317 research outputs found
Group-Theoretic Evidence for SO(10) Grand Unification
The hypercharges of the fermions are not uniquely determined in SO(10) grand
unification, but rather depend upon which linear combination of the two U(1)
subgroups of SO(10) > SU(3) X SU(2) X U(1) X U(1) remains unbroken. We show
that, in general, a given hypercharge assignment can be obtained only with very
high-dimensional Higgs representations. The observation that the standard model
is obtained with low-dimensional Higgs representations can therefore be
regarded as further evidence for SO(10) grand unification. This evidence is
independent of the fact that SO(10) > SU(5).Comment: 6 pages, Late
Polarization Diffusion from Spacetime Uncertainty
A model of Lorentz invariant random fluctuations in photon polarization is
presented. The effects are frequency dependent and affect the polarization of
photons as they propagate through space. We test for this effect by confronting
the model with the latest measurements of polarization of Cosmic Microwave
Background (CMB) photons.Comment: 4 pages, 1 figur
Interstellar dust in the BOOMERanG maps
Interstellar dust (ISD) emission is present in the mm-wave maps obtained by the BOOMERanG experiment at intermediate and high Galactic latitudes. We find that, while being sub-dominant at the lower frequencies (90,150, 240 GHz), thermal emission from ISD is dominant at 410 GHz, and is well correlated with the IRAS map at 100 µm. We find also that the angular power spectrum of ISD fluctuations at 410 GHz is a power law, and its level is negligible with respect to the angular power spectrum of the Cosmic Microwave Background (CMB) at 90 and 150 GHz
Cosmic Microwave Background Polarization
Cosmic microwave background (CMB) anisotropy is our richest source of
cosmological information; the standard cosmological model was largely
established thanks to study of the temperature anisotropies. By the end of the
decade, the Planck satellite will close this important chapter and move us
deeper into the new frontier of polarization measurements. Numerous
ground--based and balloon--borne experiments are already forging into this new
territory. Besides providing new and independent information on the primordial
density perturbations and cosmological parameters, polarization measurements
offer the potential to detect primordial gravity waves, constrain dark energy
and measure the neutrino mass scale. A vigorous experimental program is
underway worldwide and heading towards a new satellite mission dedicated to CMB
polarization.Comment: Review given at TAUP 2005; References added; Additional reference
Cosmological CPT Violation and CMB Polarization Measurements
In this paper we study the possibility of testing Charge-Parity-Time Reversal
(CPT) symmetry with cosmic microwave background (CMB) experiments. We consider
two kinds of Chern-Simons (CS) term, electromagnetic CS term and gravitational
CS term, and study their effects on the CMB polarization power spectra in
detail. By combining current CMB polarization measurements, the seven-year
WMAP, BOOMERanG 2003 and BICEP observations, we obtain a tight constraint on
the rotation angle deg (), indicating a
detection of the CPT violation. Here, we particularly take the
systematic errors of CMB measurements into account. After adding the QUaD
polarization data, the constraint becomes deg at 95%
confidence level. When comparing with the effect of electromagnetic CS term,
the gravitational CS term could only generate TB and EB power spectra with much
smaller amplitude. Therefore, the induced parameter can not be
constrained from the current polarization data. Furthermore, we study the
capabilities of future CMB measurements, Planck and CMBPol, on the constraints
of and . We find that the constraint of
can be significantly improved by a factor of 15. Therefore, if this rotation
angle effect can not be taken into account properly, the constraints of
cosmological parameters will be biased obviously. For the gravitational CS
term, the future Planck data still can not constrain very well, if
the primordial tensor perturbations are small, . We need the more
accurate CMBPol experiment to give better constraint on .Comment: 11 pages, 5 figures, 4 tables, Accepted for publication in JCA
Relating gravitational wave constraints from primordial nucleosynthesis, pulsar timing, laser interferometers, and the CMB: implications for the early universe
We derive a general master equation relating the gravitational-wave
observables r and Omega_gw(f). Here r is the tensor-to-scalar ratio,
constrained by cosmic-microwave-background (CMB) experiments; and Omega_gw(f)
is the energy spectrum of primordial gravitational-waves, constrained e.g. by
pulsar-timing measurements, laser-interferometer experiments, and Big Bang
Nucleosynthesis (BBN). Differentiating the master equation yields a new
expression for the tilt d(ln Omega_gw(f))/d(ln f). The relationship between r
and Omega_gw(f) depends sensitively on the uncertain physics of the early
universe, and we show that this uncertainty may be encapsulated (in a
model-independent way) by two quantities: w_hat(f) and nt_hat(f), where
nt_hat(f) is a certain logarithmic average over nt(k) (the primordial tensor
spectral index); and w_hat(f) is a certain logarithmic average over w_tilde(a)
(the effective equation-of-state in the early universe, after horizon
re-entry). Here the effective equation-of-state parameter w_tilde(a) is a
combination of the ordinary equation-of-state parameter w(a) and the bulk
viscosity zeta(a). Thus, by comparing constraints on r and Omega_gw(f), one can
obtain (remarkably tight) constraints in the [w_hat(f), nt_hat(f)] plane. In
particular, this is the best way to constrain (or detect) the presence of a
``stiff'' energy component (with w > 1/3) in the early universe, prior to BBN.
Finally, although most of our analysis does not assume inflation, we point out
that if CMB experiments detect a non-zero value for r, then we will immediately
obtain (as a free by-product) a new upper bound w_hat < 0.55 on the
logarithmically averaged effective equation-of-state parameter during the
``primordial dark age'' between the end of inflation and the start of BBN.Comment: v1: 12 + 6 pages (main text + appendices), 7 figures; v2: fonts fixed
in figure
WMAP confirming the ellipticity in BOOMERanG and COBE CMB maps
The recent study of BOOMERanG 150 GHz Cosmic Microwave Background (CMB)
radiation maps have detected ellipticity of the temperature anisotropy spots
independent on the temperature threshold. The effect has been found for spots
up to several degrees in size, where the biases of the ellipticity estimator
and of the noise are small. To check the effect, now we have studied, with the
same algorithm and in the same sky region, the WMAP maps. We find ellipticity
of the same average value also in WMAP maps, despite of the different
sensitivity of the two experiments to low multipoles. Large spot elongations
had been detected also for the COBE-DMR maps. If this effect is due to geodesic
mixing and hence due to non precisely zero curvature of the hyperbolic
Universe, it can be linked to the origin of WMAP low multipoles anomaly.Comment: More explanations and two references adde
Foregrounds in the BOOMERANG-LDB data: a preliminary rms analysis
We present a preliminary analysis of the BOOMERanG LDB maps, focused on
foregrounds. BOOMERanG detects dust emission at moderately low galactic
latitudes () in bands centered at 90, 150, 240, 410 GHz. At higher
Galactic latitudes, we use the BOOMERanG data to set conservative upper limits
on the level of contamination at 90 and 150 GHz. We find that the mean square
signal correlated with the IRAS/DIRBE dust template is less than 3% of the mean
square signal due to CMB anisotropy
Measurement of the Crab nebula polarization at 90 GHz as a calibrator for CMB experiments
CMB experiments aiming at a precise measurement of the CMB polarization, such
as the Planck satellite, need a strong polarized absolute calibrator on the sky
to accurately set the detectors polarization angle and the cross-polarization
leakage. As the most intense polarized source in the microwave sky at angular
scales of few arcminutes, the Crab nebula will be used for this purpose. Our
goal was to measure the Crab nebula polarization characteristics at 90 GHz with
unprecedented precision. The observations were carried out with the IRAM 30m
telescope employing the correlation polarimeter XPOL and using two orthogonally
polarized receivers. We processed the Stokes I, Q, and U maps from our
observations in order to compute the polarization angle and linear polarization
fraction. The first is almost constant in the region of maximum emission in
polarization with a mean value of alpha_Sky=152.1+/-0.3 deg in equatorial
coordinates, and the second is found to reach a maximum of Pi=30% for the most
polarized pixels. We find that a CMB experiment having a 5 arcmin circular beam
will see a mean polarization angle of alpha_Sky=149.9+/-0.2 deg and a mean
polarization fraction of Pi=8.8+/-0.2%.Comment: Accepted for publication in A&A, 9 pages, 4 figure
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