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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Constraints On Covariant WIMP-Nucleon Effective Field Theory Interactions from the First Science Run of the LUX-ZEPLIN Experiment

The first science run of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon time project chamber operating in the Sanford Underground Research Facility in South Dakota, USA, has reported leading limits on spin-independent WIMP-nucleon interactions and interactions described from a non-relativistic effective field theory (NREFT). Using the same 5.5~t fiducial mass and 60 live days of exposure we report on the results of a relativistic extension to the NREFT. We present constraints on couplings from covariant interactions arising from the coupling of vector, axial currents, and electric dipole moments of the nucleon to the magnetic and electric dipole moments of the WIMP which cannot be described by recasting previous results described by an NREFT. Using a profile-likelihood ratio analysis, in an energy region between 0~keV_{nr} to 270~keV_{nr}, we report 90% confidence level exclusion limits on the coupling strength of five interactions in both the isoscalar and isovector bases. .

Source record↗
DOE OSTI2020

Relativistic density functional theory in the full potential linear muffin tin orbital method

In this write-up, we have outlined the general methodology for treating relativity in the FP-LMTO method. The Schrodinger equation is insufficient for describing the physics of heavy elements because it leaves out any relativistic effects. Therefore DFT based on the Schrodinger equation is not sufficient for studying heavy materials. It is, however, possible to incorporate all of the effects of relativity in DFT if starting with a reformulation of the Hohenberg-Kohn theorem that proceeds from the Dirac equation, rather than the Schrodinger equation. The corresponding theorem in relativistic density functional theory (RDFT) shows that the ground-state density of the system is a functional of not only the charge density as in Schrodinger-based DFT, but also of the current density. This leads to a more elaborate procedure in practice when solving the Dirac-Kohn-Sham equations, the relativistic analogs of the Kohn-Sham equations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1986

Shell correction for the stopping power of K electrons

In view of the inapplicability of the asymptotic expressions for the stopping number available in the literature at high energies, an alternative approach is taken to compute the shell correction to the stopping number of K electrons. Anholt's formula for the K-shell ionization has been used to calculate the excitation function for longitudinal interaction and numerical integration over energy has been carried out to evaluate the shell correction. Comparison with other theoretical calculations is made. It is proposed that, with the inclusion of relativistic effects, an asymptotic expansion of the stopping number with a leading-term logarithmic in the energy of the incident particle would be more meaningful and might enable one to extract the relativistic contribution to the shell correction from it.

Leung, P. T.↗
DOE OSTI2024

The STAG code: A fully relativistic super transition array calculation using Green’s functions

Calculating opacities for a wide range of plasma conditions (i.e. temperature, density, element) requires detailed knowledge of the plasma configuration space and electronic structure. For plasmas composed of heavier elements, relativistic effects are important in both the electronic structure and the details of opacity spectra. We extend our previously described superconfiguration and super transition array capabilities (Gill et al., 2023) to include a fully relativistic formalism. Further, the use of hybrid bound-continuum supershells in our superconfigurations demonstrates the importance of a consistent treatment of bound and continuum electrons in dense plasma opacities, and we expand the discussion of these consequences to include issues associated with equation of state and electron correlations between bound and continuum electrons.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Effects of Quark Core Sizes of Baryons in Neutron Star Matter

We describe the quark substructure of hadrons and the equation of state of high-density neutron star matter by using the Nambu–Jona-Lasinio (NJL) model, which is an effective quark theory based on QCD. The interaction between quarks fully respects the chiral and flavor symmetries. Guided by the success of various low-energy theorems, we assume that the explicit breaking of these symmetries occurs only via the current quark masses, and all other symmetry breakings are of dynamical nature. In order to take into account the effects of the finite quark core sizes of the baryons on the equation of state, we make use of an excluded volume framework that respects thermodynamic consistency. The effects generated by the swelling quark cores generally act repulsively and lead to an increase in the pressure with increasing baryon density. On the other hand, in neutron star matter, these effects also lead to a decrease in the density window where hyperons appear because it becomes energetically more favorable to convert the faster moving nucleons into hyperons. Our quantitative analysis shows that the net effect of the excluded volume is too small to solve the long-standing “hyperon puzzle”, which is posed by the large observed masses of neutron stars. Thus, the puzzle persists in a relativistic effective quark theory which takes into account the short-range repulsion between baryons caused by their finite and swelling quark core sizes in a phenomenological way.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1983

The constancy of G and other gravitational experiments

Recent solar system experimental tests of the general relativity theory are reviewed. The solar system data set available at the Harvard-Smithsonian Center for Astrophysics is first reviewed. Investigations of the secular variation of G in the solar system are discussed; recent analyses using Viking data yield G-dot/G of less than 3 x 10 to the -11th/yr. The present data set will make it possible to distinguish between competitive theories. Shapiro's time-delay effect has provided the most stringent solar system test of general relativity. The effect has been measured to be consistent with the predictions of the theory to within an uncertainty of 0.1 percent. Tests which can be performed in the near future, including the measurement of relativistic effects due to the square of the solar potential and the detection of the Lense-Thirring effect, are discussed.

Reasenberg, R. D.↗
NASA NTRS1989

Investigating relativity using lunar laser ranging - Geodetic precession and the Nordtvedt effect

The emplacement of retroreflectors on the moon by Apollo astronauts and the Russian Lunakhod spacecraft marked the inception of lunar laser ranging (LLR) and provided a natural laboratory for the study of general relativity. Continuing acquisition of increasingly accurate LLR data has provided enhanced sensitivity to general relativity parameters. Two relativistic effects are investigated in this paper: (1) the Nordtvedt effect, yielding a test of the strong equivalence principle, would appear as a distortion of the geocentric lunar orbit in the direction of the sun. The inclusion of recent LLR data limits the size of any such effect to 3 + or - 4 cm. The sensitivities to the various PPN quantities are also highlighted. (2) the geodetic precession of the lunar perigee is predicted by general relativity as a consequence of the motion of the earth-moon system about the sun; its theoretical magnitude is 19.2 mas/yr. Analysis presented here confirms this value and determines this quality to a 2 percent level.

Dickey, J. O.↗
DOE OSTI2024

First Constraints on WIMP-Nucleon Effective Field Theory Couplings in an Extended Energy Region From LUX-ZEPLIN

Following the first science results of the LUX-ZEPLIN (LZ) experiment, a dual-phase xenon time projection chamber operating from the Sanford Underground Research Facility in Lead, South Dakota, USA, we report the initial limits on a model-independent non-relativistic effective field theory describing the complete set of possible interactions of a weakly interacting massive particle (WIMP) with a nucleon. These results utilize the same 5.5 t fiducial mass and 60 live days of exposure collected for the LZ spin-independent and spin-dependent analyses while extending the upper limit of the energy region of interest by a factor of 7.5 to 270~keV. No significant excess in this high energy region is observed. Using a profile-likelihood ratio analysis, we report 90% confidence level exclusion limits on the coupling of each individual non-relativistic WIMP-nucleon operators for both elastic and inelastic interactions in the isoscalar and isovector bases.

Source record↗
DOE OSTI2022

A new generation of effective core potentials from correlated and spin–orbit calculations: Selected heavy elements

We introduce new correlation consistent effective core potentials (ccECPs) for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with 4d, 5d, 6s, and 6p valence spaces. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin–orbit (SO) terms. The construction involves several steps with increasing refinements from more simple to fully correlated methods. The optimizations are carried out with objective functions that include weighted many-body atomic spectra, norm-conservation criteria, and SO splittings. Transferability tests involve molecular binding curves of corresponding hydride and oxide dimers. The constructed ccECPs are systematically better and in a few cases on par with previous effective core potential (ECP) tables on all tested criteria and provide a significant increase in accuracy for valence-only calculations with these elements. Our study confirms the importance of the AREP part in determining the overall quality of the ECP even in the presence of sizable spin–orbit effects. The subsequent quantum Monte Carlo calculations point out the importance of accurate trial wave functions that, in some cases (mid-series transition elements), require treatment well beyond a single-reference.

Wang, Guangming (ORCID:0000000231327925)↗
DOE OSTI2021

Circumbinary Disk Accretion into Spinning Black Hole Binaries

Supermassive black hole binaries are likely to accrete interstellar gas through a circumbinary disk. Shortly before merger, the inner portions of this circumbinary disk are subject to general relativistic effects. To study this regime, we approximate the spacetime metric of close orbiting black holes by superimposing two boosted Kerr–Schild terms. After demonstrating the quality of this approximation, we carry out very long-term general relativistic magnetohydrodynamic simulations of the circumbinary disk. We consider black holes with spin dimensionless parameters of magnitude 0.9, in one simulation parallel to the orbital angular momentum of the binary, but in another anti-parallel. These are contrasted with spinless simulations. We find that, for a fixed surface mass density in the inner circumbinary disk, aligned spins of this magnitude approximately reduce the mass accretion rate by 14% and counter-aligned spins increase it by 45%, leaving many other disk properties unchanged.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2021

Circumbinary Disk Accretion into Spinning Black Hole Binaries

Supermassive black hole binaries are likely to accrete interstellar gas through a circumbinary disk. Shortly before merger, the inner portions of this circumbinary disk are subject to general relativistic effects. To study this regime, we approximate the spacetime metric of close orbiting black holes by superimposing two boosted Kerr–Schild terms. After demonstrating the quality of this approximation, we carry out very long-term general relativistic magnetohydrodynamic simulations of the circumbinary disk. We consider black holes with spin dimensionless parameters of magnitude 0.9, in one simulation parallel to the orbital angular momentum of the binary, but in another anti-parallel. These are contrasted with spinless simulations. We find that, for a fixed surface mass density in the inner circumbinary disk, aligned spins of this magnitude approximately reduce the mass accretion rate by 14% and counter-aligned spins increase it by 45%, leaving many other disk properties unchanged.

AGN↗
NASA NTRS1986

Pulsar timing and general relativity

Techniques are described for accounting for relativistic effects in the analysis of pulsar signals. Design features of instrumentation used to achieve millisecond accuracy in the signal measurements are discussed. The accuracy of the data permits modeling the pulsar physical characteristics from the natural glitches in the emissions. Relativistic corrections are defined for adjusting for differences between the pulsar motion in its spacetime coordinate system relative to the terrestrial coordinate system, the earth's motion, and the gravitational potentials of solar system bodies. Modifications of the model to allow for a binary pulsar system are outlined, including treatment of the system as a point mass. Finally, a quadrupole model is presented for gravitational radiation and techniques are defined for using pulsars in the search for gravitational waves.

Backer, D. C.↗
NASA NTRS1998

The Heats of Formation of GaCl3 and its Fragments

The heats of formation of GaC13 and its fragments are computed. The geometries and frequencies are obtained at the B3LYP level. The CCSD(T) approach is used to solve the correlation problem. The effect of Ga 3d correlation is studied, and found to affect the bond energies by up to 1 kcal/mol. Both basis set extrapolation and bond functions are considered as ways to approach the basis set limit. Spin-orbit and scalar relativistic effects are also considered.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1990

All-electron molecular Dirac-Hartree-Fock calculations: The group 4 tetrahydrides CH4, SiH4, GeH4, SnH4 and PbH4

A basis-set-expansion Dirac-Hartree-Fock program for molecules is described. Bond lengths and harmonic frequencies are presented for the ground states of the group 4 tetrahydrides, CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but non of the RECP's considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.

Dyall, Kenneth G.↗
NASA NTRS1991

All-electron molecular Dirac-Hartree-Fock calculations - The group IV tetrahydrides CH4, SiH4, GeH4, SnH4, and PbH4

A basis-set-expansion Dirac-Hartree-Fock program for molecules is described. Bond lengths and harmonic frequencies are presented for the ground states of the group 4 tetrahydrides, CH4, SiH4, GeH4, SnH4, and PbH4. The results are compared with relativistic effective core potential (RECP) calculations, first-order perturbation theory (PT) calculations and with experimental data. The bond lengths are well predicted by first-order perturbation theory for all molecules, but none of the RECP's considered provides a consistent prediction. Perturbation theory overestimates the relativistic correction to the harmonic frequencies; the RECP calculations underestimate the correction.

Dyall, Kenneth G.↗
NASA NTRS2004

Experimental Design for the LATOR Mission

This paper discusses experimental design for the Laser Astrometric Test Of Relativity (LATOR) mission. LATOR is designed to reach unprecedented accuracy of 1 part in 10(exp 8) in measuring the curvature of the solar gravitational field as given by the value of the key Eddington post-Newtonian parameter gamma. This mission will demonstrate the accuracy needed to measure effects of the next post-Newtonian order (near infinity G2) of light deflection resulting from gravity s intrinsic non-linearity. LATOR will provide the first precise measurement of the solar quadrupole moment parameter, J(sub 2), and will improve determination of a variety of relativistic effects including Lense-Thirring precession. The mission will benefit from the recent progress in the optical communication technologies the immediate and natural step above the standard radio-metric techniques. The key element of LATOR is a geometric redundancy provided by the laser ranging and long-baseline optical interferometry. We discuss the mission and optical designs, as well as the expected performance of this proposed mission. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments.

Turyshev, Slava G.↗
NASA NTRS1997

Interfacing Relativistic and Nonrelativistic Methods: A Systematic Sequence of Approximations

A systematic sequence of approximations for the introduction of relativistic effects into nonrelativistic molecular finite-basis set calculations is described. The theoretical basis for the approximations is the normalized elimination of the small component (ESC) within the matrix representation of the modified Dirac equation. The key features of the normalized method are the retention of the relativistic metric and the ability to define a single matrix U relating the pseudo-large and large component coefficient matrices. This matrix is used to define a modified set of one- and two-electron integrals which have the same appearance as the integrals of the Breit-Pauli Hamiltonian. The first approximation fixes the ratios of the large and pseudo-large components to their atomic values, producing an expansion in atomic 4-spinors. The second approximation defines a local fine-structure constant on each atomic centre, which has the physical value for centres considered to be relativistic and zero for nonrelativistic centres. In the latter case, the 4-spinors are the positive-energy kinetic al ly-balanced solutions of the Levy-Leblond equation, and the integrals involving pseudo-large component basis functions on these centres, are set to zero. Some results are presented for test systems to illustrate the various approximations.

Dyall, Ken↗
NASA NTRS1999

Correlation Consistent Basis Sets for In

Correlation consistent basis sets are developed for a 13 electron correlation treatment of In atom. The basis sets are used in all-electron (AE) and effective core potential (ECP) calculations. The atomization energies of InCl and InCl3 are used as a test of the basis set. The results are extrapolated to the complete basis set (CBS) limit. The AE and ECP CCSD(T) CBS values are in very good mutal when the AE values are corrected for scalar relativistic effects. The best computed values are in good agreement with experiment.

Bauschlicher, Charles W., Jr.↗