The high energy asymptotics of scattering processes in QCD

High energy scattering in the QCD parton model was recently shown to be a reaction-diffusion process, and thus to lie in the universality class of the stochastic Fisher-Kolmogorov-Petrovsky-Piscounov equation. We recall that the latter appears naturally in the context of the parton model. We provide a thorough numerical analysis of the mean field approximation, given in QCD by the Balitsky-Kovchegov equation. In the framework of a simple stochastic toy model that captures the relevant features of QCD, we discuss and illustrate the universal properties of such stochastic models. We investigate in particular the validity of the mean field approximation and how it is broken by fluctuations. We find that the mean field approximation is a good approximation in the initial stages of the evolution in rapidity.Comment: 31 pages, 20 figures. The code for BK evolution can be downloaded from http://www.isv.uu.se/~enberg/BK/ v2: several points clarified, discussion of the solutions to the mean-field evolution enhanced through the study of a different class of initial conditions, references added; conclusions unchanged. To appear in Phys. Rev.

Fisheries-induced Life History Changes in Herring (Clupea harengus)

Fishing changes not only the population abundance of the target species, but also its population dynamics and life-history traits. A number of studies have shown that life history traits related to the timing of maturation can respond quickly to fishing mortality. Because changes in such life-history traits feed back into population dynamics and, consequently, may also affect the yield and thus profitability of a fishery, we need better understand the factors that hasten or hinder such changes. In this study we analyze how fisheries have affected the maturation process of an economically important herring ("Clupea harengus") stock, the North Sea (NSH) herring. The harvest of North Sea herring targets both mature and immature individuals. Life-history theory predicts that under this kind of mortality regime fisheries can be expected to induce an adaptive decrease in the age at maturation. This kind of studies are a critical for testing theoretical predictions, and will facilitate our understanding under which conditions large life history changes can and cannot be expected. Such understanding is needed for evolutionarily enlightened management of marine biodiversity. The results will provide guidance for evolutionarily enlightened management strategies, particularly with respect to fisheries targeting mature and immature individuals differently

Rapid life-history evolution in a wild Daphnia pulex population in response to novel size-dependent predation

The effect of size-selective predation on prey communities and their traits is well documented, but the relative roles of genetic adaptation and phenotypic plasticity continue to be debated. We looked for evidence of genetic adaption in a population of the water flea Daphnia pulex that faced a novel, introduced predator, Eurasian perch (Perca fluviatilis), selectively preying upon large zooplankton. Theory predicts adaptive changes towards a faster life history. We compared growth, age and length at maturation, egg size, and fecundity of two groups of clones kept in common-garden conditions, 13 clones isolated at around the time of the perch introduction and 14 isolated 3 years after. All animals were photographed daily and observed every third hour to detect maturation and measure the clutch size. Post-introduction clones matured earlier, but this was an indirect response triggered by genetic change in growth: post-introduction clones had faster growth prior to maturation than pre-introduction ones, reaching earlier the size threshold for maturation, but the threshold itself remained unchanged. Post-introduction clones showed also higher clutch size for 2nd and 3rd clutch, and slower growth from maturation (first appearance of eggs) to the moult after the release of the first clutch. Egg size did not differ between the periods. The experiment shows how life-history responses to predation involve multiple interlinked traits and both direct and indirect genetic responses

Vector Meson Photoproduction from the BFKL Equation II: Phenomenology

Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation which we use to compare to data collected at the HERA collider.Comment: 39 pages, 29 figure

Rapidity gaps at HERA and the Tevatron from soft colour exchanges

Models based on soft colour exchanges to rearrange colour strings in the final state provide a general framework for both diffractive and non-diffractive events in ep and hadron-hadron collisions. We study two such models and find that they can reproduce rapidity gap data from both HERA and the Tevatron. We also discuss the influence of parton cascades and multiple interactions on the results.Comment: 4 pages, 4 EPS figures, presented at UK Phenomenology Workshop on Collider Physics, Durham. Uses iopart.cl

Eight decades of adaptive changes in herring reproductive investment: the joint effect of environment and exploitation

publishedVersio

Double vector meson production from the BFKL equation

The double vector meson production in two photon collisions is addressed assuming that the color singlet $t$-channel exchange carries large momentum transfer. We consider the non-forward solution of the BFKL equation at high energy and large momentum transfer and estimate the total and differential cross section for the process $\gamma \gamma \to V_1 V_2$, where $V_1$ and $V_2$ can be any two vector mesons ($V_i = \rho, \omega, \phi, J/\Psi, \Upsilon$). A comparison between our predictions and previous theoretical results obtained at Born level or assuming the Pomeron-exchange factorization relations is presented. Our results demonstrate that the BFKL dynamics implies an enhancement of the cross sections. Predictions for the future linear colliders (TESLA, CLIC and ILC) are given.Comment: 13 pages, 3 tables, 7 figures. Minor changes. Accepted for publication in Eur. Phys. J.

An evolutionary explanation of female‐biased sexual size dimorphism in North Sea plaice, Pleuronectes platessa L.

Sexual size dimorphism (SSD) is caused by differences in selection pressures and life-history trade-offs faced by males and females. Proximate causes of SSD may involve sex-specific mortality, energy acquisition, and energy expenditure for maintenance, reproductive tissues, and reproductive behavior. Using a quantitative, individual-based, eco-genetic model parameterized for North Sea plaice, we explore the importance of these mechanisms for female-biased SSD, under which males are smaller and reach sexual maturity earlier than females (common among fish, but also arising in arthropods and mammals). We consider two mechanisms potentially serving as ultimate causes: (a) Male investments in male reproductive behavior might evolve to detract energy resources that would otherwise be available for somatic growth, and (b) diminishing returns on male reproductive investments might evolve to reduce energy acquisition. In general, both of these can bring about smaller male body sizes. We report the following findings. First, higher investments in male reproductive behavior alone cannot explain the North Sea plaice SSD. This is because such higher reproductive investments require increased energy acquisition, which would cause a delay in maturation, leading to male-biased SSD contrary to observations. When accounting for the observed differential (lower) male mortality, maturation is postponed even further, leading to even larger males. Second, diminishing returns on male reproductive investments alone can qualitatively account for the North Sea plaice SSD, even though the quantitative match is imperfect. Third, both mechanisms can be reconciled with, and thus provide a mechanistic basis for, the previously advanced Ghiselin-Reiss hypothesis, according to which smaller males will evolve if their reproductive success is dominated by scramble competition for fertilizing females, as males would consequently invest more in reproduction than growth, potentially implying lower survival rates, and thus relaxing male-male competition. Fourth, a good quantitative fit with the North Sea plaice SSD is achieved by combining both mechanisms while accounting for sex-specific costs males incur during their spawning season. Fifth, evolution caused by fishing is likely to have modified the North Sea plaice SSD

Resummation in nonlinear equation for high energy factorizable gluon density and its extension to include coherence

Motivated by forthcoming p-Pb experiments at Large Hadron Collider which require both knowledge of gluon densities accounting for saturation and for processes at a wide range of $p_t$ we study basic momentum space evolution equations of high energy QCD factorization. Solutions of those equations might be used to form a set of gluon densities to calculate observables in generalized high energy factorization. Moreover in order to provide a framework for predictions for exclusive final states in p-Pb scattering with high $p_t$ we rewrite the equation for the high energy factorizable gluon density in a resummed form, similarly to what has been done in \cite{Kutak:2011fu} for the BK equation. The resummed equation is then extended to account for colour coherence. This introduces an external scale to the evolution of the gluon density, and therefore makes it applicable in studies of final states.Comment: 14 pages, appendix added, accepted for publication in JHE