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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 793 records · Page 44
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DOE OSTI2011

Hookean atom with four electrons: On the formation of a tetrahedral Wigner molecule in the weak trapping limit

Numerical results are presented on states {sup 5}S{sub u} and {sup 3}P{sub g} of the Hookean atom with four electrons. Using standard ab initio quantum chemistry methods, the quintet configuration is shown to be the ground state for the weak harmonic trapping constant k. For large k values, there is a crossover to the triplet {sup 3}P{sub g} ground state. Finally, it is concluded that the Coulombic potential energy approaches the localized electron limit of a tetrahedral Wigner molecule as the harmonic force constant k tends to zero.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Singlet and triplet potentials of the ground-state atom pair Rb + Cs studied by Fourier-transform spectroscopy

A comprehensive study of the X {sup 1}{Sigma}{sup +} and a {sup 3}{Sigma}{sup +} electronic states of the Rb and Cs atom pair in RbCs is presented. Abundant spectroscopic data for the {sup 85}Rb{sup 133}Cs and {sup 87}Rb{sup 133}Cs isotopologues were obtained from Fourier-transform spectra of laser-induced fluorescence (LIF) from the B {sup 1}{Pi} and (4){sup 1}{Sigma}{sup +} states to the a {sup 3}{Sigma}{sup +} (4549 transitions) and X {sup 1}{Sigma}{sup +} (15 709 transitions) states. The X {sup 1}{Sigma}{sup +} state data were complemented by about 15 500 transitions obtained by Fellows et al.[J. Mol. Spectrosc. 197, 19 (1999)]. LIF progressions to the a {sup 3}{Sigma}{sup +} state range from v{sub a}=0 to 37, reaching an outer turning point at 15.97 A. For the X {sup 1}{Sigma}{sup +} state, by analyzing LIF from the shelflike (4){sup 1}{Sigma}{sup +}, the data are extended from v{sub x}=119 as observed in the above-cited paper to v{sub x}=129, extending the outer turning point from 10.7 to 17.55 A. From these data, potential energy curves were constructed simultaneously for both hyperfine coupled states X {sup 1}{Sigma}{sup +} and a {sup 3}{Sigma}{sup +} in a coupled-channels fitting routine. This allowed us to accurately model the potential close to the Rb(5s) + Cs(6s) atom-pair asymptote, which is required to simulate cold collision processes and to analyze the Feshbach resonances observed for {sup 87}Rb{sup 133}Cs by Pilch et al.[Phys. Rev. A 79, 042718 (2009)]. Dissociation energies were determined for the X {sup 1}{Sigma}{sup +} state as D{sub e}=3836.373(40) cm{sup -1} and for the a {sup 3}{Sigma}{sup +} state as D{sub e}=259.341(30) cm{sup -1}.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Singlet and triplet superfluid competition in a mixture of two-component Fermi and one-component dipolar Bose gases

We consider a mixture of two-component Fermi and (one-component) dipolar Bose gases in which both dipolar interaction and s-wave scattering between fermions of opposite spins are tunable. We show that in the long-wavelength limit, the anisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar condensate can strongly enhance the scattering in the triplet channel. We investigate in detail the conditions for achieving optimal critical temperature at which the triplet superfluid begins to compete with the singlet superfluid.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Topological superconductors as nonrelativistic limits of Jackiw-Rossi and Jackiw-Rebbi models

We argue that the nonrelativistic Hamiltonian of p{sub x}+ip{sub y} superconductor in two dimensions can be derived from the relativistic Jackiw-Rossi model by taking the limit of large Zeeman magnetic field and chemical potential. In particular, the existence of a fermion zero mode bound to a vortex in the p{sub x}+ip{sub y} superconductor can be understood as a remnant of that in the Jackiw-Rossi model. In three dimensions, the nonrelativistic limit of the Jackiw-Rebbi model leads to a 'p+is' superconductor in which spin-triplet p-wave and spin-singlet s-wave pairings coexist. The resulting Hamiltonian supports a fermion zero mode when the pairing gaps form a hedgehoglike structure. Our findings provide a unified view of fermion zero modes in relativistic (Dirac-type) and nonrelativistic (Schroedinger-type) superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Superfluid phases of triplet pairing and neutrino emission from neutron stars

Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density in the one-component condensate at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Perturbative renormalizability of chiral two-pion exchange in nucleon-nucleon scattering

We study the perturbative renormalizability of chiral two-pion exchange for singlet and triplet channels within effective field theory, provided that the one-pion exchange piece of the interaction has been fully iterated. We determine the number of counterterms/subtractions needed to obtain finite results when the cutoff is removed, resulting in three counterterms for the singlet channel and six for the triplet. The results show that perturbative chiral two-pion exchange reproduce the data up to a center-of-mass momentum of k{approx}200-300 MeV in the singlet channel and k{approx}300-400 MeV in the triplet.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Spin-isospin excitations as quantitative constraints for the tensor force

Gamow-Teller (GT) and charge-exchange spin-dipole (SD) excitation energies in {sup 90}Zr and {sup 208}Pb are systematically studied to determine the appropriate magnitude of the tensor terms of the Skyrme interactions. We have found that the centroid energies of GT and SD excitations are sensitive to the adopted strengths of the triplet-even and triplet-odd tensor interactions. Especially, the 1{sup -} SD state plays a crucial role in constraining the triplet-even part while the triplet-odd part is related rather to the GT peaks. Among the 36 TIJ parameter sets that include nonperturbatively the tensor terms, the four sets, T21, T32, T43, and T54, give reasonable results for the centroid energies in comparison with the experimental data. The sign and magnitude of the tensor terms are also discussed when these terms are added to the existing Skyrme interactions SGII and SLy5. The triplet-even strength can be constrained in a narrow range by using the available experimental data while further empirical data are needed to set a constraint on the triplet-odd term.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Zero sound in triplet-correlated superfluid neutron matter

The linear response of a superfluid neutron liquid onto external vector field is studied for the case of {sup 3}P{sub 2}-{sup 3}F{sub 2} pairing. In particular, we analyze the case of neutron condensation into the state with m{sub j}=0, which is conventionally considered as the preferable one in the bulk matter of neutron stars. Consideration is limited to the case when the wavelength of a perturbation is large as compared to the coherence length in the superfluid matter and the transferred energy is small in comparison with the gap amplitude. The obtained results are used to analyze collisionless soundlike excitations of the superfluid condensate. Zero sound (if it exists) is found to be anisotropic and undergoes a strong decrement below some temperature threshold depending substantially on the intensity of Fermi-liquid interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Origin of a sensitive dependence of calculated {beta}{beta}-decay amplitudes on the particle-particle residual interaction

In the present work the sensitivity of calculated {beta}{beta}-decay amplitudes to a realistic residual interaction is analyzed in the framework of the approach of O. A. Rumyantsev and M. H. Urin, Phys. Lett. B 443, 51 (1998). and V. A. Rodin, M. H. Urin, and A. Faessler, Nucl. Phys. A 747, 297 (2005). Both the Gamow-Teller (GT) and Fermi (F) matrix elements M{sup 2}{nu} for two-neutrino {beta}{beta} decay (2{nu}{beta}{beta} decay), along with the monopole transition contributions to the total matrix elements M{sup 0{nu}} of neutrinoless {beta}{beta} decay (0{nu}{beta}{beta} decay), are calculated within the quasiparticle random-phase approximation (QRPA). In the aforementioned approach decompositions of M{sup 2{nu}} and M{sup 0{nu}} can be obtained in terms of the corresponding energy-weighted sum rules S. It is shown that in most of the cases almost the whole dependence of M{sup 2{nu}} and M{sup 0{nu}} on the particle-particle (p-p) renormalization parameter g{sub pp} is accounted for by the g{sub pp} dependence of the corresponding sum rules S. General expressions relating S to a realistic residual particle-particle interaction are derived, which show a pronounced sensitivity of S to the singlet-channel interaction in the case of F transitions and to the triplet-channel interaction in the case of GT transitions. Thus, the sensitivity of M{sup 2{nu}} and M{sup 0{nu}} to the SU(4)-symmetry-breaking part of the p-p residual interaction is dictated by the generic structure of the {beta}{beta}-decay amplitudes. Therefore, a choice of this part in a particular calculation needs a special caution. Finally, a better isospin-consistent way of renormalization of a realistic residual p-p interaction to use in QRPA calculations is suggested.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Forward-backward asymmetry of the top quark in diquark models

Motivated by the recent unexpected large forward-backward asymmetry of the top-quark observed by D0 and CDF at the Tevatron, we investigate a possible explanation for the anomaly within the framework of diquark models. In the diquark models, the top-quark pair production is mediated by the u-channel diagram. It is found that the color-triplet diquark can generate the forward-backward asymmetry of 20% when the constraint from the cross section of the top-quark pair production is taken into account.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Phenomenology in the Higgs triplet model with the A{sub 4} symmetry

We discuss the phenomenology of doubly and singly charged Higgs bosons [of SU(2){sub L}-triplet fields] in the simplest A{sub 4}-symmetric version of the Higgs triplet model. Mass eigenstates of these Higgs bosons are obtained explicitly from the Higgs potential. It is shown that their decays into a pair of leptons have unique flavor structures which can be tested at the LHC if some of their masses are below the TeV scale. Sizable decay rates for {tau}{yields}{mu}ee and {tau}{yields}e{mu}{mu} can be obtained naturally, while other {tau}{yields}ll{sup '}l{sup ''}, {mu}{yields}eee, and l{yields}l{sup '{gamma}}, are almost forbidden in this model. Contributions of these Higgs bosons to the nonstandard interactions of neutrinos are also considered.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Raising the Higgs mass with Yukawa couplings for isotriplets in vectorlike extensions of minimal supersymmetry

Extra vectorlike matter with both electroweak-singlet masses and large Yukawa couplings can significantly raise the lightest Higgs boson mass in supersymmetry through radiative corrections. I consider models of this type that involve a large Yukawa coupling between weak isotriplet and isodoublet chiral supermultiplets. The particle content can be completed to provide perturbative gauge coupling unification, in several different ways. The impact on precision electroweak observables is shown to be acceptably small, even if the new particles are as light as the current experimental bounds of order 100 GeV. I study the corrections to the lightest Higgs boson mass, and discuss the general features of the collider signatures for the new fermions in these models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Large loop effects of extra supersymmetric Higgs doublets to CP violation in B{sup 0} mixing

We consider more than one pair of SU(2){sub L} doublet Higgs supermultiplets in a generic supersymmetric extension of the standard model, and calculate their one-loop contributions to the soft mass insertions {delta}{sub LL} etc. We find that, if large supersymmetry breaking in this sector is realized, the loop effects can give rise to large contributions to the soft mass insertions, meaning that they can generate large flavor-changing neutral currents and CP violations. We apply our result to a recently proposed model based on the discrete Q{sub 6} family group, and calculate the nondiagonal matrix element M{sub 12} of the neutral meson systems. We focus our attention on the extra phases {phi}{sub d,s}{sup {Delta}}in B{sub d,s} mixing and flavor-specific CP asymmetries a{sub sl}{sup d,s} in neutral B decays and obtain values that can be about 1 order of magnitude larger than the standard model predictions. Our final results are comparable with the recent experimental observations at D0 and CDF, but they are still about a factor of 5 smaller than the recently measured dimuon asymmetry from D0.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

A dark matter model with non-Abelian gauge symmetry.

We propose a dark-matter model in which the dark sector is gauged under a new SU(2) group. The dark sector consists of SU(2) dark gauge fields, two triplet dark Higgs fields, and two dark fermion doublets (dark-matter candidates in this model). The dark sector interacts with the standard model sector through kinetic and mass mixing operators. The model explains both PAMELA and Fermi LAT data very well and also satisfies constraints from both the dark-matter relic density and standard model precision observables. The phenomenology of the model at the LHC is also explored.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Dynamics of flat anisotropic models in Lovelock gravity: The even-dimensional case

In this article, we give a full description of the dynamics of the flat anisotropic (4+1)-dimensional cosmological model in the presence of both Gauss-Bonnet and Einstein contributions. This is the first complete description of this model with both terms taken into account. Our data is obtained using the numerical analysis, though, we use analytics to explain some features of the results obtained, and the same analytics could be applied to higher-dimensional models with higher-order Lovelock corrections. Firstly, we investigate the vacuum model and give a description of all regimes; then, we add a matter source in the form of a perfect fluid and study the influence the matter exerts upon the dynamics. Thus, we give a description of matter regimes as well. Additionally, we demonstrate that the presence of matter not only improves the situation with a smooth transition between the standard singularity and the Kasner regime, but also brings additional regimes and even partially erases the boundaries between different regimes inside the same triplet. Finally, we discuss the numerical and analytical results obtained and their generalization to the higher-order models with an even number of spatial dimensions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Noncommutative vortices and flux tubes from Yang-Mills theories with spontaneously generated fuzzy extra dimensions

We consider a U(2) Yang-Mills theory on MxS{sub F}{sup 2}, where M is an arbitrary noncommutative manifold, and S{sub F}{sup 2} is a fuzzy sphere spontaneously generated from a noncommutative U(N) Yang-Mills theory on M, coupled to a triplet of scalars in the adjoint of U(N). Employing the SU(2)-equivariant gauge field constructed in [D. Harland and S. Kurkcuoglu, Nucl. Phys. B 821, 380 (2009).], we perform the dimensional reduction of the theory over the fuzzy sphere. The emergent model is a noncommutative U(1) gauge theory coupled adjointly to a set of scalar fields. We study this model on the Groenewald-Moyal plane M=R{sub {theta}}{sup 2} and find that, in certain limits, it admits noncommutative, non-Bogomol'nyi-Prasad-Somerfield vortex as well as flux-tube (fluxon) solutions and discuss some of their properties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Superspace formulation in a three-algebra approach to D=3, N=4, 5 superconformal Chern-Simons matter theories

We present a superspace formulation of the D=3, N=4, 5 superconformal Chern-Simons Matter theories, with matter supermultiplets valued in a symplectic 3-algebra. We first construct an N=1 superconformal action and then generalize a method used by Gaitto and Witten to enhance the supersymmetry from N=1 to N=5. By decomposing the N=5 supermultiplets and the symplectic 3-algebra properly and proposing a new superpotential term, we construct the N=4 superconformal Chern-Simons matter theories in terms of two sets of generators of a (quaternion) symplectic 3-algebra. The N=4 theories can also be derived by requiring that the supersymmetry transformations are closed on-shell. The relationship between the 3-algebras, Lie superalgebras, Lie algebras, and embedding tensors (proposed in [E. A. Bergshoeff, O. Hohm, D. Roest, H. Samtleben, and E. Sezgin, J. High Energy Phys. 09 (2008) 101.]) is also clarified. The general N=4, 5 superconformal Chern-Simons matter theories in terms of ordinary Lie algebras can be re-derived in our 3-algebra approach. All known N=4, 5 superconformal Chern-Simons matter theories can be recovered in the present superspace formulation for super-Lie algebra realization of symplectic 3-algebras.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗