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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

On the planar limit of 3d $$ {\mathrm{T}}_{\rho}^{\sigma}\left[\mathrm{SU}\left(\mathrm{N}\right)\right] $$

A bstract We discuss a limit of 3d $$ {T}_{\rho}^{\sigma}\left[\mathrm{SU}(N)\right] $$ T ρ σ SU N quiver gauge theories in which the number of nodes is large and the ranks scale quadratically with the length of the quiver. The sphere free energies and topologically twisted indices are obtained using supersymmetric localization. Both scale quartically with the length of the quiver and quadratically with N , with trilogarithm functions depending on the quiver data as coefficients. The IR SCFTs have well-behaved supergravity duals in Type IIB, and the free energies match precisely with holographic results. Previously discussed theories with N 2 ln N scaling arise as limiting cases. Each balanced 3d quiver theory is linked to a 5d parent, whose matrix model is related and dominated by the same saddle point, leading to close relations between BPS observables.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Dark matter absorption via electronic excitations

We revisit the calculation of bosonic dark matter absorption via electronic excitations. Working in an effective field theory framework and consistently taking into account in-medium effects, we clarify the relation between dark matter and photon absorption. As is well-known, for vector (dark photon) and pseudoscalar (axion-like particle) dark matter, the absorption rates can be simply related to the target material’s optical properties. However, this is not the case for scalar dark matter, where the dominant contribution comes from a different operator than the one contributing to photon absorption, which is formally next-to-leading-order and does not suffer from in-medium screening. It is therefore imperative to have reliable first-principles numerical calculations and/or semi-analytic modeling in order to predict the detection rate. We present updated sensitivity projections for semiconductor crystal and superconductor targets for ongoing and proposed direct detection experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1974

Coherent propagation of charged-particle bunches in random magnetic fields

When the distribution function for energetic particles moving in interplanetary space is expressed in terms of eigenfunctions of an operator which describes pitch-angle scattering by random magnetic fields, the familiar phenomenon of diffusion is the dominant solution of the transport equations provided that the spectrum of magnetic fluctuations is not too steep. However, if the power-versus-wavenumber spectrum of the random fields has a spectral index greater than 2, the dominant solution of the same equations is a qualitatively different mode of transport in which density inhomogeneities propagate coherently along the guiding field with a characteristic velocity equal to half the particle speed. The present work, which extends classical transport theory to give a detailed treatment of the new mode, presents explicit formulae which describe the spatial and temporal structure of the coherent disturbance. It is shown that this disturbance evolves asymptotically into a moving Gaussian pulse whose width increases with time.

Earl, J. A.↗
NASA NTRS1994

An estimate of the momentum deposition in the lower thermosphere by the observed diurnal tide

This paper reports a calculation of the acceleration of the zonal mean flow induced by dissipating tides in the equatorial lower thermosphere. Estimates of the gravest symmetric gravitiational Hough mode (1,1) of the migrating diurnal tide are obtained from monthly composites of global winds observed by the Upper Atmosphere Research Satellite (UARS) High Resolution Doppler Imager (HRDI). Using the principles of classical tidal theory, the tidal momentum flux divergence is computed for a series of monthly mean (1,1) fields from January 1992 to May 1993. The contribution to the mean flow by the leading mode of the migrating tide ranges between -5 and -20 (easterly) m/s/day in the equatorial lower thermosphere. A semiannual variation is noted in the tidal amplitudes and the inferred tidal accelerations. These variations are consistent with observed trends in the zonal mean flow of the lower thermosphere.

Lieberman, Ruth S.↗
NASA NTRS1995

Light response of phytoplankton in the South Atlantic Ocean: Interpretation of observations and application to remote sensing

A simplified, nonspectral derivation of a classical theory in plant physiology is presented and used to derive an absorption-based primary productivity algorithm. Field observations from a meridional transect (4 deg N to 42 deg S) in the Atlantic Ocean are then described and interpreted in this theoretical context. The observations include photosynthesis-irradiance curve parameters (alpha and P(sub max)), chlorophyll a and phaeopigment concentration, and estimated phytoplankton absorption coefficients at wavelength = 440 nm (a(sub ph)(440)). Observations near the top (50% I(sub 0)) and bottom (6% I(sub 0)) of the euphotic zone are contrasted. At both light levels, alpha, P(sub max), a(sub ph)(440), and pigment concentration varied similarly along the transect: values were highest at the equator and at the southern end of the transect and lowest in the central South Atlantic. It is concluded that this pattern was related to increased nutrient availability due to equatorial upwelling in the north, and increased wind mixing in the south. At the 50% light level, alpha increased relative to a(sub ph) at the southern end of the transect. This result appears to reflect a large-scale meridional (southward) increase in the average quantum efficiency of the photosynthetic units of the phytoplankton. A correlation analysis of the data reveals that at the 50% light level, variations in P(sub max) were more closely related to a(sub ph)(440) than chlorophyll concentration and that phytoplankton absorption explains 90% of the variability in P(sub max). In theory, this shows that the ratio of the average quantum efficiency of the photosynthetic units of the phytoplankton to the product of their average absorption cross section and turnover time is relatively constant. This result is used to simplify the absorption-based primary productivity algorithm derived previously. The feasibility of using this model to estimate production rate from satellite ocean color observations is discussed. It is concluded that an absorption-based algorithm should provide more accurate production rate estimates than one based upon chlorophyll (pigment) concentration.

Hood, Raleigh R.↗
DOE OSTI2021

On restricting first order form of gauge theories to one-loop order

Highlights: • We prove the equivalence of the first and second-order formalism. • We use Lagrange multiplier fields to limit radiative effects to one-loop order. • We prove that the quantized theory is both renormalizable and unitary. The first order form of the Yang–Mills and Einstein–Hilbert actions are quantized, and it is shown how Green’s functions computed using the first and the second order form of these theories are related. Next we show how by use of Lagrange multiplier fields (LM), radiative effects beyond one-loop order can be eliminated. This allows one to compute Green’s functions exactly without loss of unitarity. The consequences of this restriction on radiative effects are examined for the Yang–Mills and Einstein–Hilbert actions. In these two gauge theories, we find that the quantized theory is both renormalizable and unitary once the LM field is used to eliminate effects beyond one-loop order.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Quantum chaos and unitary black hole evaporation

The formation and evaporation of small AdS black holes in a theory with a holographic dual is governed by the usual rules of quantum mechanics. The eigenstate thermalization hypothesis explains the validity of semiclassical gravity for local bulk observables and can be used to quantify the magnitude of quantum corrections to the semi-classical approximation. The holographic dual produces a basis of black hole states with finite energy width, and observables that are smooth functions on the classical phase space will self-average over a large number of energy eigenstates, exponential in the Bekenstein-Hawking entropyS, leading to results that are consistent with semiclassical gravity up to small corrections of order e –S/2 . As expected, the semiclassical description breaks down for transition amplitudes that reflect the unitary evolution of the holographic theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Solidity without inhomogeneity: perfectly homogeneous, weakly coupled, UV-complete solids

Solid-like behavior at low energies and long distances is usually associated with the spontaneous breaking of spatial translations at microscopic scales, as in the case of a lattice of atoms. We exhibit three quantum field theories that are renormalizable, Poincaré invariant, and weakly coupled, and that admit states that on the one hand are perfectly homogeneous down to arbitrarily short scales, and on the other hand have the same infrared dynamics as isotropic solids. All three examples presented here lead to the same peculiar solid at low energies, featuring very constrained interactions and transverse phonons that always propagate at the speed of light. In particular, they violate the well known c$^2_L$>$\frac{4}{3}$c$^2_T$ bound, thus showing that it is possible to have a healthy renormalizable theory that at low energies exhibits a negative bulk modulus (we discuss how the associated instabilities are absent in the presence of suitable boundary conditions). We do not know whether such peculiarities are unavoidable features of large scale solid-like behavior in the absence of short scale inhomogeneities, or whether they simply reflect the limits of our imagination.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

State-operator correspondence in celestial conformal field theory

The bulk-to-boundary dictionary for 4D celestial holography is given a new entry defining 2D boundary states living on oriented circles on the celestial sphere. The states are constructed using the 2D CFT state-operator correspondence from operator insertions corresponding to either incoming or outgoing particles which cross the celestial sphere inside the circle. The BPZ construction is applied to give an inner product on such states whose associated bulk adjoints are shown to involve a shadow transform. Scattering amplitudes are then given by BPZ inner products between states living on the same circle but with opposite orientations. 2D boundary states are found to encode the same information as their 4D bulk counterparts, but organized in a radically different manner.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Causality, unitarity and symmetry in effective field theory

Sum rules in effective field theories, predicated upon causality, place restrictions on scattering amplitudes mediated by effective contact interactions. Through unitarity of the S -matrix, these imply that the size of higher dimensional corrections to transition amplitudes between different states is bounded by the strength of their contributions to elastic forward scattering processes. This places fundamental limits on the extent to which hypothetical symmetries can be broken by effective interactions. All analysis is for dimension 8 operators in the forward limit. Included is a thorough derivation of all positivity bounds for a chiral fermion in SU(2) and SU(3) global symmetry representations resembling those of the Standard Model, general bounds on flavour violation, new bounds for interactions between particles of different spin, inclusion of loops of dimension 6 operators and illustration of the resulting strengthening of positivity bounds over tree-level expectations, a catalogue of supersymmetric effective interactions up to mass dimension 8 and 4 legs and the demonstration that supersymmetry unifies the positivity theorems as well as the new bounds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Fractons and Exotic Symmetries from Branes

The emerging study of fractons, a new type of quasi-particle with restricted mobility, has motivated the construction of several classes of interesting continuum quantum field theories with novel properties. One such class consists of foliated field theories which, roughly, are built by coupling together fields supported on the leaves of foliations of spacetime. Another approach, which we refer to as exotic field theory, focuses on constructing Lagrangians consistent with special symmetries (like subsystem symmetries) that are adjacent to fracton physics. A third framework is that of infinite-component Chern-Simons theories, which attempts to generalize the role of conventional Chern-Simons theory in describing (2+1)D Abelian topological order to fractonic order in (3+1)D. The study of these theories is ongoing, and many of their properties remain to be understood. Historically, it has been fruitful to study QFTs by embedding them into string theory. One way this can be done is via D-branes, extended objects whose dynamics can, at low energies, be described in terms of conventional quantum field theory. Further, QFTs that can be realized in this way can then be analyzed using the rich mathematical and physical structure of string theory. In this paper, we show that foliated field theories, exotic field theories, and infinite-component Chern-Simons theories can all be realized on the world-volumes of branes. We hope that these constructions will ultimately yield valuable insights into the physics of these interesting field theories.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Exotic $\mathbb{Z}_N$ symmetries, duality, and fractons in 3+1-dimensional quantum field theory

Following our earlier analyses of nonstandard continuum quantum field theories, we study here gapped systems in 3+1 dimensions, which exhibit fractonic behavior. In particular, we present three dual field theory descriptions of the low-energy physics of the X-cube model. A key aspect of our constructions is the use of discontinuous fields in the continuum field theory. Spacetime is continuous, but the fields are not.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Exotic symmetries, duality, and fractons in 2+1-dimensional quantum field theory

We discuss nonstandard continuum quantum field theories in 2+1 dimensions. They exhibit exotic global symmetries, a subtle spectrum of charged excitations, and dualities similar to dualities of systems in 1+1 dimensions. These continuum models represent the low-energy limits of certain known lattice systems. One key aspect of these continuum field theories is the important role played by discontinuous field configurations. In two companion papers, we will present 3+1-dimensional versions of these systems. In particular, we will discuss continuum quantum field theories of some models of fractons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Corrected calculation for the non-local solution to the g − 2 anomaly and novel results in non-local QED

We provide the corrected calculation of the (g − 2) μ in non-local QED previously done in the literature. In specific, we show the proper technique for calculating loops in non-local QED and use it to find the form factors F 1 (q 2 ) and F 2 (q 2 ) in non-local QED. We also utilize this technique to calculate some novel results in non-local QED, including calculating the correction to the photon self-energy, the modification to the classical Coulomb potential, the modification to the energy levels of the hydrogen atom, and the contribution to the Lamb shift. We also discuss charge dequantization through non-locality, and show that the experimental bounds on the electric charge on Dirac neutrinos, translate into strong flavor-dependent bounds on the scale on non-locality that range between 10 5 −10 10 TeV. We also discuss the inconsistencies of unrenormalized non-local Quantum Field Theories (QFTs) and the need for renormalizing them, even when they are free from UV divergences.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Dynamics of homogeneous cavitation with pressure feedback

Theoretical studies of homogeneous cavitation have largely been based on the classical nucleation theory. However, existing cavitation models cannot adequately describe its dynamics at nanosecond timescale, which has been called for in other fields. We develop a model coupling nucleation kinetics with cavity growth and pressure feedback as saturation mechanisms. Our numerical studies reveal the exponential dependence of cavitation characteristics such as saturation cavity density and most probable cavity radius on model parameters: Tolman length and initial pressure. This work also sheds light on the possibility of accurately determining Tolman length, whose value has a large spread in the literature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Optical response of a dual membrane active–passive optomechanical cavity

Highlights: • The optical response is determined by competition between photon-tunneling, two-phonon process, gain effect. • The photon-tunneling adjusts supermode frequency. • The absorption coefficient can exceed 1. • Not only realize fast/slow light but conversion between fast and slow light. We investigate a dual membrane active–passive cavity where each mechanical membrane individually quadratically coupled to passive and active cavities via two-phonon process. Due to the fact that in the quadratically coupled optomechanical system mean-field approximation fails, hence to analyze the system completely, we switch to a more generalized out of equilibrium approach, namely Keldysh Green’s functional approach. We calculate transmission rate using predetermined full retarded Green’s function, and then numerically examine the effect of the various parameters on the transmission coefficient and discuss the features and physical mechanism behind them in detail. On the basis of the optical responsivity we further extend our study to fast and slow light phenomenon. The results show that our proposed system can not only realize ultra-fast/ultra-slow light under proper choice of cavity parameters but also a realization of the conversion between fast and slow light and vice versa has also been pointed out.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

A perspective on single-crystal layered oxide cathodes for lithium-ion batteries

As the demand for lithium-ion batteries grows exponentially to feed the nascent electric-vehicle and grid-storage markets, the need for higher energy density and longer cycle life becomes more apparent. Increasing the nickel content in the layered-oxide cathodes has been a dominant strategy to increase energy density, but this has exacerbated the surface reactivity concerns. Furthermore, the high states of charge associated with increased capacity lead to cracking of the polycrystalline cathode particles, which exposes fresh surfaces and accelerates capacity fade. Single-crystal cathode particles with low susceptibility to cracking have recently taken on intense interest due to their remarkable cyclability. Many different approaches to single-crystal synthesis have been explored, but there has been no systematic analysis of the different techniques to date. Additionally, many reports have taken on a trial-and-error approach, ignoring well established literature on grain growth outside the battery field. This perspective reviews the literature on single-crystal cathode synthesis through the lens of classic grain growth theories, providing insight and hopefully accelerating the adoption of the promising single-crystal cathode morphology.

25 ENERGY STORAGE↗