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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Refining localtype primordial non-Gaussianity: Sharpened bϕ constraints through bias expansion

Local-type primordial non-Gaussianity (PNG), predicted by many nonminimal models of inflation, creates a scale-dependent contribution to the power spectrum of large-scale structure tracers. Its amplitude is characterized by the product bϕfNLloc, where bϕ is an astrophysical parameter dependent on the properties of the tracer. However, bϕ exhibits significant secondary dependence on halo concentration and other astrophysical properties, which may bias and weaken the constraints on fNLloc. In this work, we demonstrate that incorporating knowledge of the relation between Lagrangian bias parameters and bϕ can significantly enhance PNG constraints. We employ the hybrid effective field theory approach at the field level and a linear regression model to seek a connection between the bias parameters and bϕ for halo and galaxy samples, constructed using the abacussummit simulation suite and mimicking the luminous red galaxies and quasistellar objects of the Dark Energy Spectroscopic Instrument survey. For the fixed-mass halo samples, our full bias model reduces the uncertainty by more than 70%, with most of that improvement coming from b∇, which we find to be an excellent proxy for concentration. For the galaxy samples, our model reduces the uncertainty on bϕ by 80% for all tracers. By adopting Lagrangian-bias informed priors on the parameter bϕ, future analyses can thus constrain fNLloc with less bias and smaller errors.

Hadzhiyska, Boryana↗
DOE OSTI2017

Refining the detection of the zero crossing for the three-gluon vertex in symmetric and asymmetric momentum subtraction schemes

This article reports on the detailed study of the three-gluon vertex in four-dimensional $SU(3)$ Yang-Mills theory employing lattice simulations with large physical volumes and high statistics. A meticulous scrutiny of the so-called symmetric and asymmetric kinematical configurations is performed and it is shown that the associated form-factor changes sign at a given range of momenta. Here, the lattice results are compared to the model independent predictions of Schwinger-Dyson equations and a very good agreement among the two is found.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Precision Mass Measurements of Neutron-Rich Scandium Isotopes Refine the Evolution of N = 32 and N = 34 Shell Closures

In this work, we report high-precision mass measurements of 50–55 Sc isotopes performed at the LEBIT facility at NSCL and at the TITAN facility at TRIUMF. Our results provide a substantial reduction of their uncertainties and indicate significant deviations, up to 0.7 MeV, from the previously recommended mass values for 53–55 Sc. The results of this work provide an important update to the description of emerging closed-shell phenomena at neutron numbers N = 32 and N = 34 above proton-magic Z = 20. In particular, they finally enable a complete and precise characterization of the trends in ground state binding energies along the N = 32 isotone, confirming that the empirical neutron shell gap energies peak at the doubly magic 52 Ca. Moreover, our data, combined with other recent measurements, do not support the existence of a closed neutron shell in 55 Sc at N = 34. The results were compared to predictions from both ab initio and phenomenological nuclear theories, which all had success describing N = 32 neutron shell gap energies but were highly disparate in the description of the N = 34 isotone.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Crystal structure refinements of tetragonal (OH,F)-rich spessartine and henritermierite garnets

Cubic garnet (space group Ia\overline 3 d) has the general formula X 3 Y 2 Z 3 O 12 , where X , Y and Z are cation sites. In the tetragonal garnet (space group I 4 1 / acd ), the corresponding cation sites are X 1 and X 2, Y , and Z 1 and Z 2. In both space groups only the Y site is the same. The crystal chemistry of a tetragonal (OH,F)-rich spessartine sample from Tongbei, near Yunxiao, Fujian Province, China, with composition X (Mn 2.82 Fe^{2+}_{0.14}Ca 0.04 ) Σ3 Y {Al 1.95 Fe^{3+}_{0.05}} Σ2 Z [(SiO 4 ) 2.61 (O 4 H 4 ) 0.28 (F 4 ) 0.11 ] Σ3 (Sps 94 Alm 5 Grs 1 ) was studied with single-crystal X-ray diffraction and space group I 4 1 / acd . The deviation of the unit-cell parameters from cubic symmetry is small [ a = 11.64463(1), c = 11.65481 (2) Å, c / a = 1.0009]. Point analyses and back-scattered electron images, obtained by electron-probe microanalysis, indicate a homogeneous composition. The Z 2 site is fully occupied, but the Z 1 site contains vacancies. The occupied Z 1 and Z 2 sites with Si atoms are surrounded by four O atoms, as in anhydrous cubic garnets. Pairs of split sites are O1 with F11 and O2 with O22. When the Z 1 site is vacant, a larger [(O 2 H 2 )F 2 ] tetrahedron is formed by two OH and two F anions in the O22 and F11 sites, respectively. This [(O 2 H 2 )F 2 ] tetrahedron is similar to the O 4 H 4 tetrahedron in hydrogarnets. These results indicate ^{X}{{\rm Mn}^ {2+}_{3}}\,^{Y}{\rm Al}_{2}^{Z}[({\rm SiO}_{4})_{2}({\rm O}_{2}{\rm H}_{2})_{0.5}({\rm F}_{2})_{0.5}]_{\Sigma3} as a possible end member, which is yet unknown. The H atom that is bonded to the O22 site is not located because of the small number of OH groups. In contrast, tetragonal henritermierite, ideally ^{X}{\rm Ca}_{3}\,^{Y}{\rm Mn}^{3+}_{2}\,^{Z}[({\rm SiO}_{4})_{2}({\rm O}_{4}{\rm H}_{4})_1]_{\Sigma3}, has a vacant Z 2 site that contains the O 4 H 4 tetrahedron. The H atom is bonded to an O3 atom [O3—H3 = 0.73 (2) Å]. Because of O2—Mn 3+ —O2 Jahn–Teller elongation of the Mn 3+ O 6 octahedron, a weak hydrogen bond is formed to the under-bonded O2 atom. This causes a large deviation from cubic symmetry ( c / a = 0.9534).

Antao, Sytle M.↗