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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Reconstructing f ( T ) gravity and exploring the torsion driven warm inflationary cosmology

The current paper reports an investigation of a warm inflationary scenario in the context of f(T) gravity for a spatially flat FLRW universe. In our model, inflation is driven purely by the torsional sector of f(T) gravity, without introducing any additional scalar fields. We focus on the high dissipative regime (R >> 1), reconstruct the Hubble parameter as a function of the e-folding number N, and derive the slow-roll parameters ε 1 (N) and ε 2 (N). The study has encapsulated the dynamics of inflation and its duration under strong dissipation. The dissipative coefficient Γ is modeled with a temperature-dependent power-law form, linking the inflationary dynamics to thermal corrections and the particle content of the early universe. The analysis has affirmed that the torsion-induced energy density ρ T successfully transitions to radiation energy density ρ rad , facilitating a graceful exit from inflation. Finally, we have validated our model by comparing the scalar spectral index and tensor-to-scalar ratio with Planck 2018 results, demonstrating consistency within observational bounds. Additionally, it is verified that the thermal domination condition T * /H > 1 and the torsion dominance condition ρ T /ρ rad > 1 are satisfied.

Ghosh, Moli [Amity University, Kolkata (India); Mr↗
DOE OSTI2024

Mapping Dark Matter on Small Scales with the Cosmic Microwave Background (Final Report)

Sehgal was funded by DOE Grant DE-SC0020441 over the period from 11/1/2019 - 04/30/2024 (no remaining funds are anticipated). Most recently, Sehgal and her group completed a publication forecasting cosmological parameter constraints for a CMB-HD survey, in addition to SO and CMB-S4 (1). One focus of this work was determining the improvement in parameter constraints when removing the gravitational lensing effect from the primordial CMB (a process called delensing). This work also explored the bias to parameters from neglecting baryonic effects, and ways to mitigate that. In addition, this work highlighted that a CMB-HD N eff measurement could tightly constrain the QCD axion in a modelindependent way (see left panel of Figure 1). Sehgal also developed a novel way to probe inflation via CMB experiments by measuring inflationary magnetic fields (IMFs) (2). IMFs are thought to seed the large magnetic fields we observe in galaxies today, and can be measured by looking for anisotropic rotation of the CMB polarization vectors across the sky (an effect called cosmic birefringence). The cosmic birefringence from IMFs has a unique frequency dependence, allowing it to be separated from other sources of cosmic birefringence. In (2), Sehgal and her postdoc also presented a novel way to remove foreground contamination from Galactic magnetic fields using measurements of the polarization of nearby radio sources. The removal of this Galactic contamination is necessary when measuring IMFs at the level of 0.1 nG; IMFs with a strength of at least 0.1 nG are needed to seed the magnetic fields in galaxies we observe today. Since only inflation can generate such a strong magnetic field, measuring such a signal would be a “smoking gun” signature that inflation occurred. Sehgal showed in (2) that CMB-HD could detect such IMFs with at least 3σ significance (see right panel of Figure 1).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Gravity as a Portal to Reheating, Leptogenesis and Dark Matter

Considering graviton as the only messenger that exists between the inflaton, the dark sector and the Standard Model (SM), we show, it is possible to simultaneously generate the observed relic density of dark matter (DM), the baryon asymmetry via leptogenesis, as well as successful reheating after inflation. Assuming the inflaton Φ oscillates in a monomial potential V(Φ) ∝ Φ k at the end of inflation, reheating via minimal gravitational interaction turns out to be excluded due to excessive production of gravitational wave (GW) energy density from inflation. We thus (a) extend the minimal model by considering a non-minimal gravitational contribution to radiation and (b)) propose an explanation for the PeV excess observed by IceCube, when the DM has an explicit Yukawa coupling to the SM leptong and Higgs. We also propose a novel scenario, where the gravitational production is a two-step process, through the production of a pair of scalars, that eventually decay into fermionic final states. Our framework gives rise to detectable primordial GW signal, that falls within the sensitivity of several proposed GW detectors.

Barman, Basabendu↗
DOE OSTI2024

Inflaton production of scalar dark matter through fluctuations and scattering

We study the effects on particle production of a Planck-suppressed coupling between the inflaton and a scalar dark matter candidate, X. In the absence of this coupling the dominant source for the relic density of X is the long wavelength modes produced from the scalar field fluctuations during inflation. In this case, there are strong constraints on the mass of the scalar and the reheating temperature after inflation from the present-day relic density of X (assuming X is stable). When a coupling σ⁢Φ 2 ⁢X 2 is introduced, with σ = ˜σm$^{2}_{Φ}$/$M$$^{2}_{P}$ ~10 –10 ⁢ ˜σ, where m Φ is the inflaton mass, the allowed parameter space begins to open up considerably even for ˜σ as small as ≳10 –7 . For ˜σ ≳ $\frac{9}{16}$, particle production is dominated by the scattering of the inflaton condensate, either through single graviton exchange or the contact interaction between Φ and X. In this regime, the range of allowed masses and reheating temperatures is maximal. For 0.004 < ˜σ < 50, constraints from isocurvature fluctuations are satisfied, and the production from parametric resonance can be neglected.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Gravitational production of completely dark photons with nonminimal couplings to gravity

Dark photons are a theorized massive spin-1 particle which can be produced via various mechanisms, including cosmological gravitational particle production (GPP) in the early universe. In this work, we extend previous results for GPP of dark photons to include nonminimal couplings to gravity. We find that nonminimal couplings can induce a ghost instability or lead to runaway particle production at high momentum and discuss the constraints on the parameter space such that the theory is free of instabilities. Within the instability-free regime we numerically calculate the particle production and find that the inclusion of nonminimal couplings can lead to an enhancement of the particle number. As a result, GPP of nonminimally coupled dark photons can open the parameter space for production of a cosmological relevant relic density (constituting all or part of the dark matter) as compared to the minimally-coupled theory. These results are independent of the choice of inflation model, which we demonstrate by repeating the analysis for a class of rapid-turn multi-field inflation models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Technological evolution of large-scale blue hydrogen production toward the U.S. Hydrogen Energy Earthshot

Hydrogen potentially has a crucial role in the U.S. transition to a net-zero emissions economy. Learning from large-scale hydrogen projects will boost technological evolution and innovation toward the U.S. Hydrogen Energy Earthshot. We apply experience curves to estimate the evolving costs of blue hydrogen production and to further examine the economic effect on technological evolution of the Inflation Reduction Act’s tax credits for carbon sequestration and clean hydrogen. Learning-by-doing alone can decrease the production cost of blue hydrogen. Without tax incentives, however, it is hard for blue hydrogen production to reach the cost target of $\$1$/kg H 2 . Here we show that the breakeven cumulative production capacity required for gas-based blue hydrogen to reach the $\$1$/kg H 2 target highly depends on tax credit, natural gas price, inflation rate, and learning rates. We make recommendations for hydrogen hub development and for accelerating technological progress toward the Hydrogen Energy Earthshot.

08 HYDROGEN↗
DOE OSTI2025

Impact of truck electrification on air pollution disparities in the United States

Electrifying heavy-duty trucks reduces on-road diesel emissions but shifts the burden of supplying energy to power-generation facilities. The combined effect of Inflation Reduction Act investments in grid decarbonization and truck electrification will alter the magnitude and distribution of air pollution burdens across the United States. These investments are intended to facilitate a just energy transition, with 40% of the benefits flowing to disadvantaged communities per the Justice40 Initiative. Here we evaluate the combined effects of Inflation Reduction Act grid decarbonization and truck electrification investments on a national scale to determine whether the air pollution benefits would meet this 40% goal for both disadvantaged communities and the most exposed racial–ethnic groups. We find that truck electrification and decarbonization reduce air-pollution-related premature mortality in disadvantaged communities. However, the relative disparity between disadvantaged and non-disadvantaged communities increases, suggesting that a disproportionate share of benefits accrue to non-disadvantaged communities. Whereas absolute disparity in grid emissions decreases over time for all racial–ethnic groups, relative disparity remains largely unchanged, with Black populations being the most exposed. Electrifying drayage corridors would result in comparatively large health benefits for disadvantaged communities, suggesting that increasing targeted electrification investments in short-haul routes near urban areas (for example, ports) could be promising.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Axion stars: mass functions and constraints

The QCD axion and axion-like particles, as leading dark matter candidates, can also have interesting implications for dark matter substructures if the Peccei-Quinn symmetry is broken after inflation. In such a scenario, axion perturbations on small scales will lead to the formation of axion miniclusters at matter-radiation equality, and subsequently the formation of axion stars. Such compact objects open new windows for indirect searches for axions. We compute the axion star mass function based on recent axion minicluster studies and Bose star simulations. Applying this mass function, we find post-inflation axion-like particles with masses 1.8 × 10$^{-21}$ eV

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Behavior and mechanisms of Doppler wind lidar error in complex terrain: stable flow case study at Perdigão

A numerical experiment is carried out investigating the magnitude of biases in ground-based lidar measurements in complex flow conditions. Biases assessed include those arising from flow curvature and from the interaction of turbulence with the wind field reconstruction (WFR) algorithms used by a WindCube lidars and anemometers. RANS-CFD and WRF-LES simulations were performed for the Perdig˜ao Field Experiment site for a range of atmospheric conditions. Virtual anemometer and lidar data were generated for four locations: two near exposed ridge tops and two in low-speed regions in the valley. The LES data at these four locations show that the scalar inflation terms (the relation between scalar and vector averaged wind speed) for virtual lidar and virtual cups agree very well with predictions using perturbation theory. While the lidar errors vary greatly with location and height, the contribution from the flow curvature tends to be larger than the differences arising from scalar inflation. For one lidar/mast pair near the ridge top, comparisons between simulations and measurements are carried out for a resonant mountain wave event on June 14th, 2017, and for the whole duration of the Perdigão campaign for winds perpendicular to the ridges. The lidar error during the mountain wave, a period of strong stability and low inversion height, is significantly larger than the campaign average. The sensitivity of the lidar error to atmospheric stability is confirmed by the RANS simulations, which suggests strong sensitivity of flow curvature error to stability conditions and to the shape of the wind speed profile near the top of the boundary layer.

17 WIND ENERGY↗
DOE OSTI2024

Cosmological dynamics of string theory axion strings

The quantum chromodynamics (QCD) axion may solve the strong CP problem and explain the dark matter (DM) abundance of our Universe. The axion was originally proposed to arise as the pseudo-Nambu-Goldstone boson of global U⁢(1) PQ Peccei-Quinn (PQ) symmetry breaking, but axions also arise generically in string theory as zero modes of higher-dimensional gauge fields. In this work we show that string theory axions behave fundamentally differently from field theory axions in the early Universe. Field theory axions may form axion strings if the PQ phase transition takes place after inflation. In contrast, we show that string theory axions do not generically form axion strings. In special inflationary paradigms, such as D-brane inflation, string theory axion strings may form; however, their tension is parametrically larger than that of field theory axion strings. We then show that such QCD axion strings overproduce the DM abundance for all allowed QCD axion masses and are thus ruled out, except in scenarios with large warping. A loop-hole to this conclusion arises in the axiverse, where an axion string could be composed of multiple different axion mass eigenstates; a heavier eigenstate could collapse the network earlier, allowing for the QCD axion to produce the correct DM abundance and also generating observable gravitational wave signals.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Policy implications of net-zero emissions: A multi-model analysis of United States emissions and energy system impacts

Many countries, subnational jurisdictions, and companies are setting net-zero emissions goals; however, questions remain about strategies to reach these targets, policy measures, technology gaps, and economic impacts. Here, we investigate the potential policy implications of reaching economy-wide net-zero CO 2 emissions across the United States by 2050 using results from a multi-model comparison with 14 energy-economic models. Model results suggest that achieving net-zero CO 2 targets depends on policies that accelerate deployment of zero- and low-emitting technologies that have seen rapid cost reductions in recent years (including wind, solar, battery storage, and electric vehicles) as well as relatively nascent options (including carbon capture and storage, advanced biofuels, low-carbon hydrogen, advanced nuclear, and long-duration energy storage). While net-zero policies are likely to lower fossil fuel consumption, including considerable coal and petroleum reductions, achieving net-zero emissions does not necessarily mean phasing out all fossil fuels. Model results indicate that the Inflation Reduction Act’s energy and climate provisions amplify near-term decarbonization but that net-zero policies have larger impacts on long-run outcomes. Stringent climate policy can have large fiscal impacts on tax revenue and government spending—revenues from carbon pricing and subsidies for carbon removal range from 0.1 % to 3.7 % of GDP in 2050 across models. Each dollar per metric ton carbon price leads to a 0.06 % to 0.31 % reduction in economy-wide CO 2 emissions relative to a reference scenario with current policies. Spending on energy across the economy decreases relative to today for many models under reference and net-zero policies, especially as a share of GDP, due primarily to end-use electrification and energy efficiency.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Probing dark matter isocurvature with primordial non-Gaussianity

Multiple fields can become dynamical during the inflationary epoch. We consider an example where a light field acquires isocurvature fluctuations during inflation and contributes to the dark matter abundance at late times. Interactions between the light field and the adiabatic sector contribute to mixed adiabatic-isocurvature non-Gaussianity (NG). We show the resulting form of NG has a different kinematic dependence than the `local shape' commonly considered, and highlight the parameter space where a dedicated search is expected to significantly improve the current Planck sensitivity. Here, we interpret our results in the context of the QCD axion and illustrate how the proposed NG searches can improve upon the existing searches for isocurvature power spectrum and bispectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Peeking into the next decade in large-scale structure cosmology with its Effective Field Theory

After the successful full-shape analyses of BOSS data using the Effective Field Theory of Large-Scale Structure, we investigate what upcoming galaxy surveys might achieve. We introduce a “perturbativity prior” that ensures that loop terms are as large as theoretically expected, which is effective in the case of a large number of EFT parameters. After validating our technique by comparison with already-performed analyses of BOSS data, we provide Fisher forecasts using the one-loop prediction for power spectrum and bispectrum for two benchmark surveys: DESI and MegaMapper. We find overall great improvements on the cosmological parameters. In particular, we find that MegaMapper (DESI) should obtain at least a 12σ (2σ) evidence for non-vanishing neutrino masses, bound the curvature Ω k to 0.0012 (0.012), and primordial inflationary non-Gaussianities as follows: f NL loc. to ± 0.26 (3.3), f NL eq. to ±16 (92), f NL orth. to ± 4.2 (27). Such measurements would provide much insight on the theory of Inflation. We investigate the limiting factor of shot noise and ignorance of the EFT parameters.

cosmological parameters from LSS↗
DOE OSTI2025

Constraining primordial non-Gaussianity from the large scale structure two-point and three-point correlation functions

Surveys of cosmological large-scale structure (LSS) are sensitive to the presence of local primordial non-Gaussianity (PNG), and may be used to constrain models of inflation. Local PNG, characterized by f NL ⁠, the amplitude of the quadratic correction to the potential of a Gaussian random field, is traditionally measured from LSS two-point and three-point clustering via the power spectrum and bi-spectrum. We propose a framework to measure f NL using the configuration space two-point correlation function (2pcf) monopole and three-point correlation function (3pcf) monopole of survey tracers. Our model estimates the effect of the scale-dependent bias induced by the presence of PNG on the 2pcf and 3pcf from the clustering of simulated dark matter haloes. We describe how this effect may be scaled to an arbitrary tracer of the cosmological matter density. The 2pcf and 3pcf of this tracer are measured to constrain the value of f NL ⁠. In LSS surveys, the effect of imaging systematics on two-point statistics is often degenerate with the PNG signal. Our proposed model employs three-point statistics primarily to break this degeneracy. Using simulations of luminous red galaxies observed by the Dark Energy Spectroscopic Instrument (DESI), we demonstrate the accuracy and constraining power of our method. Our forecast indicates the ability to constrain f NL to a precision of σf NL ≈ 22 with one year of DESI survey data, as well as the ability to constrain the imaging systematic weights in situ.

early Universe↗
DOE OSTI2025

Plausible constraints and inflationary production for dark photons

Generic constraints on dark photons are generally presented assuming they have Stueckelberg masses. These constraints are strengthened if instead the mass is due to the Higgs mechanism and the dark Higgs is light. First, we show that under reasonable assumptions on the origin of kinetic mixing 𝜀 and perturbativity, the strengthened constraints on 𝜀 cannot be arbitrarily relaxed by making the Higgs heavy. Second, we demonstrate a simple mechanism for generating dark photon dark matter after inflation, where fluctuations of a dark Higgs by stochastic misalignment can produce stable dark photons through ℎ →𝐴′⁢𝐴′ decay. Third, we point out new lower bounds on 𝜀 in the case where the dark photon mediates thermal freeze-out of light dark matter by 𝑠-channel exchange, taking account of generic expectations for the size of 𝜀, and astrophysical upper bounds on the self-interaction cross section.

inflation↗
DOE OSTI2024

Runaway Gravitational Production of Dark Photons

We demonstrate that gravitational particle production of a massive, Abelian, vector (Proca) field during inflation in the presence of nonminimal coupling to gravity may suffer from an instability which leads to runaway production of high-momentum modes. This is untenable unless there is some mechanism to regulate the runaway. We discuss the parameter space of the particle mass and nonminimal couplings where such a runaway occurs and possible ways to tame the runaway. We find that there is no obvious way to resolve the runaway in a UV completion or with kinetic mixing to the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Carbon‐negative hydrogen from ethanol via catalytic oxidative reforming

Abstract This study evaluated a commercial technology for producing low‐ or negative‐carbon hydrogen through ethanol catalytic oxidative reforming, focusing on the life cycle greenhouse gas emissions, or carbon intensity (CI). Various scenarios were analyzed: (a) comparing corn ethanol (first‐generation or Gen1 ethanol) and cellulosic ethanol (second‐generation or Gen2 ethanol) as feedstocks; (b) assessing carbon capture and sequestration (CCS) for CO 2 from upstream fermentation; and (c) evaluating oxygen sourcing via air separation units vs. on‐site or off‐site water electrolysis using a proton exchange membrane. Findings indicate that the CI for hydrogen production using Gen2 ethanol from corn stover is lower than that of Gen1 corn ethanol. Additionally, using proton exchange membrane‐generated oxygen results in a lower CI than air separation unit‐generated oxygen, regardless of the sourcing method. Implementing CCS for the hydrogen production plant's evolved CO 2 is essential for achieving a net‐negative CI for hydrogen from Gen1 ethanol. All examined scenarios, including both ethanol generations, oxygen sources, and CCS applications, demonstrated a net‐negative carbon intensity, surpassing the life cycle greenhouse gas emissions threshold of 0.45 kg CO 2 e/kg to enable policy credits as outlined in the Inflation Reduction Act §45V. In comparison, the CI for hydrogen from steam methane reforming stands at 3.4 kg CO 2 e/kg with CCS and 9.4 kg CO 2 e/kg without CCS.

08 HYDROGEN↗
DOE OSTI2026

Seasonal variation in methane ebullition in a temperate hydropower reservoir impacts annualized estimates

Estimates of ebullitive methane (CH4) emissions from reservoirs are highly uncertain, often based on spatial and temporal upscaling from a limited number of sampling sites and periods. While some of these estimates may adjust for seasonal variation in temperature, they rarely account for drawdown and the resulting changes in site depth and the areal extent of the reservoir. In Douglas Reservoir (Tennessee, USA), we conducted monthly sampling of 20 sites over 1 year to capture temporal and spatial variation in CH4 ebullition. We then compared various approaches for obtaining annualized, whole-reservoir ebullition estimates. CH4 ebullition fluxes were zero-inflated and highly skewed, with fluxes rising appreciably above zero in July and peaking in autumn. Estimates that did not account for drawdown overestimated annualized rates by 20%, though with high uncertainty. Seasonal variability and hotspots strongly influence annualized ebullition estimates and are important to account for in inventories and global upscaling.

Cardall, Anna [Brigham Young University]↗