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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Form factor effects in the direct detection of isospin-violating dark matter

Isospin-violating dark matter (IVDM) provides a possible mechanism to ameliorate the tension among recent direct detection experiments. For IVDM, we demonstrate that the results of direct detection experiments based on neutron-rich target nuclei may depend strongly on the density dependence of the symmetry energy which is presently largely unknown and controls the neutron skin thickness that reflects the relative difference of neutron and proton form factors in the neutron-rich nuclei. In particular, using the neutron and proton form factors obtained from Skyrme-Hartree-Fock calculations by varying the symmetry energy within the uncertainty region set by the latest model-independent measurement of the neutron skin thickness of {sup 208}Pb from PREX experiment at JLab, we find that, for IVDM with neutron-to-proton coupling ratio fixed to f{sub n}/f{sub p}=-0.7, the form factor effect may enhance the sensitivity of Xe-based detectors (e.g., XENON100 and LUX) to the DM-proton cross section by a factor of 3 in the DM mass region constrained by CMDS-II(Si) and even by more than an order of magnitude for heavy DM with mass larger than 80 GeV, compared with the results using the empirical Helm form factor. Our results further indicate that the form factor effect can significantly modify the recoil spectrum of Xe-based detectors for heavy IVDM with f{sub n}/f{sub p}=-0.7.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Isospin-violating dark-matter-nucleon scattering via two-Higgs-doublet-model portals

We show that in a multi-Higgs model in which one Higgs fits the LHC 125 GeV state, one or more of the other Higgs bosons can mediate DM-nucleon interactions with maximal DM isospin violation being possible for appropriate Higgs-quark couplings, independent of the nature of DM. We then consider the explicit example of a Type II two-Higgs-doublet model, identifying the h or H as the 125 GeV state while the H or h, respectively, mediates DM-nucleon interactions. Finally, we show that if a stable scalar, S, is added then it can be a viable light DM candidate with correct relic density while obeying all direct and indirect detection limits.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Splitting of the one-body potential in spin-polarized isospin-symmetric nuclear matter

Spin-polarized symmetric nuclear matter is studied within the Dirac-Brueckner-Hartree-Fock approach. We pay particular attention to the difference between the one-body potentials of upward and downward polarized nucleons. This is formally analogous to the Lane potential for isospin-asymmetric nuclear matter. We point out the necessity for additional information on this fundamentally important quantity and suggest ways to constrain it.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

2p-2p decay of {sup 8}C and isospin-allowed 2p decay of the isobaric-analog state in {sup 8}B

{sup 8}C is found to decay to four protons and an {alpha} particle in two 2p emission steps. The correlations between the protons in the first step ({sup 8}C to {sup 6}Be) exhibit a significant enhancement in the region of the decay phase space where the two protons have small relative energy, a region sometimes called the diproton region. The decay of the isobaric analog of {sup 8}C in {sup 8}B is also found to decay by 2p emission. This is the first case of isospin-allowed 2p decay between isobaric analog states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

J/{psi} and {eta}{sub c} masses in isospin asymmetric hot nuclear matter: A QCD sum rule approach

We study the in-medium masses of the charmonium states J/{psi} and {eta}{sub c} in the nuclear medium using the QCD sum rule approach. These mass modifications arise owing to modifications of the scalar and the twist-2 gluon condensates in the hot hadronic matter. The scalar gluon condensate <({alpha}{sub s}/{pi})G{sub {mu}{nu}}{sup a}G{sup a{mu}{nu}>} and the twist-2 tensorial gluon operator <({alpha}{sub s}/{pi})G{sub {mu}{sigma}}{sup a}G{sup a}{sub {nu}}{sup {sigma}>} in the nuclear medium are calculated from the medium modification of a scalar dilaton field introduced to incorporate trace anomalies of QCD within the chiral SU(3) model used in the present investigation. The effects of isospin asymmetry, density, and temperature of the nuclear medium on the in-medium masses of the lowest charmonium states J/{psi} and {eta}{sub c} mesons are investigated in the present work. The results of the present investigation are compared with the existing results on the masses of these states. The medium modifications of the masses of these charmonium states (J/{psi} and {eta}{sub c}) seem to be appreciable at high densities and should modify the experimental observables arising from the compressed baryonic matter produced in asymmetric heavy-ion collision experiments at the future facility of Facility for Antiproton and Ion Research, GSI.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Spin and spin-isospin instabilities in asymmetric nuclear matter at zero and finite temperatures using Skyrme functionals

Self-consistent mean-field methods based on phenomenological Skyrme effective interactions are known to exhibit spurious spin and spin-isospin instabilities both at zero and finite temperatures when applied to homogeneous nuclear matter at the densities encountered in neutron stars and in supernova cores. The origin of these instabilities is revisited in the framework of the nuclear energy density functional theory, and a simple prescription is proposed to remove them. The stability of several Skyrme parametrizations is reexamined.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Comparative tests of isospin-symmetry-breaking corrections to superallowed 0{sup +}{yields}0{sup +} nuclear {beta} decay

We present a test with which to evaluate the calculated isospin-symmetry-breaking corrections to superallowed 0{sup +}{yields}0{sup +} nuclear {beta} decay. The test is based on the corrected experimental Ft values being required to satisfy conservation of the vector current (CVC). When applied to six sets of published calculations, the test demonstrates quantitatively that only one set, the one based on the shell model with Saxon-Woods radial wave functions, provides satisfactory agreement with CVC. This test can easily be applied to any sets of calculated correction terms that are produced in future.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

QCD phase diagram at finite baryon and isospin chemical potentials

The phase structure of two-flavor QCD is explored for thermal systems with finite baryon- and isospin-chemical potentials, {mu}{sub B} and {mu}{sub iso}, by using the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. The PNJL model with the scalar-type eight-quark interaction can reproduce lattice QCD data at not only {mu}{sub iso}={mu}{sub B}=0, but also {mu}{sub iso}>0 and {mu}{sub B}=0. In the {mu}{sub iso}-{mu}{sub B}-T space, where T is temperature, the critical endpoint of the chiral phase transition in the {mu}{sub B}-T plane at {mu}{sub iso}=0 moves to the tricritical point of the pion-superfluidity phase transition in the {mu}{sub iso}-T plane at {mu}{sub B}=0 as {mu}{sub iso} increases. The thermodynamics at small T is controlled by {radical}({sigma}{sup 2}+{pi}{sup 2}) defined by the chiral and pion condensates, {sigma} and {pi}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Isospin in halo nuclei: Borromean halo, tango halo, and halo isomers

It is shown that the wave functions for isobaric analog, double isobaric analog, configuration, and double configuration states may simultaneously have components corresponding to nn, np, and pp halos. The difference in the halo structure between the ground and excited states of a nucleus may lead to the formation of halo isomers. A halo structure of both Borromean and tango types can be observed for np configurations. The structure of ground and excited states with various isospins in halo-like nuclei is discussed. The reduced probabilities B(Mλ) and B(Eλ) for gamma transitions in {sup 6−8}Li, {sup 8−10}Be, {sup 8,10,11}B, {sup 10−14}C, {sup 13−17}N, {sup 15−17,19}O, and {sup 17}F nuclei are analyzed. Particular attention is given to the cases where the ground state of a nucleus does not have a halo structure, but where its excited state may have it.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Angular and Isospin Asymmetries in the Decays B->K(*)l l-

We use a sample of 384 million B{bar B} decays collected with the BABAR detector at the PEP-II asymmetric e{sup +}e{sup -} storage ring to study the flavor-changing neutral current decays B {yields} K{sup (*)}{ell}{sup +}{ell}{sup -}, where {ell}{sup +}{ell}{sup -} is either e{sup +}e{sup -} or {mu}{sup +}{mu}{sup -}. We present measurements in two dilepton mass bins, one below the J/{psi} resonance and the other above, of the lepton forward-backward asymmetry {Alpha}{sub FB} and the longitudinal K* polarization F{sub L} in B {yields} K* {ell}{sup +}{ell}{sup -}, along with isospin rate asymmetries in B {yields} K*{ell}{sup +}{ell}{sup -} and B {yields} K{ell}{sup +}{ell}{sup -} final states.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Investigations of QCD at non-zero isospin density

We investigate the QCD phase diagram as a function of isospin chemical potential at a fixed temperature by directly putting large numbers of {pi}{sup +}s into the system. Correlation functions of N {pi}{sup +}s systems involves N!N! contractions, and become extremely expensive when N is large. In order to alleviate this problem, a recursion relation of correlation functions has been derived in Ref. [1] that substantially reduces the number of independent contractions needed and makes the study of many pions systems be possible. In this proceeding this method is investigated numerically. We have also constructed a new method that is even more efficient, enabling us to study systems of up to 72 {pi}{sup +}s.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Isospin-violating contributions to ϵ'/ϵ

The known isospin-breaking contributions to the K → ππ amplitudes are reanalyzed, taking into account our current understanding of the quark masses and the relevant non-perturbative inputs. We present a complete numerical reappraisal of the direct CP-violating ratio ϵ'/ϵ, where these corrections play a quite significant role. We obtain the Standard Model prediction Re (ϵ'/ϵ) = (14 ± 5) · 10 -4 , which is in very good agreement with the measured ratio. The uncertainty, which has been estimated conservatively, is dominated by our current ignorance about 1/N C -suppressed contributions to some relevant chiral-perturbation-theory low-energy constants.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Interactions of πK, ππK and KKπ systems at maximal isospin from lattice QCD

We study the interactions of systems of two and three nondegenerate mesons composed of pions and kaons at maximal isospin using lattice QCD, specifically $π^+K^+, π^+π^+K^+$ and $K^+K^+π^+$. Utilizing the stochastic LapH method, we determine the spectrum of these systems on two CLS $N_f$ = 2 + 1 ensembles with pion masses of 200 MeV and 340 MeV, and include many levels in different momentum frames. We constrain the K matrices describing two- and three-particle interactions by fitting the spectrum to the results predicted by the finite-volume formalism, including up to p waves. This requires also results for the $π^+π^+$ and $K^+K^+$ spectrum, which have been obtained previously on the same configurations. We explore different fitting strategies, comparing fits to energy shifts with fits to energies boosted to the rest frame, and also comparing simultaneous global fits to all relevant two- and three-particle channels to those where we first fit twoparticle channels and then add in the three-particle information. We provide the first determination of the three-particle K matrix in $π^+π^+K^+$ and $K^+K^+π^+$ systems, finding statistically significant nonzero results in most cases. We include s and $\textit{p}$ waves in the K matrix for $π^+K^+$ scattering, finding evidence for an attractive p-wave scattering length. We compare our results to Chiral Perturbation Theory, including an investigation of the impact of discretization errors, for which we provide the leading order predictions obtained using Wilson Chiral Perturbation Theory.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

The isospin-3 three-particle K -matrix at NLO in ChPT

The three-particle K-matrix, K df,3 , is a scheme-dependent quantity that parametrizes short-range three-particle interactions in the relativistic-field-theory three-particle finite-volume formalism. In this work, we compute its value for systems of three pions at maximal isospin through next-to-leading order (NLO) in Chiral Perturbation Theory (ChPT). We compare the values to existing lattice QCD results and find that the agreement between lattice QCD data and ChPT in the first two coefficients of the threshold expansion of K df,3 is significantly improved with respect to leading order once NLO effects are incorporated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Dynamically-coupled partial-waves in ρπ isospin-2 scattering from lattice QCD

We present the first determination of ρπ scattering, incorporating dynamically-coupled partial-waves, using lattice QCD, a first-principles numerical approach to QCD. Considering the case of isospin-2 ρπ, we calculate partial-wave amplitudes with J ≤ 3 and determine the degree of dynamical mixing between the coupled S and D-wave channels with J P = 1 + . The analysis makes use of the relationship between scattering amplitudes and the discrete spectrum of states in the finite volume lattice. Constraints on the scattering amplitudes are provided by over one hundred energy levels computed on two lattice volumes at various overall momenta and in several irreducible representations of the relevant symmetry groups. The spectra follow from variational analyses of matrices of correlations functions computed with large bases of meson-meson operators. Calculations are performed with degenerate light and strange quarks tuned to the physical strange quark mass so that m π ~700 MeV, ensuring that the ρ is stable against strong decay. Furthermore, this work demonstrates the successful application of techniques, opening the door to calculations of scattering processes that incorporate the effects of dynamically-coupled partial-waves, including those involving resonances or bound states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Isospin-breaking effects in the three-pion contribution to hadronic vacuum polarization

Isospin-breaking (IB) effects are required for an evaluation of hadronic vacuum polarization at subpercent precision. While the dominant contributions arise from the e + e - → π + π - channel, also IB in the subleading channels can become relevant for a detailed understanding, e.g., of the comparison to lattice QCD. Here, we provide such an analysis for e + e - → 3π by extending our dispersive description of the process, including estimates of final-state radiation (FSR) and ρ–ω mixing. In particular, we develop a formalism to capture the leading infrared-enhanced effects in terms of a correction factor η3π that generalizes the analog treatment of virtual and final-state photons in the 2π case. The global fit to the e+e- → 3π data base, subject to constraints from analyticity, unitarity, and the chiral anomaly, gives for the total 3π contribution to the anomalous magnetic moment of the muon, of which ${a}^{FSR}_\mu [3\pi]$ = 0.51(1) x 10 -10 and ${a}^{\rho - \omega}_\mu [3\pi]$ = -2.68(70) x 10 -10 can be ascribed to IB. We argue that the resulting cancellation with ρ–ω mixing in e + e - → 2π can be understood from a narrow-resonance picture, and provide updated values for the vacuum-polarization-subtracted vector-meson parameters M ω = 782.70(3) MeV, M Φ = 1019.21(2) MeV, Γ ω = 8.71(3) MeV, and Γ Φ = 4.27(1) MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Isospin symmetry holds beyond the proton drip line: First observation of excited states in 55Cu

Isospin symmetry, combined with shell-model description, has long been successful in reproducing nuclear structure and predicting mirror energy differences. However, these descriptions have been primarily limited to mirror nuclei with well-bound ground states. As one approaches the proton drip line, coupling to the continuum becomes important. Despite this, little is known about medium-mass nuclei at the drip line. Here we report the measurement of the excitation energies of several unbound states in a nucleus beyond the proton drip line, 55Cu, performed via γ-ray spectroscopy at the Radioactive Isotope Beam Factory (RIKEN). Several low-lying yrast states are observed to decay predominantly by γ-ray emission. In contrast, the state–predicted to be strongly populated in the one-proton knockout reaction–is notably absent, suggesting that it decays primarily via prompt proton emission. We show that even for such an unbound system, shell-model calculations based on a harmonic oscillator potential reproduce the observed mirror energy differences remarkably well in all the observed states. Based on this result, we propose that a general pattern might emerge where, in medium-mass systems at the proton drip line, the stronger Coulomb barrier together with the centrifugal barrier effectively confines the wave functions, so that the shell model is able to describe low-lying states, enabling accurate predictions of mirror energy differences between isobaric analogue states.

Pigliapoco, S [Dipartimento di Fisica e Astronomia↗
DOE OSTI2022

Inter-valley coherent order and isospin fluctuation mediated superconductivity in rhombohedral trilayer graphene

Superconductivity was recently discovered in rhombohedral trilayer graphene (RTG) in the absence of a moiré potential. Superconductivity is observed proximate to a metallic state with reduced isospin symmetry, but it remains unknown whether this is a coincidence or a key ingredient for superconductivity. Using a Hartree-Fock analysis and constraints from experiments, we argue that the symmetry breaking is inter-valley coherent (IVC) in nature. We evaluate IVC fluctuations as a possible pairing glue, and find that they lead to chiral unconventional superconductivity when the fluctuations are strong. We further elucidate how the inter-valley Hund’s coupling determines the spin-structure of the IVC ground state and breaks the degeneracy between spin-singlet and triplet superconductivity. Remarkably, if the normal state is spin-unpolarized, we find that a ferromagnetic Hund’s coupling favors spin-singlet superconductivity, in agreement with experiments. Instead, if the normal state is spin-polarized, then IVC fluctuations lead to spin-triplet pairing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗