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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

A quantum dot close to Stoner instability: The role of the Berry phase

The physics of a quantum dot with electron-electron interactions is well captured by the so called 'Universal Hamiltonian' if the dimensionless conductance of the dot is much higher than unity. Within this scheme interactions are represented by three spatially independent terms which describe the charging energy, the spin-exchange and the interaction in the Cooper channel. In this paper we concentrate on the exchange interaction and generalize the functional bosonization formalism developed earlier for the charging energy. This turned out to be challenging as the effective bosonic action is formulated in terms of a vector field and is non-abelian due to the non-commutativity of the spin operators. Here we develop a geometric approach which is particularly useful in the mesoscopic Stoner regime, i.e., when the strong exchange interaction renders the system close to the Stoner instability. We show that it is sufficient to sum over the adiabatic paths of the bosonic vector field and, for these paths, the crucial role is played by the Berry phase. Using these results we were able to calculate the magnetic susceptibility of the dot. The latter, in close vicinity of the Stoner instability point, matches very well with the exact solution [I.S. Burmistrov, Y. Gefen, M.N. Kiselev, JETP Lett. 92 (2010) 179]. - Highlights: Black-Right-Pointing-Pointer We consider a conducting QD whose dynamics is governed by exchange interaction. Black-Right-Pointing-Pointer We study the model within the 'Universal Hamiltonian' framework. Black-Right-Pointing-Pointer The ensuing bosonic action is non-abelian (hence non-trivial). Black-Right-Pointing-Pointer We find that the low energy dynamics is governed by a fluctuating Berry phase term. Black-Right-Pointing-Pointer We calculate the partition function and the zero frequency magnetic susceptibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Generalized Beth–Uhlenbeck approach to mesons and diquarks in hot, dense quark matter

An important first step in the program of hadronization of chiral quark models is the bosonization in meson and diquark channels. This procedure is presented at finite temperatures and chemical potentials for the SU(2) flavor case of the NJL model with special emphasis on the mixing between scalar meson and scalar diquark modes which occurs in the 2SC color superconducting phase. The thermodynamic potential is obtained in the Gaussian approximation for the meson and diquark fields and it is given in the Beth–Uhlenbeck form. This allows a detailed discussion of bound state dissociation in hot, dense matter (Mott effect) in terms of the in-medium scattering phase shift of two-particle correlations. It is shown for the case without meson–diquark mixing that the phase shift can be separated into a continuum and a resonance part. In the latter, the Mott transition manifests itself by a change of the phase shift at threshold by π in accordance with Levinson’s theorem, when a bound state transforms to a resonance in the scattering continuum. The consequences for the contribution of pionic correlations to the pressure are discussed by evaluating the Beth–Uhlenbeck equation of state in different approximations. A similar discussion is performed for the scalar diquark channel in the normal phase. Further developments and applications of the developed approach are outlined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Collective mode evidence of high-spin bosonization in a trapped one-dimensional atomic Fermi gas with tunable spin

We calculate the frequency of collective modes of a one-dimensional repulsively interacting Fermi gas with high-spin symmetry confined in harmonic traps at zero temperature. This is a system realizable with fermionic alkaline-earth-metal atoms such as {sup 173}Yb, which displays an exact SU(κ) spin symmetry with κ⩾2 and behaves like a spinless interacting Bose gas in the limit of infinite spin components κ→∞, namely high-spin bosonization. We solve the homogeneous equation of state of the high-spin Fermi system by using Bethe ansatz technique and obtain the density distribution in harmonic traps based on local density approximation. The frequency of collective modes is calculated by exactly solving the zero-temperature hydrodynamic equation. In the limit of large number of spin-components, we show that the mode frequency of the system approaches that of a one-dimensional spinless interacting Bose gas, as a result of high-spin bosonization. Our prediction of collective modes is in excellent agreement with a very recent measurement for a Fermi gas of {sup 173}Yb atoms with tunable spin confined in a two-dimensional tight optical lattice.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thermofield-bosonization on compact space

We develop the construction of fermionic fields in terms of bosonic ones to describe free and interaction models in the circle, using thermofielddynamics. The description in the case of finite temperature is developed for both normal modes and zero modes. The treatment extends the thermofield-bosonization for periodic space.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Double-exchange mechanism in rare-earth compounds

We show that double-exchange mechanism is responsible for ferromagnetism in low dimensional rare-earth compounds. We use the bosonized version of the one-dimensional Anderson lattice model in Toulouse limit to characterize the properties of the emerging ferromagnetic phase. We give a comprehensive description of the ferromagnetic ordering of the correlated electrons which appears at intermediate couplings and doping. The obtained ferromagnetic phase transitions have been identified to be an order–disorder transition of the quantum random transverse-field Ising type.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Screenings and vertex operators of quantum superalgebra U{sub q}(sl-caret(N|1))

We construct the screening currents of the quantum superalgebra U{sub q}(sl-caret(N|1)) for an arbitrary level k{ne}-N+ 1. We show that these screening currents commute with the superalgebra modulo total difference. We propose bosonizations of the vertex operators by using the screening currents. We check that these vertex operators are the intertwiners among the Fock-Wakimoto representation and the typical representation for rank N Less-Than-Or-Slanted-Equal-To 4.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Double-bosonization and Majid’s conjecture, (I): Rank-inductions of ABCD

Majid developed in [S. Majid, Math. Proc. Cambridge Philos. Soc. 125, 151–192 (1999)] the double-bosonization theory to construct U{sub q}(g) and expected to generate inductively not just a line but a tree of quantum groups starting from a node. In this paper, the authors confirm Majid’s first expectation (see p. 178 [S. Majid, Math. Proc. Cambridge Philos. Soc. 125, 151–192 (1999)]) through giving and verifying the full details of the inductive constructions of U{sub q}(g) for the classical types, i.e., the ABCD series. Some examples in low ranks are given to elucidate that any quantum group of classical type can be constructed from the node corresponding to U{sub q}(sl{sub 2})

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Spontaneous population imbalance in two-component Bose and Fermi gases

We study two-component (or pseudo-spin-(1/2)) Bose or Fermi gases in one dimension, in which particles are convertible between the components. Through bosonization and numerical analyses of a simple lattice model, we demonstrate that, in such gases, a strong intercomponent repulsion induces spontaneous population imbalance between the components, namely, the ferromagnetism of the pseudo spins. The imbalanced phase contains gapless charge excitations characterized as a Tomonaga-Luttinger liquid and gapped spin excitations. We uncover a crucial effect of the intercomponent particle hopping on the transition to the imbalanced phase. In the absence of this hopping, the transition is of first order. At the transition point, the energy spectrum reveals certain degeneracy indicative of an emergent SU(2) symmetry. With an infinitesimal intercomponent hopping, the transition becomes of Ising type. We determine the phase diagram of the model accurately and test the reliability of the weak-coupling bosonization formalism.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Pauli potential from Heilmann-Lieb electron density obtained by summing hydrogenic closed-shell densities over the entire bound-state spectrum

Independently, in the mid-1980s, several groups proposed to bosonize the density-functional theory (DFT) for fermions by writing a Schroedinger equation for the density amplitude {rho}(r){sup 1/2}, with {rho}(r) as the ground-state electron density, the central tool of DFT. The resulting differential equation has the DFT one-body potential V(r) modified by an additive term V{sub P}(r) where P denotes Pauli. To gain insight into the form of the Pauli potential V{sub P}(r), here, we invoke the known Coulombic density, {rho}{sub {infinity}}(r) say, calculated analytically by Heilmann and Lieb (HL), by summation over the entire hydrogenic bound-state spectrum. We show that V{sub P{infinity}}(r) has simple limits for both r tends to infinity and r approaching zero. In particular, at large r, V{sub P{infinity}}(r) precisely cancels the attractive Coulomb potential -Ze{sup 2}/r, leaving V(r)+V{sub P{infinity}}(r) of O(r{sup -2}) as r tends to infinity. The HL density {rho}{sub {infinity}}(r) is finally used numerically to display V{sub P{infinity}}(r) for all r values.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Density profile of interacting fermions in a one-dimensional optical trap

The density distribution of the one-dimensional Hubbard model in a harmonic trapping potential is investigated in order to study the effect of the confining trap. Strong superimposed oscillations are always present on top of a uniform density cloud, which show universal scaling behavior as a function of increasing interactions. An analytical formula is proposed on the basis of bosonization, which describes the density oscillations for all interaction strengths. The wavelength of the dominant oscillation changes with interaction, which indicates the crossover to a spin-incoherent regime. Using the Bethe ansatz the shape of the uniform fermion cloud is analyzed in detail, which can be described by a universal scaling form.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

SU(N) magnetism in chains of ultracold alkaline-earth-metal atoms: Mott transitions and quantum correlations

We investigate one-dimensional SU(N) Hubbard chains at zero temperature, which can be emulated with ultracold alkaline-earth-metal atoms, by using the density matrix renormalization group (DMRG), Bethe ansatz (BA), and bosonization. We compute experimental observables and use the DMRG to benchmark the accuracy of the Bethe ansatz for N>2 where the BA is only approximate. In the worst case, we find a relative error {epsilon} < or approx. 4% in the BA ground-state energy for N{<=}4 at filling 1/N, which is due to the fact that BA improperly treats the triply and higher occupied states. Using the DMRG for N{<=}4 and the BA for large N, we determine the regimes of validity of strong- and weak-coupling perturbation theory for all values of N and, in particular, the parameter range in which the system is well described by a SU(N) Heisenberg model at filling 1/N. We find this depends only weakly on N. We investigate the Berezinskii-Kosterlitz-Thouless phase transition from a Luttinger liquid to a Mott insulator by computing the fidelity susceptibility and the Luttinger parameter K{sub {rho}} at 1/N filling. The numerical findings give strong evidence that the fidelity susceptibility develops a minimum at a critical interaction strength which is found to occur at a finite positive value for N>2.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Superconductivity in Zigzag CuO Chains

Superconductivity has recently been discovered in Pr{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15-{delta}} with a maximum T{sub c} of about 15K. Since the CuO planes in this material are believed to be insulating, it has been proposed that the superconductivity occurs in the double (or zigzag) CuO chain layer. On phenomenological grounds we propose a theoretical interpretation of the experimental results in terms of a new phase for the zigzag chain, labelled by C{sub 1}S{sub 3/2}. This phase has a gap in the relative charge mode and a partial gap in the relative spin mode. It has gapless uniform charge and spin excitations and can have a divergent superconducting susceptibility, even for repulsive interactions. A microscopic model for the zigzag CuO chain is proposed, and on the basis of density matrix renormalization group (DMRG) and bosonization studies, we adduce evidence that supports our proposal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Chiral symmetry breaking and quark confinement in the nilpotency expansion of QCD

We apply to lattice QCD a bosonization method previously developed in which dynamical bosons are generated by time-dependent Bogoliubov transformations. The transformed action can be studied by an expansion in the inverse of the nilpotency index, which is the number of fermionic states in the structure function of composite bosons. When this number diverges the model is solved by the saddle-point method which has a variational interpretation. We give a stationary covariant solution for a background matter field whose fluctuations describe mesons. In the saddle-point approximation fermionic quasiparticles exist which have quark quantum numbers. They are confined in the sense that they propagate only in pointlike color singlets. Conditions for chiral symmetry breaking are determined, to be studied numerically, and a derivation of a mesons-nucleons action is outlined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Decomposition of fractional quantum Hall model states: Product rule symmetries and approximations

We provide a detailed description of a product rule structure of the monomial (Slater) expansion coefficients of bosonic (fermionic) fractional quantum Hall (FQH) states derived recently, which we now extend to spin-singlet states. We show that the Haldane-Rezayi spin-singlet state can be obtained without exact diagonalization through a differential equation method that we conjecture to be generic to other FQH model states. The product rule symmetries allow us to build approximations of FQH states that exhibit increasing overlap with the exact state (as a function of system size) even though our approximation omits more than half of the Hilbert space. We show that the product rule is valid for any FQH state that can be written as an expectation value of parafermionic operators.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Large-𝑁 SU(4) Schwinger boson theory for coupled-dimer antiferromagnets

Here, we develop a systematic large-𝑁 expansion based on the Schwinger boson representation of SU(4) coherent states of dimers for the paradigmatic spin-1/2 bilayer square lattice Heisenberg antiferromagnet. This system exhibits a quantum phase transition between a quantum paramagnetic state and a Néel order state, driven by the coupling constant 𝑔 = 𝐽′/𝐽, which is defined as the ratio between the interdimer 𝐽′ and intradimer 𝐽 exchange interactions. We demonstrate that this approach accurately describes static and dynamic properties on both sides of the quantum phase transition. The critical coupling constant 𝑔 𝑐 ≈ 0.42 and the dynamic spin structure factor reproduce quantum Monte Carlo results with high precision. Notably, the 1/𝑁 corrections reveal the longitudinal mode of the magnetically ordered phase along with the overdamping caused by its decay into the two-magnon continuum. The present large-𝑁 SU(4) Schwinger boson theory can be extended to more general cases of quantum paramagnets that undergo a quantum phase transition into magnetically ordered states.

Schwinger boson method↗
DOE OSTI2011

Inclusive charged-current neutrino-nucleus reactions

We present a model for weak charged-current induced nuclear reactions at energies of interest for current and future neutrino oscillation experiments. This model is a natural extension of the work in Refs. [1,2], where the quasielastic contribution to the inclusive electron and neutrino scattering on nuclei was analyzed. The model is based on a systematic many-body expansion of the gauge boson absorption modes that includes one, two, and even three-body mechanisms, as well as the excitation of {Delta} isobars. The whole scheme has no free parameters, besides those previously adjusted to the weak pion production off the nucleon cross sections in the deuteron, since all nuclear effects were set up in previous studies of photon, electron, and pion interactions with nuclei. We have discussed at length the recent charged-current quasielastic MiniBooNE cross section data, and showed that two-nucleon knockout mechanisms are essential to describing these measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Collective Modes in BCS-Like Models

The Hamiltonian of the gapped modes in the BCS model of superconductivity is derived using the nilpotency expansion. It has the form of the Bogoliubov Hamiltonian of a boson superfluid. The gapped modes have a quadratic dispersion law. The smallest energy gap is smaller than twice the fermionic energy gap. The nilpotency expansion respects all the symmetries and it has been previously applied to nuclear physics and relativistic field theories including QCD. In particular, it reproduces exactly the bosonization occurring in a relativistic 4-fermion interaction model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

UPR/Mayaguez High Energy Physics

For the period of sixteen years covered by this report (June 1, 1997 - July 31, 2013) the High Energy Physics Group at the University of Puerto Rico’s Mayaguez Campus (UPRM) carried out an extensive research program that included major experiments at Fermi National Accelerator Laboratory (Fermilab), the Cornell Electron-positron Collider and CERN. In particular, these were E831 (FOCUS) at Fermilab, CLEOc at Cornell and the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) at CERN. The group’s history is one of successful execution and growth. Beginning with one faculty researcher in 1985, it eventually included four faculty researchers, one post-doctoral research associate, two undergraduates and as many as six graduate students at one time working on one of the experiments that discovered the Higgs boson. Some of this expansion was due to the group’s leveraging of funds from the Department of Energy’s core grant to attract funds from National Science Foundation programs not targeted to high energy physics. Besides the group’s research productivity, its other major contribution was the training of a large number of MS students who later went on to successful technical careers in industry as well as academia including many who obtained PhD degrees at US universities. In an attempt to document this history, this final report gives a general description of the Group’s work prior to June 1, 2010, the starting date for the last grant renewal period. Much more detail can, of course, be found in the annual reports submitted up to that date. The work during the last grant period is discussed in detail in a separate section. To summarize the group’s scientific accomplishments, one can point to the results of the experiments. Both FOCUS and CLEOc were designed to carry out precise measurements of processes involving the heavy quarks, charm and bottom. Heavy quarks are particularly interesting because, due to their mass, theoretical calculations based on the Standard Model have less uncertainty than those for the light quarks. Precise heavy quark experiments can therefore yield some of the best tests of the Standard Model and of the approximations that are made in calculating measurable observables. Both FOCUS and CLEOc were highly successful achieving significant improvement in the precision of measurements such as lifetimes and decay branching ratios. For example, FOCUS obtained a data sample that contained ten times as many heavy quark decay events as its predecessor. CMS was a big shift in the group’s research. During the first decade of the century it became clear that the LHC would be the world’s highest energy accelerator offering a unique opportunity for discovery. Given the UPRM’s group record of achievement, it was successful in obtaining admission to the CMS collaboration in March, 2006, becoming the first institution to do so that did not have a PhD program. CMS is one of two major experiments at the LHC. Although the plans are for these experiments to run for many years with increased energy and event rates, they have already achieved one of their principal goals. The test for the existence of the Higgs boson, a particle which plays a unique role in the Standard Model but had not been observed, was answered in the affirmative in 2012.The particular contributions of the UPRM group to these experiments make up the majority of this report although other contributions such as the training of students, outreach to the general community and the organization of scientific meetings are also discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗