4,988 research outputs found
On the molecular origin of high-pressure effects in nanoconfinement: The role of surface chemistry and roughness
On Glauber modes in Soft-Collinear Effective Theory
Gluon interactions involving spectator partons in collisions at hadronic
machines are investigated. We find a class of examples in which a mode, called
Glauber gluons, must be introduced to the effective theory for consistency.Comment: 19 pages, three figures. Uses JHEP3.cl
The relationship between DRD4 polymorphisms and phenotypic correlations of behaviors in the collared flycatcher
There is increasing evidence that the genetic architecture of exploration behav-
ior includes the dopamine receptor D4 gene (
DRD4
). Such a link implies that
the within-individual consistency in the same behavior has a genetic basis.
Behavioral consistency is also prevalent in the form of between-individual cor-
relation of functionally different behaviors; thus, the relationship between
DRD4
polymorphism and exploration may also be manifested for other behav-
iors. Here, in a Hungarian population of the collared flycatcher,
Ficedula albi-
collis
, we investigate how males with distinct
DRD4
genotypes differ in the
consistent elements of their behavioral displays during the courtship period. In
completely natural conditions, we assayed novelty avoidance, aggression and
risk-taking, traits that were previously shown repeatable over time and correlate
with each other, suggesting that they could have a common mechanistic basis.
We identified two single-nucleotide polymorphisms (SNP554 and SNP764) in
the exon 3 of the
DRD4
gene by sequencing a subsample, then we screened 202
individuals of both sexes for these SNPs. Focusing on the genotypic variation in
courting males, we found that “AC” heterozygote individuals at the SNP764
take lower risk than the most common “AA” homozygotes (the “CC” homo-
zygotes were not represented in our subsample of males). We also found a con-
siderable effect size for the relationship between SNP554 polymorphism and
novelty avoidance. Therefore, in addition to exploration,
DRD4
polymorphisms
may also be associated with the regulation of behaviors that may incur fear or
stress. Moreover, polymorphisms at the two SNPs were not independent indi-
cating a potential role for genetic constraints or another functional link, which
may partially explain behavioral correlations
Parton Fragmentation within an Identified Jet at NNLL
The fragmentation of a light parton i to a jet containing a light energetic
hadron h, where the momentum fraction of this hadron as well as the invariant
mass of the jet is measured, is described by "fragmenting jet functions". We
calculate the one-loop matching coefficients J_{ij} that relate the fragmenting
jet functions G_i^h to the standard, unpolarized fragmentation functions D_j^h
for quark and gluon jets. We perform this calculation using various IR
regulators and show explicitly how the IR divergences cancel in the matching.
We derive the relationship between the coefficients J_{ij} and the quark and
gluon jet functions. This provides a cross-check of our results. As an
application we study the process e+ e- to X pi+ on the Upsilon(4S) resonance
where we measure the momentum fraction of the pi+ and restrict to the dijet
limit by imposing a cut on thrust T. In our analysis we sum the logarithms of
tau=1-T in the cross section to next-to-next-to-leading-logarithmic accuracy
(NNLL). We find that including contributions up to NNLL (or NLO) can have a
large impact on extracting fragmentation functions from e+ e- to dijet + h.Comment: expanded introduction, typos fixed, journal versio
Fluctuating selection models and Mcdonald-Kreitman type analyses
It is likely that the strength of selection acting upon a mutation varies through time due to changes in the environment. However, most population genetic theory assumes that the strength of selection remains constant. Here we investigate the consequences of fluctuating selection pressures on the quantification of adaptive evolution using McDonald-Kreitman (MK) style approaches. In agreement with previous work, we show that fluctuating selection can generate evidence of adaptive evolution even when the expected strength of selection on a mutation is zero. However, we also find that the mutations, which contribute to both polymorphism and divergence tend, on average, to be positively selected during their lifetime, under fluctuating selection models. This is because mutations that fluctuate, by chance, to positive selected values, tend to reach higher frequencies in the population than those that fluctuate towards negative values. Hence the evidence of positive adaptive evolution detected under a fluctuating selection model by MK type approaches is genuine since fixed mutations tend to be advantageous on average during their lifetime. Never-the-less we show that methods tend to underestimate the rate of adaptive evolution when selection fluctuates
The scalar gluonium correlator: large-beta_0 and beyond
The investigation of the scalar gluonium correlator is interesting because it
carries the quantum numbers of the vacuum and the relevant hadronic current is
related to the anomalous trace of the QCD energy-momentum tensor in the chiral
limit. After reviewing the purely perturbative corrections known up to
next-next-to-leading order, the behaviour of the correlator is studied to all
orders by means of the large-beta_0 approximation. Similar to the QCD Adler
function, the large-order behaviour is governed by the leading ultraviolet
renormalon pole. The structure of infrared renormalon poles, being related to
the operator product expansion are also discussed, as well as a low-energy
theorem for the correlator that provides a relation to the renormalisation
group invariant gluon condensate, and the vacuum matrix element of the trace of
the QCD energy-momentum tensor.Comment: 14 pages, references added, discussion of IR renormalon pole at u=3
extended, similar version to appear in JHE
Heavy quark flavour dependence of multiparticle production in QCD jets
After inserting the heavy quark mass dependence into QCD partonic evolution
equations, we determine the mean charged hadron multiplicity and second
multiplicity correlators of jets produced in high energy collisions. We thereby
extend the so-called dead cone effect to the phenomenology of multiparticle
production in QCD jets and find that the average multiplicity of heavy-quark
initiated jets decreases significantly as compared to the massless case, even
taking into account the weak decay products of the leading primary quark. We
emphasize the relevance of our study as a complementary check of -tagging
techniques at hadron colliders like the Tevatron and the LHC.Comment: Version revised, accepted for publication in JHEP, 21 pages and 7
figure
Eikonal methods applied to gravitational scattering amplitudes
We apply factorization and eikonal methods from gauge theories to scattering
amplitudes in gravity. We hypothesize that these amplitudes factor into an
IR-divergent soft function and an IR-finite hard function, with the former
given by the expectation value of a product of gravitational Wilson line
operators. Using this approach, we show that the IR-divergent part of the
n-graviton scattering amplitude is given by the exponential of the one-loop IR
divergence, as originally discovered by Weinberg, with no additional subleading
IR-divergent contributions in dimensional regularization.Comment: 16 pages, 3 figures; v2: title change and minor rewording (published
version); v3: typos corrected in eqs.(3.2),(4.1
Theoretical Aspects of Particle Production
These lectures describe some of the latest data on particle production in
high-energy collisions and compare them with theoretical calculations and
models based on QCD. The main topics covered are: fragmentation functions and
factorization, small-x fragmentation, hadronization models, differences between
quark and gluon fragmentation, current and target fragmentation in deep
inelastic scattering, and heavy quark fragmentation.Comment: 26 pages, 27 figures. Lectures at International Summer School on
Particle Production Spanning MeV and TeV Energies, Nijmegen, The Netherlands,
August 199
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