Coarctation of the aorta in infants under one year of age

During the 10-year period 1962 - 1971, coarctation of the aorta was diagnosed within the first 5 months of life in 35 hospital cases. Of these, 29 (83%) were symptomatic, and 18 (54%) underwent surgery to correct the coarctation. Thirteen of the 18 patients (72%) survived the procedure. Of the 5 patients who died, 2 had single-ventricle complexes, and 1 had an associated ventricular septal defect and died at a subsequent operation for pulmonary artery banding. One patient who survived had a thoracotomy with no procedure done to the aorta.All survivors were followed up for at least 1 year. Residual gradients were found in 6 of the 12 patients (50%), but classified as severe in only 2 cases.Of the 11 patients who were symptomatic but who did not undergo surgery, 7 died (mortality 63%). There were 6 remaining patients who were asymptomatic. There have been 3 deaths in this series-all unrelated to their cardiac pathology.It is strongly recommended that young babies with coarctation of the aorta, who develop congestive cardiac failure, undergo 36 - 48 hours of medical therapy, after which surgical resection of the coiucted segment is carried out. This approach offers the best prospects for survival.S. Afr. Med. J, 48, 397 (1974)

On possible implications of gluon number fluctuations in DIS data

We study the effect of gluon number fluctuations (Pomeron loops) on deep inelastic scattering (DIS) in the fixed coupling case. We find that the description of the DIS data is improved once gluon number fluctuations are included. Also the values of the parameters, like the saturation exponent and the diffussion coefficient, turn out reasonable and agree with values obtained from numerical simulations of toy models which take into account fluctuations. This outcome seems to indicate the evidence of geometric scaling violations, and a possible implication of gluon number fluctuations, in the DIS data. However, we cannot exclude the possibility that the scaling violations may also come from the diffusion part of the solution to the BK-equation, instead of gluon number fluctuations.Comment: 9 pages, 2 figures; references added, minor changes, matches published versio

A Langevin equation for high energy evolution with pomeron loops

We show that the Balitsky-JIMWLK equations proposed to describe non-linear evolution in QCD at high energy fail to include the effects of fluctuations in the gluon number, and thus to correctly describe both the low density regime and the approach towards saturation. On the other hand, these fluctuations are correctly encoded (in the limit where the number of colors is large) in Mueller's color dipole picture, which however neglects saturation. By combining the dipole picture at low density with the JIMWLK evolution at high density, we construct a generalization of the Balitsky hierarchy which includes the particle number fluctuations, and thus the pomeron loops. After an additional coarse-graining in impact parameter space, this hierarchy is shown to reduce to a Langevin equation in the universality class of the stochastic Fisher-Kolmogorov-Petrovsky-Piscounov (sFKPP) equation. This equation implies that the non-linear effects in the evolution become important already in the high momentum regime where the average density is small, which signals the breakdown of the BFKL approximation.Comment: 56 pages, 10 figure

On the Probabilistic Interpretation of the Evolution Equations with Pomeron Loops in QCD

We study some structural aspects of the evolution equations with Pomeron loops recently derived in QCD at high energy and for a large number of colors, with the purpose of clarifying their probabilistic interpretation. We show that, in spite of their appealing dipolar structure and of the self-duality of the underlying Hamiltonian, these equations cannot be given a meaningful interpretation in terms of a system of dipoles which evolves through dissociation (one dipole splitting into two) and recombination (two dipoles merging into one). The problem comes from the saturation effects, which cannot be described as dipole recombination, not even effectively. We establish this by showing that a (probabilistically meaningful) dipolar evolution in either the target or the projectile wavefunction cannot reproduce the actual evolution equations in QCD.Comment: 31 pages, 2 figure

Traveling wave fronts and the transition to saturation

We propose a general method to study the solutions to nonlinear QCD evolution equations, based on a deep analogy with the physics of traveling waves. In particular, we show that the transition to the saturation regime of high energy QCD is identical to the formation of the front of a traveling wave. Within this physical picture, we provide the expressions for the saturation scale and the gluon density profile as a function of the total rapidity and the transverse momentum. The application to the Balitsky-Kovchegov equation for both fixed and running coupling constants confirms the effectiveness of this method.Comment: 9 pages, 3 figures, references adde

Duality and Pomeron effective theory for QCD at high energy and large N_c

We propose an effective theory which governs Pomeron dynamics in QCD at high energy, in the leading logarithmic approximation, and in the limit where N_c, the number of colors, is large. In spite of its remarkably simple structure, this effective theory generates precisely the evolution equations for scattering amplitudes that have been recently deduced from a more complete microscopic analysis. It accounts for the BFKL evolution of the Pomerons together with their interactions: dissociation (one Pomeron splitting into two) and recombination (two Pomerons merging into one). It is constructed by exploiting a duality principle relating the evolutions in the target and the projectile, more precisely, splitting and merging processes, or fluctuations in the dilute regime and saturation effects in the dense regime. The simplest Pomeron loop calculated with the effective theory is free of both ultraviolet or infrared singularities.Comment: 13 pages, 1 figur

Cronin effect and high-p_T suppression in the nuclear gluon distribution at small x

We present a systematic, and fully analytic, study of the ratio R_{pA} between the gluon distribution in a nucleus and that in a proton scaled up by the atomic number A. We consider initial conditions of the McLerran-Venugopalan type, and quantum evolution in the Color Glass Condensate, with both fixed and running coupling. We perform an analytic study of the Cronin effect in the initial conditions and point out an interesting difference between saturating effects and twist effects in the nuclear gluon distribution. We show that the distribution of the gluons which make up the condensate in the initial conditions is localized at low momenta, but this particular feature does not survive after the quantum evolution. We demonstrate that the rapid suppression of the ratio R_{pA} in the early stages of the evolution is due to the DGLAP-like evolution of the proton, whose gluon distribution grows much faster than that in the nucleus because of the large separation between the respective saturation momenta. The flattening of the Cronin peak, on the other hand, is due to the evolution of the nucleus. We show that the running coupling effects slow down the evolution, but eventually lead to a stronger suppression in R_{pA} at sufficiently large energies.Comment: 87 pages, 11 figures. More explanations added (especially on the A-dependence of the ratio R_{pA}), and also more acknowledgements and references. The discussion of the running coupling case has been considerably extende

Magnetotransport Mechanisms in Strongly Underdoped YBa_2Cu_3O_x Single Crystals

We report magnetoresistivity measurements on strongly underdoped YBa_2Cu_3O_x (x=6.25, 6.36) single crystals in applied magnetic fields H || c-axis. We identify two different contributions to both in-plane and out-of-plane magnetoresistivities. The first contribution has the same sign as the temperature coefficient of the resistivity \partial ln(\rho_i)/\partial T (i={c,ab}). This contribution reflects the incoherent nature of the out-of-plane transport. The second contribution is positive, quadratic in field, with an onset temperature that correlates to the antiferromagnetic ordering.Comment: 4 pages, 3 figure

A small universe after all?

The cosmic microwave background radiation allows us to measure both the geometry and topology of the universe. It has been argued that the COBE-DMR data already rule out models that are multiply connected on scales smaller than the particle horizon. Here we show the opposite is true: compact (small) hyperbolic universes are favoured over their infinite counterparts. For a density parameter of Omega_o=0.3, the compact models are a better fit to COBE-DMR (relative likelihood ~20) and the large-scale structure data (sigma_8 increases by ~25%).Comment: 4 pages, RevTeX, 7 Figure

A zero-dimensional model for high-energy scattering in QCD

We investigate a zero-dimensional toy model originally introduced by Mueller and Salam which mimics high-energy scattering in QCD in the presence of both gluon saturation and gluon number fluctuations, and hence of Pomeron loops. Unlike other toy models of the reaction-diffusion type, the model studied in this paper is consistent with boost invariance and, related to that, it exhibits a mechanism for particle saturation close to that of the JIMWLK equation in QCD, namely the saturation of the emission rate due to high-density effects. Within this model, we establish the dominant high-energy behaviour of the S-matrix element for the scattering between a target obtained by evolving one particle and a projectile made with exactly n particles. Remarkably, we find that all such matrix elements approach the black disk limit S=0 at high rapidity Y, with the same exponential law: ~ exp(-Y) for all values of n. This is so because the S-matrix is dominated by rare target configurations which involve only few particles. We also find that the bulk distribution for a saturated system is of the Poisson type.Comment: 34 pages, 9 figures. Some explanations added on the frame-dependence of the relevant configurations (new section 3.3