1,257 research outputs found
From correlation functions to Wilson loops
We start with an n-point correlation function in a conformal gauge theory. We
show that a special limit produces a polygonal Wilson loop with sides. The
limit takes the points towards the vertices of a null polygonal Wilson loop
such that successive distances . This produces a fast moving
particle that generates a "frame" for the Wilson loop. We explain in detail how
the limit is approached, including some subtle effects from the propagation of
a fast moving particle in the full interacting theory. We perform perturbative
checks by doing explicit computations in N=4 super-Yang-Mills.Comment: 37 pages, 10 figures; typos corrected, references adde
Gluon Scattering Amplitudes in Finite Temperature Gauge/Gravity Dualities
We examine the gluon scattering amplitude in N=4 super Yang-Mills at finite
temperature with nonzero R-charge densities, and in Non-Commutative gauge
theory at finite temperature. The gluon scattering amplitude is defined as a
light-like Wilson loop which lives at the horizon of the T-dual black holes of
the backgrounds we consider. We study in detail a special amplitude, which
corresponds to forward scattering of a low energy gluon off a high energy one.
For this kinematic configuration in the considered backgrounds, we find the
corresponding minimal surface which is directly related to the gluon scattering
amplitude. We find that for increasing the chemical potential or the
non-commutative parameter, the on-shell action corresponding to our Wilson loop
in the T-dual space decreases. For all of our solutions the length of the short
side of the Wilson loop is constrained by an upper bound which depends on the
temperature, the R-charge density and the non-commutative parameter. Due to
this constraint, in the limit of zeroth temperature our approach breaks down
since the upper bound goes to zero, while by keeping the temperature finite and
letting the chemical potential or the non-commutative parameter to approach to
zero the limit is smooth.Comment: 30 pages, 16 figures, minor corrections (plus improved numerical
computation for the non-commutative case
The Quark Beam Function at NNLL
In hard collisions at a hadron collider the most appropriate description of
the initial state depends on what is measured in the final state. Parton
distribution functions (PDFs) evolved to the hard collision scale Q are
appropriate for inclusive observables, but not for measurements with a specific
number of hard jets, leptons, and photons. Here the incoming protons are probed
and lose their identity to an incoming jet at a scale \mu_B << Q, and the
initial state is described by universal beam functions. We discuss the
field-theoretic treatment of beam functions, and show that the beam function
has the same RG evolution as the jet function to all orders in perturbation
theory. In contrast to PDF evolution, the beam function evolution does not mix
quarks and gluons and changes the virtuality of the colliding parton at fixed
momentum fraction. At \mu_B, the incoming jet can be described perturbatively,
and we give a detailed derivation of the one-loop matching of the quark beam
function onto quark and gluon PDFs. We compute the associated NLO Wilson
coefficients and explicitly verify the cancellation of IR singularities. As an
application, we give an expression for the next-to-next-to-leading logarithmic
order (NNLL) resummed Drell-Yan beam thrust cross section.Comment: 54 pages, 9 figures; v2: notation simplified in a few places, typos
fixed; v3: journal versio
Quantum folded string and integrability: from finite size effects to Konishi dimension
Using the algebraic curve approach we one-loop quantize the folded string
solution for the type IIB superstring in AdS(5)xS(5). We obtain an explicit
result valid for arbitrary values of its Lorentz spin S and R-charge J in terms
of integrals of elliptic functions. Then we consider the limit S ~ J ~ 1 and
derive the leading three coefficients of strong coupling expansion of short
operators. Notably, our result evaluated for the anomalous dimension of the
Konishi state gives 2\lambda^{1/4}-4+2/\lambda^{1/4}. This reproduces correctly
the values predicted numerically in arXiv:0906.4240. Furthermore we compare our
result using some new numerical data from the Y-system for another similar
state. We also revisited some of the large S computations using our methods. In
particular, we derive finite--size corrections to the anomalous dimension of
operators with small J in this limit.Comment: 20 pages, 1 figure; v2: references added, typos corrected; v3: major
improvement of the references; v4: Discussion of short operators is
restricted to the case n=1. This restriction does not affect the main results
of the pape
Willingness to participate in future HIV prevention studies among gay and bisexual men in Scotland, UK: a challenge for intervention trials
This article examines willingness to participate in future HIV prevention research among gay and bisexual men in Scotland, UK. Anonymous, self-complete questionnaires and Orasure Gäó oral fluid samples were collected in commercial gay venues. 1,320 men were eligible for inclusion. 78.2% reported willingness to participate in future HIV prevention research; 64.6% for an HIV vaccine, 57.4% for a behaviour change study, and 53.0% for a rectal microbicide. In multivariate analysis, for HIV vaccine research, greater age, minority ethnicity, and not providing an oral fluid sample were associated with lower willingness; heterosexual orientation and not providing an oral fluid sample were for microbicides; higher education and greater HIV treatment optimism were for behaviour change. STI testing remained associated with being more willing to participate in microbicide research and frequent gay scene use remained associated with being more willing to participate in behaviour change research. Having an STI in the past 12 months remained significantly associated with being willing to participate in all three study types. There were no associations between sexual risk behaviour and willingness. Although most men expressed willingness to participate in future research, recruitment of high-risk men, who have the potential to benefit most, is likely to be more challenging
Wilson-loop formalism for Reggeon exchange in soft high-energy scattering
We derive a nonperturbative expression for the non-vacuum,
qqbar-Reggeon-exchange contribution to the meson-meson elastic scattering
amplitude at high energy and low momentum transfer, in the framework of QCD.
Describing the mesons in terms of colourless qqbar dipoles, the problem is
reduced to the two-fermion-exchange contribution to the dipole-dipole
scattering amplitudes, which is expressed as a path integral, over the
trajectories of the exchanged fermions, of the expectation value of a certain
Wilson loop. We also show how the resulting expression can be reconstructed
from a corresponding quantity in the Euclidean theory, by means of analytic
continuation. Finally, we make contact with previous work on Reggeon exchange
in the gauge/gravity duality approach.Comment: A few misprints in the expressions for the relevant Wilson loops have
been corrected. 55 pages, 7 figure
High Energy Bounds on Soft N=4 SYM Amplitudes from AdS/CFT
Using the AdS/CFT correspondence, we study the high-energy behavior of
colorless dipole elastic scattering amplitudes in N=4 SYM gauge theory through
the Wilson loop correlator formalism and Euclidean to Minkowskian analytic
continuation. The purely elastic behavior obtained at large impact-parameter L,
through duality from disconnected AdS_5 minimal surfaces beyond the
Gross-Ooguri transition point, is combined with unitarity and analyticity
constraints in the central region. In this way we obtain an absolute bound on
the high-energy behavior of the forward scattering amplitude due to the
graviton interaction between minimal surfaces in the bulk. The dominant
"Pomeron" intercept is bounded by alpha less than or equal to 11/7 using the
AdS/CFT constraint of a weak gravitational field in the bulk. Assuming the
elastic eikonal approximation in a larger impact-parameter range gives alpha
between 4/3 and 11/7. The actual intercept becomes 4/3 if one assumes the
elastic eikonal approximation within its maximally allowed range L larger than
exp{Y/3}, where Y is the total rapidity. Subleading AdS/CFT contributions at
large impact-parameter due to the other d=10 supergravity fields are obtained.
A divergence in the real part of the tachyonic KK scalar is cured by
analyticity but signals the need for a theoretical completion of the AdS/CFT
scheme.Comment: 25 pages, 3 eps figure
Decreased Th1-Type Inflammatory Cytokine Expression in the Skin Is Associated with Persisting Symptoms after Treatment of Erythema Migrans
Background: Despite the good prognosis of erythema migrans (EM), some patients have persisting symptoms of various character and duration post-treatment. Several factors may affect the clinical outcome of EM, e. g. the early interaction between Borrelia (B.) burgdorferi and the host immune response, the B. burgdorferi genotype, antibiotic treatment as well as other clinical circumstances. Our study was designed to determine whether early cytokine expression in the skin and in peripheral blood in patients with EM is associated with the clinical outcome. Methods: A prospective follow-up study of 109 patients with EM was conducted at the A land Islands, Finland. Symptoms were evaluated at 3, 6, 12 and 24 months post-treatment. Skin biopsies from the EM and healthy skin were immunohistochemically analysed for expression of interleukin (IL)-4, IL-10, IL-12p70 and interferon (IFN)-gamma, as well as for B. burgdorferi DNA. Blood samples were analysed for B. burgdorferi antibodies, allergic predisposition and levels of systemic cytokines. Findings: None of the patients developed late manifestations of Lyme borreliosis. However, at the 6-month follow-up, 7 of 88 patients reported persisting symptoms of diverse character. Compared to asymptomatic patients, these 7 patients showed decreased expression of the Th1-associated cytokine IFN-gamma in the EM biopsies (p = 0.003). B. afzelii DNA was found in 48%, B. garinii in 15% and B. burgdorferi sensu stricto in 1% of the EM biopsies, and species distribution was the same in patients with and without post-treatment symptoms. The two groups did not differ regarding baseline patient characteristics, B. burgdorferi antibodies, allergic predisposition or systemic cytokine levels. Conclusion: Patients with persisting symptoms following an EM show a decreased Th1-type inflammatory response in infected skin early during the infection, which might reflect a dysregulation of the early immune response. This finding supports the importance of an early, local Th1-type response for optimal resolution of LB.Original Publication: Johanna Sjöwall, Linda Fryland, Marika Nordberg, Florence Sjögren, Ulf Garpmo, Christian Jansson, Sten-Anders Carlsson, Sven Bergstrom, Jan Ernerudh, Dag Nyman, Pia Forsberg and Christina Ekerfelt, Decreased Th1-Type Inflammatory Cytokine Expression in the Skin Is Associated with Persisting Symptoms after Treatment of Erythema Migrans, 2011, PLOS ONE, (6), 3, 0018220. http://dx.doi.org/10.1371/journal.pone.0018220 Copyright: Public Library of Science (PLoS) http://www.plos.org
Learning HCI Across Institutions, Disciplines and Countries: A Field Study of Cognitive Styles in Analytical and Creative Tasks
Human-computer interaction (HCI) is increasingly becoming a subject taught in universities around the world. However, little is known of the interactions of the HCI curriculum with students in different types of institutions and disciplines internationally. In order to explore these interactions, we studied the performance of HCI students in design, technology and business faculties in universities in UK, India, Namibia, Mexico and China who participated in a common set of design and evaluation tasks. We obtained participants’ cognitive style profiles based on Allinson and Hayes scale in order to gain further insights into their learning styles and explore any relation between these and performance. We found participants’ cognitive style preferences to be predominantly in the adaptive range, i.e. with combined analytical and intuitive traits, compared to normative data for software engineering, psychology and design professionals. We further identified significant relations between students’ cognitive styles and performance in analytical and creative tasks of a HCI professional individual. We discuss the findings in the context of the distinct backgrounds of the students and universities that participated in this study and the value of research that explores and promotes diversity in HCI education
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