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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Global Λ hyperon polarization in low-energy heavy ion collisions: A scenario without vorticity

Since its discovery, global polarization of the Λ hyperon in heavy-ion collisions has been firmly established and is widely attributed to the large vorticity generated in the rotating quark-gluon plasma. In contrast, nearly fifty years after the first observation of unexpectedly large transverse Λ polarization in unpolarized hadron collisions, its underlying mechanism remains an open and long-standing puzzle, despite being observed across a broad range of collision systems. Although these two phenomena exhibit notable similarities, they are generally regarded as arising from distinct physical origins. In this work, we propose a direct connection between Λ global polarization in heavy-ion collisions and the long-standing transverse polarization observed in unpolarized collision systems. We demonstrate that the alignment between the Λ production plane and the reaction plane, driven by directed flow, can transfer transverse polarization into the measured global polarization signal. Realistic Monte Carlo simulations of Au+Au collisions at √𝑠 NN =3 GeV indicate that this mechanism can generate a sizable global polarization, accounting for approximately 23% ±6% of the magnitude reported by the STAR Collaboration. Our results establish, for the first time, a quantitative link between these two well-known phenomena and have important implications for the interpretation of Λ global polarization measurements in low-energy heavy-ion collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Observation of 𝑊⁢𝑍⁢𝛾 production and constraints on new physics scenarios in proton-proton collisions at $\sqrt{s}$ =13 TeV

A measurement of the 𝑊⁢𝑍⁢𝛾 triboson production cross section is presented. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ =13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb −1 . The analysis focuses on the final state with three charged leptons, ℓ ± ⁢𝜈⁢ℓ + ⁢ℓ − , where ℓ = 𝑒 or 𝜇, accompanied by an additional photon. The observed (expected) significance of the 𝑊⁢𝑍⁢𝛾 signal is 5.4 (3.8) standard deviations. The cross section is measured in a fiducial region, where events with an ℓ originating from a tau lepton decay are excluded, to be 5.48 ± 1.11 fb, which is compatible with the prediction of 3.69 ± 0.24 fb at next-to-leading order in quantum chromodynamics. Exclusion limits are set on anomalous quartic gauge couplings and on the production cross sections of massive axionlike particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Distinguishing the gapped and Weyl semimetal scenario in ZrTe 5 : insights from an effective two-band model

In this work, we study the static and dynamic transport properties of a low-energy two-band model proposed previously in Martino et al. [PRL 122, 217402 (2019)], with an anisotropic in-plane linear momentum dependence and a parabolic out-of-plane dispersion. The model is extended to include a negative band gap, which leads to the emergence of a Weyl semimetal (WSM) state, as opposed to the gapped semimetal (GSM) state when the band gap is positive. Furthermore, we calculate and compare the zero- and finite-frequency transport properties of the GSM and WSM cases. The DC properties that are calculated for the GSM and WSM cases are Drude spectral weight, mobility, and resistivity. We determine their dependence on the Fermi energy and crystal direction. The in- and out-of-plane optical conductivities are calculated in the limit of the vanishing interband relaxation rate for both semimetals. The main common features are an ω 1/2 in-plane and ω 3/2 out-of-plane frequency dependence of the optical conductivity. We seek particular features related to the charge transport that could unambiguously point to one ground state over the other, based on the comparison with the experiment. Differences between the WSM and GSM are in principle possible only at extremely low carrier concentrations and at low temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Early structure formation constraints on the ultralight axion in the postinflation scenario

Many works have concentrated on the observable signatures of the dark matter being an ultralight axion-like particle (ALP). We concentrate on a particularly dramatic signature in the late-time cosmological matter power spectrum that occurs if the symmetry breaking that establishes the ALP happens after inflation -- white-noise density fluctuations that dominate at small scales over the adiabatic fluctuations from inflation. Here, these fluctuations alter the early history of nonlinear structure formation. We find that for symmetry breaking scales of f A ~ 10 13 – 10 15 GeV, which requires a high effective maximum temperature after inflation, ALP dark matter with particle mass of m A ~ 10 –13 – 10 –20 eV could significantly change the number of high-redshift dwarf galaxies, the reionization history, and the Lyα forest. We consider all three observables. We find that the Lyα forest is the most constraining of current observables, excluding f A ≳ 10 15 GeV (m A ≲ 10 –17 eV) in the simplest model for the ALP and considerably lower values in models coupled to a hidden strongly interacting sector (f A ≳ 10 13 GeV and m A ≲ 10 –13 eV). Observations that constrain the extremely high-redshift tail of reionization may disfavor similar levels of isocurvature fluctuations as the forest. Future z ~ 20–30 21cm observations have the potential to improve these constraints further using that the supersonic motions of the isocurvature-enhanced abundance of ~10 4 M ⊙ halos would shock heat the baryons, sourcing large BAO features.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Evolution of decaying particles and decay products in various scenarios for the future expansion of the Universe

We examine nonrelativistic particles that decay into relativistic products in big rip, little rip, and pseudorip models for the future evolution of the Universe. In contrast to decays that occur in standard ΛCDM, the evolution of the ratio r of the energy density of the relativistic decay products to the energy density of the initially decaying particles can decrease with time in all of these models. In big rip and little rip models, r always goes to zero asymptotically, while this ratio evolves to infinity or a constant in pseudorip models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Cosmological implications of photon-flux upper limits at ultrahigh energies in scenarios of Planckian-interacting massive particles for dark matter

Here using the data of the Pierre Auger Observatory, we report on a search for signatures that would be suggestive of super-heavy particles decaying in the Galactic halo. From the lack of signal, we present upper limits for different energy thresholds above ≳10 8 GeV on the secondary by-product fluxes expected from the decay of the particles. Assuming that the energy density of these super-heavy particles matches that of dark matter observed today, we translate the upper bounds on the particle fluxes into tight constraints on the couplings governing the decay process as a function of the particle mass. Instantons, which are nonperturbative solutions to Yang-Mills equations, can give rise to decay channels otherwise forbidden and transform stable particles into metastable ones. Assuming such instanton-induced decay processes, we derive a bound on the reduced coupling constant of gauge interactions in the dark sector: α X ≲ 0.09, for 10 9 ≲ M X /GeV < 10 19 . Conversely, we obtain that, for instance, a reduced coupling constant α X = 0.09 excludes masses M X ≳ 3 x 10 13 GeV . In the context of dark matter production from gravitational interactions alone during the reheating epoch, we derive constraints on the parameter space that involves, in addition to M X and α X , the Hubble rate at the end of inflation, the reheating efficiency, and the nonminimal coupling of the Higgs with curvature.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Enhancing the sensitivity to seesaw mechanism predictions in gauged B − L scenarios

New gauge bosons coupled to heavy neutral leptons (HNLs) are simple and well-motivated extensions of the Standard Model. In searches for HNLs in proton fixed-target experiments, we find that a large population of gauge bosons ( Z ′ ) produced by proton bremsstrahlung may decay to HNLs, leading to a significant improvement in existing bounds on the ( m HNL , U α ), where U α represent the mixing between HNL and the active neutrinos with flavor α . We study this possibility in fixed target experiments with the 8 GeV proton beams, including SBND, MicroBooNE, and ICARUS, as well as DUNE and DarkQuest at 120 GeV. We find the projected sensitivities to additional Z ′ -mediated HNL production can bring the seesaw mechanism of the neutrino masses within a broadened experimental reach. Published by the American Physical Society 2025

Capozzi, Francesco (ORCID:0000000161351531)↗
DOE OSTI2025

Expanding on the BRIAR Dataset: A Comprehensive Whole Body Biometric Recognition Resource at Extreme Distances and Real-World Scenarios (Collections 1-4)

The state-of-the-art in biometric recognition algorithms and operational systems has advanced quickly in recent years providing high accuracy and robustness in more challenging collection environments and consumer applications. However, the technology still suffers greatly when applied to non-conventional settings such as those seen when performing identification at extreme distances or from elevated cameras on buildings or mounted to UAVs. This paper summarizes an extension to the largest dataset currently focused on addressing these operational challenges, and describes its composition as well as methodologies of collection, curation, and annotation.

Cornett, David [ORNL] (ORCID:0000000222910860)↗
DOE OSTI2024

Long-Range Biometric Identification in Real World Scenarios: A Comprehensive Evaluation Framework Based on Missions

The considerable body of data available for evaluating biometric recognition systems in Research and Development (R&D) environments has contributed to the increasingly common problem of target performance mismatch. Biometric algorithms are frequently tested against data that may not reflect the real world applications they target. From a Testing and Evaluation (T&E) standpoint, this domain mismatch causes difficulty assessing when improvements in State-of-the-Art (SOTA) research actually translate to improved applied outcomes. This problem can be addressed with thoughtful preparation of data and experimental methods to reflect specific use-cases and scenarios.To that end, this paper evaluates research solutions for identifying individuals at ranges and altitudes, which could support various application areas such as counterterrorism, protection of critical infrastructure facilities, military force protection, and border security. We address challenges including image quality issues and reliance on face recognition as the sole biometric modality. By fusing face and body features, we propose developing robust biometric systems for effective long-range identification from both the ground and steep pitch angles. Preliminary results show promising progress in whole-body recognition. This paper presents these early findings and discusses potential future directions for advancing long-range biometric identification systems based on mission-driven metrics.

Aykac, Deniz↗
DOE OSTI2023

Developing a Disaster-Ready Power Grid Agent Through Geophysically-Informed Fault Event Scenarios

Management of the nation’s power grid over the coming decades will need to factor multiple climate-driven threats to the power system that can be stressful or even detrimental to its operations. During disasters, grid operators suffer from cognitive overload where the electric grid is severely impacted by the weather, yet grid operators have limited awareness of these factors. Meanwhile, the electric grid is facing an explosion of data coming from a variety of sources which can enable the operator to evaluate the risks and develop mitigation strategies against hazardous events. In this work, we processed heterogeneous environmental and power grid data to learn and model grid behavior caused by extreme weather events. In this study, we focused on two weather-driven hazards, hurricanes and wildfires, which were analysed for the electric grid of Texas. We the used this data to train a Reinforcement Learning (RL) agent by analysing and predicting future behaviour of the grid during those hazard events. All these parts are incorporated in one framework to have a geophysically informed power simulators that can be used to train RL agents.

electic grid, reinforcement learning, climate adap↗