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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Minimal warm inflation

Slow-roll inflation is a successful paradigm. However we find that even a small coupling of the inflaton to other light fields can dramatically alter the dynamics and predictions of inflation. As an example, the inflaton can generically have an axion-like coupling to gauge bosons. Even relatively small couplings will automatically induce a thermal bath during inflation. The thermal friction from this bath can easily be stronger than Hubble friction, significantly altering the usual predictions of any particular inflaton potential. Thermal effects suppress the tensor-to-scalar ratio r significantly, and predict unique non-gaussianities. This axion-like coupling provides a minimal model of warm inflation which avoids the usual problem of thermal backreaction on the inflaton potential. As a specific example, we find that hybrid inflation with this axion-like coupling can easily fit the current cosmological data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Inflection-point B - L Higgs inflation

Inflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field with its initial value below the Planck mass (ΦI≲M Pl ). In order for a renormalization group (RG) improved effective λΦ 4 potential to develop an inflection-point, the quartic coupling λ(Φ) must exhibit a minimum with an almost vanishing value in its RG evolution, namely λ( ΦI )≃0 and β λ (ΦI)≃0, where β λ is the beta-function of the quartic coupling. As an example, we consider the minimal gauged B-L extended Standard Model at the TeV scale, where we identify the B-L Higgs field as the inflaton field. For a successful inflection-point inflation, which is consistent with the current cosmological observations, the mass ratios among the Z' gauge boson, the right-handed neutrinos and the B-L Higgs boson are fixed. Our scenario can be tested in the future collider experiments such as the High-Luminosity LHC and the SHiP experiments. Finally, in addition, the inflection-point inflation provides a unique prediction for the running of the spectral index α≃-2.7×10 -3 ($60\atop{N}$) 2 (N is the e-folding number), which can be tested in the near future.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Inflation in a closed universe

To derive a power spectrum for energy density inhomogeneities in a closed universe, we investigate a spatially-closed inflation-modified hot big bang model whose evolutionary history is divided into three epochs: an early slowly-rolling scalar field inflation epoch and the usual radiation and nonrelativistic matter epochs. (For our usage it is not necessary to consider a final dark energy dominated epoch.) We derive general solutions of the relativistic linear perturbation equations in each epoch. The constants of integration in the inflation epoch solutions are determined from de Sitter invariant quantum-mechanical initial conditions in the Lorentzian section of the inflating closed de Sitter space derived from Hawking’s prescription that the quantum state of the universe only include field configurations that are regular on the Euclidean (de Sitter) sphere section. The constants of integration in the radiation and matter epoch solutions are determined from joining conditions derived by requiring that the linear perturbation equations remain nonsingular at the transitions between epochs. The matter epoch power spectrum of gauge-invariant energy density inhomogeneities is not a power law, and depends on spatial wave number in the way expected for a generalization to the closed model of the standard flat-space scale-invariant power spectrum. The power spectrum we derive appears to differ from a number of other closed inflation model power spectra derived assuming different (presumably non de Sitter invariant) initial conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

HATS-25B THROUGH HATS-30B: A HALF–DOZEN NEW INFLATED TRANSITING HOT JUPITERS FROM THE HATSOUTH SURVEY

We report six new inflated hot Jupiters (HATS-25b through HATS-30b) discovered using the HATSouth global network of automated telescopes. The planets orbit stars with V magnitudes in the range of ∼12–14 and have masses in the largely populated 0.5M{sub J}--0.7M{sub J} region of parameter space but span a wide variety of radii, from 1.17R{sub J} to 1.75R{sub J}. HATS-25b, HATS-28b, HATS-29b, and HATS-30b are typical inflated hot Jupiters (R{sub p}=1.17--1.26R{sub J}) orbiting G–type stars in short period (P = 3.2-4.6 days) orbits. However, HATS-26b (R{sub p}=1.75R{sub J}, P=3.3024 days) and HATS-27b (R{sub p}=1.50R{sub J}, P=4.6370 days) stand out as highly inflated planets orbiting slightly evolved F stars just after and in the turn–off points, respectively, which are among the least dense hot Jupiters, with densities of 0.153 g cm{sup −3} and 0.180 g cm{sup −3}, respectively. All the presented exoplanets but HATS-27b are good targets for future atmospheric characterization studies, while HATS-27b is a prime target for Rossiter—McLaughlin monitoring in order to determine its spin–orbit alignment given the brightness (V = 12.8) and stellar rotational velocity (vsin i≈9.3 km s{sup −1}) of the host star. These discoveries significantly increase the number of inflated hot Jupiters known, contributing to our understanding of the mechanism(s) responsible for hot Jupiter inflation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Stellar Characterization and Radius Inflation of Hyades M-dwarf Stars from the APOGEE Survey

We present a spectroscopic analysis of a sample of 48 M-dwarf stars (0.2 M ⊙ < M < 0.6 M ⊙ ) from the Hyades open cluster using high-resolution H-band spectra from the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Our methodology adopts spectrum synthesis with LTE MARCS model atmospheres, along with the APOGEE Data Release 17 line list, to determine effective temperatures, surface gravities, metallicities, and projected rotational velocities. The median metallicity obtained for the Hyades M dwarfs is [M/H] = 0.09 ± 0.03 dex, indicating a small internal uncertainty and good agreement with optical results for Hyades red giants. Overall, the median radii are larger than predicted by stellar models by 1.6% ± 2.3% and 2.4% ± 2.3%, relative to a MIST and DARTMOUTH isochrone, respectively. We emphasize, however, that these isochrones are different, and the fractional radius inflation for the fully and partially convective regimes have distinct behaviors depending on the isochrone. Using a MIST isochrone there is no evidence of radius inflation for the fully convective stars, while for the partially convective M dwarfs the radii are inflated by 2.7% ± 2.1%, which is in agreement with predictions from models that include magnetic fields. For the partially convective stars, rapid rotators present on average higher inflation levels than slow rotators. The comparison with SPOTS isochrone models indicates that the derived M-dwarf radii can be explained by accounting for stellar spots in the photosphere of the stars, with 76% of the studied M dwarfs having up to 20% spot coverage, and the most inflated stars with ~20%–40% spot coverage.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

Initial '80s Development of Inflated Antennas

State of the art technology was considered in the definition and documentation of a membrane surface suitable for use in a space reflector system for long durations in orbit. Requirements for a metal foil-plastic laminate structural element were determined and a laboratory model of a rigidized element to test for strength characteristics was constructed. Characteristics of antennas ranging from 10 meters to 1000 meters were determined. The basic antenna configuration studied consists of (1) a thin film reflector, (2) a thin film cone, (3) a self-rigidizing structural torus at the interface of the cone and reflector; and (4) an inflation system. The reflector is metallized and, when inflated, has a parabolic shape. The cone not only completes the enclosure of the inflatant, but also holds the antenna feed at its apex. The torus keeps the inflated cone-reflector from collapsing inward. Laser test equipment determined the accuracy of the inflated paraboloids.

Friese, G. J.↗
NASA NTRS1989

Advances in large inflatable reflectors

For most applications in space for which they were tried, inflatable structures show a significant weight reduction when compared to mechanical structures. Inflatables are unmatched when compared to mechanical structures when packaged volume is considered. The reliability of deployment of inflatable structures was known for years. When properly designed, such a system is inherently more reliable because it has very few points of failure. Fully inflatable vs. rigidized inflatable structures are discussed. The L'Garde solar concentrator experience is described. Reflector surface and cylinder rigidization, improvement in gore design tools, and expected advances in rigidization schemes with near future are examined.

Thomas, M.↗
NASA NTRS1990

Soft inflation

The cosmology resulting from two coupled scalar fields was studied, one which is either a new inflation or chaotic type inflation, and the other which has an exponentially decaying potential. Such a potential may appear in the conformally transformed frame of generalized Einstein theories like the Jordan-Brans-Dicke theory. The constraints necessary for successful inflation are examined. Conventional GUT models such as SU(5) were found to be compatible with new inflation, while restrictions on the self-coupling constant are significantly loosened for chaotic inflation.

Berkin, Andrew L.↗
NASA NTRS1990

Origin of density fluctuations in extended inflation

The density fluctuations (both curvature and isocurvature) that arise due to quantum fluctuations in a simple model of extended inflation based upon the Jordan-Brans-Dicke theory are calculated. Curvature fluctuations arise due to quantum fluctuations in the Brans-Dicke field, in general have a nonscale-invariant spectrum, and can have an amplitude that is cosmologically acceptable and interesting without having to tune any coupling constant to a very small value. The density perturbations that arise due to the inflation field are subdominant. If there are other massless fields in the theory, e.g., an axion or an ilion, then isocurvature fluctuations arise in these fields too. Production of gravitational waves and the massless particles associated with excitations of the Brans-Dicke field are also discussed. Several attempts at more realistic models of extended inflation are also analyzed. The importance of the Einstein conformal frame in calculating curvature fluctuations is emphasized. When viewed in this frame, extended inflation closely resembles slow-rollover inflation with an exponential potential and the usual formula for the amplitude of curvature perturbations applies.

Kolb, Edward W.↗
NASA NTRS1990

Soft inflation

The cosmology resulting from two coupled scalar fields was studied, one which is either a new inflation or chaotic type inflation, and the other which has an exponentially decaying potential. Such a potential may appear in the conformally transformed frame of generalized Einstein theories like the Jordan-Brans-Dicke theory. The constraints necessary for successful inflation are examined. Conventional GUT models such as SU(5) were found to be compatible with new inflation, while restrictions on the self-coupling constant are significantly loosened for chaotic inflation.

Berkin, Andrew L.↗
NASA NTRS1992

First-order inflation

I discuss the most recent model of inflation. In first-order inflation the inflationary epoch is associated with a first-order phase transition, with the most likely candidate being GUT symmetry breaking. The transition from the false-vacuum inflationary phase to the true-vacuum radiation-dominated phase proceeds through the nucleation and percolation of true-vacuum bubbles. The first successful and simplest model of first-order inflation, extended inflation, is discussed in some detail: evolution of the cosmic-scale factor, reheating, density perturbations, and the production of gravitational waves both from quantum fluctuations and bubble collisions. Particular attention is paid to the most critical issue in any model of first-order inflation: the requirements on the nucleation rate to ensure a graceful transition from the inflationary phase to the radiation-dominated phase.

Turner, Michael S.↗
NASA NTRS1959

Free-Flight Test of a Technique for Inflating an NASA 12-Foot-Diameter Sphere at High Altitudes

A free-flight test has been conducted to check a technique for inflating an NASA 12-foot-diameter inflatable sphere at high altitudes. Flight records indicated that the nose section was successfully separated from the booster rocket, that the sphere was ejected, and that the nose section was jettisoned from the fully inflated sphere. On the basis of preflight and flight records, it is believed that the sphere was fully inflated by the time of peak altitude (239,000 feet). Calculations showed that during descent, jettison of the nose section occurred above an altitude of 150,000 feet. The inflatable sphere was estimated to start to deform during descent at an altitude of about 120,000 feet.

Kehlet, Alan B.↗
NASA NTRS2001

Inflatable Vehicles for In-Situ Exploration of Titan

Space Inflatable vehicles have been finding popularity in recent years for applications as varied as spacecraft antennas, space-based telescopes, solar sails, and manned habitats. Another branch of space inflatable technology has also considered developing ambient-filled, solar balloons for Mars as well as ambient-filled inflatable rovers. More recently, some of these inflatable technologies have been applied to the outer solar system bodies with the result that there are some rather unique and compelling inflatable mission capabilities for in situ explorations of Titan, Triton, Uranus, and Neptune. Additional information is contained in the original extended abstract.

Jones, J. A.↗
NASA NTRS2007

Aerocapture Inflatable Decelerator for Planetary Entry

Forward Attached Inflatable Decelerators, more commonly known as inflatable aeroshells, provide an effective, cost efficient means of decelerating spacecrafts by using atmospheric drag for aerocapture or planetary entry instead of conventional liquid propulsion deceleration systems. Entry into planetary atmospheres results in significant heating and aerodynamic pressures which stress aeroshell systems to their useful limits. Incorporation of lightweight inflatable decelerator surfaces with increased surface-area footprints provides the opportunity to reduce heat flux and induced temperatures, while increasing the payload mass fraction. Furthermore, inflatable aeroshell decelerators provide the needed deceleration at considerably higher altitudes and Mach numbers when compared with conventional rigid aeroshell entry systems. Inflatable aeroshells also provide for stowage in a compact space, with subsequent deployment of a large-area, lightweight heatshield to survive entry heating. Use of a deployable heatshield decelerator enables an increase in the spacecraft payload mass fraction and may eliminate the need for a spacecraft backshell.

Reza, Sajjad↗
NASA NTRS2007

Aerocapture Inflatable Decelerator (AID)

Forward Attached Inflatable Decelerators, more commonly known as inflatable aeroshells, provide an effective, cost efficient means of decelerating spacecrafts by using atmospheric drag for aerocapture or planetary entry instead of conventional liquid propulsion deceleration systems. Entry into planetary atmospheres results in significant heating and aerodynamic pressures which stress aeroshell systems to their useful limits. Incorporation of lightweight inflatable decelerator surfaces with increased surface-area footprints provides the opportunity to reduce heat flux and induced temperatures, while increasing the payload mass fraction. Furthermore, inflatable aeroshell decelerators provide the needed deceleration at considerably higher altitudes and Mach numbers when compared with conventional rigid aeroshell entry systems. Inflatable aeroshells also provide for stowage in a compact space, with subsequent deployment of a large-area, lightweight heatshield to survive entry heating. Use of a deployable heatshield decelerator not only enables an increase in the spacecraft payload mass fraction and but may also eliminate the need for a spacecraft backshell and cruise stage. This document is the viewgraph slides for the paper's presentation.

Reza, Sajjad↗
NASA NTRS2008

Application of Ruze Equation for Inflatable Aperture Antennas

Inflatable aperture reflector antennas are an emerging technology that NASA is investigating for potential uses in science and exploration missions. As inflatable aperture antennas have not been proven fully qualified for space missions, they must be characterized properly so that the behavior of the antennas can be known in advance. To properly characterize the inflatable aperture antenna, testing must be performed in a relevant environment, such as a vacuum chamber. Since the capability of having a radiofrequency (RF) test facility inside a vacuum chamber did not exist at NASA Glenn Research Center, a different methodology had to be utilized. The proposal to test an inflatable aperture antenna in a vacuum chamber entailed performing a photogrammetry study of the antenna surface by using laser ranging measurements. A root-mean-square (rms) error term was derived from the photogrammetry study to calculate the antenna surface loss as described by the Ruze equation. However, initial testing showed that problems existed in using the Ruze equation to calculate the loss due to errors on the antenna surface. This study utilized RF measurements obtained in a near-field antenna range and photogrammetry data taken from a laser range scanner to compare the expected performance of the test antenna (via the Ruze equation) with the actual RF patterns and directivity measurements. Results showed that the Ruze equation overstated the degradation in the directivity calculation. Therefore, when the photogrammetry study is performed on the test antennas in the vacuum chamber, a more complex equation must be used in light of the fact that the Ruze theory overstates the loss in directivity for inflatable aperture reflector antennas.

Welch, Bryan W.↗
NASA NTRS2008

Probing Inflation via Cosmic Microwave Background Polarimetry

The Cosmic Microwave Background (CMB) has been a rich source of information about the early Universe. Detailed measurements of its spectrum and spatial distribution have helped solidify the Standard Model of Cosmology. However, many questions still remain. Standard Cosmology does not explain why the early Universe is geometrically flat, expanding, homogenous across the horizon, and riddled with a small anisotropy that provides the seed for structure formation. Inflation has been proposed as a mechanism that naturally solves these problems. In addition to solving these problems, inflation is expected to produce a spectrum of gravitational waves that will create a particular polarization pattern on the CMB. Detection of this polarized signal is a key test of inflation and will give a direct measurement of the energy scale at which inflation takes place. This polarized signature of inflation is expected to be -9 orders of magnitude below the 2.7 K monopole level of the CMB. This measurement will require good control of systematic errors, an array of many detectors having the requisite sensitivity, and a reliable method for removing polarized foregrounds, and nearly complete sky coverage. Ultimately, this measurement is likely to require a space mission. To this effect, technology and mission concept development are currently underway.

Chuss, David T.↗
NASA NTRS2010

System and method of designing a load bearing layer that interfaces to a structural pass-through of an inflatable vessel

A method for determining a design of an inflatable module including a rigid member disposed in a restraint layer, wherein the restraint layer includes orthogonal straps, includes modeling a strap adjacent to the rigid member and a strap connected to the rigid member. The adjacent strap and the member strap extend in a first direction. The method further includes selecting a first length of the member strap such that the adjacent strap carries load before the member strap during pressurization of the inflatable module, modeling tensions in the member strap with the first length and the adjacent strap during pressurization of the inflatable model, and outputting the modeled tensions in the member strap with the first length and the adjacent strap. An inflatable module includes a member strap having a length such that an adjacent strap carries load before the member strap during pressurization of the inflatable module.

Spexarth, Gary R.↗