10145699
Logarithms of alpha in QED bound states from the renormalization group
The velocity renormalization group is used to determine lnalpha contributions to QED bound state energies. The leading-order anomalous dimension for the potential gives the alpha(5)lnalpha Lamb shift. The next-to-leading-order anomalous dimension determines the alpha(6)lnalpha, alpha(7)ln (2)alpha, and alpha(8)ln (3)alpha corrections to the energy. These are used to obtain the alpha(8)ln (3)alpha Lamb shift and alpha(7)ln (2)alpha hyperfine splitting for hydrogen, muonium, and positronium, as well as the alpha(2)lnalpha and alpha(3)ln (2)alpha corrections to the ortho- and parapositronium lifetimes. This shows for the first time that these logarithms can be computed from the renormalization group.
119475756
On differences between SCET and QCDf for B ---> pi pi decays
We give a detailed description of the differences between the factorization and results derived from SCET and QCDF for decays B -> M1 M2. This serves as a reply to a comment about our work "B-> M1 M2: Factorization, charming penguins, strong phases, and polarization" [1] made by the authors in [2]. We disagree with their criticisms.
8184878
COMMENT ON VUB FROM EXCLUSIVE SEMILEPTONIC B AND D DECAYS
Abstract The prospects for determining | V ub | from exclusive B semileptonic decay are discussed. The double ratio of form factors (f (B→ρ) /f (B→K ∗ ) )/(f (D→ρ) /f (D→K ∗ ) ) is calculated using chiral perturbation theory. Its deviation from unity due to contributions that are non-analytic in the symmetry breaking parameters is very small. Combining experimental data obtainable from B→ρ l ν l , B→K ∗ l l and D→ρ l ν l can lead to a model independent determination of | V ub | with an uncertainty from theory of about 10%.
32242436
Wigner symmetry in the limit of large scattering lengths
We note that, in the limit where the NN {sup 1}S{sub 0} and {sup 3}S{sub 1} scattering lengths, a{sup ({sup 1}S{sub 0})} and a{sup ({sup 3}S{sub 1})} , go to infinity, the leading terms in the effective field theory for strong NN interactions are invariant under Wigner`s SU(4) spin-isospin symmetry. This explains why the leading effects of radiation pions on the S -wave NN scattering amplitudes vanish as a{sup ({sup 1}S{sub 0})} and a{sup ({sup 3}S{sub 1})} go to infinity. The implications of Wigner symmetry for NN{r_arrow}NN axion and {gamma}d{r_arrow}np are also considered. {copyright} {ital 1999} {ital The American Physical Society}
119185983
Designing gapped soft functions for jet production
Abstract Distributions in jet production often depend on a soft function, S , which describes soft large angle hadronic radiation between the jets. Near kinematic thresholds S encodes nonperturbative information, while far from thresholds S can be computed with an expansion in operators. We design soft functions for jet factorization theorems that serve this dual purpose, reducing to the perturbative result in the tail region and to a consistent model in the nonperturbative region. We use the MS ¯ scheme, and in both regions S displays the appropriate renormalization group scale dependence. We point out that viable soft functions in jet production should have a gap associated with the minimum soft hadronic energy deposit. This gap is connected to the leading O ( Λ QCD ) renormalon ambiguity in massless jet event shapes. By defining the gap in a suitable scheme we demonstrate that the leading renormalon can be eliminated. This improves the convergence of perturbative results, and also the stability by which nonperturbative parameters encode the underlying soft physics.
14754036
The R-evolution of QCD matrix elements
Perturbation series in QCD are generally asymptotic and suffer from so-called infrared renormalon ambiguities. In the context of the standard operator product expansion in MS-bar these ambiguities are compensated by matrix elements of higher dimension operators, but the procedure can be difficult to control due to large numerical cancellations. Explicit subtractions for matrix elements and coefficients, depending on a subtraction scale R, can avoid this problem. The appropriate choice for R in the Wilson coefficients can widely vary for different processes. In this talk we discuss renormalization group evolution with the scale R, and show that it sums large logarithms in the difference of processes with widely different R's. We also show that the solution of the R-evolution equations can be used to recover the all order asymptotic form of the singularities in the Borel transform of the perturbative series. For the normalization of these singularities we obtain a quickly converging sum rule that only needs the known perturbative coefficients as an input. This sum rule can be used as a novel test for renormalon ambiguities without replying on the large-beta_0 approximation.
40903316
Semiclassical Wheeler-DeWitt equation: Solutions for long-wavelength fields.
In the long-wavelength approximation, a general set of semiclassical wave functionals is given for gravity and matter interacting in 3 + 1 dimensions. In the long-wavelength theory, one neglects second-order spatial gradients in the energy constraint. These solutions satisfy the Hamilton-Jacobi equation, the momentum constraint, and the equation of continuity. It is essential to introduce inhomogeneities to discuss the role of time. The time hypersurface is chosen to be a homogeneous field in the wave functional. It is shown how to introduce tracer particles through a dust field χ into the dynamical system. The formalism can be used to describe stochastic inflation
22301721
Cosmological fluids as time variables in general relativity.
125299154
SERPENTINE:A NEW CODE FOR PARTICLE TRACKING
39797190
Solving the Hamilton-Jacobi equation for general relativity.
We demonstrate a systematic method for solving the Hamilton-Jacobi equation for general relativity with the inclusion of matter fields. The generating functional is expanded in a series of spatial gradients. Each term is manifestly invariant under reparametrizations of the spatial coordinates ("gauge invariant"). At each order we solve the Hamiltonian constraint using a conformal transformation of the three-metric as well as a line integral in superspace. This gives a recursion relation for the generating functional which then may be solved to arbitrary order simply by functionally differentiating previous orders. At fourth order in spatial gradients we demonstrate solutions for irrotational dust as well as for a scalar field. We explicitly evolve the three-metric to the same order. This method can be used to derive the Zel'dovich approximation for general relativity.
28227992
First test of the Siberian snake magnet arrangement to overcome depolarizing resonances in a circular accelerator.
We studied the G\ensuremath{\gamma}=2 imperfection depolarizing resonance at 108 MeV, both with and without a Siberian snake, by varying the resonance strength while storing beams of 104- and 120-MeV polarized protons at the Indiana University Cooler Ring. We used a cylindrically symmetric polarimeter to simultaneously study the effect of a depolarizing resonance on both the vertical and radial components of the polarization. AT 104 MeV we found that the Siberian snake eliminated the effect of the nearby G\ensuremath{\gamma}=2 depolarizing resonance.