Weak Coupling Calculation Research Articles

Static Aeroelastic Research of Supersonic Wing

The thin airfoil design and the supersonic flight condition make the aeroelastic deformation have an important effect on the aerodynamic characteristics of the supersonic aircraft. In this paper, a supersonic Unmanned Aerial Vehicle (UAV) wing is taken as the research object, and the static aeroelastic weak coupling calculation method (CFD/CSD) is used to carry out the modification of the aerodynamic coefficient of the wing. The analysis results show that the aeroelastic deformation reduces the lift coefficient, and the pitch moment produces a head-up increment. At the same time, the aerodynamic focus of the wing moves forward, which reduces the static stability margin of the aircraft. The influence of aeroelastic deformation on aerodynamic characteristics increases with increasing Mach number.

Degeneracy between even- and odd-parity superconductivity in the quasi-one-dimensional Hubbard model and implications for Sr2RuO4

Based on a weak coupling calculation, we show that an accidental degeneracy appears between even- and odd-parity superconductivity in the quasi-one-dimensional (1D) limit of the repulsive Hubbard model on the square lattice. We propose that this effect could be at play on the quasi-1D orbitals Ru ${d}_{zx}$ and ${d}_{zy}$ of ${\text{Sr}}_{2}{\text{RuO}}_{4}$, leading to a gap of the form ${\mathrm{\ensuremath{\Delta}}}_{\text{even}}+i{\mathrm{\ensuremath{\Delta}}}_{\text{odd}}$ which could help reconcile several experimental results.

Poromechanical Modeling and Numerical Simulation of Hydraulic Fracture Propagation.

Hydraulic fracturing (HF) is an important technique for enhancing the permeability of petroleum and gas reservoirs. To understand the coupling response mechanism of fluid pressure and in situ stress during the expansion of hydraulic fractures—based on the theory of the fluid flow of seepage porous media and damage mechanics—a poromechanical model of hydraulic fracture propagation is proposed and the finite element method (FEM) numerical weak coupling calculation method of hydraulic fracturing is realized. First, the effect of the coupling stress field is described by introducing the β value of the amount of pore volume that varies, resulting from internal pressure per unit of fluid internal, and the coupling calculation method of the pore pressure-effective stress-element damage-pore pressure expansion coefficient is formulated. Second, based on the concept of damage localization, a calculation method for the hydraulic fracture opening equation is proposed, and then the element damage-hydraulic fracture opening-permeability tensor-pore pressure field calculation cycle is established. The model indicates four stages of fracture propagation: I, fracture nucleation, II, kinetic propagation, III, steady propagation, and IV, propagation termination. Finally, as an example, a numerical simulation of three-dimension hydraulic fracturing is performed. In comparison to previous research, the morphology of the fracture zone and the fluid pressure contour of the horizontal section are approximately ellipses, which verify the feasibility of the weak coupling calculation method; the fracture parameters verify its accuracy, which include the length, width, and fluid pressure.

Deformations of the circular Wilson loop and spectral (in)dependence

In this paper we study the expectation value of deformations of the circular Wilson loop in mathcal{N}=4 super Yang-Mills theory. The leading order deformation, known as the Bremsstrahlung function, can be obtained exactly from supersymmetric localization, so our focus is on deformations at higher orders. We find simple expressions for the expectation values for generic deformations at the quartic order at one-loop at weak coupling and at leading order at strong coupling. We also present a very simple algorithm (not requiring integration) to evaluate the two-loop result. We find that an exact symmetry of the strong coupling sigma-model, known as the spectral-parameter independence, is an approximate symmetry at weak coupling, modifying the expectation value starting only at the sextic order in the deformation. Furthermore, we find very simple patterns for how the spectral parameter can appear in the weak coupling calculation, suggesting all-order structures.

Leggett modes and multiband superconductivity inSr2RuO4

Sr$_2$RuO$_4$ is a prototypical multi-band superconductor with three bands crossing the Fermi level. These bands exhibit distinct dimensional characteristics, with one quasi-2D $\gamma$-band and two quasi-1D $\alpha$- and $\beta$-bands. This leads to the expectation that the superconductivity on the $\gamma$-band may be only weakly Josephson-coupled to that on the other two bands. Based on an explicit microscopic weak coupling calculation appropriate for Sr$_2$RuO$_4$, we study the collective Leggett modes associated with the relative phase oscillations between the bands and show that a relatively soft Leggett mode exists due to the comparatively weaker inter-band Josephson coupling. These calculations also provide insight into why the superconducting gap magnitudes may be comparable on all three bands, despite the noticeable differences between the $\gamma$ and $\alpha, \beta$ bands. The analyses can be readily applied to other multi-band superconductors.

Realization of center symmetry in two adjoint flavor large-N Yang-Mills

We report on the results of numerical simulations of $SU(N)$ lattice Yang Mills with two flavors of (light) Wilson fermion in the adjoint representation. We analytically and numerically address the question of center symmetry realization on lattices with $\Gamma$ sites in each direction in the large-$N$ limit. We show, by a weak coupling calculation that, for massless fermions, center symmetry realization is independent of $\Gamma$, and is unbroken. Then, we extend our result by conducting simulations at non zero mass and finite gauge coupling. Our results indicate that center symmetry is intact for a range of fermion mass in the vicinity of the critical line on lattices of volume $2^4$. This observation makes it possible to compute infinite volume physical observables using small volume simulations in the limit $N\to\infty$, with possible applications to the determination of the conformal window in gauge theories with adjoint fermions.

Heavy-quarks in the QGP: study of medium effects through euclidean propagators and spectral functions

The heavy-quark spectral function in a hot plasma is reconstructed from the corresponding euclidean propagator. The latter is evaluated through a path-integral simulation. A weak-coupling calculation is also performed, allowing to interpret the qualitative behavior of the spectral function in terms of quite general physical processes.

Lateral Casimir forces on parallel plates and concentric cylinders with corrugations

In this paper we are giving a quantitative description of two different configurations for noncontact gears. We consider the solutions from a perturbative calculation for two semitransparent parallel plates and concentric cylinders both with corrugations on the inner surfaces. In the case of corrugated parallel plates we discuss results from first- and second-order perturbation calculation in the corrugation amplitudes and we will concentrate on the first-order perturbation for the case of the corrugated concentric cylinders (the second order calculation is under study), both for the weak and strong couplings. We compare the perturbative results with the results from the proximity force approximation (PFA) and an exact weak coupling calculation.

Conformal properties of four-gluon planar amplitudes and Wilson loops

We present further evidence for a dual conformal symmetry in the four-gluon planar scattering amplitude in N = 4 SYM. We show that all the momentum integrals appearing in the perturbative on-shell calculations up to four loops are dual to true conformal integrals, well defined off shell. Assuming that the complete off-shell amplitude has this dual conformal symmetry and using the basic properties of factorization of infrared divergences, we derive the special form of the finite remainder previously found at weak coupling and recently reproduced at strong coupling by AdS/CFT. We show that the same finite term appears in a weak coupling calculation of a Wilson loop whose contour consists of four light-like segments associated with the gluon momenta. We also demonstrate that, due to the special form of the finite remainder, the asymptotic Regge limit of the four-gluon amplitude coincides with the exact expression evaluated for arbitrary values of the Mandelstam variables.

Interplay of electromagnetic noise and Kondo effect in quantum dots

We investigate the influence of an electromagnetic environment, characterized by a finite impedance $Z(\omega)$, on the Kondo effect in quantum dots. The circuit voltage fluctuations couple to charge fluctuations in the dot and influence the spin exchange processes transferring charge between the electrodes. We discuss how the low-energy properties of a Kondo quantum dot subject to dynamical Coulomb blockade resemble those of Kondo impurities in Luttinger liquids. Using previous knowledge based on the bosonization of quantum impurity models, we show that low-voltage conductance anomalies appear at zero temperature. The conductance can vanish at low temperatures even in presence of a screened impurity spin. Moreover, the quantitative determination of the corresponding Kondo temperature depends on the full frequency-dependent impedance of the circuit. This is demonstrated by a weak-coupling calculation in the Kondo interaction, taking into account the full distribution $P(E)$ of excited environmental modes.

Thermal phase transitions and gapless quark spectra in quark matter at high density

Thermal color superconducting phase transitions in three-flavor quark matter at high baryon density are investigated in the Ginzburg-Landau (GL) approach. We constructed the GL potential near the boundary with a normal phase by taking into account nonzero quark masses, electric charge neutrality, and color charge neutrality. We found that the density of states averaged over paired quarks plays a crucial role in determining the phases near the boundary. By performing a weak coupling calculation of the parameters characterizing the GL potential terms of second order in the pairing gap, we show that three successive second-order phase transitions take place as the temperature increases: a modified color-flavor locked phase (ud, ds, and us pairings) -> a ``dSC'' phase (ud and ds pairings) -> an isoscalar pairing phase (ud pairing) -> a normal phase (no pairing). The Meissner masses of the gluons and the number of gapless quark modes are also studied analytically in each of these phases.

Excited States in 207Rn

Excited states in 207Rn are investigated via the196Pt(16O,Sn)207Rn reaction at beam energies from85 to 95 MeV using techniques of in-beam γ-ray spectroscopy.Measurements of γ-ray excitation function, x-γ and γ-γ-tcoincidences are performed with ten BGO(AC)HPGe detectors. Based onthese measurements, a level scheme of 207Rn, including 17 γ-raysand 18 levels, is established. Spins for most of the levels areproposed according to the measured DCO ratios. The level structure iscompared with a weak-coupling calculation using the interactionenergies extracted from neighbouring nuclei.

Fractional branes and the entropy of 4D black holes

We reconsider the four dimensional extremal black hole constructed in type IIB string theory as the bound state of D1-branes, D5-branes, momentum, and Kaluza-Klein monopoles. Specifically, we examine the case of an arbitrary number of monopoles. Consequently, the weak coupling calculation of the microscopic entropy requires a study of the D1-D5 system on an ALE space. We find that the complete expression for the Bekenstein-Hawking entropy is obtained by taking into account the massless open strings stretched between the fractional D-branes which arise in the orbifold limit of the ALE space. The black hole sector therefore arises as a mixed Higgs-Coulomb branch of an effective 1+1 dimensional gauge theory.

Self-consistent analysis of single-particle excitations in a spin-density-wave antiferromagnet.

We present the results of a self-consistent weak-coupling calculation for the renormalized single-particle properties in an itinerant antiferromagnet. Multiple spin-wave excitations accompany the carrier motion and lead to incoherent contributions to the electronic spectrum. We evaluate the quasiparticle spectral weight and energy dispersoin. In agreement with strong-coupling theories we find the minimum of the dispersion of the quasihole energy to have momentum (\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}/2,\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}/2) and the dispersion to be flat around the corners of the Brillouin zone. Very good agreement is achieved with available exact diagonalization data.

Quasi-Particle Density of States of Two-Dimensional Hubbard Model

The density of states (DOS) of the two-dimensional Hubbard model is calculated in second-order perturbation with respect to the on-site Coulomb interaction U . The direct analytic continuation formula is presented to calculate the self-energy on the real-frequency axis. The momentum as well as the energy integral in the self-energy is seriously carried out with use of the Fast-Fourier-Transformation algorithm. Near the half-filling, the imaginary part of the self-energy becomes proportional to the energy in the vicinity of the Fermi level in our weak-coupling calculation. In the interacting case, the van Hove singularity (VHS) in DOS is smeared by the self-energy effect, but there still exists a sharp peak structure due to VHS.

The quark propagator at finite temperature

We study the quark propagator at finite temperature on euclidean lattices in the Landau gauge, and compare the results to an O( g 2) lattice weak coupling calculation. The screening mass obtained from spatial correlation functions in the chiral symmetric phase is close to the Matsubara frequency. The temporal correlation functions yield a much smaller screening mass, which approaches the perturbative result, m eff 2= g 2 T 2/6, for T≳1.75 T c. Deviations from the perturbative behaviour are seen for T c⩽ T⩽1.75 T c. For T⩽ T c, the screening masses from both spatial and temporal correlation functions are large and close to half the mass of the ϱ-meson. Dispersion relations do not show any significant deviations from free particle behaviour.

Weak-coupling caluclation on the deformed regions of Zr and Mo isotopes

A neutro-proteon weak-coupling model calculation is performed on the deformed regions of Zr and Mo isotopes. The simultaneous occupation of neutrons and protons of spin-orbit partner orbitals plays a crucial role in determining the onset of deformation. It is shown that the ground rotational band can be produced qualitatively by the isoscalar component of the n-p interaction in the100, 102Zr and102–106Mo isotopes.

Constraints on matrix elements of the effective nucleon-nucleon interaction for nuclei around mass 40

The Kuo-Brown realistic d 3 2 − f 7 2 interaction is compared with several sets of matrix elements extracted from experimental spectra, and with constraints on centroids imposed by a weak-coupling calculation for particle-hole states around mass 40. It is shown that the Kuo-Brown T = 1 interaction is too attractive, whereas the T = 0 interaction is insufficiently attractive by a substantial amount.

Reduced lattice gauge theory in two dimensions

We show explicitly that the free energy in the Eguchi-Kawai model in two dimensions is equal to the free energy in (QCD(∞)) 2. The same applies to the expectation values of a loop running an arbitrary number of times around a plaquette. We also present a weak coupling calculation for the free energy, which turns out to be exact.

Weak-coupling calculation on N = 83 isotones

A proton-neutron weak-coupling model calculation is performed on those N=83 isotones that are far fromZ = 50 proton closed shell. The agreement between the experimental and the calculated energy level schemes is quite good. The result suggests that the weak-coupling model proposed by McGrory is applicable not only to even-even nuclei, but also to even-odd and odd-odd nuclei.