Strong-coupling Calculation Research Articles

Three-dimensional transient analysis of coupled RCS-containment integral system

The integral analysis of reactor cooling system (RCS) and containment is becoming increasingly important for advanced reactors, especially reactors with passive safety technology. In this study, a new three-dimensional containment thermal–hydraulic analysis method is established using the equations and solutions similar to the reactor cooling system program for a strong coupling calculation of the containment and RCS. The integral program was verified by simulating the gravity drain line break accident of the PUMA test facility. The simulation results indicate that the coupled RCS-containment integral analysis program can be applied for analyzing the thermal–hydraulic coupling of the containment and RCS. The integral program was applied to simulate the LOCA for the RCS-containment integral system of AP1000. The results indicate that the integral program can be applied to analyse the AP1000 LOCA.

Strong-coupling jet energy loss from AdS/CFT

We propose a novel definition of a holographic light hadron jet and consider the phenomenological consequences, including the very first fully self-consistent, completely strong-coupling calculation of the jet nuclear modification factor $R_{AA}$, which we find compares surprisingly well with recent preliminary data from LHC. We show that the thermalization distance for light parton jets is an extremely sensitive function of the \emph{a priori} unspecified string initial conditions and that worldsheets corresponding to non-asymptotic energy jets are not well approximated by a collection of null geodesics. Our new string jet prescription, which is defined by a separation of scales from plasma to jet, leads to the re-emergence of the late-time Bragg peak in the instantaneous jet energy loss rate; unlike heavy quarks, the energy loss rate is unusually sensitive to the very definition of the string theory object itself. A straightforward application of the new jet definition leads to significant jet quenching, even in the absence of plasma. By renormalizing the in-medium suppression by that in the vacuum we find qualitative agreement with preliminary CMS $R_{AA}^{jet}(p_T)$ data in our simple plasma brick model. We close with comments on our results and an outlook on future work.

Minimal conformal technicolor and precision electroweak tests

We study the minimal model of conformal technicolor, an SU(2) gauge theory near a strongly coupled conformal fixed point, with conformal symmetry softly broken by technifermion mass terms. Conformal symmetry breaking triggers chiral symmetry breaking in the pattern SU(4) -> Sp(4), which gives rise to a pseudo-Nambu-Goldstone boson that can act as a composite Higgs boson. The top quark is elementary, and the top and electroweak gauge loop contributions to the Higgs mass are cut off entirely by Higgs compositeness. In particular, the model requires no top partners and no "little Higgs" mechanism. A nontrivial vacuum alignment results from the interplay of the top loop and technifermion mass terms. The composite Higgs mass is completely determined by the top loop, in the sense that m_h/m_t is independent of the vacuum alignment and is computable by a strong-coupling calculation. There is an additional composite pseudoscalar A with mass larger than m_h and suppressed direct production at LHC. We discuss the electroweak fit in this model in detail. Corrections to Z -> bb and the T parameter from the top sector are suppressed by the enhanced Sp(4) custodial symmetry. Even assuming that the strong contribution to the S parameter is positive and usuppressed, a good electroweak fit can be obtained for v/f ~ 0.25, where v and f are the electroweak and chiral symmetry breaking scales respectively. This requires fine tuning at the 10% level.

Visibility of cold atomic gases in optical lattices for finite temperatures

In nearly all experiments with ultracold atoms time-of-flight pictures are the only data available. In this paper we present an analytical strong-coupling calculation for those time-of-flight pictures of bosons in an optical lattice in the Mott phase. This allows us to determine the visibility, which quantifies the contrast of peaks in the time-of-flight pictures, and we suggest how to use it as a thermometer.

ℤNdomain walls in hot 𝒩 = 4 SYM at weak and strong coupling

We study the tensions of domain walls in the deconfined phase of N=4 SUSY Yang-Mills theory on R^3 x S^1, at weak and strong coupling. We calculate the k-wall tension at one-loop order and find that it is proportional to k(N-k) (Casimir scaling). The two-loops analysis suggests that Casimir scaling persists to this order. The strong coupling calculation is performed by using the AdS/CFT correspondence. We argue that the k-wall should be identified with an NS5-brane wrapping an S^4 inside S^5 in the AdS-Schwarzschild x S^5 background in Type IIB string theory. The tension at strong coupling is compared with the weak coupling result. We also compare our results with those from lattice simulations in pure Yang-Mills theory.

Calculating the Jet Quenching Parameter

Models of medium-induced radiative parton energy loss account for the strong suppression of high-p(T) hadron spectra in square root of (S)NN=200 GeV Au-Au collisions at BNL RHIC in terms of a single "jet quenching parameter" q. We observe that q can be given a model-independent, nonperturbative, quantum field theoretic definition in terms of the short-distance behavior of a particular lightlike Wilson loop. We then use the anti-de Sitter/conformal-field-theory correspondence to obtain a strong-coupling calculation of q in hot N=4 supersymmetric QCD, finding q(SYM)=26.69 square root of alpha(SYM)N(c)T(3) in the limit in which both N(c) and 4pialpha(SYM)N(c) are large. Thus, at strong coupling q is not proportional to the entropy density s, or to some "number density of scatterers" since, unlike the number of degrees of freedom, q does not grow like N(c)(2).

On the rate of Tc suppression by interband impurity scattering inMgB2

We calculate the change in the superconducting transition temperatureTc ofMgB2 caused by interband nonmagnetic impurity scattering using the Eliashbergtheory for the two-band model of this compound. A much slower rate ofTc suppression is obtained compared to the prediction based on the BCS treatment of the two-bandmodel which ignores renormalization and damping associated with the electron–phononinteraction. Hence, the interband impurity scattering rates deduced from experiments onMgB2 using the formula which results from the BCS approach to the two-band model areunderestimated. We generalize the BCS treatment of the two-band model to includerenormalization effects of the electron–phonon interaction and find an excellent agreementwith the full strong coupling calculation.

Excitation of resonance lines of the cadmium ion by monoenergetic electrons

The excitation of resonance lines at 226.5 and 214.4 nm, corresponding to the transitions 226.5 (5p 2 P 1 2/0 →5s 2 S 1/2) and 5p 2 P 3 2/0 → 5s 2 S 1/2, respectively, in the Cd+ ion upon collisions with monoenergetic electrons with an energy in the range of 4–130 eV is studied with high precision by a spectroscopic method in crossing beams. It is found that the dependence of the effective excitation cross sections of the resonance doublet components on the energy of the electrons has a distinct resonance structure. It is shown that the dominant mechanism responsible for this structure is the capture of an incident electron by a Cd+ ion with the simultaneous excitation of an electron from the subvalence 4d 10 shell to the autoionizing states of the Cd atom with their subsequent decay (directly or via cascade transitions) to resonance levels of the ion. The results obtained are compared with data from other experiments and with the results of the R-matrix strong-coupling calculation of 15 states and of semiempirical calculation using the Van Regemorter formula.

Strongly coupled 't Hooft model on the lattice

A lattice strong coupling calculation of the spectrum and chiral condensate of the 't Hooft model is presented. The agreement with the results of the continuum theory is strikingly good even at the fourth order in the strong coupling expansions.

From black holes to glueballs: The QCD3 tensor glueball at strong coupling

A strong coupling calculation of glueball masses based on the duality between supergravity and Yang-Mills theory is presented. Earlier work is extended to non-zero spin. Fluctuations in the gravitational metric lead to the 2 ++ state on the leading Pomeron trajectory with a mass relation: m(0 ++) < m(2 ++) < m(1 −+). Contrary to expectation, the mass of our new 0 ++ state ( m 2 = 5.4573) associated with the graviton is smaller than the mass of the 0 ++ state ( m 2 = 11.588) from the dilaton, which in fact is exactly degenerate with the tensor 2 ++.

Strong-coupling calculation of fluctuation pressure of a membrane between walls

We calculate analytically the proportionality constant in the pressure law of a membrane between parallel walls from the strong-coupling limit of variational perturbation theory up to third order. Extrapolating the zeroth to third approximations to infinity yields the pressure constant α=0.0797149. This result lies well within the error bounds of the most accurate available Monte Carlo result α MC=0.0798±0.0003.

Spin dynamics and transport in gapped one-dimensional Heisenberg antiferromagnets at nonzero temperatures

We present the theory of nonzero temperature ($T$) spin dynamics and transport in one-dimensional Heisenberg antiferromagnets with an energy gap $\Delta$. For $T << \Delta$, we develop a semiclassical picture of thermally excited particles. Multiple inelastic collisions between the particles are crucial, and are described by a two-particle S-matrix which has a super-universal form at low momenta. This is established by computations on the O(3) $\sigma$-model, and strong and weak coupling expansions (the latter using a Majorana fermion representation) for the two-leg S=1/2 Heisenberg antiferromagnetic ladder. As an aside, we note that the strong-coupling calculation reveals a S=1, two particle bound state which leads to the presence of a second peak in the T=0 inelastic neutron scattering (INS) cross-section for a range of values of momentum transfer. We obtain exact, or numerically exact, universal expressions for the thermal broadening of the quasi-particle peak in the INS cross-section, for the magnetization transport, and for the field dependence of the NMR relaxation rate $1/T_1$ of the effective semiclassical model: these are expected to be asymptotically exact for the quantum antiferromagnets. The results for $1/T_1$ are compared with the experimental findings of Takigawa et al and the agreement is quite good. In the regime $\Delta < T < (a typical microscopic exchange)$ we argue that a complementary description in terms of semiclassical waves applies, and give some exact results for the thermodynamics and dynamics.

An adapted strong coupling calculation in disordered solids yielding acoustic bistability

We consider single well anharmonic oscillator like defects coupled to a perfect elastic medium, the coupling term being bilinear in the strain field and in the defect variables. The elastostatic self-interaction energy of the defects is negative and can turn efficiently the single well into a double well, giving a natural explanation for the existence of two level systems in glasses.

Charge-fluctuation-mediated superconductivity in the d-p model Strong-coupling calculation

Charge-fluctuation-mediated superconductivity in the simplest d-p model is investigated with the help of the auxiliary particle method together with the 1 N expansion theory. Transition temperatures, T c, for various pairing symmetric are calculated by solving the linearized Eliashberg equation retaining full momentum and frequency dependences of the vertex functions, which are repulsive almost over the entire momentum and frequency space. Strong frequency dependence of the vertex functions due to the charge fluctuation turn out to be essential to realize such superconducting states. The extended s symmetric pairing composed of mainly on-site and nearest-neighbor pairing has the highest T c ≌ 85 K at half-filling with a rather small charge-transfer energy where the system is metallic in contrast to the actual high- T c materials.

The Response of the Strongly Coupled AB System of Citrate to Typical 1H MRS Localization Sequences

The response of the strongly coupled AB system of citrate to the STEAM and PRESS spatial localization sequences is developed analytically and then verified experimentally at 2.35 T. At this field strength, the response predicted by the complete Strong-coupling calculation is shown to differ greatly from that of the simpler weak-coupling approximation. It is shown that the strong-coupling effects induce a significant field-strength dependence in the time-dependent modulations of the response to either sequence. These effects are illustrated for the STEAM and PRESS responses at field strengths of 1.5, 2.35, and 4.7 T. Independent of the chosen sequence, the increase in the signal-to-noise ( S/ N) of the frequency response with increasing field strength is shown to be significantly less for the citrate system than for uncoupled spins. The factors which weaken the S/ N dependence of the citrate AB signal with increasing field strength are quantified and discussed.

Eliashberg treatment of the microwave conductivity of niobium.

High-precision microwave measurements have recently been carried out on superconducting Nb samples. A BCS-like coherence peak has been observed below ${\mathit{T}}_{\mathit{c}}$. We find that a strong-coupling calculation of the microwave conductivity, using electron-phonon spectral functions obtained from tunneling measurements, is unable to account for the height of the peak. We also explain how, for microwave measurements at lower frequency, the height of the coherence peak can be used to provide information about the low-frequency part of the electron-phonon spectral function and the associated inelastic scattering rate.

Reaching the unreachable: critical scaling at the superconducting transition

The large coherence length of conventional superconductors causes the critical region near T c to be unobservably small, leading to the impression that mean-field theory can adequately explain properties near the transition. The high-temperature superconductors, however, have such strongly type-II character that the critical, or at least an intermediate critical, region is experimentally accessible. We demonstrate the applicability of XY-like critical scaling to magnetization, heat capacity and conductivity data and through the fitting parameters, make contact with a strong-coupling calculation of the critical temperature. Further, the scaled conductivity data show clear evidence for a thermodynamic transition along the freezing line H m(T)∝(1 − T/T c) 4 3 .

Spin-Fluctuation-Induced Superconductivity in the Copper Oxides: A Strong Coupling Calculation

Spin-Fluctuation-Induced Superconductivity in the Copper Oxides: A Strong Coupling Calculation

Spin-fluctuation-induced superconductivity in the copper oxides: A strong coupling calculation.

We have carried out a strong coupling calculation of spin-fluctuation-induced superconductivity for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ using the experimentally determined spin excitation spectrum. We find that it is extremely important to take full account of the momentum and frequency dependence of the interaction and that while lifetime effects substantially reduce ${\mathit{T}}_{\mathit{c}}$ from its value calculated in a weak coupling approximation, it is still possible for spin fluctuations to give rise to high-temperature superconductivity.

3He as an almost-localized Fermi liquid: Strong-coupling calculation of the superfluid transition temperature.

We reexamine the integral equations for the Cooper instability of the Hubbard model in the Gutzwiller boson formation. We solve numerically for the frequency dependence of the fermion-fermion vertex and, following conventional Eliashberg techniques, obtain ${\mathit{T}}_{\mathit{c}}$ versus pressure for $^{3}\mathrm{He}$. The calculated results are within a factor of 2 of the experimental ones.