Low-energy Behavior Research Articles

Coulomb and Nuclear Breakup at Low Energies: Scaling Laws

We report on a recent work on the low-energy behavior of the breakup cross section in so far as it has important role in the fusion of weakly bound and halo nuclei at near-barrier energies. We assess the way the nuclear component of this cross section scales with the target mass. In complete accord with previous finding at higher energies we verify that the low energy behavior of the breakup cross section for a given projectile and relative center of mass energy with respect to the Coulomb barrier height scales as the cubic root of the mass number of the target. Surprisingly we find that the Coulomb component of the breakup cross section at these low energies also obeys scaling, but with a linear dependence on the target charge. Our findings are important when planning for experiments involving these exotic nuclei.

Discovering new gauge bosons of electroweak symmetry breaking at LHC-8

We study the physics potential of the 8 TeV LHC (LHC-8) to discover, during its 2012 run, a large class of extended gauge models or extradimensional models whose low-energy behavior is well represented by an $SU(2{)}^{2}\ensuremath{\bigotimes}U(1)$ gauge structure. We analyze this class of models and find that, with a combined integrated luminosity of $40--60\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ at the LHC-8, the first new Kaluza-Klein mode of the $W$ gauge boson can be discovered up to a mass of about 370--400 GeV when produced in association with a $Z$ boson.

Holographic fermions in charged dilaton black branes

By imposing the relativistic boundary term and Lorentz violating that in the dilatonic black brane with a Lifshitz like IR geometry and AdS4 boundary, we study the properties of the spectral functions of the fermions. We find that in the two fixed points, there are emergent Fermi-surface structures and many properties seem to be in agreement with that of Fermi liquid. Especially, the low energy behavior exhibits a linear dispersion relation. In addition, we also find that a holographic flat band also emerges in this background of the dilatonic black brane.

Phase diagram and critical points of a double quantum dot

We apply a combination of numerical renormalization group (NRG) and renormalized perturbation theory (RPT) to a model of two quantum dots (impurities) described by two Anderson impurity models hybridized to their respective baths. The dots are coupled via a direct interaction $U_{12}$ and an exchange interaction $J$. The model has two types of quantum critical points, one at $J=J_c$ to a local singlet state and one at $U_{12}=U_{12}^c$ to a locally charge ordered state. The renormalized parameters which determine the low energy behavior are calculated from the NRG. The results confirm the values predicted from the RPT on the approach to the critical points, which can be expressed in terms of a single energy scale $T^*$ in all cases. This includes cases without particle-hole symmetry, and cases with asymmetry between the dots, where there is also a transition at $J=J_c$. The results give a comprehensive quantitative picture of the behavior of the model in the low energy Fermi liquid regimes, and some of the conclusions regarding the emergence of a single energy scale may apply to a more general class of quantum critical points, such as those observed in some heavy fermion systems.

Laboratory Investigation on the Feasibility of Light-Oil Autoignition for Application of the High-Pressure Air Injection (HPAI) Process

Whether thermal effects have a contribution on oil recovery mechanisms in the high-pressure air injection (HPAI) process in a light-oil reservoir has confused many people over several decades. The argument is due to the lack of convictive evidence from both direct laboratory and simulation studies. This paper is the prelusion for the subsequent study for a better understanding of the influence of thermal effects on oil production. In a previous study, thermogravimetry/differential thermogravimetry (TG/DTG) and differential thermal analysis (DTA) tests were employed to investigate the kinetic parameters and exothermic behavior of Keke Ya light crude oil (Tarim Basin, China) and oil + cuttings, showing that Keke Ya light crude oil as well as oil + cuttings exhibited very low activation energy and favorable exothermic behavior. In this study, we develop a thermal effect monitoring device, which is similar to the isothermal oxidation tube, and we have detected the obvious exothermic phenomenon of Keke Ya light crude oil in porous media in the isothermal aging test at reservoir conditions (80 °C and 16.7 MPa). The witness of the combustion (or high-temperature) process is exhibited, which is expressed in specific characteristics made up of the self-heating behavior, low hydrogen/carbon (H/C) ratio of 1.50 from gas composition analysis, and generated precipitation coverings (halite crystalloid) in the core section surface through scanning electron microscopy (SEM) analysis. This study provides new insight that thermal effects should exist during the light-oil isothermal aging process in porous media and proposes a laboratory analysis method to understand the feasibility of light-oil autoignition at the oil-bearing reservoir during application of HPAI.

Phenomenology of a semi-Dirac semi-Weyl semimetal

We extend the semiclassical study of fermionic particle-hole symmetric semi-Dirac (more appropriately, semi-Dirac semi-Weyl) dispersion of quasiparticles, ${\ensuremath{\varepsilon}}_{K}=\ifmmode\pm\else\textpm\fi{}\sqrt{({k}_{x}^{2}{/2m)}^{2}+{(v{k}_{y})}^{2})}=\ifmmode\pm\else\textpm\fi{}{\ensuremath{\varepsilon}}_{0}\sqrt{{K}_{x}^{4}+{K}_{y}^{2}}$ in dimensionless units, discovered computationally in oxide heterostructures by Pardo and collaborators. This unique system is a highly anisotropic sister phase of both (symmetric) graphene and what has become known as a Weyl semimetal, having ${\ensuremath{\langle}{v}_{y}^{2}\ensuremath{\rangle}}^{1/2}\ensuremath{\approx}v$ independent of energy, and ${\ensuremath{\langle}{v}_{x}^{2}\ensuremath{\rangle}}^{1/2}\ensuremath{\propto}{m}^{\ensuremath{-}1/2}\sqrt{\ensuremath{\varepsilon}}$ being very strongly dependent on energy ($\ensuremath{\varepsilon}$) and depending only on the effective mass $m$. Each of these systems is distinguished by bands crossing (sometimes referred to as touching) at a point Fermi surface, with one consequence being that for this semi-Dirac system the ratio $|{\ensuremath{\chi}}_{\mathrm{orb}}/{\ensuremath{\chi}}_{\mathrm{sp}}|$ of orbital to spin susceptibilities diverges at low doping. We extend the study of the low-energy behavior of the semi-Dirac system, finding the plasmon frequency to be highly anisotropic while the Hall coefficient scales with carrier density in the usual manner. The Faraday rotation behavior is also reported. For Klein tunneling at normal incidence on an arbitrarily oriented barrier, the kinetic energy mixes both linear (massless) and quadratic (massive) contributions depending on orientation. Analogous to graphene, perfect transmission occurs under resonant conditions, except for the specific orientation that eliminates massless dispersion. Comparisons of the semi-Dirac system are made throughout with both other types of point Fermi surface systems.

Higher-order renormalization of graphene many-body theory

We study the many-body theory of graphene Dirac quasiparticles interacting via the long-range Coulomb potential, taking as a starting point the ladder approximation to different vertex functions. We test in this way the low-energy behavior of the electron system beyond the simple logarithmic dependence of electronic correlators on the high-energy cutoff, which is characteristic of the large-N approximation. We show that the graphene many-body theory is perfectly renormalizable in the ladder approximation, as all higher powers in the cutoff dependence can be absorbed into the redefinition of a finite number of parameters (namely, the Fermi velocity and the weight of the fields) that remain free of infrared divergences even at the charge neutrality point. We illustrate this fact in the case of the vertex for the current density, where a complete cancellation between the cutoff dependences of vertex and electron self-energy corrections becomes crucial for the preservation of the gauge invariance of the theory. The other potentially divergent vertex corresponds to the staggered (sublattice odd) charge density, which is made cutoff independent by a redefinition in the scale of the density operator. This allows to compute a well-defined, scale invariant anomalous dimension to all orders in the ladder series, which becomes singular at a value of the interaction strength marking the onset of chiral symmetry breaking (and gap opening) in the Dirac field theory. The critical coupling we obtain in this way matches with great accuracy the value found with a quite different method, based on the resolution of the gap equation, thus reassuring the predictability of our renormalization approach.

The gradient flow of the [formula omitted] curvature energy near the round sphere

We investigate the low-energy behavior of the gradient flow of the L2 norm of the Riemannian curvature on four-manifolds. We show long time existence and exponential convergence to a metric of constant sectional curvature when the initial metric has positive Yamabe constant and small initial energy.

Impurity quantum phase transition in a current-carryingd-wave superconductor

We study an Anderson impurity embedded in a d-wave superconductor carrying a supercurrent. The low-energy impurity behavior is investigated by using the numerical renormalization group method developed for arbitrary electronic bath spectra. The results explicitly show that the local impurity state is completely screened upon the non-zero current intensity. The impurity quantum criticality is in accordance with the well-known Kosterlitz-Thouless transition.

Measurement of the17O(p,γ)18F reaction rate at astrophysically relevant energies

The ${}^{17}$O($p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma}$)${}^{18}$F reaction plays an important role in hydrogen-burning nucleosynthesis. Conflicting values for the low-energy behavior of its cross section exist in the literature. We present direct measurements of the astrophysical $S$ factor of the ${}^{17}$O($p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma}$)${}^{18}$F reaction at center-of-mass energies between 250 and 500 keV. These measurements were conducted in inverse kinematics at the DRAGON recoil separator.

Convergence of Energy Scales on the Approach to a Local Quantum Critical Point

We find the emergence of strong correlations and universality on the approach to the quantum critical points of a two-impurity Anderson model. The two impurities are coupled by an interimpurity exchange interaction J and direct interaction U{12} and are hybridized with separate conduction channels. The low energy behavior is described in terms of renormalized parameters. We show that on the approach to the transitions to a local singlet and a local charged ordered state, the quasiparticle weight factor z→0, and the renormalized parameters can be expressed in terms of a single energy scale T{*}. The values of the renormalized interaction parameters in terms of T{*} can be predicted from the condition of continuity of the spin and charge susceptibilities, and correspond to strong correlation. These predictions are confirmed by the numerical renormalization group calculations, including the case when the on site interaction U=0.

Structure and electronic properties of a benzene-water solution

Electronic properties of benzene in water were investigated by a sequential quantum mechanical/molecular dynamics approach. Emphasis was placed on the analysis of the structure, polarization effects, and ionization spectrum. By adopting a polarizable model for both benzene and water the structure of the benzene-water solution is in good agreement with data from first principles molecular dynamics. Further, strong evidence that water molecules acquire enhanced orientational order near the benzene molecule is found. Upon hydration, the quadrupole moment of benzene is not significantly changed in comparison with the gas-phase value. We are also reporting results for the dynamic polarizability of benzene in water. Our results indicate that the low energy behaviour of the dynamic polarizability of gas-phase and hydrated benzene is quite similar. Outer valence Green's function calculations for benzene in liquid water show a splitting of the gas-phase energy levels associated with the 1e(1g)(π), 2e(2g), and 2e(1u) orbitals upon hydration. Lifting of the orbitals degeneracy and redshift of the outer valence bands is related to symmetry breaking of the benzene structure in solution and polarization effects from the surrounding water molecules.

Holographic non-relativistic fermionic fixed point by the charged dilatonic black hole

Driven by the landscape of garden-variety condensed matter systems, we have investigated how the dual spectral function behaves at the non-relativistic as well as relativistic fermionic fixed point by considering the probe Dirac fermion in an extremal charged dilatonic black hole with zero entropy. Although the pattern for both of the appearance of flat band and emergence of Fermi surface is qualitatively similar to that given by the probe fermion in the extremal Reissner-Nordstrom AdS black hole, we find a distinctly different low energy behavior around the Fermi surface, which can be traced back to the different near horizon geometry. In particular, with the peculiar near horizon geometry of our extremal charged dilatonic black hole, the low energy behavior exhibits the universal linear dispersion relation and scaling property, where the former indicates that the dual liquid is a Fermi one while the latter implies that the dual liquid is not exactly of Landau Fermi type.

Low-energy expansion formula for one-dimensional Fokker–Planck and Schrödinger equations with asymptotically periodic potentials

We consider one-dimensional Fokker–Planck and Schrödinger equations with a potential that approaches a periodic function at spatial infinity. We extend the low-energy expansion method, which was introduced in previous papers, to be applicable to such asymptotically periodic cases. Using this method, we study the low-energy behavior of the Green function.

Order by disorder and phase transitions in a highly frustrated spin model on the triangular lattice

Frustration has proved to give rise to an extremely rich phenomenology in both quantum and classical systems. The leading behavior of the system can often be described by an effective model, where only the lowest-energy degrees of freedom are considered. In this paper we study a system corresponding to the strong trimerization limit of the spin 1/2 kagome antiferromagnet in a magnetic field. It has been suggested that this system can be realized experimentally by a gas of spinless fermions in an optical kagome lattice at 2/3 filling. We investigate the low-energy behavior of both the spin 1/2 quantum version and the classical limit of this system by applying various techniques. We study in parallel both signs of the coupling constant J since the two cases display qualitative differences. One of the main peculiarities of the J>0 case is that, at the classical level, there is an exponentially large manifold of lowest-energy configurations. This renders the thermodynamics of the system quite exotic and interesting in this case. For both cases, J>0 and J<0, a finite-temperature phase transition with a breaking of the discrete dihedral symmetry group D_6 of the model is present. For J<0, we find a transition temperature T^<_c/|J| = 1.566 +/- 0.005, i.e., of order unity, as expected. We then analyze the nature of the transition in this case. While we find no evidence for a discontinuous transition, the interpretation as a continuous phase transition yields very unusual critical exponents violating the hyperscaling relation. By contrast, in the case J>0 the transition occurs at an extremely low temperature, T^>_c ~= 0.0125 J. Presumably this low transition temperature is connected with the fact that the low-temperature ordered state of the system is established by an order-by-disorder mechanism in this case.

An exploratory analysis of active and low energy behaviour in Australian adolescents

Adolescents engage in a complex range of low energy-consuming and active behaviours not easily captured by single behavioural measures. This study aims to describe the associations among adolescent active and low energy behaviours. Data were obtained from adolescents aged 12-16 years (n=1532) participating in a nationally representative survey. Thirty-nine variables measuring activities were stratified by sex and age and then analysed using principal components analysis with Varimax rotation. Four components were derived for younger girls (21.7% of the variance) and younger boys (20.2%), six for older girls (29.7%) and five for older boys (25.6%). Academic-related behaviours positively correlated with each other and negatively with television use for all age-sex groups. Computer use correlated positively with academic-related behaviours for older boys but negatively with active behaviours for younger boys and girls. Active behaviours correlated positively with each other. For older girls, low energy expenditure, household-based behaviours were negatively correlated with active behaviours. Computer use appears to differ across age groups, and leisure and academic use should be differentiated. The positive associations among different active behaviours and their negative associations with home-based, low energy expenditure behaviours are of interest for intervention development.

Studies on p+6Li Fusion Reaction using 3-Parameter Model

The 3-parameter model introduces 3 parame- ters (radius of a square nuclear potential well, the real part and the imaginary part of the nuclear potential depth) to describe the low energy behavior of the fusion cross-sec- tion for light nuclei. It has been justified by the experi- mental data from the National Nuclear Data Center (NNDC) for 3 major fusion reactions (d ? T, d ? D, and d ? 3 He). In the present paper this 3-parameter model has been extended to p? 6 Li fusion reaction. It agrees with the fusion cross-section data from NNDC again. Moreover it is able to calculate the astrophysical S-factor with an electron screening potential for p? 6 Li fusion reaction as well. As a development of the 3-parameter model, the necessary condition for a low energy resonant tunneling through Coulomb barrier is derived. It reveals further the possibility of resonant tunneling at very low energy for p? 6 Li system.

Two routes to magnetic order by disorder in underdoped cuprates

We study disorder-induced magnetism within the Gutzwiller approximation applied to the t-J model relevant for cuprate superconductors. In particular, we show how disorder generates magnetic phases by inducing local droplets of antiferromagnetic order which eventually merge, and form a quasi-long range ordered state in the underdoped regime. We identify two distinct disorder-induced magnetic phases of this type depending on the strength of the scatterers. For weak potential scatterers used to model dopant disorder, charge reorganization may push local regions in-between the impurities across the magnetic phase boundary, whereas for strong scatterers used to model substitutional ions, a local static magnetic moment is formed around each impurity. We calculate the density of states and find a remarkably universal low-energy behavior largely independent of both disorder and magnetization. However, the magnetic regions are characterized by larger (reduced) superconducting gap (coherence peaks) and a sub-gap kink in the density of states.

AN INFRARED ORIGIN OF LEPTONIC MIXING AND ITS TEST AT DEEPCORE

Fermion mixing is generally believed to be a low-energy manifestation of an underlying theory whose energy scale is much larger than the electroweak scale. In this paper we investigate the possibility that the parameters describing lepton mixing actually arise from the low-energy behavior of the neutrino interacting fields. In particular, we conjecture that the measured value of the mixing angles for a given process depends on the number of unobservable flavor states at the energy of the process. We provide a covariant implementation of such conjecture, draw its consequences in a two-neutrino family approximation and compare these findings with current experimental data. Finally we show that this infrared origin of mixing will be manifest at the Ice Cube DeepCore array, which measures atmospheric oscillations at energies much larger than the tau lepton mass; it will hence be experimentally tested in a short time scale.

Effect of Dzyaloshinskii−Moriya interactions on Kagome anti-ferromagnetic clusters

The low energy and low temperature behavior of a few finite size Kagome clusters, including mixed spin systems of S=1/2 and S=1, with the nearest neighbor Heisenberg antiferromagnetic model is studied under the influence of out-of-plane Dzyaloshinskii−Moriya interactions (DMI) within the exact diagonalization formalism. The ground state of all the finite size systems is found to be present in the lowest spin sector with a finite gap to the lowest magnetic excitation irrespective of the strength of out-of-plane DMI. The energy level structures within the non-magnetic ground state and the lowest magnetic state have been studied for all the systems as a function of DMI. The characteristic signature of such low-lying non-magnetic excitations is reflected in the low temperature behavior of the specific heat. It is also found that the ground state chiral structure (characterized by the vector chiral order of the system) in the xy-plane shows sharp changes as a function of out-of-plane DMI at level crossing or avoided crossing regions. The in-plane spin ordering for each system is also studied with the estimation of static structure factor as a response to the varying strength of DMI.