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All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Inflation model selection meets dark radiation

We investigate how inflation model selection is affected by the presence of additional free-streaming relativistic degrees of freedom, i.e. dark radiation. We perform a full Bayesian analysis of both inflation parameters and cosmological parameters taking reheating into account self-consistently. We compute the Bayesian evidence for a few representative inflation scenarios in both the standard ΛCDM model and an extension including dark radiation parametrised by its effective number of relativistic species N {sub eff}. Using a minimal dataset (Planck low-ℓ polarisation, temperature power spectrum and lensing reconstruction), we find that the observational status of most inflationary models is unchanged. The exceptions are potentials such as power-law inflation that predict large values for the scalar spectral index that can only be realised when N {sub eff} is allowed to vary. Adding baryon acoustic oscillations data and the B-mode data from BICEP2/Keck makes power-law inflation disfavoured, while adding local measurements of the Hubble constant H {sub 0} makes power-law inflation slightly favoured compared to the best single-field plateau potentials. This illustrates how the dark radiation solution to the H {sub 0} tension would have deep consequences for inflation model selection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Low-ℓ power suppression in punctuated inflation

Motivated by Planck confirmation of an anomalously low value of the CMB temperature fluctuations up to multipole ℓ < 40, we in this paper try to explain such feature by investigating case of punctuated inflation scenario. This form of inflation potential is inspired by Minimal Super-symmetric Standard Model (MSSM) wherein suppression of curvature perturbation power at large scales is produced by introducing period of fast-roll phase of the inflation sandwiched between two stages of slow-roll phase. We apply Markov Chain Monte Carlo analysis to determine posterior distribution and the best fit values of the model parameters using recent WMAP9 and Planck data. We show that WMAP9 and Planck results are consistent with each other and that with Planck data we obtain tighter constraints for punctuated inflation parameters. We find that punctuated inflation leads to better fit in CMB data compared to simple power law model. The improvement in the fit to the WMAP9 data is Δ χ{sup 2} ∼ 3.6 and for Planck the improvement is Δ χ{sup 2} ∼ 5.4. We find that AIC does not discriminate between punctuated inflation and simple power law model for WMAP9 data. However, for Planck data we find that punctuated inflation is moderately preferred over a simple power law model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Is a Higgs vacuum instability fatal for high-scale inflation?

We study the inflationary evolution of a scalar field h with an unstable potential for the case where the Hubble parameter H during inflation is larger than the instability scale Λ I of the potential. Quantum fluctuations in the field of size δh ~ H/2π imply that the unstable part of the potential is sampled during inflation. We investigate the evolution of these fluctuations to the unstable regime and in particular whether they generate cosmological defects or even terminate inflation. We apply the results of a toy scalar model to the case of the Standard Model (SM) Higgs boson, the quartic of which evolves to negative values at high scales, and extend previous analyses of Higgs dynamics during inflation utilizing statistical methods to a perturbative and fully gauge-invariant formulation. We show that the dynamics are controlled by the renormalization group-improved quartic coupling λ(μ) evaluated at a scale μ = H, such that Higgs fluctuations are enhanced by the instability if H > Λ I . Even if H > Λ I , the instability in the Standard Model Higgs potential does not end inflation; instead the universe slowly sloughs off crunching patches of space that never come to dominate the evolution. As inflation proceeds past 50 e-folds, a significant proportion of patches exits inflation in the unstable vacuum, and as much as 1% of the spacetime can rapidly evolve to a defect. Depending on the nature of these defects, however, the resulting universe could still be compatible with ours.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

RE-INFLATED WARM JUPITERS AROUND RED GIANTS

Since the discovery of the first transiting hot Jupiters, models have sought to explain the anomalously large radii of highly irradiated gas giants. We now know that the size of hot Jupiter radius anomalies scales strongly with a planet's level of irradiation and numerous models like tidal heating, ohmic dissipation, and thermal tides have since been developed to help explain these inflated radii. In general, however, these models can be grouped into two broad categories: models that directly inflate planetary radii by depositing a fraction of the incident irradiation into the interior and models that simply slow a planet's radiative cooling, allowing it to retain more heat from formation and thereby delay contraction. Here we present a new test to distinguish between these two classes of models. Gas giants orbiting at moderate orbital periods around post-main-sequence stars will experience enormous increases to their irradiation as their host stars move up the sub-giant and red-giant branches. If hot Jupiter inflation works by depositing irradiation into the planet's deep interiors then planetary radii should increase in response to the increased irradiation. This means that otherwise non-inflated gas giants at moderate orbital periods of >10 days can re-inflate as their host stars evolve. Here we explore the circumstances that can lead to the creation of these “re-inflated” gas giants and examine how the existence or absence of such planets can be used to place unique constraints on the physics of the hot Jupiter inflation mechanism. Finally, we explore the prospects for detecting this potentially important undiscovered population of planets.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

First-order inflation

In the original proposal, inflation occurred in the process of a strongly first-order phase transition. This model was soon demonstrated to be fatally flawed. Subsequent models for inflation involved phase transitions that were second-order, or perhaps weakly first-order; some even involved no phase transition at all. Recently the possibility of inflation during a strongly first-order phase transition has been revived. In this paper, some models for first-order inflation are discussed, and unique signatures that result if inflation is realized in a first-order transition are emphasized. Some of the history of inflation is reviewed to demonstrate how first-order inflation differs from other models.

Kolb, Edward W.↗
NASA NTRS1992

A preliminary structural analysis of space-based inflatable tubular frame structures

The use of inflatable structures has often been proposed for aerospace and planetary applications. The advantages of such structures include low launch weight and easy assembly. The use of inflatables for applications requiring very large frame structures intended for aerospace use are proposed. In order to consider using an inflated truss, the structural behavior of the inflated frame must be examined. The statics of inflated tubes as beams was discussed in the literature, but the dynamics of these elements has not received much attention. In an effort to evaluate the vibration characteristics of the inflated beam a series of free vibration tests of an inflated fabric cantilevers were performed. Results of the tests are presented and models for system behavior posed.

Main, John A.↗
NASA NTRS2000

Comparison of Dynamic Characteristics for an Inflatable Solar Concentrator in Atmospheric and Thermal Vacuum Conditions

Dynamic testing of an inflatable solar concentrator structure in a thermal vacuum chamber as well as in ambient laboratory conditions is described in detail. Unique aspects of modal testing for the extremely lightweight inflatable are identified, including the use of a noncontacting laser vibrometer measurement system. For the thermal vacuum environment, mode shapes and frequency response functions are compared for three different test article inflation pressures at room temperature. Modes that persist through all the inflation pressure regimes are identified, as well as modes that are unique for each pressure. In atmospheric pressure and room temperature conditions, dynamic measurements were obtained for the expected operational inflation pressure of 0.5 psig. Experimental mode shapes and frequency response functions for ambient conditions are described and compared to the 0.5 psig results from the thermal vacuum tests. Only a few mode shapes were identified that occurred in both vacuum and atmospheric environments. This somewhat surprising result is discussed in detail, and attributed at least partly to 1.) large differences in modal damping, and 2.) significant differences in the mass of air contained by the structure, in the two environments. Results of this investigation point out the necessity of testing inflatable space structures in vacuum conditions before they can be launched. Ground testing in atmospheric pressure is not sufficient for predicting on-orbit dynamics of non-rigidized inflatable systems.

Slade, Kara N.↗
NASA NTRS2005

Review of NASA In-Space Propulsion Technology Program Inflatable Decelerator Investments

The NASA In-Space Propulsion Technology (ISPT) Program is managed by the NASA Headquarters Science Mission Directorate and is implemented by the Marshall Space Flight Center in Huntsville, Alabama. The ISPT objective is to fund development of promising in- space propulsion technologies that can decrease flight times, decrease cost, or increase delivered payload mass for future science missions. Before ISPT will invest in a technology, the Technology Readiness Level (TRL) of the concept must be estimated to be at TRL 3. A TRL 3 signifies that the technical community agrees that the feasibility of the concept has been proven through experiment or analysis. One of the highest priority technology investments for ISPT is Aerocapture. The aerocapture maneuver uses a planetary atmosphere to reduce or alter the speed of a vehicle allowing for quick, propellantless (or using very little propellant) orbit capture. The atmosphere is used as a brake, transferring the energy associated with the vehicle s high speed into thermal energy. The ISPT Aerocapture Technology Area (ATA) is currently investing in the development of advanced lightweight ablative thermal protection systems, high temperature composite structures, and heat-flux sensors for rigid aeroshells. The heritage of rigid aeroshells extends back to the Apollo era and this technology will most likely be used by the first generation aerocapture vehicle. As a second generation aerocapture technology, ISPT is investing in three inflatable aerodynamic decelerator concepts for planetary aerocapture. They are: trailing ballute (balloon-parachute), attached afterbody ballute, and an inflatable aeroshell. ISPT also leverages the NASA Small Business Innovative Research Program for additional inflatable decelerator technology development. In mid-2004 ISPT requested an independent review of the three inflatable decelerator technologies funded directly by ISPT to validate the TRL and to identify technology maturation concerns. An independent panel with expertise in advanced thin film materials, aerothermodynamics, trajectory design, and inflatable structures was convened to assess the ISPT investments. The panel considered all major technical subsystems including materials, aerothermodynamics, structural dynamics, packaging, and inflation systems. The panel assessed the overall technology readiness of inflatable decelerators to be a 3 and identified fluid-structure interaction, aeroheating, and structural adhesives to be of highest technical concern.

Richardson, Erin H.↗
NASA NTRS2005

Review of NASA In-Space Propulsion Technology Program Inflatable Decelerator Investments

The NASA In-Space Propulsion Technology (ISPT) Program is managed by the NASA Headquarters Science Mission Directorate and is implemented by the Marshall Space Flight Center in Huntsville, Alabama. The ISPT objective is to fund development of promising in-space propulsion technologies that can decrease flight times, decrease cost, or increase delivered payload mass for future science missions. Before ISPT will invest in a technology, the Technology Readiness Level (TRL) of the concept must be estimated to be at TRL 3. A TRL 3 signifies that the technical community agrees that the feasibility of the concept has been proven through experiment or analysis. One of the highest priority technology investments for ISPT is Aerocapture. The aerocapture maneuver uses a planetary atmosphere to reduce or alter the speed of a vehicle allowing for quick, propellantless (or using very little propellant) orbit capture. The atmosphere is used as a brake, transferring the energy associated with the vehicle's high speed into thermal energy. The ISPT Aerocapture Technology Area (ATA) is currently investing in the development of advanced lightweight ablative thermal protection systems, high temperature composite structures, and heat-flux sensors for rigid aeroshells. The heritage of rigid aeroshells extends back to the Apollo era and this technology will most likely be used by the first generation aerocapture vehicle. As a second generation aerocapture technology, ISPT is investing in three inflatable aerodynamic decelerator concepts for planetary aerocapture. They are: trailing ballute (balloon-parachute), attached afterbody ballute, and an inflatable aeroshell. ISPT also leverages the NASA Small Business Innovative Research Program for additional inflatable decelerator technology development. In mid-2004 ISPT requested an independent review of the three inflatable decelerator technologies funded directly by ISPT to validate the TRL and to identify technology maturation concerns. An independent panel with expertise in advanced thin film materials, aerothermodynamics, trajectory design, and inflatable structures was convened to assess the ISPT investments. The panel considered all major technical subsystems including materials, aerothermodynamics, structural dynamics, packaging, and inflation systems. The panel assessed the overall technology readiness of inflatable decelerators to be a 3 and identified fluid- structure interaction, aeroheating, and structural adhesives to be of highest technical concern.

Richardson, E. H.↗
NASA NTRS2011

Estimating Mass of Inflatable Aerodynamic Decelerators Using Dimensionless Parameters

This paper describes a technique for estimating mass for inflatable aerodynamic decelerators. The technique uses dimensional analysis to identify a set of dimensionless parameters for inflation pressure, mass of inflation gas, and mass of flexible material. The dimensionless parameters enable scaling of an inflatable concept with geometry parameters (e.g., diameter), environmental conditions (e.g., dynamic pressure), inflation gas properties (e.g., molecular mass), and mass growth allowance. This technique is applicable for attached (e.g., tension cone, hypercone, and stacked toroid) and trailing inflatable aerodynamic decelerators. The technique uses simple engineering approximations that were developed by NASA in the 1960s and 1970s, as well as some recent important developments. The NASA Mars Entry and Descent Landing System Analysis (EDL-SA) project used this technique to estimate the masses of the inflatable concepts that were used in the analysis. The EDL-SA results compared well with two independent sets of high-fidelity finite element analyses.

Samareh, Jamshid A.↗
NASA NTRS2014

Performing a Launch Depressurization Test on an Inflatable Space Habitat

In July, 2014 JPL's Environmental Test Laboratory successfully performed a launch depressurization test on an inflatable space habitat proposed to be installed on the International Space Station. The inflatable habitat is to be launched in the SpaceX Dragon Trunk. During the launch, the unpressurized Dragon Trunk will rapidly change from ground level atmospheric pressure to the vacuum of space. Since the inflatable habitat is tightly folded during launch with multiple layers of bladder, Kevlar fabric sections, and micro-meteoroid shielding, it was not possible to analyze or simulate how the residual air pockets would behave during the launch. If the inflatable habitat does not vent adequately and expands, it could rupture the payload bay of the launch vehicle. A launch depressurization test was chosen as the best way to qualify the inflatable habitat. When stowed, the inflatable habitat measured approximately 241 cm (95 inches) in diameter by 152 cm (60 inches) high and weighed close to 1361 kg (3,000 pounds). Two vacuum chambers connected by a large vacuum line were used to perform this test. The inflatable habitat was mounted in the smaller chamber, which was 396 cm (13 feet) in diameter and 1128 cm (37 feet) high. The larger chamber, which was 823 cm (27 feet) in diameter and 2,591 cm (85 feet) high, was rough pumped and used as a vacuum reservoir. A two stage axial type compressor and ten Stokes vacuum pumps were also used during the depressurization. Opening a butterfly valve on the vacuum line, at the smaller chamber, was manually controlled so that the smaller chamber's depressurization rate matched the launch pressure profile.

ETL↗
NASA NTRSDate not supplied

Fiber Optics Sensing System (FOSS) deployment on Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID)

Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) is a technology demonstration of an inflatable aeroshell to slow down and protect heavy and valuable payloads when entering atmospheres such as those of the Earth and Mars. The ultimate project goal is to enable future payload deliveries to Mars. The LOFTID is based on more than a decade of development of the hypersonic inflatable aerodynamic decelerator (HIAD) technology, which consists of a stack of the inflatable concentric rings that make up the inflatable structure that is covered with a Flexible Thermal Protection System (FTPS) and, when combined, form the inflatable aeroshell. The goal of the LOFTID demonstration was to verify that a flexible heat shield, packed into a small-volume payload, can be inflated exoatmospherically to sizes much larger than that of the launch vehicle fairing and survive re-entry into the Earth atmosphere while withstanding a temperature excess of 1,600 °C. The LOFTID is part of Technology Demonstration Missions (TDM) under the National Aeronautics and Space Administration (NASA) Space Technology Mission Directorate (STMD). The NASA Armstrong Flight Research Center (AFRC) (Edwards, California) is part of the LOFTID program, where a space-launch version of the fiber optic sensing system (FOSS) is integrated into the avionics bay of the re-entry vehicle to provide high-spatial-density temperature measurements in three strategic locations of the vehicle. The program is part of a partnership agreement between the NASA Launch Service Program (LSP) at Kennedy Space Center (KSC) (Merritt Island, Florida) and the main Center of the LOFTID program at NASA Langley Research Center (LaRC) (Hampton, Virginia). This paper will first give a brief introduction of the FOSS, then discuss how the FOSS was integrated into LOFTID, in terms of fiber sensor integration into various sections of the vehicle, as well as integration of the FOSS interrogator into the avionics bay. Finally, data analysis during the LOFTID re-entry will be discussed.

Allen R Parker↗
DOE OSTI2013

Power suppression at large scales in string inflation

We study a possible origin of the anomalous suppression of the power spectrum at large angular scales in the cosmic microwave background within the framework of explicit string inflationary models where inflation is driven by a closed string modulus parameterizing the size of the extra dimensions. In this class of models the apparent power loss at large scales is caused by the background dynamics which involves a sharp transition from a fast-roll power law phase to a period of Starobinsky-like slow-roll inflation. An interesting feature of this class of string inflationary models is that the number of e-foldings of inflation is inversely proportional to the string coupling to a positive power. Therefore once the string coupling is tuned to small values in order to trust string perturbation theory, enough e-foldings of inflation are automatically obtained without the need of extra tuning. Moreover, in the less tuned cases the sharp transition responsible for the power loss takes place just before the last 50-60 e-foldings of inflation. We illustrate these general claims in the case of Fibre Inflation where we study the strength of this transition in terms of the attractor dynamics, finding that it induces a pivot from a blue to a redshifted power spectrum which can explain the apparent large scale power loss. We compute the effects of this pivot for example cases and demonstrate how magnitude and duration of this effect depend on model parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

R{sup 2}-inflation with conformal SM Higgs field

We introduce conformal coupling of the Standard Model Higgs field to gravity and discuss the subsequent modification of R{sup 2}-inflation. The main observation is a lower temperature of reheating which happens mostly through scalaron decays into gluons due to the conformal (trace) anomaly. This modifies all predictions of the original R{sup 2}-inflation. To the next-to-leading order in slow roll parameters we calculate amplitudes and indices of scalar and tensor perturbations produced at inflation. The results are compared to the next-to-leading order predictions of R{sup 2}-inflation with minimally coupled Higgs field and of Higgs-inflation. We discuss additional features in gravity wave signal that may help to distinguish the proposed variant of R{sup 2}-inflation. Remarkably, the features are expected in the region available for study at future experiments like BBO and DECIGO. Finally, we check that (meta)stability of electroweak vacuum in the cosmological model is consistent with recent results of searches for the Higgs boson at LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Delaying the waterfall transition in warm hybrid inflation

We analyze the dynamics and observational predictions of supersymmetric hybrid inflation in the warm regime, where dissipative effects are mediated by the waterfall fields and their subsequent decay into light degrees of freedom. This produces a quasi-thermal radiation bath with a slowly-varying temperature during inflation and further damps the inflaton's motion, thus prolonging inflation. As in the standard supercooled scenario, inflation ends when the waterfall fields become tachyonic and can no longer sustain a nearly constant vacuum energy, but the interaction with the radiation bath makes the waterfall fields effectively heavier and delays the phase transition to the supersymmetric minimum. In this work, we analyze for the first time the effects of finite temperature corrections and SUSY mass splittings on the quantum effective potential and the resulting dissipation coefficient. We show, in particular, that dissipation can significantly delay the onset of the tachyonic instability to yield 50–60 e-folds of inflation and an observationally consistent primordial spectrum, which is not possible in the standard supercooled regime when inflation is driven by radiative corrections.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Accidental inflation from Kähler uplifting

We analyze the possibility of realizing inflation with a subsequent dS vacuum in the Käahler uplifting scenario. The inclusion of several quantum corrections to the 4d effective action evades previous no-go theorems and allows for construction of simple and successful models of string inflation. The predictions of several benchmark models are in accord with current observations, i.e., a red spectral index, negligible non-gaussianity, and spectral distortions similar to the simplest models of inflation. A particularly interesting subclass of models are ''left-rolling'' ones, where the overall volume of the compactified dimensions shrinks during inflation. We call this phenomenon ''inflation by deflation'' (IBD), where deflation refers to the internal manifold. This subclass has the appealing features of being insensitive to initial conditions, avoiding the overshooting problem, and allowing for observable running α ∼ 0.012 and enhanced tensor-to-scalar ratio r ∼ 10{sup −5}. The latter results differ significantly from many string inflation models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Hybrid inflation in the complex plane

Supersymmetric hybrid inflation is an exquisite framework to connect inflationary cosmology to particle physics at the scale of grand unification. Ending in a phase transition associated with spontaneous symmetry breaking, it can naturally explain the generation of entropy, matter and dark matter. Coupling F-term hybrid inflation to soft supersymmetry breaking distorts the rotational invariance in the complex inflaton plane — an important fact, which has been neglected in all previous studies. Based on the δ N formalism, we analyze the cosmological perturbations for the first time in the full two-field model, also taking into account the fast-roll dynamics at and after the end of inflation. As a consequence of the two-field nature of hybrid inflation, the predictions for the primordial fluctuations depend not only on the parameters of the Lagrangian, but are eventually fixed by the choice of the inflationary trajectory. Recognizing hybrid inflation as a two-field model resolves two shortcomings often times attributed to it: the fine-tuning problem of the initial conditions is greatly relaxed and a spectral index in accordance with the PLANCK data can be achieved in a large part of the parameter space without the aid of supergravity corrections. Our analysis can be easily generalized to other (including large-field) scenarios of inflation in which soft supersymmetry breaking transforms an initially single-field model into a multi-field model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Sub-Planckian two-field inflation consistent with the Lyth bound

The BICEP2 observation of a large tensor-to-scalar ratio, r = 0.20{sup +0.07}{sub -0.05}, implies that the inflaton φ in single-field inflation models must satisfy φ ∼ 10M{sub Pl} in order to produce sufficient inflation. This is a problem if interaction terms suppressed by the Planck scale impose a bound φ ∼< M{sub Pl}. Here we consider whether it is possible to have successful sub-Planckian inflation in the case of two-field inflation. The trajectory in field space cannot be radial if the effective single-field inflaton is to satisfy the Lyth bound. By considering a complex field Φ, we show that a near circular but aperiodic modulation of a |Φ|{sup 4} potential can reproduce the results of φ{sup 2} chaotic inflation for n{sub s} and r while satisfying |Φ| ∼< 0.01 M{sub Pl} throughout. More generally, for models based on a |Φ|{sup 4} potential, the simplest sub-Planckian models are equivalent to φ{sup 2} and φ{sup 4/3} chaotic inflation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗