7 research outputs found
Spin-frame field theory of a three-sublattice antiferromagnet
We present a nonlinear field theory of a three-sublattice hexagonal
antiferromagnet. The order parameter is the spin frame, an orthogonal triplet
of vectors related to sublattice magnetizations and spin chirality. The
exchange energy, quadratic in spin-frame gradients, has three coupling
constants, only two of which manifest themselves in the bulk. As a result, the
three spin-wave velocities satisfy a universal relation. Vortices generally
have an elliptical shape with the eccentricity determined by the Lam\'e
parameters.Comment: 4+eps pages, 3+1 figure
Scale invariance of the primordial tensor power spectrum
Future cosmic microwave background polarization experiments will search for
evidence of primordial tensor modes at large angular scales, in the multipole
range Because in that range there is some mild evidence
of departures from scale invariance in the power spectrum of primordial
curvature perturbations, one may wonder about the possibility of similar
deviations appearing in the primordial power spectrum of tensor modes. Here we
address this issue and analyze the possible presence of features in the tensor
spectrum resulting from the dynamics of primordial fluctuations during
inflation. We derive a general, model independent, relation linking features in
the spectra of curvature and tensor perturbations. We conclude that even with
large deviations from scale invariance in the curvature power spectrum, the
tensor spectrum remains scale invariant for all observational purposes.Comment: 22 pages, 4 figures; v2: added references and clarifying comments;
v3: added reference and few more comments. Matches published versio
Two Year Cosmology Large Angular Scale Surveyor (CLASS) Observations: Long Timescale Stability Achieved with a Front-End Variable-delay Polarization Modulator at 40 GHz
The Cosmology Large Angular Scale Surveyor (CLASS) is a four-telescope array
observing the largest angular scales () of the
cosmic microwave background (CMB) polarization. These scales encode information
about reionization and inflation during the early universe. The instrument
stability necessary to observe these angular scales from the ground is achieved
through the use of a variable-delay polarization modulator (VPM) as the first
optical element in each of the CLASS telescopes. Here we develop a demodulation
scheme used to extract the polarization timestreams from the CLASS data and
apply this method to selected data from the first two years of observations by
the 40 GHz CLASS telescope. These timestreams are used to measure the
noise and temperature-to-polarization () leakage present in the
CLASS data. We find a median knee frequency for the pair-differenced
demodulated linear polarization of 15.12 mHz and a leakage of
(95\% confidence) across the focal plane. We examine the
sources of noise present in the data and find the component of due
to atmospheric precipitable water vapor (PWV) has an amplitude of for 1 mm of PWV when evaluated at 10 mHz;
accounting for of the noise in the central pixels of the focal
plane. The low level of leakage and noise achieved
through the use of a front-end polarization modulator enables the observation
of the largest scales of the CMB polarization from the ground by the CLASS
telescopes.Comment: Submitted to Ap
The Cosmology Large Angular Scale Surveyor Receiver Design
The Cosmology Large Angular Scale Surveyor consists of four instruments
performing a CMB polarization survey. Currently, the 40 GHz and first 90 GHz
instruments are deployed and observing, with the second 90 GHz and a
multichroic 150/220 GHz instrument to follow. The receiver is a central
component of each instrument's design and functionality. This paper describes
the CLASS receiver design, using the first 90 GHz receiver as a primary
reference. Cryogenic cooling and filters maintain a cold, low-noise environment
for the detectors. We have achieved receiver detector temperatures below 50 mK
in the 40 GHz instrument for 85% of the initial 1.5 years of operation, and
observed in-band efficiency that is consistent with pre-deployment estimates.
At 90 GHz, less than 26% of in-band power is lost to the filters and lenses in
the receiver, allowing for high optical efficiency. We discuss the mounting
scheme for the filters and lenses, the alignment of the cold optics and
detectors, stray light control, and magnetic shielding.Comment: Fixed formatting of abstract; 20 Pages, 11 Figures, SPIE Conference
Proceeding
Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance
The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale (1 degrees less than or similar to theta <= 90 degrees) CMB polarization to constrain the tensor-to-scalar ratio at the r similar to 0.01 level and the optical depth to last scattering to the sample variance limit. This paper presents the optical characterization of the 40 GHz telescope during its first observation era, from 2016 September to 2018 February. High signal-to-noise observations of the Moon establish the pointing and beam calibration. The telescope boresight pointing variation is <0.degrees 023 (<1.6% of the beam's full width at half maximum (FWHM)). We estimate beam parameters per detector and in aggregate, as in the CMB survey maps. The aggregate beam has an FWHM of 1.degrees 579 +/- 0.degrees 001 and a solid angle of 838 +/- 6 mu sr, consistent with physical optics simulations. The corresponding beam window function has a sub-percent error per multipole at l < 200. An extended 90 degrees beam map reveals no significant far sidelobes. The observed Moon polarization shows that the instrument polarization angles are consistent with the optical model and that the temperature-to-polarization leakage fraction is <10(-4) (95% C.L.). We find that the Moon-based results are consistent with measurements of M42, RCW.38, and Tau A from CLASS's CMB survey data. In particular, Tau A measurements establish degree-level precision for instrument polarization angles.National Science Foundation Division of Astronomical Sciences
0959349
1429236
1636634
1654494
National Aeronautics & Space Administration (NASA)
NNX14AB76A
Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)
CONICYT FONDECYT
1171811
CONICYT-PFCHA Magister Nacional Scholarship
2016-22161360
Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)
Anillo ACT-1417
QUIMAL 160009
BASAL AFB170002
BASAL CATA AFB-170002
CATA
Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)
CONICYT PIA/BASAL
AFB-170002
Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT)
CONICYT FONDECYT
1181620
Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT