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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 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Search for lightly ionizing particles using CDMS-II data and fabrication of CDMS detectors with improved homogeneity in properties

Fundamental particles are always observed to carry charges which are integral multiples of one-third charge of electron, e/3. While this is a well established experimental fact, the theoretical understanding for the charge quantization phenomenon is lacking. On the other hand, there exist numerous theoretical models that naturally allow for existence of particles with fractional electromagnetic charge. These particles, if existing, hint towards existence of physics beyond the standard model. Multiple high energy, optical, cosmological and astrophysical considerations restrict the allowable mass-charge parameter space for these fractional charges. Still, a huge unexplored region remains. The Cryogenic Dark Matter Search (CDMS-II), located at Soudan mines in northern Minnesota, employs germanium and silicon crystals to perform direct searches for a leading candidate to dark matter called Weakly Interacting Massive Particles (WIMPs). Alternately, the low detection threshold allows search for fractional electromagnetic-charged particles, or Lightly Ionizing Particles (LIPs), moving at relativistic speed. Background rejection is obtained by requiring that the magnitude and location of energy deposited in each detector be consistent with corresponding \signatures" resulting from the passage of a fractionally charged particle. In this dissertation, the CDMS-II data is analyzed to search for LIPs, with an expected background of 0.078 0.078 events. No candidate events are observed, allowing exclusion of new parameter space for charges between e/6 and e/200.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Constraints on Lorentz Invariance Violation from Optical Polarimetry of Astrophysical Objects

Theories of quantum gravity suggest that Lorentz invariance, the fundamental symmetry of the Theory of Relativity, may be broken at the Planck energy scale. While any deviation from conventional Physics must be minuscule in particular at attainable energies, this hypothesis motivates ever more sensitive tests of Lorentz symmetry. In the photon sector, astrophysical observations, in particular polarization measurements, are a very powerful tool because tiny deviations from Lorentz invariance will accumulate as photons propagate over cosmological distances. The Standard-Model Extension (SME) provides a theoretical framework in the form of an effective field theory that describes low-energy effects due to a more fundamental quantum gravity theory by adding additional terms to the Standard Model Lagrangian. These terms can be ordered by the mass dimension d of the corresponding operator and lead to a wavelength, polarization, and direction dependent phase velocity of light. Lorentz invariance violation leads to an energy-dependent change of the Stokes vector as photons propagate, which manifests itself as a rotation of the polarization angle in measurements of linear polarization. In this paper, we analyze optical polarization measurements from 63 Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRBs) to search for Lorentz violating signals. We use both spectropolarimetric measurements, which directly constrain the change of linear polarization angle, as well as broadband spectrally integrated measurements. In the latter, Lorentz invariance violation manifests itself by reducing the observed net polarization fraction. Any observation of non-vanishing linear polarization thus leads to constraints on the magnitude of Lorentz violating effects. We derive the first set limits on each of the 10 individual birefringent coefficients of the minimal SME with d = 4 , with 95% confidence limits on the order of 10−34 on the dimensionless coefficients.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

On the universal late X-ray emission of binary-driven hypernovae and its possible collimation

It has previously been discovered that there is a universal power-law behavior exhibited by the late X-ray emission (LXRE) of a “golden sample” of six long energetic GRBs, when observed in the rest frame of the source. This remarkable feature, independent of the different isotropic energy (E {sub iso}) of each GRB, has been used to estimate the cosmological redshift of some long GRBs. This analysis is extended here to a new class of 161 long GRBs, all with E{sub iso}>10{sup 52} erg. These GRBs are indicated as binary-driven hypernovae (BdHNe) in view of their progenitors: a tight binary system composed of a carbon–oxygen core (CO{sub core}) and a neutron star undergoing an induced gravitational collapse (IGC) to a black hole triggered by the CO{sub core} explosion as a supernova (SN). We confirm the universal behavior of the LXRE for the “enlarged sample” (ES) of 161 BdHNe observed up to the end of 2015, assuming a double-cone emitting region. We obtain a distribution of half-opening angles peaking at θ=17.62{sup ∘}, with a mean value of 30.05{sup ∘}, and a standard deviation of 19.65{sup ∘}. This, in turn, leads to the possible establishment of a new cosmological candle. Within the IGC model, such universal LXRE behavior is only indirectly related to the GRB and originates from the SN ejecta, of a standard constant mass, being shocked by the GRB emission. The fulfillment of the universal relation in the LXRE and its independence of the prompt emission, further confirmed in this article, establishes a crucial test for any viable GRB model.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

Gravitational lensing frequencies - Galaxy cross-sections and selection effects

Four issues - (1) the best currently available data on the galaxy velocity-dispersion distribution, (2) the effects of finite core radii potential ellipticity on lensing cross sections, (3) the predicted distribution of lens image separations compared to observational angular resolutions, and (4) the preferential inclusion of lens systems in flux limited samples - are considered in order to facilitate more realistic predictions of multiple image galaxy-quasar lensing frequencies. It is found that (1) the SIS lensing parameter F equals 0.047 +/-0.019 with almost 90 percent contributed by E and S0 galaxies, (2) observed E and S0 core radii are remarkably small, yielding a factor of less than about 2 reduction in total lensing cross sections, (3) 50 percent of galaxy-quasar lenses have image separations greater than about 1.3 arcsec, and (4) amplification bias factors are large and must be carefully taken into account. It is concluded that flat universe models excessively dominated by the cosmological constant are not favored by the small observed galaxy-quasar lensing rate.

Fukugita, Masataka↗
NASA NTRS1997

The Optical Counterpart to Gamma-Ray Burst GRB 970228 Observed Using the Hubble Space Telescope

Although more than 2,000 astronomical gamma-ray bursts (GRBS) have been detected, and numerous models proposed to explain their occurrence, they have remained enigmatic owing to the lack of an obvious counterpart at other wavelengths. The recent ground-based detection of a transient optical source in the vicinity of GRB970228 may therefore have provided a breakthrough. The optical counterpart appears to be embedded in an extended source which, if a galaxy, as has been suggested would lend weight to those models that place GRBs at cosmological distances. Here we report, observations using the Hubble Space Telescope of the transient counterpart and extended source 26 and 39 days after the initial gamma-ray outburst. We find that the counterpart has faded since the initial detection (and continues to fade), but the extended source exhibits no significant change in brightness between the two dates of the observations reported here. The size and apparent constancy of the extended source imply that it is extragalactic, but its faintness makes a definitive statement about its nature difficult. Nevertheless, the decay profile of the transient source is consistent with a popular impulsive-fireball model13, which assumes a merger between two neutron stars in a distant galaxy.

Sahu, K. C.↗
NASA NTRS2000

Sunyaev - Zel'dovich Effect Imaging of Massive Clusters of Galaxies at Redshift > 0.8

We present Sunyaev-Zel'dovich Effect (SZE) imaging observations of three distant (z greater than 0.8) and highly X-ray luminous clusters of galaxies, C1J1226+33, C1J0152-13 and MS1054-03. Two of the clusters, C1J1226+33 and C1J0152-13, were recently discovered in the WARPS X-ray survey. Their high X-ray luminosity suggests they are massive systems and, if confirmed, would provide strong constraints on the cosmological parameters of structure formation models. Our Sunyaev-Zel'dovich Effect data provide confirmation that they are massive clusters similar to the well studied cluster MS1054-03. Assuming the clusters have the same gas mass fraction derived from SZE measurements of eighteen known massive clusters, we are able to infer their mass and electron temperatures from the SZE data. The derived electron temperatures are 10.0, 8.5, and 10.3 KeV, respectively, and we infer total masses of approximately 2 x 10(circumflex) 14 h(circumflex) -l M - sun within a radius of 65" for all three clusters. For C1J0152-13 and MS1054-03 we find good agreement between our SZE derived temperatures and those derived from X-ray spectroscopic measurements. No X-ray derived temperatures are available for C1J1226+33, and thus the SZE data provide the first confirmation that it is indeed a massive system. The demonstrated ability to determine cluster temperatures and masses from SZE observations without access to X-ray data illustrates the power of using deep SZE surveys to probe the distant universe.

Joy, Marshall↗
NASA NTRS2012

Constraining the Statistics of Population III Binaries

We perform a cosmological simulation in order to model the growth and evolution of Population III (Pop III) stellar systems in a range of host minihalo environments. A Pop III multiple system forms in each of the ten minihaloes, and the overall mass function is top-heavy compared to the currently observed initial mass function in the Milky Way. Using a sink particle to represent each growing protostar, we examine the binary characteristics of the multiple systems, resolving orbits on scales as small as 20 AU. We find a binary fraction of approx. 36, with semi-major axes as large as 3000 AU. The distribution of orbital periods is slightly peaked at approx. < 900 yr, while the distribution of mass ratios is relatively flat. Of all sink particles formed within the ten minihaloes, approx. 50 are lost to mergers with larger sinks, and 50 of the remaining sinks are ejected from their star-forming disks. The large binary fraction may have important implications for Pop III evolution and nucleosynthesis, as well as the final fate of the first stars.

Statistics↗
DOE OSTI2019

Dynamical Masses for a Complete Census of Local Dwarf Galaxies

The 2020s are poised to continue the past two decades of significant advances based on observations of dwarf galaxies in the nearby universe. Upcoming wide-field photometric surveys will probe substantially deeper than previous data sets, pushing the discovery frontier for new dwarf galaxies to fainter magnitudes, lower surface brightnesses, and larger distances. These dwarfs will be compelling targets for testing models of galaxy formation and cosmology, including the properties of dark matter and possible modifications to gravity. However, most of the science that can be extracted from nearby dwarf galaxies relies on spectroscopy with large telescopes. We suggest that maximizing the scientific impact of near-future imaging surveys will require both major spectroscopic surveys on 6-10m telescopes and multiplexed spectroscopy with even larger apertures.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

The 3D clustering of Lyman Alpha Emitters measured with DESI

We present a clustering analysis of Lyman-$α$ emitters (LAEs) using spectroscopic observations from the Dark Energy Spectroscopic Instrument (DESI) of candidates selected from the Blanco/DECam Intermediate-Band Imaging Survey (IBIS). We measure the two-point correlation function and the power spectrum, including cross-correlations with DESI quasars. Using both analytical and halo occupation distribution (HOD) simulation-based modeling, we find a linear bias of $b \sim 2.31$--$2.62$ for LAEs over the redshift range $2.26 < z < 3.41$. The analytical modeling also provides constraints on the strength of radiative transfer effects, while the HOD analysis characterizes the LAE-halo connection across multiple models. Finally, we quantify the magnitude of non-perturbative clustering effects such as Fingers of God in the LAE population, providing essential input for the accurate modeling of LAE-based cosmological analyses in forthcoming high-redshift surveys such as DESI-II.

Ebina, H. [UC, Berkeley; LBL, Berkeley] (ORCID:000↗
DOE OSTI2013

DARK SECTOR COUPLING BENDS THE SUPERCLUSTERS

Galaxy clusters exhibit a noticeably anisotropic pattern in their clustering, which is vividly manifested by the presence of rich filament-like superclusters. The more anisotropic the clustering of galaxy clusters is, the more straight the rich filament-like superclusters become. Given that the degree of the anisotropy in the largest-scale clustering depends sensitively on the nature of dark energy, the supercluster straightness may play a complimentary role in testing dynamic dark energy models. Here, we focus on the coupled dark energy (cDE) models which assume the existence of dark sector coupling between scalar field dark energy and nonbaryonic dark matter. By determining the spines of the superclusters identified in the publicly available group catalogs from the COupled Dark Energy Cosmological Simulations for four different cDE models as well as for the ΛCDM model, we quantify the straightness of each supercluster as the spatial extent of its spine per member cluster, where a supercluster spine represents the main stem of the minimal spanning tree constructed out of the member clusters. It is shown that the dark sector coupling plays a role in making the supercluster less straight relative to the ΛCDM case and that in a cDE model with supergravity potential the superclusters are least straight. We also find that the difference in the degree of the supercluster straightness between the cDE and the ΛCDM cases increases with redshift. A physical interpretation of our result as well as its cosmological implication are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

A portalino to the dark sector

“Portal” models that connect the Standard Model to a Dark Sector allow for a wide variety of scenarios beyond the simplest WIMP models. Kinetic mixing of gauge fields in particular has allowed a broad range of new ideas. However, the models that evade CMB constraints are often non-generic, with new mass scales and operators to split states and suppress indirect detection signals. Models with a “portalino”, a neutral fermion that marries a linear combination of a standard model neutrino and dark sector fermion and carries a conserved quantum number, can be simpler. This is especially interesting for interacting dark sectors; then the unmarried linear combination which we identify as the standard model neutrino inherits these interactions too, and provides a new, effective interaction between the dark sector and the standard model. These interactions can be simple Z' type interactions or lepton-flavor changing. Dark matter freezes out into neutrinos, thereby evading CMB constraints, and conventional direct detection signals are largely absent. The model offers different signals, however. The “portalino” mechanism itself predicts small corrections to the standard model neutrino couplings as well as the possibility of discovering the portalino particle in collider experiments. Possible cosmological and astroparticle signatures include monochromatic neutrino signals from annihilation, spectral features in high energy CR neutrinos as well as conventional signals of additional light species and dark matter interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Cogenerating and pre-annihilating dark matter by a new gauge interaction in a unified model

Grand unified theories based on large groups (with rank ≥6) are a natural context for dark matter models. They contain Standard-Model-singlet fermions that could be dark matter candidates, and can contain new non-abelian interactions whose sphalerons convert baryons, leptons, and dark matter into each other, “cogenerating' a dark matter asymmetry comparable to the baryon asymmetry. In this paper it is shown that the same non-abelian interactions can “pre-annihilate' the symmetric component of heavy dark matter particles χ, which then decay late into light stable dark matter particles ζ that inherit their asymmetry. We derive cosmological constraints on the parameters of such models. The mass of χ must be <3000 TeV and their decays must happen when 2×10{sup −7}<T{sub dec}/m{sub χ}<10{sup −4}. It is shown that such decays can come from d=5 operators with coefficients of order 1/M{sub GUT} or 1/M{sub Pℓ}. We present a simple realization of our model based on the group SU(7).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Star cluster formation in cosmological simulations. I. Properties of young clusters

We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is $\alpha \approx 1.8\mbox{–}2$, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. As a result, comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Enabling electroweak baryogenesis through dark matter

We study the impact on electroweak baryogenesis from a swifter cosmological expansion induced by dark matter. We detail the experimental bounds that one can place on models that realize it, and we investigate the modifications of these bounds that result from a non-standard cosmological history. The modifications can be sizeable if the expansion rate of the Universe increases by several orders of magnitude. We illustrate the impact through the example of scalar field dark matter, which can alter the cosmological history enough to enable a strong-enough first-order phase transition in the Standard Model when it is supplemented by a dimension six operator directly modifying the Higgs boson potential. We show that due to the modified cosmological history, electroweak baryogenesis can be realized, while keeping deviations of the triple Higgs coupling below HL-LHC sensitivies. The required scale of new physics to effectuate a strong-enough first order phase transition can change by as much as twenty percent as the expansion rate increases by six orders of magnitude.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Cosmological implications of axion-matter couplings

Axions and other light particles appear ubiquitously in physics beyond the Standard Model, with a variety of possible couplings to ordinary matter. Cosmology offers a unique probe of these particles as they can thermalize in the hot environment of the early universe for any such coupling. For sub-MeV particles, their entropy must leave a measurable cosmological signal, usually via the effective number of relativistic particles, N eff . Here, in this paper, we will revisit the cosmological constraints on the couplings of axions and other pseudo-Nambu-Goldstone bosons to Standard Model fermions from thermalization below the electroweak scale, where these couplings are marginal and give contributions to the radiation density of ΔN eff > 0.027. We update the calculation of the production rates to eliminate unnecessary approximations and find that the cosmological bounds on these interactions are complementary to astrophysical constraints, e.g. from supernova SN 1987A. We additionally provide quantitative explanations for these bounds and their relationship.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

On quasar evolution.

We examine the consequences for quasar statistics of a class of models describing the evolution of individual strong sources. The continuity equation for the change of density and luminosity with cosmological epoch determines the population, once a model for the evolution of an individual object is chosen. A dynamical model of spinning objects seems to agree satisfactorily with the present observational sample, both in density and in luminosity function; such a model requires that an individual object strongly brightens as time goes on. A genetic relationship between quasars and radio galaxies which qualitatively fits the observations is suggested by the model.

Cavaliere, A.↗
DOE OSTI2022

Simple and statistically sound recommendations for analysing physical theories

Physical theories that depend on many parameters or are tested against data from many different experiments pose unique challenges to statistical inference. Many models in particle physics, astrophysics and cosmology fall into one or both of these categories. These issues are often sidestepped with statistically unsound ad hoc methods, involving intersection of parameter intervals estimated by multiple experiments, and random or grid sampling of model parameters. Whilst these methods are easy to apply, they exhibit pathologies even in low-dimensional parameter spaces, and quickly become problematic to use and interpret in higher dimensions. In this article we give clear guidance for going beyond these procedures, suggesting where possible simple methods for performing statistically sound inference, and recommendations of readily-available software tools and standards that can assist in doing so. Our aim is to provide any physicists lacking comprehensive statistical training with recommendations for reaching correct scientific conclusions, with only a modest increase in analysis burden. Furthermore, our examples can be reproduced with the code publicly available at Zenodo.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Early time solution as an alternative to the late time evolving dark energy with DESI DR2 BAO

Recently the Dark Energy Spectroscopic Instrument (DESI) provided constraints on the expansion history from their Data Release 2. The DESI baryon acoustic oscillation measurements are well described by a flat Λ CDM model, but the preferred parameters are in mild ( 2.3 σ ) tension with those determined from the cosmic microwave background. The DESI Collaboration has already explored a variety of solutions to this tension relying on variations in the late-time evolution of dark energy. Here we test an alternative—the introduction of an “early dark energy” (EDE) component. We find that EDE models can alleviate the tension, though they lead to differences in other cosmological parameters that have observational implications. Particularly the EDE models that fit the acoustic datasets prefer lower Ω m , higher H 0 , n s and σ 8 in contrast to the late-time solutions. Finally, we discuss the current status and near-future prospects for distinguishing amongst these solutions.

Baryon acoustic oscillations↗