Narrow Results

I review the exciting science that awaits cosmologists in precision measurements of the cosmic microwave background radiation, particularly its polarization. The conclusions of the Interagency Taskforce ("Weiss Panel") will also be presented. I conclude with an update based primarily on the new WMAP results from their three-year analysis.

In this paper we briefly present our work on relic gravitational waves (RGW) and the CMB polarization in the accelerating universe. The spectrum of RGW has been obtained, showing the influence of dark energy. Compared with those from non-accelerating models, the shape of the spectrum is approximately similar, nevertheless, the amplitude of RGW now acquires a suppressing factor of the ratio of matter over dark energy ∝ Ω_m/Ω_Λ ~ 0.4 over almost the whole range of frequencies. The RGW Spectrum is then used as the source to calculate the spectra of CMB polarization. By using two half-Gaussian functions as an approximation to the visibility function during the photon decoupling, both the "electric" and "magnetic" spectra have been analytically derived and they are quite close to those obtained numerically. Several physical elements that affect the spectra have been examined, such as the decoupling process, inflation, dark energy, the baryons, etc.

We show that a nonminimal coupling of electromagnetism with background torsion can produce birefringence of the electromagnetic waves. This birefringence gives rise to a B-mode polarization of the CMB. From the bounds on CMB polarization from QUaD experiment, one can put limits on the background torsion at ξ₁T_i = (2.78 ± 4.85) × 10^-20 GeV^-1.

A flavor-space locked gauge field is shown to behave like a birefringent medium, imparting a preferred left- or right-circular polarization onto gravitational waves. In a cosmological scenario, such a gauge field can cause a primordial spectrum of gravitational waves to develop a net handedness. The degree of chiral asymmetry depends on the wavelength, the abundance of the gauge field, and the strength of the gauge coupling. An asymmetry in the gravitational wave spectrum would be imprinted on the photon polarization pattern of the cosmic microwave background at last scattering. In this scenario, cosmic parity violation is written on the sky, as we predict nonzero correlation of the curl polarization with the temperature, as well as curl with gradient polarization. We compare this phenomena with parity violation in models of chiral gravity, in which the chiral asymmetry is primordial, and with models of quintessence cosmic birefringence, in which parity-violating correlations are induced along the line of sight.

A decade ago, the first leptogenesis model based on inflation was proposed, where the complex phase of the inflaton field carries lepton number [S. H. S. Alexander, M. E. Peskin and M. M. Sheikh-Jabbari, Phys. Rev. Lett.96 (2006) 081301, arXiv:hep-th/0403069]. If the inflaton field is an axion, it can couple to gravitational waves and gauge fields via Chern–Simons invariants. Due to these couplings, birefringent gravitational and gauge primordial perturbations are created during inflation to generate a lepton asymmetry, establishing a possible connection between nonvanishing TB-parity-violating polarization cross-correlations and leptogenesis. We also discuss the prospect for a subset of these models which can directly source circular (V-mode) polarization in the CMB.

We provide an update to S. di Serego Alighieri, Int. J. Mod. Phys. D 24 (2015) 1530016, arXiv:1501.06460 [astro-ph.CO], focusing on recent developments regarding constraints on Cosmic Polarization Rotation (CPR), also known as Cosmic Birefringence (CB), derived from Cosmic Microwave Background (CMB) polarization data.

We describe a low-cost, open-access, CubeSat-based calibration instrument that is designed to support ground-based and sub-orbital experiments searching for various polarization signals in the cosmic microwave background (CMB). All modern CMB polarization experiments require a robust calibration program that will allow the effects of instrument-induced signals to be mitigated during data analysis. A bright, compact and linearly polarized astrophysical source with polarization properties known to adequate precision does not exist. Therefore, we designed a space-based millimeter-wave calibration instrument, called CalSat, to serve as an open-access calibrator, and this paper describes the results of our design study. The calibration source on board CalSat is composed of five “tones” with one each at 47.1, 80.0, 140, 249 and 309GHz. The five tones we chose are well matched to (i) the observation windows in the atmospheric transmittance spectra, (ii) the spectral bands commonly used in polarimeters by the CMB community and (iii) the Amateur Satellite Service bands in the Table of Frequency Allocations used by the Federal Communications Commission. CalSat would be placed in a polar orbit allowing visibility from observatories in the Northern Hemisphere, such as Mauna Kea in Hawaii and Summit Station in Greenland, and the Southern Hemisphere, such as the Atacama Desert in Chile and the South Pole. CalSat also would be observable by balloon-borne instruments launched from a range of locations around the world. This global visibility makes CalSat the only source that can be observed by all terrestrial and sub-orbital observatories, thereby providing a universal standard that permits comparison between experiments using appreciably different measurement approaches.

We present a preliminary analysis of the optical system of the STRIP instrument of the Large Scale Polarization (LSPE) experiment, which aims at polarization measurements of the Cosmic Microwave Background on large angular scales. STRIP will observe approximately 25% of the Northern sky from the Observatorio del Teide in Tenerife, using an array of forty-nine coherent polarimeters at 43 GHz (Q-band), coupled to a 1.5 m fully rotating crossed-Dragone telescope. An additional frequency channel with six-elements at 95 GHz (W-band) will be exploited as an atmospheric monitor.

Non-idealities in the optical system may introduce limitations in achieving high precision measurements, if not well understood and controlled. For this reason, we studied the optical design of STRIP, its characteristics in terms of performance on angular resolution, sidelobes, main beam symmetry, polarization purity and feedhorns orientation, by means of electromagnetic simulations.

I review the exciting science that awaits cosmologists in precision measurements of the cosmic microwave background radiation, particularly its polarization. The conclusions of the Interagency Taskforce (“Weiss Panel”) will also be presented. I conclude with an update based primarily on the new WMAP results from their three-year analysis.

We present the newest statistical and numerical analysis of the matter and cosmic microwave background (CMB) power spectrum with effects of the primordial magnetic field (PMF) included. New limits to the PMF strength and power spectral index are obtained based upon the accumulated data for both the matter and CMB power spectra on small angular scales. We find that a maximum develops in the probability distribution for a magnitude of the PMF of |B_λ| = 0.85±1.25(±1σ) nG on a comoving scale of at 1 Mpc, corresponding to upper limits of < 2.10nG(68%CL) and < 2.98nG(95%CL). While for the power spectral index we find , corresponding to upper limits of < −1.19(68%CL) and < −0.25(95%CL). This result provides new constraints on models for magnetic field generation and the physics of the early universe. We have also made an analysis of limits on the neutrino mass which includes the formation of large scale structure in the presence of a primordial magnetic field. We find that new upper and lower bounds on the neutrino mass are possible based upon fits to the CMB power spectrum which include the existing independent constrains on the matter density fluctuation parameter σ₈ and the primordial magnetic field.

We mainly summarize the results reported in a previous work with Pagano, Amelino-Camelia, Melchiorri and Cooray (JCAP 0908:021,2009), which showed, working within a phenomenological model first proposed by Myers and Pospelov, that presently-available Cosmic Microwave Background (CMB) polarization data can provide Planck-scale sensitivity to quantum-gravity-induced in-vacuo-birefringence effects. We also observe that improvements in sensitivity of a few orders of magnitude is achievable with planned CMB polarization measurements, and we comment on how systematic effects of CMB experiments could influence these constraints.

Generation of the B-mode of CMB polarization by background of relic gravitational wave is discussed in connection with the BICEP2 measurements. Description of the polarization maps in terms of the eigenvectors of the polarization matrix is considered. is emphasized.