Low-energy Behavior Research Articles

Low energy limit from high energy expansion in mass gapped theory

We present a method to extract the low energy behavior of physical observables from their high energy expansions, systematically calculable via the operator product expansion (OPE), in asymptotically free and mass-gapped theories. By applying the inverse Laplace transform to correlation functions, their analytic structure is modified such that low-energy information connects with high energy expansions. Furthermore, this transformation alleviates the renormalon problem, enabling a more straightforward application of the OPE compared to the OPE before the transformation. We demonstrate that the low energy limit of correlation functions can be accurately extracted using the OPE in the two dimensional O(N) nonlinear σ model, serving as a first testing ground.

Bipartite Sachdev-Ye models with Read-Saleur symmetries

We introduce an SU(M)-symmetric disordered bipartite spin model with unusual characteristics. Although superficially similar to the Sachdev-Ye (SY) model, it has several markedly different properties for M≥3. In particular, it has a large nontrivial nullspace whose dimension grows exponentially with system size. The states in this nullspace are frustration-free and are ground states when the interactions are ferromagnetic. The exponential growth of the nullspace leads to Hilbert-space fragmentation and a violation of the eigenstate thermalization hypothesis. We demonstrate that the commutant algebra responsible for this fragmentation is a nontrivial subalgebra of the Read-Saleur commutant algebra of certain nearest-neighbor models such as the spin-1 biquadratic spin chain. We also discuss the low-energy behavior of correlations for the disordered version of this model in the limit of a large number of spins and large M, using techniques similar to those applied to the SY model. We conclude by generalizing the Shiraishi-Mori embedding formalism to nonlocal models, and apply it to turn some of our nullspace states into quantum many-body scars. Published by the American Physical Society 2024

Weyl fermion excitations in the ideal Weyl semimetal CuTlSe2

An ideal Weyl semimetal is characterized by a dispersion in which only Weyl cones intersect the Fermi level, with low-energy behavior being governed by Weyl fermions. Although ideal Weyl semimetals have long been anticipated, only a few are realized in nonmagnetic materials. In this study, we confirm the presence of Weyl-fermion excitations in the ideal Weyl semimetal CuTlSe2 via a combination of magnetoresistance, Hall-effect, magnetic-susceptibility, nuclear magnetic resonance (NMR), and muon-spin relaxation (µSR) experiments. Magnetoresistance measurements reveal a negative longitudinal magnetoresistance (LMR), which scales as B2, while Hall-effect results indicate a predominant contribution from Weyl fermions with a hole-type charge. Magnetic susceptibility and µSR measurements indicate the lack of any intrinsic spontaneous magnetic moments down to base temperature. Finally, the NMR results can be modeled by a two-component effective Hamiltonian, which reproduces well the temperature-dependent Cu63 NMR (T1T)−1 factor, shown to scale as T2 below 100 K and as T1 above 100 K. Overall, we find that the extremely low concentration (1017cm−3) of carriers in CuTlSe2 originates from an ideal nonmagnetic Weyl semimetallic state, persisting up to a thermal excitation energy of 9 meV (100 K), above which trivial electronic bands close to EF take over. Our findings highlight CuTlSe2 as a new member of the intriguing class of Weyl semimetals. Published by the American Physical Society 2024

Beliaev Damping in Bose Gas

According to the Bogoliubov theory the low energy behaviour of the Bose gas at zero temperature can be described by non-interacting bosonic quasiparticles called phonons. In this work the damping rate of phonons at low momenta, the so-called Beliaev damping, is explained and computed with simple arguments involving the Fermi Golden Rule and Bogoliubov’s quasiparticles.

A supersymmetric SYK model with a curious low energy behavior

We consider N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 2, 4 supersymmetric SYK models that have a peculiar low energy behavior, with the entropy going like S = S0 + (constant)Ta, where a ≠ 1. The large N equations for these models are a generalization of equations that have been previously studied as an unjustified truncation of the planar diagrams describing the BFSS matrix quantum mechanics or other related matrix models. Here we reanalyze these equations in order to better understand the low energy physics of these models. We find that the scalar fields develop large expectation values which explore the low energy valleys in the potential. The low energy physics is dominated by quadratic fluctuations around these values. These models were previously conjectured to have a spin glass phase. We did not find any evidence for this phase by using the usual diagnostics, such as searching for replica symmetry breaking solutions.

Lithium inelastic cross-sections and their impact on micro and nano dosimetry of boron neutron capture

Objective. To present a new set of lithium-ion cross-sections for (i) ionization and excitation processes down to 700 eV, and (ii) charge-exchange processes down to 1 keV u−1. To evaluate the impact of the use of these cross-sections on micro a nano dosimetric quantities in the context of boron neutron capture (BNC) applications/techniques. Approach. The Classical Trajectory Monte Carlo method was used to calculate Li ion charge-exchange cross sections in the energy range of 1 keV u−1 to 10 MeV u−1. Partial Li ion charge states ionization and excitation cross-sections were calculated using a detailed charge screening factor. The cross-sections were implemented in Geant4-DNA v10.07 and simulations and verified using TOPAS-nBio by calculating stopping power and continuous slowing down approximation (CSDA) range against data from ICRU and SRIM. Further microdosimetric and nanodosimetric calculations were performed to quantify differences against other simulation approaches for low energy Li ions. These calculations were: lineal energy spectra (yf(y) and yd(y)), frequency mean lineal energy yF― , dose mean lineal energy yD― and ionization cluster size distribution analysis. Microdosimetric calculations were compared against a previous MC study that neglected charge-exchange and excitation processes. Nanodosimetric results were compared against pure ionization scaled cross-sections calculations. Main results. Calculated stopping power differences between ICRU and Geant4-DNA decreased from 33.78% to 6.9%. The CSDA range difference decreased from 621% to 34% when compared against SRIM calculations. Geant4-DNA/TOPAS calculated dose mean lineal energy differed by 128% from the previous Monte Carlo. Ionization cluster size frequency distributions for Li ions differed by 76%–344.11% for 21 keV and 2 MeV respectively. With a decrease in the N 1 within 9% at 10 keV and agreeing after the 100 keV. With the new set of cross-sections being able to better simulate low energy behaviors of Li ions. Significance. This work shows an increase in detail gained from the use of a more complete set of low energy cross-sections which include charge exchange processes. Significant differences to previous simulation results were found at the microdosimetric and nanodosimetric scales that suggest that Li ions cause less ionizations per path length traveled but with more energy deposits. Microdosimetry results suggest that the BNC’s contribution to cellular death may be mainly due to alpha particle production when boron-based drugs are distributed in the cellular membrane and beyond and by Li when it is at the cell cytoplasm regions.

Celestial soft currents at one-loop and their OPEs

Conformally soft operators and their associated soft theorems on the celestial sphere encode the low energy behaviour of bulk scattering amplitudes. They lead to an infinite dimensional symmetry algebra of the celestial CFT at tree-level. In this paper, focusing our attention to Yang-Mills theory, we introduce new operators in the boundary celestial CFT in order to extend the definition of conformally soft currents to include one-loop effects. We then compute their OPEs with other operators in the theory. We also examine new subtleties that arise in defining OPEs of two conformally soft operators. We elucidate the connection between the new operators and loop corrected soft theorems in the bulk. Finally, we conclude by demonstrating how these operators fit into the framework of a logarithmic CFT.

Characteristic features of strong correlation: lessons from a 3-fermion one-dimensional harmonic trap

Abstract Many quantum phenomena responsible for key applications in material science and quantum chemistry arise in the strongly correlated regime. This is at the same time, a costly regime for computer simulations. In the limit of strong correlation analytic solutions exist, but as we move away from this limit numerical simulation are needed, and accurate quantum solutions do not scale well with the number of interacting particles. In this work we propose to use few-particle harmonic traps in combination with twisted light as a quantum emulator to investigate the transition into a strongly-correlated regime. Using both analytic derivations and numerical simulations we generalize previous findings on 2 Coulomb interacting fermions trapped in a one-dimensional harmonic trap to the case of 3 fermions. The 4 signatures of strong correlation we have identified in the one-dimensional harmonic trap are: (i) the ground state density is highly localized around N equilibrium positions, where N is the number of particles, (ii) the symmetric and antisymmetric ground state wavefunctions become degenerate, (iii) the von Neumann entropy grows, (iv) the energy spectrum is fully characterized by N normal modes or less. Our findings describe the low-energy behavior of electrons in quantum wires and ions in Paul traps. Similar features have also been reported for cold atoms in optical lattices.

Elastic cross section data for precursor molecules used in low-temperature plasmas: Sn(CH3)4 and Ga(CH3)3

Tetramethyltin [Sn(CH3)4] and trimethylgallium [Ga(CH3)3] are important source molecules of Sn and Ga atoms which are used in manufacturing techniques involving low-temperature plasmas. Accurate numerical modeling of plasma environments requires a comprehensive set of electron scattering cross sections by these precursor molecules. Here, we report the elastic integral, differential, and momentum transfer cross sections for electron collisions with Sn(CH3)4 and Ga(CH3)3 for energies ranging from 0 to 30 eV. Our calculations were carried out with the Schwinger multichannel method implemented with pseudopotentials and considered two levels of approximation in our calculations, namely static-exchange and static-exchange plus polarization. We identified three shape resonances for Sn(CH3)4 and one clear low-lying resonance for Ga(CH3)3. The low-energy behavior of the s-wave cross section and eigenphase was investigated and, for both molecules, we found evidence of a Ramsauer–Townsend (RT) minimum and a virtual state. Our results indicate that negative differential conductivity would occur in a gas composed of Sn(CH3)4. On the other hand, this effect would be suppressed in a gas of Ga(CH3)3 due to an overlap between the position of the RT minimum and the shape resonance in the momentum-transfer cross section.

Simulating a numerical UV completion of quartic Galileons

The Galileon theory is a prototypical effective field theory that incorporates the Vainshtein screening mechanism—a feature that arises in some extensions of general relativity, such as massive gravity. The Vainshtein effect requires that the theory contain higher order derivative interactions, which results in Galileons, and theories like them, failing to be technically well posed. While this is not a fundamental issue when the theory is correctly treated as an effective field theory, it nevertheless poses significant practical problems when numerically simulating this model. These problems can be tamed using a number of different approaches: introducing an active low-pass filter and/or constructing a UV completion at the level of the equations of motion, which controls the high momentum modes. These methods have been tested on cubic Galileon interactions, and have been shown to reproduce the correct low-energy behavior. Here we show how the numerical UV-completion method can be applied to quartic Galileon interactions, and present the first simulations of the quartic Galileon model using this technique. We demonstrate that our approach can probe physics in the regime of the effective field theory in which the quartic term dominates, while successfully reproducing the known results for cubic interactions. Published by the American Physical Society 2024

Complete UV resonances of the dimension-8 SMEFT operators

The effective field theory approach parameterizes the low energy behaviors of all possible ultraviolet (UV) theories in a systematic way. One of the most important tasks is thus to find the connection between the effective operators and their UV origins. The redundancy relations among operators make the connection very subtle, hence we proposed the J-basis prescription to illuminate the correspondence between operators and their UV resonances in the bottom-up way. In this work, we work out the dimension-8 J-basis operators in the standard model effective field theory (SMEFT), and find all the 146 (82) tree-level UV resonances along with their couplings up to mass dimension 5 (4). Furthermore, we point out a few subtleties on operator generation via field redefinition and on the UV Lagrangian for generic spin resonances. We also provide a data base storing our results and a Mathematica notebook for extracting those results for the reader’s conveinence.

Signatures of Hund metal and finite-frequency nesting in Sr2RuO4 revealed by electronic Raman scattering

We investigate the electronic Raman scattering of Sr2RuO4 using a material-realistic dynamical mean-field theory approach. We identify the low-energy Fermi liquid behavior and point out that the enhanced Raman response at higher energies is a fingerprint of Hund metals. These signatures originate in the two-stage coherence of Hund metals and associated quasiparticle “unrenormalization.” In agreement with recent experimental observations, we find the B1g and B2g responses differ, but our calculations suggest a novel interpretation of this dichotomy. The B1g response is dominated by the xy orbital and the B2g response receives contributions from all orbitals and is strongly affected by previously unnoticed finite-frequency interband nesting. We calculate the vertex-corrections to Raman response and show that their effect is nonvanishing but small. Published by the American Physical Society 2024

Weakly interacting Bose gas with two-body losses

We study the many-body dynamics of weakly interacting Bose gases with two-particle losses. We show that both the two-body interactions and losses in atomic gases may be tuned by controlling the inelastic scattering process between atoms by an optical Feshbach resonance. Interestingly, the low-energy behavior of the scattering amplitude is governed by a single parameter, i.e. the complex ss-wave scattering length a_cac. The many-body dynamics are thus described by a Lindblad master equation with complex scattering length. We solve this equation by applying the Bogoliubov approximation in analogy to the closed systems. Various peculiar dynamical properties are discovered, some of them may be regarded as the dissipative counterparts of the celebrated results in closed Bose gases. For example, we show that the next-order correction to the mean-field particle decay rate is to the order of |n a_c^{3}|^{1/2}|nac3|1/2, which is an analogy of the Lee-Huang-Yang correction of Bose gases. It is also found that there exists a dynamical symmetry of symplectic group Sp(4,\mathbb{C})(4,ℂ) in the quadratic Bogoliubov master equation, which is an analogy of the SU(1,1) dynamical symmetry of the corresponding closed system. We further confirmed the validity of the Bogoliubov approximation by comparing its results with a full numerical calculation in a double-well toy model. Generalizations of other alternative approaches such as the dissipative version of the Gross-Pitaevskii equation and hydrodynamic theory are also discussed in the last.

Experimental and numerical investigation of impact behavior in honeycomb sandwich composites

This paper presents an experimental and numerical study on the low-energy impact fatigue and bending behavior of sandwich panels reinforced with composite laminate glass and carbon fabric facesheets, supported by a honeycomb core made of Nomex. The crushing behavior of honeycomb sandwich specimens subjected to the impact test was compared and discussed. Our results indicate that the carbon composite facesheets have a significant effect on the impact, resulting in an increase in impact resistance and a 157.14% increase in crack depth in the elastic region compared to glass facesheets reinforcement. This increase serves as an indicator of the laminate's ability to resist damage initiation and impact fracture mechanisms. Also, an increasing in flexural strength about 45.72% was observed in carbon facesheets honeycomb specimens compared to glass facesheets reinforcement. Microscopic illustration of the damaged honeycomb sandwich specimens was conducted to evaluate the interfacial characteristics and describe the damage mechanics of the composite facesheets and core adhesion under the impact test. The numerical approach proves to be efficient in terms of accuracy and simplicity compared to existing methods for predicting the damage mechanisms of honeycomb sandwich structures. It was noted that results of numerical study show best agreements with experiment results and the model can be used to predict the low-energy impact fatigue.

Universal correlations along the BEC-BCS crossover

Universality of the long-distance behavior across the Bardeen–Cooper–Schrieffer (BEC)-Bose–Einstein condensate (BCS) smooth transition for two-body density correlation functions and the Cooper-pair probability density is demonstrated in a balanced mixture of a two-component Fermi gas at T = 0. It is numerically shown at the mean-field level that these two-body quantities exhibit an exponential decay in terms of the chemical potential and the low-energy behavior of the gap. A general expression is found for the two-body distributions holding for different features of finite-range potentials, such as divergences at the origin, discontinuities at a finite radius, power-law decay, and exponential decay. The correlation length characterizing the long-distance behavior unravels the dependence on the energy needed to break pairs along the BEC-BCS crossover, a quantity meaningful to the stability of the many-body state.

Simple Route to [PSH][B9H14] and a Contemporary Study of Its Solid-State Dynamic Behavior.

The 1,8-bis(dimethylamino)naphthalenium ([PSH]+) decaborane salt, [PSH][B10H13], has been found to react in ethanol to form [PSH][B9H14] (1), affording a simple route to the synthesis of the arachno-nonaborate anion. This new polyhedral salt is characterized by NMR spectroscopy and X-ray diffraction. The measurement of diffusion coefficients by NMR methods demonstrates that the [PSH]+ cation and the [B9H14]- anion form ion pairs in a non-coordinating solvent such as CH2Cl2, whereas in CD3CN the formation of ion pairs was not observed. Insights into the long-known low-energy dynamic behavior, which involves the bridging and endo-terminal hydrogen atoms, are elucidated using DFT calculations. Salts [PSH][B9H14] (1) and [PSH][B9H14]·0.5CHCl3 (solvated, 1·0.5CHCl3) have also been studied by X-ray diffraction analysis. A solid-state NMR study has demonstrated that K[B9H14] and [PSH][B9H14] (1) undergo significantly different motion regimes, being a low-energy, weakly temperature-dependent process for 1, which may be ascribed to some type of low-amplitude reorientation of the whole boron cages. This process may be the mechanism for the low- to-room-temperature order-disorder hidden transition found by X-ray analysis.

Cold Ion-Molecule Chemistry: The Very Different Reactions of He⁺ with CO and NO.

The ion-molecule reactions He+ + CO → He + C+ + O and He+ + NO → He + N+ + O have been measured at collision energies between 0 and kB · 10 K. Strong variations of the rate coefficients are observed below kB · 5 K. The rate of the He+ + CO reaction decreases by ~30% whereas that of the He+ + NO reaction increases by a factor of ~1.5. These observations are interpreted in the realm of an adiabatic-channel capture model as arising from interactions between the ion charge and the dipole and quadrupole moments of CO and NO. We show that the different low-energy behavior of these reactions originates from the closed- vs. open-shell electronic structures of CO and NO.

A model of pseudo-Nambu–Goldstone dark matter from a softly brokenSU(2) global symmetry with aU(1) gauge symmetry

AbstractA model of the pseudo-Nambu–Goldstone (pNG) dark matter (DM) is proposed. We assume that there is an SU(2)g global symmetry and a U(1)X gauge symmetry in the dark sector, and they are spontaneously broken into a U(1)D global symmetry after a scalar field develops a vacuum expectation value. We add a soft symmetry-breaking term that breaks the SU(2)g global symmetry into the U(1)g global symmetry explicitly. Our model predicts a stable complex pNG particle under the U(1)D global symmetry. One of the virtues of the pNG DM models is that the models can explain the current null results of the direct detection experiments. The small momentum transfer suppresses the scattering amplitudes thanks to the low-energy behavior of the Nambu–Goldstone boson. In our model, the soft symmetry-breaking term is uniquely determined. This is the advantage of our model compared to some earlier works in which some soft symmetry-breaking terms cannot be forbidden but are simply assumed to be absent to avoid the constraints from the direct detection experiments. We calculate the thermal relic abundance of the pNG DM and find that the model can explain the measured value of the DM energy density under some constraints from perturbative unitarity.

Thermoplastic polyurethane film performance improvement by incorporation of furfuryl alcohol and polydimethylsiloxane

Thermoplastic polyurethanes (TPUs) films, widely used in industry and domestic, are required to have self/stimulate-healing ability and multifunction to achieve its recycling usage and adapt complex environment. Herein, the novel TPUs (PDMS/FA-PUDAs) were prepared by incorporation of biomass furfuryl alcohol (FA) and non-toxic polydimethylsiloxane (PDMS) through classic polymerization route accompanied by Diels-Alder (DA) reaction. This study investigated the combined effect of DA/rDA reaction and PDMS on improving TPU films' stimulate-healing, mechanical and anti-adhesion properties by adjusting PDMS additive amount. The experimental results demonstrated that 10 wt% PDMS and FA modified TPU film (10 % PDMS/FA-PUDA) still remained high stimulate-healing efficiency (73.48 %) after three times repair process, owing to the DA/rDA reaction was reversible between FA and bismaleimide (BMI). Besides, 10 % PDMS/FA-PUDA had superior pristine mechanical properties (Ts: 72.06 MPa, Eb: 162.45 %, Tt: 10.89 MJ/m3) because PDMS promoted the formation of microphase separation structure. Moreover, the film surface presented low surface free energy (16.79 mJ/m2) and satisfactory anti-adhesion behavior ascribed to the hydrophobicity of PDMS. This investigation might give a new perspective for designing multifunctional TPU using renewable and non-toxic materials.

Studies of the low-energy neutral behavior using the low-energy neutral particle analyzer on EAST

• The neutral energy spectrums with an energy range of 20–3000 eV was measured by the low energy neutral particle analyzer (LENPA). • In the LENPA detection range, more than 85 % of neutral particles are in the energy range of 20–1000 eV. • The integrated neutral flux in the energy range of 20–1000 eV increases with line-averaged density in ohmic discharges due to the increased charge exchange reaction rates in a higher density plasma. • Due to the deeper penetration depth by SMBI fueling, the neutral particles are generated closer to the core plasma and have higher energy. • The neutral flux increases with heating power in all energy range. The neutral energy spectrums with an energy range of 20–3000 eV was measured by the low energy neutral particle analyzer (LENPA) in the 2021 EAST summer campaign. The proportion of the neutral particles below 1000 eV measured by LENPA is more than 85 %. In the ohmic discharges, the integrated neutral flux increases with increasing the line-averaged density. However, the neural particles with higher energy (1000–3000 eV) are insensitive to the line-averaged density. In addition, the neutral flux in the energy range of 20–1000 eV of the discharges with supersonic molecular beam injection (SMBI) was lower than those without SMBI, which was different from neutrals in the range of 1000–3000 eV. The neutral flux increases with higher auxiliary heating power in all energy range. Compared to the ohmic discharges, the mean energy of neutral particles in auxiliary heated discharges is increased significantly.