A stagnant gauge for QCD

It is shown that the gauge-fixing parameter α of standard covariant gauges may legitimately be replaced by an operator α(□). In particular, α may be chosen so that the gluon propagator has a “stagnant” tensor structure proportional to g_ην for all momenta. This choice of gauge simplifies explicit calculations and leads to renormalization group equations with no $\text{?}\text{?α}$ term.     

Lepton energy spectra in e+e− annihilation and other processes

An analysis is presented of the single inclusive lepton spectra expected from the decay of charmed hadrons or heavier particles with new flavors produced in e⁺e^? annihilation. Extremely soft spectra are found, in contrast to the heavy lepton signal. Good detection efficiency at low momentum will therefore continue to be important in future experiments. A range of plausible inclusive D meson spectra abstracted from a parton fragmentation picture is employed. The model is applicable to other processes.     

Can charm account for prompt lepton production?

The production and subsequent semi-leptonic decay of charmed particles is investigated in order to determine whether it could account for the prompt lepton data. Most of the central region data is easily accommodated but there are difficulties at large x. Large cross-sections for charmed particle production are implied. Correlations in $\text{pp}\text{→}\text{D}\text{(→}\text{e}\text{) +}\text{D}\text{?}\text{(→ μ) + …}$ events are discussed.     

An unsteady point vortex method for coupled fluid–solid problems

A method is proposed for the study of the two-dimensional coupled motion of a general sharp-edged solid body and a surrounding inviscid flow. The formation of vorticity at the body’s edges is accounted for by the shedding at each corner of point vortices whose intensity is adjusted at each time step to satisfy the regularity condition on the flow at the generating corner. The irreversible nature of vortex shedding is included in the model by requiring the vortices’ intensity to vary monotonically in time. A conservation of linear momentum argument is provided for the equation of motion of these point vortices (Brown–Michael equation). The forces and torques applied on the solid body are computed as explicit functions of the solid body velocity and the vortices’ position and intensity, thereby providing an explicit formulation of the vortex–solid coupled problem as a set of non-linear ordinary differential equations. The example of a falling card in a fluid initially at rest is then studied using this method. The stability of broadside-on fall is analysed and the shedding of vorticity from both plate edges is shown to destabilize this position, consistent with experimental studies and numerical simulations of this problem. The reduced-order representation of the fluid motion in terms of point vortices is used to understand the physical origin of this destabilization.      

On the observation and origin of kinetic isotope effects in exchange dephasing: motional collapse of vibrational structure for SF6 isolated in a xe

High-resolution infrared spectra of SF₆ in a xenon matrix give evidence for dynamic exchange among trapping sites on the IR time scale. A ³²S-³⁴S kinetic isotope effect has been observed and attributed to differences in the dephasing mode frequencies and the resulting disparity in coupling to the phonon bath.     

How the LHC came to be

Approval of a project the size of the Large Hadron Collider is an exercise in politics and high finance.     

Evidence of CO(2) molecule acting as an electron acceptor on a nanoporous metal-organic-framework MIL-53 or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2))

The adsorption mode of CO(2) at low coverage in the nanoporous metal benzenedicarboxylate MIL-53(Cr) or Cr(3+)(OH)(O(2)C-C(6)H(4)-CO(2)) has been identified using IR spectroscopy; the red shift of the nu(3) band and the splitting of the nu(2) mode of CO(2) in addition to the shifts of the nu(OH) and delta(OH) bands of the MIL-53(Cr) hydroxyl groups provide evidence that CO(2) interacts with the oxygen atoms of framework OH groups as an electron-acceptor via its carbon atom; this is the first example of such an interaction between CO(2) and bridged OH groups in a solid.     

Electroweak radiative corrections to neutrino and electron scattering and the value of sin2θw

We describe in detail the calculation of all first-order electroweak radiative corrections to total and differential neutrino cross sections and to the parity-violating asymmetry in ed scattering. We find that leading log approximations agree well with our exact result for the shape, but not necessarily the magnitude, of the corrections to $\text{d}\text{σ}{}^{\mathrm{<mtext>\nu ,</mtext><mtext>\nu </mtext>}}\text{/}\text{d}\text{γ}$ except for γ → 1. Corrections to total neutrino cross sections have also been calculated by Marciano and Sirlin; our results agree with theirs. The corrections to sin²θ_w are experiment dependent. If sin²θ_w is defined in the $\text{MS}$ scheme at a scale M_w, they reduce the average value found from the ratio of charged to neutral current neutrino scattering by 0.012 to 0.215 ± 0.015. They reduce the value obatained from the Paschos Wolfenstein relation by 0.008 to 0.221 ± 0.014. In ed scattering they reduce the value by 0.008 to 0.215 ± 0.015. Using a corrected value of 0.215 ± 0.015 and the first-order corrections to the mass formulae, the SU(2) × U(1) predictions for the vector boson masses are M_w = 83.1_?2.8^+3.1rmGeV and M_z = 93.8_?2.2^+2.5 GeV, about five GeV larger than obtained from the lowest order analysis.     

Photoproduction of μ pairs and large-pT particles in QCD

We calculate cross sections for $\text{γ}\text{N}\text{→ μ}\text{μ}\text{X}\text{, γ}\text{N}\text{→ (}\text{jet)X and}\text{γ}\text{N}\text{→ π}{}^{\mathrm{+}}\text{X}$ using the distribution functions for quarks in the photon predicted by QCD. The Drell-Yan contribution to the μ-pair cross section is masked by the Bethe-Heitler process in the region where it is interesting. However, the characteristic cross section for photoproduction of large-p_T particles, which is predicted by QCD, is measurable.     

CO2 adsorption in LiY and NaY at high temperature: molecular simulations compared to experiments

Grand Canonical Monte Carlo simulations combined with adsorption measurements have been carried out to gain further insight into the CO₂ adsorption process at the microscopic scale in both LiY and NaY faujasites at various temperatures. A new Li⁺−CO₂ force field derived by ab initio calculations was validated by a reasonable agreement between the simulated isotherms and those obtained by experiments in a wide range of temperature (from 323 K to 473 K). In addition, the microscopic mechanisms of CO₂ adsorption in both systems, consistent with the trends observed for the simulated differential enthalpies of adsorption as a function of the loading, were proposed. It was observed that two different types of adsorption behaviour exist for NaY and LiY at 323 K and 373 K, mainly caused by the significant more exposed position of the SII Na⁺ from the six-ring plane of the supercage compared to those occupied by the SII Li⁺, whereas at higher temperature, both faujasites exhibit the same flat profile for the differential enthalpy of adsorption as a function of loading.