67 research outputs found
Impact of Anisotropic Birefringence on Measuring Cosmic Microwave Background Lensing
The power spectrum of cosmic microwave background lensing is a powerful tool
for constraining fundamental physics such as the sum of neutrino masses and the
dark energy equation of state. Current lensing measurements primarily come from
distortions to the microwave background temperature field, but the polarization
lensing signal will dominate upcoming experiments with greater sensitivity.
Cosmic birefringence refers to the rotation of the linear polarization
direction of microwave photons propagating from the last scattering surface to
us, which can be induced by parity-violating physics such as axion-like dark
matter or primordial magnetic fields. We find that, for an upcoming CMB-S4-like
experiment, if there exists the scale-invariant anisotropic birefringence with
an amplitude corresponding to the current upper bound, the measured
lensing power spectrum could be biased by up to a factor of few at small
scales, . We show that the bias scales linearly with the
amplitude of the scale-invariant birefringence spectrum. The signal-to-noise of
the contribution from anisotropic birefringence is larger than unity even if
the birefringence amplitude decreases to of the current upper bound.
Our results indicate that a measurement and characterization of the anisotropic
birefringence is important for lensing analysis in future low-noise
polarization experiments.Comment: 13 pages, 5 figures, to be submitted to PR
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Reversible Interlayer Sliding and Conductivity Changes in Adaptive Tetrathiafulvalene-Based Covalent Organic Frameworks.
Ordered interlayer stacking is intrinsic in two-dimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors
Extending the wavelength tunability from 2.01 to 2.1 μm and simultaneous dual-wavelength operation at 2.05 and 2.3 μm in diode-pumped Tm:YLF lasers
Abstract(#br)We report on wavelength extension of diode-pumped Tm:YLF crystal lasers. Using specifically coated end-face mirrors, we have achieved a simulataneous dual-wavelength laser at 2.05 and 2.3 μm with a maximum output power up to 1.33 W and slope efficiency of about 9.7% in continuous-wave regime, for the first time to the best of our knowledge. Moreover, using an un-doped YAG etalon for wavelength tuning, the 2.05 μm lasing wavelength can be shifted to as far as 2.1 μm. We believe that it is the first time that a Tm:YLF laser has been wavelength extended to that far. Using a Cr:ZnSe saturable absorber, a passively Q-switched Tm:YLF laser at 2.05 μm has also attained with a maximum average output power of 0.66 W. The shortest pulse width is 91.7 ns at pulse repetition rate of 8.47 kHz. This work has extended the operating wavelengths of Tm 3+ lasers to that in general for Ho 3+ lasers, which could be practically meaningful for various applications
Enhancing Model Performance in Multilingual Information Retrieval with Comprehensive Data Engineering Techniques
In this paper, we present our solution to the Multilingual Information
Retrieval Across a Continuum of Languages (MIRACL) challenge of WSDM CUP
2023\footnote{https://project-miracl.github.io/}. Our solution focuses on
enhancing the ranking stage, where we fine-tune pre-trained multilingual
transformer-based models with MIRACL dataset. Our model improvement is mainly
achieved through diverse data engineering techniques, including the collection
of additional relevant training data, data augmentation, and negative sampling.
Our fine-tuned model effectively determines the semantic relevance between
queries and documents, resulting in a significant improvement in the efficiency
of the multilingual information retrieval process. Finally, Our team is pleased
to achieve remarkable results in this challenging competition, securing 2nd
place in the Surprise-Languages track with a score of 0.835 and 3rd place in
the Known-Languages track with an average nDCG@10 score of 0.716 across the 16
known languages on the final leaderboard
The Atacama Cosmology Telescope: Mitigating the impact of extragalactic foregrounds for the DR6 CMB lensing analysis
We investigate the impact and mitigation of extragalactic foregrounds for the
CMB lensing power spectrum analysis of Atacama Cosmology Telescope (ACT) data
release 6 (DR6) data. Two independent microwave sky simulations are used to
test a range of mitigation strategies. We demonstrate that finding and then
subtracting point sources, finding and then subtracting models of clusters, and
using a profile bias-hardened lensing estimator, together reduce the fractional
biases to well below statistical uncertainties, with the inferred lensing
amplitude, , biased by less than . We also show
that another method where a model for the cosmic infrared background (CIB)
contribution is deprojected and high frequency data from Planck is included has
similar performance. Other frequency-cleaned options do not perform as well,
incurring either a large noise cost, or resulting in biased recovery of the
lensing spectrum. In addition to these simulation-based tests, we also present
null tests performed on the ACT DR6 data which test for sensitivity of our
lensing spectrum estimation to differences in foreground levels between the two
ACT frequencies used, while nulling the CMB lensing signal. These tests pass
whether the nulling is performed at the map or bandpower level. The
CIB-deprojected measurement performed on the DR6 data is consistent with our
baseline measurement, implying contamination from the CIB is unlikely to
significantly bias the DR6 lensing spectrum. This collection of tests gives
confidence that the ACT DR6 lensing measurements and cosmological constraints
presented in companion papers to this work are robust to extragalactic
foregrounds.Comment: Companion paper to Qu et al and Madhavacheril et a
The Atacama Cosmology Telescope: A Measurement of the DR6 CMB Lensing Power Spectrum and its Implications for Structure Growth
We present new measurements of cosmic microwave background (CMB) lensing over
sq. deg. of the sky. These lensing measurements are derived from the
Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) CMB dataset, which
consists of five seasons of ACT CMB temperature and polarization observations.
We determine the amplitude of the CMB lensing power spectrum at
precision ( significance) using a novel pipeline that minimizes
sensitivity to foregrounds and to noise properties. To ensure our results are
robust, we analyze an extensive set of null tests, consistency tests, and
systematic error estimates and employ a blinded analysis framework. The
baseline spectrum is well fit by a lensing amplitude of
relative to the Planck 2018 CMB power spectra
best-fit CDM model and relative to
the best-fit model. From our lensing power
spectrum measurement, we derive constraints on the parameter combination
of
from ACT DR6 CMB lensing alone and
when combining ACT DR6 and Planck NPIPE
CMB lensing power spectra. These results are in excellent agreement with
CDM model constraints from Planck or
CMB power spectrum measurements. Our lensing measurements from redshifts
-- are thus fully consistent with CDM structure growth
predictions based on CMB anisotropies probing primarily . We find no
evidence for a suppression of the amplitude of cosmic structure at low
redshiftsComment: 45+21 pages, 50 figures. Prepared for submission to ApJ. Also see
companion papers Madhavacheril et al and MacCrann et a
The Atacama Cosmology Telescope: High-resolution component-separated maps across one-third of the sky
Observations of the millimeter sky contain valuable information on a number
of signals, including the blackbody cosmic microwave background (CMB), Galactic
emissions, and the Compton- distortion due to the thermal Sunyaev-Zel'dovich
(tSZ) effect. Extracting new insight into cosmological and astrophysical
questions often requires combining multi-wavelength observations to spectrally
isolate one component. In this work, we present a new arcminute-resolution
Compton- map, which traces out the line-of-sight-integrated electron
pressure, as well as maps of the CMB in intensity and E-mode polarization,
across a third of the sky (around 13,000 sq.~deg.). We produce these through a
joint analysis of data from the Atacama Cosmology Telescope (ACT) Data Release
4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from
the \textit{Planck} satellite at frequencies between 30 GHz and 545 GHz. We
present detailed verification of an internal linear combination pipeline
implemented in a needlet frame that allows us to efficiently suppress Galactic
contamination and account for spatial variations in the ACT instrument noise.
These maps provide a significant advance, in noise levels and resolution, over
the existing \textit{Planck} component-separated maps and will enable a host of
science goals including studies of cluster and galaxy astrophysics, inferences
of the cosmic velocity field, primordial non-Gaussianity searches, and
gravitational lensing reconstruction of the CMB.Comment: The Compton-y map and associated products will be made publicly
available upon publication of the paper. The CMB T and E mode maps will be
made available when the DR6 maps are made publi
The Atacama Cosmology Telescope: DR6 Gravitational Lensing Map and Cosmological Parameters
We present cosmological constraints from a gravitational lensing mass map
covering 9400 sq. deg. reconstructed from CMB measurements made by the Atacama
Cosmology Telescope (ACT) from 2017 to 2021. In combination with BAO
measurements (from SDSS and 6dF), we obtain the amplitude of matter
fluctuations at 1.8% precision,
and the Hubble
constant at
1.6% precision. A joint constraint with CMB lensing measured by the Planck
satellite yields even more precise values: ,
and . These measurements agree
well with CDM-model extrapolations from the CMB anisotropies measured
by Planck. To compare these constraints to those from the KiDS, DES, and HSC
galaxy surveys, we revisit those data sets with a uniform set of assumptions,
and find from all three surveys are lower than that from ACT+Planck
lensing by varying levels ranging from 1.7-2.1. These results motivate
further measurements and comparison, not just between the CMB anisotropies and
galaxy lensing, but also between CMB lensing probing on
mostly-linear scales and galaxy lensing at on smaller scales. We
combine our CMB lensing measurements with CMB anisotropies to constrain
extensions of CDM, limiting the sum of the neutrino masses to eV (95% c.l.), for example. Our results provide independent
confirmation that the universe is spatially flat, conforms with general
relativity, and is described remarkably well by the CDM model, while
paving a promising path for neutrino physics with gravitational lensing from
upcoming ground-based CMB surveys.Comment: 30 pages, 16 figures, prepared for submission to ApJ. Cosmological
likelihood data is here:
https://lambda.gsfc.nasa.gov/product/act/actadv_prod_table.html ; likelihood
software is here: https://github.com/ACTCollaboration/act_dr6_lenslike . Also
see companion papers Qu et al and MacCrann et al. Mass maps will be released
when papers are publishe
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