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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Neutron Radiation, Radiation Measurement and the JLab APEX Experiment

The A-prime Experiment (APEX), which is approved to run at the Thomas Jefferson Accelerator Facility (JLab) Hall A, will search for a new vector boson that is hypothesized to be a possible force carrier that couples to dark matter. APEX results should be sensitive to the mass range of 65 MeV to 550 MeV, and high sensitivity will be achieved by means of a high intensity 100 muA beam on a 0.3 g/cm 2 Tungsten target resulting in very high luminosity. The experiment should be able to observe an A-prime with a coupling constant 1 x 10 7 times smaller than the electromagnetic coupling constant. To deal safely with such enormous intensity and luminosity, a full radiation analysis must be used. A Geant4 Monte Carlo simulation was performed to study the radiation environments expected in the JLab Hall A during the APEX experiment. We benchmarked our simulations with measurements carried out during past experiments such as the Pb Radius Experiment (PREX-I). Our PREX-I simulations agreed reasonably well with measurements performed by measuring the change in dark current in a Silicon Photomultipliers as a means of radiation damage. However, our simulations were initially significantly higher than the neutron dose measurements (using NP100) in Hall A. The apparent disagreement hints to several potential problems in NP100 measurements including the dead-time. Further, we identified radiation sources in the beam line and tested several shielding strategies to lower the radiation in Hall A. We characterized several thermal neutron detectors and also studied possibility of damage to electronics due to neutron radiation. We successfully demonstrated that the APEX experiment can be carried out in JLab Hall A without worrying about radiation damage to expensive electronics. The A-prime will appear as a narrow resonance in the invariant mass spectrum of e + e - pairs resulting from the electron beam scattering off the APEX target. In this search for the A-prime, it is critical to have a good mass resolution which is mainly dominated by the track measurement uncertainties. We studied a novel method to calibrate the HRS optics which will improve the accuracy of track measurements. Our results will be used to design HRS calibration runs for the APEX experiment.

Kaluarachchi, Maduka↗
DOE OSTI2015

Exploring the parameter space of warm-inflation models

Warm inflation includes inflaton interactions with other fields throughout the inflationary epoch instead of confining such interactions to a distinct reheating era. Previous investigations have shown that, when certain constraints on the dynamics of these interactions and the resultant radiation bath are satisfied, a low-momentum-dominated dissipation coefficient ∝T{sup 3}/m{sub χ}{sup 2} can sustain an era of inflation compatible with CMB observations. In this work, we extend these analyses by including the pole-dominated dissipation term ∝√(m{sub χ}T)exp (−m{sub χ}/T). We find that, with this enhanced dissipation, certain models, notably the quadratic hilltop potential, perform significantly better. Specifically, we can achieve 50 e-folds of inflation and a spectral index compatible with Planck data while requiring fewer mediator field (O(10{sup 4}) for the quadratic hilltop potential) and smaller coupling constants, opening up interesting model-building possibilities. We also highlight the significance of the specific parametric dependence of the dissipative coefficient which could prove useful in even greater reduction in field content.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Results from the Solar Hidden Photon Search (SHIPS)

We present the results of a search for transversely polarised hidden photons (HPs) with ∼3 eV energies emitted from the Sun. These hypothetical particles, known also as paraphotons or dark sector photons, are theoretically well motivated for example by string theory inspired extensions of the Standard Model. Solar HPs of sub-eV mass can convert into photons of the same energy (photon ↔ HP oscillations are similar to neutrino flavour oscillations). At SHIPS this would take place inside a long light-tight high-vacuum tube, which tracks the Sun. The generated photons would then be focused into a low-noise photomultiplier at the far end of the tube. Our analysis of 330 h of data (and 330 h of background characterisation) reveals no signal of photons from solar hidden photon conversion. We estimate the rate of newly generated photons due to this conversion to be smaller than 25 mHz/m{sup 2} at the 95% C.L. Using this and a recent model of solar HP emission, we set stringent constraints on χ, the coupling constant between HPs and photons, as a function of the HP mass.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Constraining ALP-photon coupling using galaxy clusters

We study photon-ALP conversion by resonance effects in the magnetized plasma of galaxy clusters and compare the predicted distortion of the cosmic microwave background spectrum in the direction of such objects to measurements of the thermal Sunyaev-Zeldovich effect. Using galaxy cluster models based on current knowledge, we obtain upper limits on the photon-ALP coupling constant g of ≲O(10{sup −11} GeV{sup −1}). The constraints apply to the mass range of 2⋅10{sup −14} eV ≲m{sub ALP}≲3⋅10{sup −12} eV in which resonant photon-ALP conversions can occur. These limits are slightly stronger than current limits, and furthermore provide an independent constraint. We find that a next generation PRISM-like experiment would allow limits down to g≈O(10{sup −14} GeV{sup −1}), two orders of magnitude stronger than the currently strongest limits in this mass range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Comparison of the processes of Higgs boson pair production and associated production of a radion and a Higgs boson

It is demonstrated that a radion and a Higgs boson are similar up to the replacement of masses and coupling constants (m {sub r }→ m {sub h }and Λ{sub r }→ v {sub 0}) in the processes of their single production and the additional rescaling of the coupling constant at the cubic self-action of a Higgs boson (1→1+((m{sub r}{sup 2}−m{sub h}{sup 2})/(3m{sub h}{sup 2}))) in the processes of their associated production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Four-fermion interaction in relativistic heavy ion collisions

A (nearly) perfect liquid discovered in experiments with ultrarelativistic heavy ion collisions is investigated by studying the quark ensembles with four-fermion interaction considered as a fundamental theoretical approach. A comparative analysis of several quantum liquid models is performed, allowing one to conclude that the presence of gas-liquid phase transition is a characteristic feature of those models. The problem of the instability of the quark droplets with the small number of quarks, related with a possible formation of a chiral soliton, is discussed. A mixed phase of vacuum and baryon matter, as a possible scenario of its stability, is studied. Some aspects of the color superconductivity are considered. In addition, a recently proposed nontrivial thermodynamic state, called the fermion condensate, is studied. An analysis of unexpected opportunity to link the bare and effective coupling constants is performed within the framework of a simple model. It is pointed out that a simple subtraction procedure leads to the finite result without a typical logarithmic singularity for the observed coupling constant as a function of the transferred energy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Decaying leptophilic dark matter at IceCube

We present a novel interpretation of IceCube high energy neutrino events (with energy larger than 60 TeV) in terms of an extraterrestrial flux due to two different contributions: a flux originated by known astrophysical sources and dominating IceCube observations up to few hundreds TeV, and a new flux component where the most energetic neutrinos come from the leptophilic three-body decays of dark matter particles with a mass of few PeV. Differently from other approaches, we provide two examples of elementary particle models that do not require extremely tiny coupling constants. We find the compatibility of the theoretical predictions with the IceCube results when the astrophysical flux has a cutoff of the order of 100 TeV (broken power law). In this case the most energetic part of the spectrum (PeV neutrinos) is due to an extra component such as the decay of a very massive dark matter component. Due to the low statistics at our disposal we have considered for simplicity the equivalence between deposited and neutrino energy, however such approximation does not affect dramatically the qualitative results. Of course, a purely astrophysical origin of the neutrino flux (no cutoff in energy below the PeV scale — unbroken power law) is still allowed. If future data will confirm the presence of a sharp cutoff above few PeV this would be in favor of a dark matter interpretation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

The finite and large-N behaviors of independent-value matrix models

We investigate the finite and large N behaviors of independent-value O(N)-invariant matrix models. These are models defined with matrix-type fields and with no gradient term in their action. They are generically nonrenormalizable but can be handled by nonperturbative techniques. We find that the functional integral of any O(N) matrix trace invariant may be expressed in terms of an O(N)-invariant measure. Based on this result, we prove that, in the limit that all interaction coupling constants go to zero, any interacting theory is continuously connected to a pseudo-free theory. This theory differs radically from the familiar free theory consisting in putting the coupling constants to zero in the initial action. The proof is given for generic, finite-size matrix models, whereas, in the limiting case N → ∞, we succeed in showing this behavior for restricted types of actions using a particular scaling of the parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The one and a half monopoles solution of the SU(2) Yang–Mills–Higgs field theory

Recently we have reported on the existence of finite energy SU(2) Yang–Mills–Higgs particle of one-half topological charge. In this paper, we show that this one-half monopole can co-exist with a ’t Hooft–Polyakov monopole. The magnetic charge of the one-half monopole is of opposite sign to the magnetic charge of the ’t Hooft–Polyakov monopole. However the net magnetic charge of the configuration is zero due to the presence of a semi-infinite Dirac string along the positive z-axis that carries the other half of the magnetic monopole charge. The solution possesses gauge potentials that are singular along the z-axis, elsewhere they are regular. The total energy is found to increase with the strength of the Higgs field self-coupling constant λ. However the dipole separation and the magnetic dipole moment decrease with λ. This solution is non-BPS even in the BPS limit when the Higgs self-coupling constant vanishes. -- Highlights: •This one-half monopole can co-exist with a ’t Hooft–Polyakov monopole. •The magnetic charge of the one-half monopole and one monopole is of opposite sign. •This solution is non-BPS. •The net magnetic charge of the configuration is zero. •This solution upon Cho decomposition is only singular along the negative z-axis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Constraints on variations in inflaton decay rate from modulated preheating

Modulated (p)reheating is thought to be an alternative mechanism for producing super-horizon curvature perturbations in CMB. But large non-gaussianity and iso-curvature perturbations produced by this mechanism rule out its acceptability as the sole process responsible for generating CMB perturbations. We explore the situation where CMB perturbations are mostly generated by usual quantum fluctuations of inflaton during inflation, but a modulated coupling constant between inflaton and a secondary scalar affects the preheating process and produces some extra curvature perturbations. If the modulating scalar field is considered to be a dark matter candidate, coupling constant between the fields has to be unnaturally fine tuned in order to keep the local-form non-gaussianity and the amplitude of iso-curvature perturbations within observational limit; otherwise parameters of the models have to be tightly constrained. Those constraints imply that the curvature perturbations generated by modulated preheating should be less than 15% of the total observed CMB perturbations. On the other hand if the modulating scalar field is not a dark matter candidate, parameters of the models could not be constrained, but the constraints on the maximum amount of the curvature perturbations coming from modulated preheating remain valid.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Environment-induced uncertainties on moving mirrors in quantum critical theories via holography

Environment effects on a n-dimensional mirror from the strongly coupled d-dimensional quantum critical fields with a dynamic exponent z in weakly squeezed states are studied by the holographic approach. The dual description is a n+1-dimensional probe brane moving in the d+1-dimensional asymptotic Lifshitz geometry with gravitational wave perturbations. Using the holographic influence functional method, we find that the large coupling constant of the fields reduces the position uncertainty of the mirror, but enhances the momentum uncertainty. As such, the product of the position and momentum uncertainties is independent of the coupling constant. The proper choices of the phase of the squeezing parameter might reduce the uncertainties, nevertheless large values of its amplitude always lead to the larger uncertainties due to the fact that more quanta are excited as compared with the corresponding normal vacuum and thermal states. In the squeezed vacuum state, the position and momentum of the mirror gain maximum uncertainties from the field at the dynamic exponent z=n+2 when the same squeezed mode is considered. As for the squeezed thermal state, the contributions of thermal fluctuations to the uncertainties decrease as the temperature increases in the case 1 n+2 the contributions increase as the temperature increases. These results are in sharp contrast with those in the environments of the relativistic free field. Some possible observable effects are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Universal low-energy behavior in three-body systems

We consider a pairwise interacting quantum 3-body system in 3-dimensional space with finite masses and the interaction term V{sub 12} + λ(V{sub 13} + V{sub 23}), where all pair potentials are assumed to be nonpositive. The pair interaction of the particles (1, 2) is tuned to make them have a zero energy resonance and no negative energy bound states. The coupling constant λ > 0 is allowed to take the values for which the particle pairs (1, 3) and (2, 3) have no bound states with negative energy. Let λ{sub cr} denote the critical value of the coupling constant such that E(λ) → −0 for λ → λ{sub cr}, where E(λ) is the ground state energy of the 3-body system. We prove the theorem, which states that near λ{sub cr}, one has E(λ) = C(λ − λ{sub cr})[ln(λ − λ{sub cr})]{sup −1} + h.t., where C is a constant and h.t. stands for “higher terms.” This behavior of the ground state energy is universal (up to the value of the constant C), meaning that it is independent of the form of pair interactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

On stars, galaxies and black holes in massive bigravity

In this paper we study the phenomenology of stars and galaxies in massive bigravity. We give parameter conditions for the existence of viable star solutions when the radius of the star is much smaller than the Compton wavelength of the graviton. If these parameter conditions are not met, we constrain the ratio between the coupling constants of the two metrics, in order to give viable conditions for e.g. neutron stars. For galaxies, we put constraints on both the Compton wavelength of the graviton and the conformal factor and coupling constants of the two metrics. The relationship between black holes and stars, and whether the former can be formed from the latter, is discussed. We argue that the different asymptotic structure of stars and black holes makes it unlikely that black holes form from the gravitational collapse of stars in massive bigravity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Thermodynamic and magnetic properties of a three-state Potts model on a triangular lattice with next-neighbor interactions

Using Monte Carlo calculations, we study the thermodynamic and magnetic properties of 2D structures that can be described by a three-state Potts model on a triangular lattice with nearest- and secondnearest- neighbor interactions characterized by the coupling constants J{sub 1} and J{sub 2}, respectively. Analyzing the thermodynamic parameters of heat capacity, the order parameter, the susceptibility, and fourth-order Binder cumulants, we show that the three-state Potts model with coupling constants J{sub 1} > 0 and J{sub 2} < 0 predicts a phase transition of the second kind for 0 ≤ |r| ≤ 1/3, where r = J{sub 2}/J{sub 1}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The Kondo lattice state in the presence of Van Hove singularities: Next-to-leading order scaling

Renormalization group analysis of the Kondo model with a logarithmic Van Hove singularity in the electron density of states has been carried out in the next-to-leading scaling approximation in different magnetic phases. The effective coupling constant remains small, while the renormalized magnetic moment and the frequency of spin fluctuations decrease by several orders of magnitude. In this way, broad regions of non-Fermi-liquid behavior are found from scaling trajectories in a large interval of the bare coupling constant. Applications to the physics of itinerant magnetism are considered.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

On the connection between perturbation theory and new semiclassical expansion in quantum mechanics

Here, it is shown that for the one-dimensional anharmonic oscillator with potential V(x) = ax 2 + bgx 3 + ... = $\frac{1}{g^2}$ $\hat{V}$ (gx), as well as for the radial oscillator V(r) = $\frac{1}{g^2}$ $\hat{V}$ (gr) and for the perturbed Coulomb problem V(r) = $\frac{a}{r}$ + βgr + ... = g $\tilde{V}$ (gr), the Perturbation Theory in powers of the coupling constant g (weak coupling regime) and the semiclassical expansion in powers of $\hbar$ 1/2 for the energies coincide. This is related to the fact that the dynamics developed in two spaces: x (r)-space and gx (gr)-space, lead to the same energy spectra. The equations which govern dynamics in these two spaces, the Riccati-Bloch equation and the Generalized Bloch equation, respectively, are presented. It is shown that the perturbation theory for the logarithmic derivative of the wavefunction in - space leads to (true) semiclassical expansion in powers of $\hbar$ 1/2 ; for the one-dimensional case this corresponds to the flucton calculus for the density matrix in the path integral formalism in Euclidean (imaginary) time proposed by one of the authors. Matching the perturbation theory in powers of g and the semiclassical expansion in powers of $\hbar$ 1/2 for the wavefunction leads to a highly accurate local approximation in the entire coordinate space, its expectation value for the Hamiltonian provides a prescription for the summation of the perturbative (trans)-series.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

BICEP/ K e c k XIV: Improved constraints on axionlike polarization oscillations in the cosmic microwave background

We present an improved search for axionlike polarization oscillations in the cosmic microwave background (CMB) with observations from the Keck Array . An all-sky, temporally sinusoidal rotation of CMB polarization, equivalent to a time-variable cosmic birefringence, is an observable manifestation of a local axion field and potentially allows a CMB polarimeter to detect axionlike dark matter directly. We describe improvements to the method presented in previous work, and we demonstrate the updated method with an expanded dataset consisting of the 2012–2015 observing seasons. We set limits on the axion-photon coupling constant for mass m in the range 10 - 23 – 10 - 18 eV , which corresponds to oscillation periods on the order of hours to years. Our results are consistent with the background model. For periods between 1 and 30 d ( 1.6 × 10 - 21 ≤ m ≤ 4.8 × 10 - 20 eV ), the 95%-confidence upper limits on rotation amplitude are approximately constant with a median of 0.27°, which constrains the axion-photon coupling constant to g φ γ < ( 4.5 × 10 - 12 GeV - 1 ) m / ( 10 - 21 eV ) , if axionlike particles constitute all of the dark matter. More than half of the collected BICEP dataset has yet to be analyzed, and several current and future CMB polarimetry experiments can apply the methods presented here to achieve comparable or superior constraints. In the coming years, oscillation measurements can achieve the sensitivity to rule out unexplored regions of the axion parameter space.

79 ASTRONOMY AND ASTROPHYSICS↗