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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

THE GALACTIC PLANE INFRARED POLARIZATION SURVEY (GPIPS): DATA RELEASE 1

The Galactic Plane Infrared Polarization Survey (GPIPS) covers 76 deg{sup 2} of the first Galactic quadrant midplane, 18 Degree-Sign {<=} l {<=} 56 Degree-Sign and -1 Degree-Sign {<=} b {<=} +1 Degree-Sign , in H-band (1.6 {mu}m) linear polarimetry to reveal the plane-of-the-sky orientation of the magnetic field in diffuse and denser atomic and molecular clouds. The Survey consists of 3237 overlapping 10 Multiplication-Sign 10 arcmin fields observed using the Mimir instrument on the 1.8 m Perkins telescope. Here, the first community release of GPIPS data for 559 fields (17% of the Survey) is announced and basic characteristics are described. Data products consist of H-band stellar photometry and polarimetry as well as combined images. The formats and contents of the products are described and quality cuts are explored to provide insight into opportunities and limitations of the data. The Survey probes to distances as far as the Galactic bulge, revealing magnetic field properties that correlate with spiral arms and also show significant small-scale structure. The polarizations are classified into three 'usage' samples, based on stellar brightness and polarimetric uncertainty. The brightest, lowest uncertainty polarizations are suitable for individual use and direct magnetic field mapping. The next two fainter samples are useful, once averaged, for probing magnetic fields to greater distances, albeit with lower resolution. Based on this release, the full GPIPS data set will number about 5.6 million stars, with more than 1 million in the high-quality sample. This increases, by many orders of magnitude, the number of polarimetric probes of the Milky Way's magnetic field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Non-linear mode coupling and the growth of perturbations in ΛCDM

Cosmic structures at small non-linear scales k > L ∼ 0.2h Mpc{sup −1} have an impact on the longer (quasi-)linear wavelengths with k < L via non-linear UV-IR mode coupling. We evaluate this effect for a ΛCDM universe applying the effective fluid method of Baumann, Nicolis, Senatore and Zaldarriaga. For k < L the ΛCDM growth function for the density contrast is found to receive a scale dependent correction and an effective anisotropic stress sources a shift between the two gravitational potentials, setting φ−ψ≠0. Since such a situation is generically considered as a signature of modified gravity and/or dark energy, these effects should be taken into account before any conclusions on the dark sector are drawn from the interpretation of future observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Heart of darkness: the significance of the zeptobarn scale for neutralino direct detection

The direct detection of dark matter through its elastic scattering off nucleons is among the most promising methods for establishing the particle identity of dark matter. The current bound on the spin-independent scattering cross section is σ{sup SI} < 10 zb for dark matter masses m{sub Χ} ∼ 100 GeV, with improved sensitivities expected soon. We examine the implications of this progress for neutralino dark matter. We work in a supersymmetric framework well-suited to dark matter studies that is simple and transparent, with models defined in terms of four weak-scale parameters. We first show that robust constraints on electric dipole moments motivate large sfermion masses m-tilde ≥ 1 TeV, effectively decoupling squarks and sleptons from neutralino dark matter phenomenology. In this case, we find characteristic cross sections in the narrow range 1 zb ≤ σ{sup SI} ≤ 40 zb for m{sub Χ} ≥ 70 GeV. As sfermion masses are lowered to near their experimental limit m-tilde ∼ 400 GeV, the upper and lower limits of this range are extended, but only by factors of around two, and the lower limit is not significantly altered by relaxing many particle physics assumptions, varying the strange quark content of the nucleon, including the effects of galactic small-scale structure, or assuming other components of dark matter. Experiments are therefore rapidly entering the heart of dark matter-favored supersymmetry parameter space. If no signal is seen, supersymmetric models must contain some level of fine-tuning, and we identify and analyze several possibilities. Barring large cancellations, however, in a large and generic class of models, if thermal relic neutralinos are a significant component of dark matter, experiments will discover them as they probe down to the zeptobarn scale.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Cosmological signatures of tilted isocurvature perturbations: reionization and 21cm fluctuations

We investigate cosmological signatures of uncorrelated isocurvature perturbations whose power spectrum is blue-tilted with spectral index 2∼<p∼<4. Such an isocurvature power spectrum can promote early formation of small-scale structure, notably dark matter halos and galaxies, and may thereby resolve the shortage of ionizing photons suggested by observations of galaxies at high redshifts (z ≅ 7−8) but that are required to reionize the universe at z ∼ 10. We mainly focus on how the formation of dark matter halos can be modified. Based on the Δχ{sup 2} analysis with other cosmological parameters being fixed, we explore the connection between the spectral shape of CMB anisotropies and the reionization optical depth as a powerful probe of a highly blue-tilted isocurvature primordial power spectrum. We also study the consequences for 21cm line fluctuations due to neutral hydrogens in minihalos. Combination of measurements of the reionization optical depth and 21cm line fluctuations will provide complementary probes of a highly blue-tilted isocurvature power spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Self-interacting scalar dark matter with local Z{sub 3} symmetry

We construct a self-interacting scalar dark matter (DM) model with local discrete Z{sub 3} symmetry that stabilizes a weak scale scalar dark matter X. The model assumes a hidden sector with a local U(1){sub X} dark gauge symmetry, which is broken spontaneously into Z{sub 3} subgroup by nonzero VEV of dark Higgs field φ{sub X} ((φ{sub X})≠0). Compared with global Z{sub 3} DM models, the local Z{sub 3} model has two new extra fields: a dark gauge field Z{sup '} and a dark Higgs field φ (a remnant of the U(1){sub X} breaking). After imposing various constraints including the upper bounds on the spin-independent direct detection cross section and thermal relic density, we find that the scalar DM with mass less than 125 GeV is allowed in the local Z{sub 3} model, in contrary to the global Z{sub 3} model. This is due to new channels in the DM pair annihilations open into Z{sup '} and φ in the local Z{sub 3} model. Most parts of the newly open DM mass region can be probed by XENON1T and other similar future experiments. Also if φ is light enough (a few MeV ∼<m{sub φ}∼< O(100) MeV), it can generate a right size of DM self-interaction and explain the astrophysical small scale structure anomalies. This would lead to exotic decays of Higgs boson into a pair of dark Higgs bosons, which could be tested at LHC and ILC.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Production regimes for Self-Interacting Dark Matter

In the context of Self-Interacting Dark Matter as a solution for the small-scale structure problems, we consider the possibility that Dark Matter could have been produced without being in thermal equilibrium with the Standard Model bath. We discuss one by one the following various dark matter production regimes of this kind: freeze-in, reannihilation and dark freeze-out. We exemplify how these mechanisms work in the context of the particularly simple Hidden Vector Dark Matter model. In contrast to scenarios where there is thermal equilibrium with the Standard Model bath, we find two regimes which can easily satisfy all the laboratory and cosmological constraints. These are dark freeze-out with 3-to-2 annihilations and freeze-in via a light mediator. In the first regime, different temperatures in the visible and the Dark Matter sectors allow us to avoid the constraints coming from cosmic structure formation as well as the use of non-perturbative couplings to reproduce the observed relic density. For the second regime, different couplings are responsible for Dark Matter relic density and self-interactions, permitting to surpass BBN, X-ray, CMB and direct detection constraints.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Bayesian forecasts for dark matter substructure searches with mock pulsar timing data

Dark matter substructure, such as primordial black holes (PBHs) and axion miniclusters, can induce phase shifts in pulsar timing arrays (PTAs) measurements due to gravitational effects. In order to gain a more realistic forecast for the detectability of such models of dark matter with PTAs, we propose a Bayesian inference framework to search for phase shifts generated by PBHs and perform the analysis on mock PTA data. Furthermore, for most PBH masses the constraints on the dark matter abundance agree with previous (frequentist) analyses (without mock data) to $\mathcal{O}$(1) factors. This further motivates a dedicated search for PBHs (and dense small scale structures) in the mass range from 10 -8 M ⊙ to well above 10 2 M ⊙ with the Square Kilometer Array. Moreover, with a more optimistic set of timing parameters, future PTAs are predicted to constrain PBHs down to 10 -11 M ⊙ . Lastly, we discuss the impact of backgrounds, such as Supermassive Black Hole Mergers, on detection prospects, suggesting a future program to separate a dark matter signal from other astrophysical sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Kinetic recoupling of dark matter

Abstract We study the possibility that dark matter re-enters kinetic equilibrium with a radiation bath after kinetic decoupling, a scenario we dubkinetic recoupling. This naturally occurs, for instance, with certain types of resonantly-enhanced interactions, or as the result of a phase transition. While late kinetic decoupling damps structure on small scales below a cutoff, kinetic recoupling produces more complex changes in the power spectrum that depend on the nature and extent of the recoupling period. We explore the features that kinetic recoupling imprints upon the matter power spectrum, and discuss how such features can be traced to dark matter microphysics with future observations.

Astronomy & Astrophysics↗
DOE OSTI2019

Fabrication and performance of AC-coupled LGADs

Detectors that can simultaneously provide fine time and spatial resolution have attracted wide-spread interest for applications in several fields such as high-energy and nuclear physics as well as in low-energy electron detection, photon science, photonics and imaging. Low-Gain Avalanche Diodes (LGADs), being fabricated on thin silicon substrates and featuring a charge gain of up to 100, exhibit excellent timing performance. Since pads much larger than the substrate thickness are necessary to achieve a spatially uniform multiplication, a fine pad pixelation is difficult. To overcome this limitation, the AC-coupled LGAD approach was introduced. In this type of device, metal electrodes are placed over an insulator at a fine pitch, and signals are capacitively induced on these electrodes. At Brookhaven National Laboratory, we have designed and fabricated prototypes of AC-coupled LGAD sensors. The performance of small test structures with different particle beams from radioactive sources are shown.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

LUKEWARM DARK MATTER: BOSE CONDENSATION OF ULTRALIGHT PARTICLES

We discuss the thermal evolution and Bose-Einstein condensation of ultralight dark matter particles at finite, realistic cosmological temperatures. We find that if these particles decouple from regular matter before Standard Model particles annihilate, their temperature will be about 0.9 K. This temperature is substantially lower than the temperature of cosmic microwave background neutrinos and thus big bang nucleosynthesis remains unaffected. In addition, the temperature is consistent with WMAP 7-year+BAO+H0 observations without fine-tuning. We focus on particles of mass of m {approx} 10{sup -23} eV, which have Compton wavelength of galactic scales. Agglomerations of these particles can form stable halos and naturally prohibit small-scale structure. They avoid over-abundance of dwarf galaxies and may be favored by observations of dark matter distributions. We present numerical as well as approximate analytical solutions of the Friedmann-Klein-Gordon equations and study the cosmological evolution of this scalar field dark matter from the early universe to the era of matter domination. Today, the particles in the ground state mimic pressureless matter, while the excited state particles are radiation like.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DIFFUSION OF SOLAR MAGNETIC ELEMENTS UP TO SUPERGRANULAR SPATIAL AND TEMPORAL SCALES

The study of spatial and temporal scales on which small magnetic structures (magnetic elements) are organized in the quiet Sun may be approached by determining how they are transported on the solar photosphere by convective motions. The process involved is diffusion. Taking advantage of Hinode high spatial resolution magnetograms of a quiet-Sun region at the disk center, we tracked 20,145 magnetic elements. The large field of view ({approx}50 Mm) and the long duration of the observations (over 25 hr without interruption at a cadence of 90 s) allowed us to investigate the turbulent flows at unprecedented large spatial and temporal scales. In the field of view an entire supergranule is clearly recognizable. The magnetic element displacement spectrum shows a double-regime behavior: superdiffusive ({gamma} = 1.34 {+-} 0.02) up to granular spatial scales ({approx}1500 km) and slightly superdiffusive ({gamma} = 1.20 {+-} 0.05) up to supergranular scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

JWST lensed quasar dark matter survey – I. Description and first results

ABSTRACT The flux ratios of gravitationally lensed quasars provide a powerful probe of the nature of dark matter. Importantly, these ratios are sensitive to small-scale structure, irrespective of the presence of baryons. This sensitivity may allow us to study the halo mass function even below the scales where galaxies form observable stars. For accurate measurements, it is essential that the quasar’s light is emitted from a physical region of the quasar with an angular scale of milliarcseconds or larger; this minimizes microlensing effects by stars within the deflector. The warm dust region of quasars fits this criterion, as it has parsec-size physical scales and dominates the spectral energy distribution of quasars at wavelengths greater than 10 μm. The JWST Mid-Infrared Instrument is adept at detecting redshifted light in this wavelength range, offering both the spatial resolution and sensitivity required for accurate gravitational lensing flux ratio measurements. Here, we introduce our survey designed to measure the warm dust flux ratios of 31 lensed quasars. We discuss the flux-ratio measurement technique and present results for the first target, DES J0405-3308. We find that we can measure the quasar warm dust flux ratios with 3 per cent precision. Our simulations suggest that this precision makes it feasible to detect the presence of 107 M⊙ dark matter haloes at cosmological distances. Such haloes are expected to be completely dark in cold dark matter models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Dark matter substructure or source model systematics? A case study of cluster lens Abell S1063

Mapping the small-scale structure of the universe through gravitational lensing is a promising tool for probing the particle nature of dark matter. Curved Arc Basis (CAB) has been proposed as a local lensing formalism in galaxy clusters, with the potential to detect low-mass dark matter substructure. In this work, we analyse the cluster lens Abell S1063 in search of dark matter substructure with the CAB formalism, using multiband imaging data from James Webb Space Telescope ( JWST ). We use two different source modelling methods: shapelets and pixel-based source reconstruction based on Delaunay triangulation. We find that source modelling systematics from shapelets result in a disagreement between CAB parameters measured from different filters. Source modelling with Delaunay significantly alleviates this systematic, as seen in the improvement in agreement across filters. We also find that inadequate complexity in source modelling can result in convincing spurious detections of dark matter substructure from strong gravitational lenses, as seen by our $\Delta \text{BIC} > 20$ measurement of a $M \sim 10^{10}$ ${\rm M}_{\odot }$ subhalo with shapelets, a spurious detection that is not reproduced with Delaunay source modelling. We demonstrate that multiband analysis with different JWST filters is key for disentangling source and lens model systematics from dark matter substructure detections.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Low-energy fine-structure resonances in photoionization of O ii

Resonant features in low-energy photoionization cross sections are reported in coupled-channel calculations for O ii including relativistic fine structure. The calculations reveal extensive near-threshold resonant structures in the small energy region between the fine structure levels of the ground state 2p{sup 2}({sup 3}P{sub 0,1,2}) of the residual ion O iii. Although the resonances have not yet been observed, they are similar to other experimentally observed features. They are expected to significantly enhance the very-low-temperature dielectronic recombination rates, potentially leading to the resolution of an outstanding nebular abundances anomaly. Higher energy partial and total photoionization cross sections of the ground configuration levels 2p{sup 3}({sup 4}S{sub 3/2}{sup o},{sup 2}D{sub 3/2,5/2}{sup o},{sup 2}P{sub 1/2,3/2}{sup o}) are found to be in agreement with experimental measurements on synchrotron-based photon sources [1-3], thereby identifying the excited O iii levels present in the ion beams. These are also the first results from a recently developed version of Breit-Pauli R-matrix (BPRM) codes, with inclusion of two-body magnetic interaction terms. The improved relativistic treatment could be important for other astrophysical applications and for more precise benchmarking of experimental measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Energy landscape of ZnO clusters and low-density polymorphs

In this paper, we report on an extensive study of ZnO materials with cagelike motifs in clusters and bulk phases through structural searches using the minima hopping method. A novel putative ground state was discovered for the (ZnO) 32 cluster with a tubelike structure, closely related to the previously reported (ZnO) 24 ground-state cage geometry. Furthermore, the effect of ionization on the geometries and energetic ordering of (ZnO) n clusters with n=3–10,12 was studied by directly sampling the energy landscape of the ionized system. Our results indicate that the transition from ring and planar structures to three-dimensional cages occurs at larger cluster sizes than in the neutral system. Inspired by the bottom-up design philosophy and the predominance of cagelike structures in medium-sized clusters, a search for crystalline ZnO was conducted aimed specifically at low-density polymorphs, resulting in the discovery of 57 novel metastable phases. The voids in these low-density materials closely resemble the hollow cage structures of small (ZnO) n /(ZnO)$^+_n$ clusters with n < 16. Analogous to clathrate materials, these voids could serve to accommodate guest atoms to tailor the materials properties for various applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

3D structure of anisotropic flow in small collision systems at energies available at the BNL Relativistic Heavy Ion Collider

Here, we present (3 + 1)-dimensional [(3 + 1)D] dynamical simulations of asymmetric nuclear collisions at the BNL Relativistic Heavy Ion Collider (RHIC). Employing a dynamical initial state model coupled to (3 + 1)D viscous relativistic hydrodynamics, we explore the rapidity dependence of anisotropic flow in the RHIC small system scan at 200 GeV center-of-mass energy. We calibrate parameters to describe central 3 He + Au collisions and make extrapolations to d + Au and p + Au collisions. Our calculations demonstrate that approximately 50% of the v 3 (p T ) difference between the measurements by the STAR and PHENIX Collaborations can be explained by the use of reference flow vectors from different rapidity regions. This emphasizes the importance of longitudinal flow decorrelation for anisotropic flow measurements in asymmetric nuclear collisions, and the need for (3 + 1)D simulations. We also present results for the beam energy dependence of particle spectra and anisotropic flow in d + Au collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Dark matter microhalos from simplified models

Here, we introduce simplified models for enhancements in the matter power spectrum at small scales and study their implications for dark matter substructure and gravitational observables. These models capture the salient aspects of a variety of early Universe scenarios that predict enhanced small-scale structure, such as axionlike particle dark matter, light vector dark matter, and epochs of early matter domination. We use a model-independent, semianalytic treatment to map bumps in the matter power spectrum to early forming subsolar mass dark matter halos and estimate their evolution, disruption, and contribution to the substructure of clusters and galaxies at late times. We discuss the sensitivity of gravitational observables, including pulsar timing arrays and caustic microlensing, to both the presence of bumps in the power spectrum and variations in their basic properties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Detecting dark matter substructures on small scales with fast radio bursts

The matter power spectrum is only weakly constrained on subgalactic scales, while physics beyond the Standard Model can leave unique imprints, especially on sub-parsec scales. We propose measuring the arrival-time difference of fast radio bursts (FRBs) along two adjacent sightlines as a new probe to dark matter substructures on scales down to ∼ 1 AU . We discuss two observational scenarios in which it may be possible to place interesting constraints on such models through the monitoring of repeating FRB sources: (i) By sending radio receivers to space to form a baseline of tens of AU or more and measuring the temporal variation of the arrival-time difference between receivers. (ii) By measuring the temporal variation of the arrival-time difference between two lensed images of one strongly lensed repeater. In both scenarios, obtaining interesting constraints requires correlating the voltage time series to measure the radio signal arrival time to sub-nanosecond precision. We find that two radio dishes separated by 20 AU may be sensitive to the enhancement of small-scale structures at ∼ 10 - 8 M ⊙ masses in the QCD axion dark matter scenario, or from an early epoch of matter domination with a reheating temperature up to 60 MeV. Other dark matter models, such as those composed of ∼ 10 - 13 M ⊙ primordial black holes produced during inflation, would also be probed by this method. We further show that a strong lensing situation of multiple images provides an equivalent ∼ 2000 AU ( σ v / 10 3 km s - 1 ) ( δ t / 10 yr ) baseline, for a typical velocity of dark matter substructures σ v and an observational time span δ . This is much more sensitive, but with the uncertainty that intervening decoherence from the interstellar medium may degrade the timing precision, and that spatial variation in the FRB emission spot may result in confounding signals. We show that the lensing magnifications of Type Ia supernovae constrain a similar quantity to such FRB timing, with present limits being equivalent to ruling out the same parameter space that would be probed by a 0.14 AU baseline.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗