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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: anisotropic galaxy clustering in Fourier space

We investigate the anisotropic clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 sample, which consists of 1198 006 galaxies in the redshift range 0.2 < z < 0.75 and a sky coverage of 10 252 deg 2 . We analyse this data set in Fourier space, using the power-spectrum multipoles to measure redshift-space distortions simultaneously with the Alcock–Paczynski effect and the baryon acoustic oscillation scale. We include the power-spectrum monopole, quadrupole and hexadecapole in our analysis and compare our measurements with a perturbation-theory-based model, while properly accounting for the survey window function. To evaluate the reliability of our analysis pipeline, we participate in a mock challenge, which results in systematic uncertainties significantly smaller than the statistical uncertainties. While the high-redshift constraint on fσ8 at z eff = 0.61 indicates a small (~1.4σ) deviation from the prediction of the Planck ΛCDM (Λ cold dark matter) model, the low-redshift constraint is in good agreement with Planck ΛCDM. This paper is part of a set that analyses the final galaxy clustering data set from BOSS. Lastly, the measurements and likelihoods presented here are combined with others in Alam et al. to produce the final cosmological constraints from BOSS.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

CMB signatures of metal-free star formation and Planck 2015 polarization data

Standard analyses of the reionization history of the Universe from Planck cosmic microwave background (CMB) polarization measurements consider only the overall optical depth to electron scattering (τ), and further assume a step-like reionization history. However, the polarization data contain information beyond the overall optical depth, and the assumption of a step-like function may miss high redshift contributions to the optical depth and leads to biased τ constraints. Accounting for its full reionization information content, we reconsider the interpretation of Planck 2015 Low-Frequency Instrument (LFI) polarization data using simple, yet physically motivated reionization models. We show that these measurements still, in fact, allow a non-negligible contribution from metal-free (Pop-III) stars forming in mini-haloes of mass M ~ 10 5 –10 6 M ⊙ at z ≳ 15, provided this mode of star formation is fairly inefficient. We find that an early, self-regulated phase of Pop-III star formation with a gradual, plateau feature in the ionization history provides a good match to the Planck LFI measurements. In this case, as much as 20 percent of the volume of the Universe is ionized by z ~ 20. Although preferred when the full information content of the data is incorporated, this model would spuriously be disfavoured in the standard analysis. This preference is driven mostly by excess power from E-mode polarization at multipoles of 10 ≲ ℓ ≲ 20, which may reflect remaining systematic errors in the data, a statistical fluctuation or signatures of the first stars. Measurements from the Planck High-Frequency Instrument should be able to confirm or refute this hint and future cosmic-variance-limited E-mode polarization surveys can provide substantially more information on these signatures.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

A practical computational method for the anisotropic redshift-space three-point correlation function

Here, we present an algorithm enabling computation of the anisotropic redshift-space galaxy threepoint correlation function ( 3 PCF) scaling as N 2 , with N the number of galaxies. Our previous work showed how to compute the isotropic 3 PCF with this scaling by expanding the radially binned density field around each galaxy in the survey into spherical harmonics and combining these coefficients to form multipole moments. The N 2 scaling occurred because this approach never explicitly required the relative angle between a galaxy pair about the primary galaxy. Here, we generalize this work, demonstrating that in the presence of azimuthally symmetric anisotropy produced by redshift-space distortions (RSD), the 3 PCF can be described by two triangle side lengths, two independent total angular momenta, and a spin. This basis for the anisotropic 3 PCF allows its computation with negligible additional work over the isotropic 3 PCF. We also present the covariance matrix of the anisotropic 3 PCF measured in this basis. Our algorithm tracks the full 5 D redshift-space 3 PCF, uses an accurate line of sight to each triplet, is exact in angle, and easily handles edge correction. It will enable use of the anisotropic large-scale 3 PCF as a probe of RSD in current and upcoming large-scale redshift surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The Zeldovich approximation and wide-angle redshift-space distortions

The contribution of line-of-sight (LOS) peculiar velocities to the observed redshift of objects breaks the translational symmetry of the underlying theory, modifying the predicted two-point functions. These 'wide-angle effects' have mostly been studied using linear perturbation theory in the context of the multipoles of the correlation function and power spectrum. Here, we present the first calculation of wide-angle terms in the Zeldovich approximation, which is known to be more accurate than linear theory on scales probed by the next generation of galaxy surveys.We present the exact result for dark matter and perturbatively biased tracers as well as the small angle expansion of the configuration- and Fourier-space two-point functions and the connection to the multifrequency angular power spectrum. We compare different definitions of the LOS direction and discuss how to translate between them. Finally, we show that wide-angle terms can reach tens of percent of the total signal in a measurement at low redshift in some approximations, and that a generic feature of wide-angle effects is to slightly shift the Baryon Acoustic Oscillation scale.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Tests of acoustic scale shifts in halo-based mock galaxy catalogues

ABSTRACT We utilize mock catalogues from high-accuracy cosmological N-body simulations to quantify shifts in the recovery of the acoustic scale that could potentially result from galaxy clustering bias. The relationship between galaxies and dark matter haloes presents a complicated source of systematic errors in modern redshift surveys, particularly when aiming to make cosmological measurements to sub-per cent precision. Apart from a scalar, linear bias parameter accounting for the density contrast ratio between matter tracers and the true matter distribution, other types of galaxy bias, such as assembly and velocity biases, may also significantly alter clustering signals from small to large scales. We create mocks based on generalized halo occupation populations of 36 periodic boxes from the abacus cosmosrelease, and test various biased models along with an unbiased base case in a total volume of $48 \, h^{-3} \, {\rm Gpc}^{3}$. Two reconstruction methods are applied to galaxy samples and the apparent acoustic scale is derived by fitting the two-point correlation function multipoles. With respect to the baseline, we find a 0.3 per cent shift in the line-of-sight acoustic scale for one variation in the satellite galaxy population, and we find a 0.7 per cent shift for an extreme level of velocity bias of the central galaxies. All other bias models are consistent with zero shift at the 0.2 per cent level after reconstruction. We note that the bias models explored are relatively large variations, producing sizeable and likely distinguishable changes in small-scale clustering, the modelling of which would further calibrate the baryon acoustic oscillations standard ruler.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Computing the small-scale galaxy power spectrum and bispectrum in configuration space

ABSTRACT We present a new class of estimators for computing small-scale power spectra and bispectra in configuration space via weighted pair and triple counts, with no explicit use of Fourier transforms. Particle counts are truncated at $R_0\sim 100\, h^{-1}\, \mathrm{Mpc}$ via a continuous window function, which has negligible effect on the measured power spectrum multipoles at small scales. This gives a power spectrum algorithm with complexity $\mathcal {O}(NnR_0^3)$ (or $\mathcal {O}(Nn^2R_0^6)$ for the bispectrum), measuring N galaxies with number density n. Our estimators are corrected for the survey geometry and have neither self-count contributions nor discretization artefacts, making them ideal for high-k analysis. Unlike conventional Fourier-transform-based approaches, our algorithm becomes more efficient on small scales (since a smaller R0 may be used), thus we may efficiently estimate spectra across k-space by coupling this method with standard techniques. We demonstrate the utility of the publicly available power spectrum algorithm by applying it to BOSS DR12 simulations to compute the high-k power spectrum and its covariance. In addition, we derive a theoretical rescaled-Gaussian covariance matrix, which incorporates the survey geometry and is found to be in good agreement with that from mocks. Computing configuration- and Fourier-space statistics in the same manner allows us to consider joint analyses, which can place stronger bounds on cosmological parameters; to this end we also discuss the cross-covariance between the two-point correlation function and the small-scale power spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Likelihood non-Gaussianity in large-scale structure analyses

The standard present-day large-scale structure (LSS) analyses make a major assumption in their Bayesian parameter inference – that the likelihood has a Gaussian form. For summary statistics currently used in LSS, this assumption, even if the underlying density field is Gaussian, cannot be correct in detail. We investigate the impact of this assumption on two recent LSS analyses: the Beutler et al. power spectrum multipole ($P_ℓ$) analysis and the Sinha et al. group multiplicity function ($ζ$) analysis. Using non-parametric divergence estimators on mock catalogues originally constructed for covariance matrix estimation, we identify significant non-Gaussianity in both the $P_ℓ$ and $ζ$ likelihoods. We then use Gaussian mixture density estimation and independent component analysis on the same mocks to construct likelihood estimates that approximate the true likelihood better than the Gaussian pseudo-likelihood. Using these likelihood estimates, we accurately estimate the true posterior probability distribution of the Beutler et al. and Sinha et al. parameters. Likelihood non-Gaussianity shifts the fσ8 constraint by -0.44σ, but otherwise does not significantly impact the overall parameter constraints of Beutler et al. For the $ζ$ analysis, using the pseudo-likelihood significantly underestimates the uncertainties and biases the constraints of the Sinha et al. halo occupation parameters. For log $M_1$ and α, the posteriors are shifted by +0.43σ and -0.51σ and broadened by 42 per cent and 66 per cent, respectively. The divergence and likelihood estimation methods we present provide a straightforward framework for quantifying the impact of likelihood non-Gaussianity and deriving more accurate parameter constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Extraction of the non-spin- and spin-transfer isovector responses via the 12 C ⁡( 10 Be, 10 B + 𝛾)⁢ 12 B reaction

The isovector response in 12 B was investigated via the 12 C ⁡( 10 Be, 10 B + 𝛾)⁢ 12 B* reaction at 100⁢𝐴MeV. By utilizing the 𝛾-decay properties of the 1.74 MeV 0 + and 0.718 MeV 1 + states in 10 B, the separate extraction of the non-spin-transfer (Δ⁢𝑆 = 0) and spin-transfer (Δ⁢𝑆 = 1) isovector responses up to an excitation energy of 50 MeV in 12 B in a single measurement is demonstrated. The experimental setup employed the S800 spectrometer to detect and analyze the 10 B ejectiles and the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) for obtaining the Doppler-reconstructed spectrum for 𝛾 rays emitted in flight by 10 B. A 12 C foil was placed at the pivot point of the spectrograph. Here, the 12 B reaction product was not detected. Contributions from transitions associated with the transfer of different units of angular momentum in the non-spin- and spin-transfer responses were analyzed using a multipole decomposition analysis. The extracted non-spin-dipole (Δ⁢𝑆 = 0, Δ⁢𝐿 = 1) and spin-dipole (Δ⁢𝑆 = 1, Δ⁢𝐿 = 1) responses were found to be consistent with available data from other charge-exchange probes, validating the non-spin- and spin-transfer filters used. While statistical uncertainties and experimental resolutions were relatively large due to the modest intensity of the 10 Be secondary beam, the results show that, with the much higher intensities that will be available at new rare-isotope beam facilities, the ( 10 Be, 10 B + 𝛾) reaction and its Δ⁢𝑇 𝑧 = −1 partner, the ( 10 C, 10 B + 𝛾) reaction, are powerful tools for elucidating the isovector non-spin- and spin-transfer responses in nuclei.

Charge-exchange reactions↗
DOE OSTI2025

Towards constraining cosmological parameters with SPT-3G observations of 25% of the sky

The South Pole Telescope (SPT), using its third-generation camera, SPT-3G, is conducting observations of the cosmic microwave background (CMB) in temperature and polarization across approximately 10 000 deg$^2$ of the sky at 95, 150, and 220 GHz. This comprehensive dataset should yield stringent constraints on cosmological parameters. In this work, we explore its potential to address the Hubble tension by forecasting constraints from temperature, polarization, and CMB lensing on early dark energy (EDE) and the variation in electron mass in spatially flat and curved universes. For this purpose, we investigate first whether analyzing the distinct SPT-3G observation fields independently, as opposed to as a single, unified region, results in a loss of information relevant to cosmological parameter estimation. We develop a realistic temperature and polarization likelihood pipeline capable of analyzing these fields in these two ways, and subsequently forecast constraints on cosmological parameters. Our findings indicate that any loss of constraining power from analyzing the fields separately is primarily concentrated at low multipoles ($\ell$ < 50) and the overall impact on the relative uncertainty on standard $Λ$ cold dark matter parameters is minimal (< 3%). Our forecasts suggest that SPT-3G data should improve by more than a factor of 90 and 190 the figure of merit of the EDE and the varying electron mass models, respectively, when combined with Planck data. The likelihood pipeline developed and used in this work is made publicly available online.

Vitrier, A. [Paris, Inst. Astrophys.]↗
DOE OSTI2025

Cosmological implications of DESI DR2 BAO measurements in light of the latest ACT DR6 CMB data

We report cosmological results from the Dark Energy Spectroscopic Instrument (DESI) measurements of baryon acoustic oscillations (BAO) when combined with recent data from the Atacama Cosmology Telescope (ACT). By jointly analyzing ACT and Planck data and applying conservative cuts to overlapping multipole ranges, we assess how different 𝑃⁢𝑙⁢𝑎⁢𝑛⁢𝑐⁢𝑘 + ACT dataset combinations affect consistency with DESI. While ACT alone exhibits a tension with DESI exceeding 3⁢𝜎 within the Λ⁢ CDM model, this discrepancy is reduced when ACT is analyzed in combination with Planck. For our baseline DESI DR2 BAO + 𝑃⁢𝑙⁢𝑎⁢𝑛⁢𝑐⁢𝑘 P⁢R⁢4 + ACT likelihood combination, the preference for evolving dark energy over a cosmological constant is about 3⁢𝜎, increasing to over 4⁢𝜎 with the inclusion of type Ia supernova data. While the dark energy results remain quite consistent across various combinations of Planck and ACT likelihoods with those obtained by the DESI collaboration, the constraints on neutrino mass are more sensitive, ranging from ∑𝑚 𝜈 < 0.061 eV in our baseline analysis, to ∑𝑚 𝜈 < 0.077 eV (95% confidence level) in the CMB likelihood combination chosen by ACT when imposing the physical prior ∑𝑚 𝜈 > 0 eV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

QCD splitting functions beyond kinematical limits

We present a systematic decomposition of QCD splitting functions into scalar dipole radiators and pure splitting remainders up to second order in the strong coupling. The individual components contain terms that are formally subleading in soft or collinear scaling parameters, but well understood and universal due to their origin in scalar QCD. The multipole radiator functions which we derive share essential features of the known double-soft and one-loop soft gluon currents, and are not based on kinematical approximations.

Campbell, John M. [Fermilab] (ORCID:00000002136193↗
DOE OSTI2025

Impact of Galactic non-Gaussian foregrounds on CMB lensing measurements

Weak gravitational lensing of the cosmic microwave background (CMB) has been established as a robust and powerful observable for precision cosmology. However, the impact of Galactic foregrounds, which has been studied less extensively than many other potential systematics, could in principle pose a problem for CMB lensing measurements. These foregrounds are inherently non-Gaussian and hence might mimic the characteristic signal that lensing estimators are designed to measure. We present an analysis that quantifies the level of contamination from Galactic dust in lensing measurements, focusing particularly on measurements with the Atacama Cosmology Telescope and the Simons Observatory. We employ a whole suite of foreground models and study the contamination of lensing measurements with both individual frequency channels and multifrequency combinations. We test the sensitivity of different estimators to the level of foreground non-Gaussianity and the dependence on sky fraction and multipole range used. We find that Galactic foregrounds do not present a problem for the Atacama Cosmology Telescope experiment (the bias in the inferred CMB lensing power spectrum amplitude remains below 0.3σ). For Simons Observatory, not all foreground models remain below this threshold. Although our results are conservative upper limits, they suggest that further work on characterizing dust biases and determining the impact of mitigation methods is well motivated, especially for the largest sky fractions.

cosmic microwave background↗
DOE OSTI2025

Extraction of ground-state nuclear deformations from ultrarelativistic heavy-ion collisions: Nuclear structure physics context

The collective-flow-assisted nuclear shape-imaging method in ultrarelativistic heavy-ion collisions (UHICs) has recently been used to characterize nuclear collective states. In this paper, we assess the foundations of the shape-imaging technique employed in these studies. We argue that some current UHIC nuclear imaging techniques neglect fundamental aspects of spontaneous symmetry breaking and symmetry restoration in colliding ions and incorrectly infer one-body multipole moments from studies of nucleonic correlations. Therefore, the impact of this approach on nuclear structure research has been overstated. Conversely, efforts to incorporate existing knowledge on nuclear shapes into analysis pipelines can be beneficial for benchmarking tools and calibrating models used to extract information from ultrarelativistic heavy-ion experiments.

Nuclear data analysis & compilation↗
DOE OSTI2025

Complete definition of 𝑁 →Δ transition generalized parton distributions

We revisit the definition of the leading-twist chiral-even generalized parton distributions (GPDs) for 𝑁 →Δ baryon transitions. We identify and address deficiencies in previous definitions of the transition GPDs inspired by the transition form factors of the vector and axial vector currents. Through systematic analysis of all possible covariant structures, respecting discrete symmetries and the baryon spinor equations of motion, we derive complete sets of independent structures for the transition matrix elements of the vector and axial vector partonic operators. They contain additional structures proportional to the light-cone vector, corresponding to transition GPDs of vanishing first moment, which were not included in previous parametrizations. Their presence is confirmed independently by the light-front multipole expansion and the cross-channel SO(3) partial-wave analysis of the transition matrix elements. Our analysis provides a complete definition of the 𝑁 →Δ transition GPDs for use in theoretical and phenomenological studies.

baryons↗
DOE OSTI2025

Analytical expression of a finite, long, conical canted-cosine-theta coil for particle collider interaction regions

Magnets in the accelerator interaction region (IR) present significant challenges because of high field requirements and limited available space. Conical-shaped magnets offer advantages in these environments by allowing closer placement to the interaction point while maintaining clearance from synchrotron radiation. Interestingly, numerical studies have shown that conical canted-cosine-theta (CCT) designs produce a constant field distribution along the axial direction in the IR quadrupoles for the Electron-Ion Collider (EIC) at Brookhaven National Laboratory. However, the field harmonics generated by conical CCT windings are not yet fully understood. This paper presents an analytical approach to describe the magnetic field produced by a conical surface current and proposes a method for designing conical CCT magnets for accelerator applications. First, we begin with a surface current sheet having a general cosine-theta distribution in spherical coordinates and solve the vector potential using the Green’s function. The magnetic fields generated by the conical current sheet are expressed using associated Legendre polynomials. These results are then related to circular field harmonics and integral field harmonics for designing a coil that produces a pure multipole field. Next, a single layer of the conical CCT winding path is produced based on the cosine-theta current distribution. Finally, the magnetic field quality of dipole and quadrupole conical CCT coils with multiple layers is verified using the Biot-Savart law.

Yang, Ye↗
DOE OSTI2023

Exact solutions for the electromagnetic fields of a flying focus

The intensity peak of a “flying” focus travels at a programmable velocity over many Rayleigh ranges while maintaining a near-constant profile. Assessing the extent to which these features can enhance laser-based applications requires an accurate description of the electromagnetic fields. Here we present exact analytical solutions to Maxwell’s equations for the electromagnetic fields of a constant-velocity flying focus, generalized for arbitrary polarization and orbital angular momentum. Furthermore, the approach combines the complex source-point method, which transforms multipole solutions into beam-like solutions, with the Lorentz invariance of Maxwell’s equations. Propagating the fields backward in space reveals the space-time profile that an optical assembly must produce to realize these fields in the laboratory. Comparisons with simpler paraxial solutions provide conditions for their reliable use when modeling a flying focus.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Solitons in PT-symmetric nonlinear lattices

The existence of localized modes supported by the PT-symmetric nonlinear lattices is reported. The system considered reveals unusual properties: unlike other typical dissipative systems, it possesses families (branches) of solutions, which can be parametrized by the propagation constant; relatively narrow localized modes appear to be stable, even when the conservative nonlinear lattice potential is absent; and finally, the system supports stable multipole solutions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Two-photon absorption of few-electron heavy ions

The two-photon absorption of few-electron ions has been studied by using second-order perturbation theory and Dirac's relativistic equation. Within this framework, the general expressions for the excitation cross sections and rates are derived including a full account of the higher-order multipole terms in the expansion of the electron-photon interaction. While these expressions can be applied to any ion, independent of its particular shell structure, detailed computations are carried out for the two-photon absorption of hydrogen-, helium-, and berylliumlike ions and are compared with the available theoretical and experimental data. The importance of relativistic and nondipole effects in the analysis and computation of induced two-photon transitions is pointed out. Moreover, we discuss the potential of these transitions for atomic parity-violation studies in the high-Z domain.

74 ATOMIC AND MOLECULAR PHYSICS↗