triply-lensed images of systems "G" and "H" straddling the critical curve of the bullet component will show the largest frequency shifts up to ~0.5 km/sec. This is within the range of the Atacama Large Millimeter/sub-millimeter Array (ALMA) for molecular emission, and is near the resolution limit of the new generation high-throughput optical-IR spectrographs. A detection of this effect measures the tangential motion of the subclusters directly, thereby clarifying the tension with LCDM, which is inferred from gas motion less directly. This method may be extended to smaller redshift differences using the Ly-alpha forest towards QSOs lensed by more typical clusters of galaxies. More generally, the tangential component of the peculiar velocities of clusters derived by our method complements the radial component determined by the kinematic SZ effect, providing a full 3-dimensional description of velocities.

astro-ph.CO↗

arXiv2013

Bias-Limited Extraction of Cosmological Parameters

It is known that modeling uncertainties and astrophysical foregrounds can potentially introduce appreciable bias in the deduced values of cosmological parameters. While it is commonly assumed that these uncertainties will be accounted for to a sufficient level of precision, the level of bias has not been properly quantified in most cases of interest. We show that the requirement that the bias in derived values of cosmological parameters does not surpass nominal statistical error, translates into a maximal level of overall error $O(N^{-1/2})$ on $|ΔP(k)|/P(k)$ and $|ΔC_{l}|/C_{l}$, where $P(k)$, $C_{l}$, and $N$ are the matter power spectrum, angular power spectrum, and number of (independent Fourier) modes at a given scale $l$ or $k$ probed by the cosmological survey, respectively. This required level has important consequences on the precision with which cosmological parameters are hoped to be determined by future surveys: In virtually all ongoing and near future surveys $N$ typically falls in the range $10^{6}-10^{9}$, implying that the required overall theoretical modeling and numerical precision is already very high. Future redshifted-21-cm observations, projected to sample $\sim 10^{14}$ modes, will require knowledge of the matter power spectrum to a fantastic $10^{-7}$ precision level. We conclude that realizing the expected potential of future cosmological surveys, which aim at detecting $10^{6}-10^{14}$ modes, sets the formidable challenge of reducing the overall level of uncertainty to $10^{-3}-10^{-7}$.

astro-ph.CO↗

arXiv2012

Self-Calibration of CMB Polarization Experiments

Precision measurements of the polarization of the cosmic microwave background (CMB) radiation, especially experiments seeking to detect the odd-parity "B-modes", have far-reaching implications for cosmology. To detect the B-modes generated during inflation the Flux response and polarization angle of these experiments must be calibrated to exquisite precision. While suitable flux calibration sources abound, polarization angle calibrators are deficient in many respects. Man-made polarized sources are often not located in the antenna's far-field, have spectral properties that are radically different from the CMB's, are cumbersome to implement and may be inherently unstable over the (long) duration these searches require to detect the faint signature of the inflationary epoch. Astrophysical sources suffer from time, frequency and spatial variability, are not visible from all CMB observatories, and none are understood with sufficient accuracy to calibrate future CMB polarimeters seeking to probe inflationary energy scales of $10^{15}$ GeV. CMB $TB$ and $EB$ modes, expected to identically vanish in the standard cosmological model, can be used to calibrate CMB polarimeters. By enforcing the observed $EB$ and $TB$ power spectra to be consistent with zero, CMB polarimeters can be calibrated to levels not possible with man-made or astrophysical sources. All of this can be accomplished without any loss of observing time using a calibration source which is spectrally identical to the CMB B-modes. The calibration procedure outlined here can be used for any CMB polarimeter.

astro-ph.CO↗

arXiv2012

Revealing Cosmic Rotation

Cosmological Birefringence (CB), a rotation of the polarization plane of radiation coming to us from distant astrophysical sources, may reveal parity violation in either the electromagnetic or gravitational sectors of the fundamental interactions in nature. Until only recently this phenomenon could be probed with only radio observations or observations at UV wavelengths. Recently, there is a substantial effort to constrain such non-standard models using observations of the rotation of the polarization plane of cosmic microwave background (CMB) radiation. This can be done via measurements of the $B$-modes of the CMB or by measuring its TB and EB correlations which vanish in the standard model. In this paper we show that $EB$ correlations-based estimator is the best for upcoming polarization experiments. The $EB$ based estimator surpasses other estimators because it has the smallest noise and of all the estimators is least affected by systematics. Current polarimeters are optimized for the detection of $B$-mode polarization from either primordial gravitational waves or by large scale structure via gravitational lensing. In the paper we also study optimization of CMB experiments for the detection of cosmological birefringence, in the presence of instrumental systematics, which by themselves are capable of producing $EB$ correlations; potentially mimicking CB.

astro-ph.CO↗

arXiv2012

SZ power spectrum and cluster numbers from an extended merger-tree model

We have recently developed an extended merger-tree model that efficiently follows hierarchical evolution of galaxy clusters and provides a quantitative description of both their dark matter and gas properties. We employed this diagnostic tool to calculate the thermal SZ power spectrum and cluster number counts, accounting explicitly for uncertainties in the relevant statistical and intrinsic cluster properties, such as the halo mass function and the gas equation of state. Results of these calculations are compared with those obtained from a direct analytic treatment and from hydrodynamical simulations. We show that under certain assumptions on the gas mass fraction our results are consistent with the latest SPT measurement. Our approach can be particularly useful in predicting cluster number counts and their dependence on cluster and cosmological parameters.

astro-ph.CO↗

arXiv2010

Impact of Instrumental Systematics on the CMB Bispectrum

We study the effects of instrumental systematics on the estimation of primordial non-Gaussianity using the cosmic microwave background (CMB) bispectrum from both the temperature and the polarization anisotropies. For temperature systematics we consider gain fluctuation and beam distortions. For polarization we consider effects related to known instrumental systematics: calibration, pixel rotation, differential gain, pointing, and ellipticity of the instrument beam. We consider these effects at next to leading order, which we refer to as non-linear systematic effects. We find that if the instrumental response is linearly proportional to the received CMB intensity, then only the shape of the primordial CMB bispectrum, if there is any, will be distorted. We show that the nonlinear response of the instrument can in general result in spurious non-Gaussian features on both the CMB temperature and polarization anisotropies, even if the primordial CMB is completely Gaussian. We determine the level for both the linear and non-linear systematics parameters for which they would cause no significant degradation of our ability to constrain the primordial non-Gaussianity amplitude f_{nl}. We find that the non-linear systematics are potentially bigger worry for extracting the primordial non-Gaussianity than the linear systematics. Especially because the current and near future CMB probes are optimized for CMB power-spectrum measurements which are not particularly sensitive to the non-linear instrument response. We find that if instrumental non-linearities are not controlled by dedicated calibration, the effective local non-Gaussianity can be as large as f_{nl} ~ O(10) before the corresponding non-linearities show up in the CMB dipole measurements. The higher order multipoles are even less sensitive to instrumental non-linearities.

astro-ph.CO↗

arXiv2009

Study of the Experimental Probe of Inflationary Cosmology (EPIC)-Intemediate Mission for NASA's Einstein Inflation Probe

Measurements of Cosmic Microwave Background (CMB) anisotropy have served as the best experimental probe of the early universe to date. The inflationary paradigm, inspired in part by the extreme isotropy of the CMB, is now a cornerstone in modern cosmology. Inflation has passed a series of rigorous experimental tests, but we still do not understand the physical mechanism or energy scale behind inflation. A general prediction of inflation and one that can provide certain insights into inflationary physics is a background of primordial gravitational waves. These perturbations leave a distinct signature in the CMB B-modes of polarization. The EPIC (Experimental Probe of Inflationary Cosmology) study team has investigated several CMB polarization mission concepts to carry out a definitive measurement of the inflationary B-mode polarization spectrum. In this report we study a mission with an aperture intermediate between the two missions discussed in our previous report. EPIC-IM's increased aperture allows access to a broader science case than the small EPIC-Low Cost mission. In addition to the search for inflationary gravitational waves, the increase aperture allows us to mine the scale polarization and lensing shear polarization signals down to cosmological limits, so that we extract virtually all the cosmological information available from the CMB. In addition, a modest number of channels operating at higher frequencies allows for an all-sky measurement of polarized Galactic dust, which will provide a rich dataset for Galactic science related to magnetic fields. Using a combination of a large sensitivity focal plane with a new optical design, and an efficient 4K mechanical cooler, EPIC-IM realizes higher sensitivity than EPIC-Comprehensive Science mission.

astro-ph.CO↗

arXiv2008

CMBPol Mission Concept Study: Gravitational Lensing

Gravitational lensing of the cosmic microwave background by large-scale structure in the late universe is both a source of cosmological information and a potential contaminant of primordial gravity waves. Because lensing imprints growth of structure in the late universe on the CMB, measurements of CMB lensing will constrain parameters to which the CMB would not otherwise be sensitive, such as neutrino mass. If the instrumental noise is sufficiently small (<~ 5 uK-arcmin), the gravitational lensing contribution to the large-scale B-mode will be the limiting source of contamination when constraining a stochastic background of gravity waves in the early universe, one of the most exciting prospects for future CMB polarization experiments. High-sensitivity measurements of small-scale B-modes can reduce this contamination through a lens reconstruction technique that separates the lensing and primordial contributions to the B-mode on large scales. A fundamental design decision for a future CMB polarization experiment such as CMBpol is whether to have coarse angular resolution so that only the large-scale B-mode (and the large-scale E-mode from reionization) is measured, or high resolution to additionally measure CMB lensing. The purpose of this white paper is to evaluate the science case for CMB lensing in polarization: constraints on cosmological parameters, increased sensitivity to the gravity wave B-mode via lens reconstruction, expected level of contamination from non-CMB foregrounds, and required control of beam systematics.

astro-ph↗

arXiv2008

CMB Polarization Systematics Due to Beam Asymmetry: Impact on Inflationary Science

CMB polarization provides a unique window into cosmological inflation; the amplitude of the B-mode polarization from last scattering is uniquely sensitive to the energetics of inflation. However, numerous systematic effects arising from optical imperfections can contaminate the observed B-mode power spectrum. In particular, systematic effects due to the coupling of the underlying temperature and polarization fields with elliptical or otherwise asymmetric beams yield spurious systematic signals. This paper presents a non-perturbative analytic calculation of some of these signals. We show that results previously derived in real space can be generalized, formally, by including infinitely many higher-order corrections to the leading order effects. These corrections can be summed and represented as analytic functions when a fully Fourier-space approach is adopted from the outset. The formalism and results presented in this paper were created to determine the susceptibility of CMB polarization probes of the primary gravitational wave signal but can be easily extended to the analysis of gravitational lensing of the CMB.

astro-ph↗

arXiv2003

Quantitative Description of the Sunyaev-Zeldovich Effect: Analytic Approximations

Various aspects of relativistic calculations of the Sunyaev-Zeldovich effect are explored and clarified. We first formally show that the main previous approaches to the calculation of the relativistically generalized thermal component of the effect are equivalent. Our detailed description of the full effect results in a somewhat improved formulation. Analytic approximations to the exact calculation of the change of the photon occupation number in the scattering, $Δn$, are extended to powers of the gas temperature and cluster velocity that are higher than in similar published treatments. For the purely thermal and purely kinematic components, we obtain identical terms up to the highest common orders in temperature and cluster velocity, and to second order in the Thomson optical depth, as reported in previous treatments, but we get slightly different expressions for the terms that depend on both the gas temperature and cluster velocity. We also obtain an accurate expression for the crossover frequency.

astro-ph↗

arXiv2002

CMB Comptonization by Energetic Nonthermal Electrons in Clusters of Galaxies

Use of the Sunyaev-Zeldovich effect as a precise cosmological probe necessitates a realistic assessment of all possible contributions to Comptonization of the cosmic microwave background in clusters of galaxies. We have calculated the additional intensity change due to various possible populations of energetic electrons that have been proposed in order to account for measurements of intracluster radio, nonthermal X-ray and (possibly also) EUV emission. Our properly normalized estimates of (the highly model dependent value of) the predicted intensity change due to these electrons is well below $\sim 6%$ and $\sim 35%$ of the usual Sunyaev-Zeldovich effect due to electrons in the hot gas in Coma and A2199, respectively. These levels constitute high upper limits since they are based on energetic electron populations whose energy densities are {\it comparable} to those of the thermal gas. The main impact of nonthermal Comptonization is a shift of the crossover frequency (where the thermal effect vanishes) to higher values. Such a shift would have important consequences for our ability to measure cluster peculiar velocities from the kinematic component of the Sunyaev-Zeldovich effect.

astro-ph↗