797 research outputs found
Gravitational couplings of charged leptons in a medium
We calculate the leading order matter-induced corrections to the
gravitational interactions of charged leptons and their antiparticles in a
medium that contains electrons but not the other charged leptons, such as
normal matter. The gravitational coupling, which is universal at the tree
level, is found to be flavor-dependent, and also different for the
corresponding antiparticles, when the corrections of are taken into
account. General expressions are obtained for the matter-induced corrections to
the gravitational mass in a generic matter background, and explicit formulas
for those corrections are given in terms of the macroscopic parameters of the
medium for particular conditions of the background gases.Comment: Latex, axodraw, 39 pages. Added a few stylistic corrections and
clarifying statements in the treatment of the photon tadpole diagra
Looking for a time independent Hamiltonian of a dynamical system
In this paper we introduce a method for finding a time independent
Hamiltonian of a given dynamical system by canonoid transformation. We also
find a condition that the system should satisfy to have an equivalent time
independent formulation. We study the example of damped oscillator and give the
new time independent Hamiltonian for it, which has the property of tending to
the standard Hamiltonian of the harmonic oscillator as damping goes to zero.Comment: Some references added, LATEX fixing
Does dysphoria lead to divergent mental fatigue effects on a cognitive task?
Objective: Tiredness, low energy, and listlessness are common symptoms to be associated with depression. The question remains to what extent these symptoms influence the effects of fatigue on sustained performance tasks, such as impaired task engagement and performance. Based on earlier findings, it was hypothesized that dysphoric (i.e., mildly depressed) individuals, compared to healthy controls, would display earlier fatigue onset and more severe fatigue effects on task engagement and performance during a cognitive task. Methods: Sixty-one dysphoric and twenty-one non-dysphoric control participants were compared during one hour of continuous performance on a 2-back task. During the task subjective fatigue, subjective engagement, objective task performance, baseline pupil diameter and stimulus-evoked pupil dilation were measured. Results: While we found that the dysphoric group reported relatively higher subjective fatigue than the healthy control group at the start of the experiment, we did not find any other divergent fatigue effects during the experimental task. Conclusion: One explanation for the absence of divergent effect is that dysphoria may not have such a profound impact on available cognitive resources, like attention, as initially thought. Based on the results of the present study, we conclude that dysphoria is not necessarily an increased risk factor for impaired sustained performance on cognitive tasks that may induce mental fatigue
Sums over Graphs and Integration over Discrete Groupoids
We show that sums over graphs such as appear in the theory of Feynman
diagrams can be seen as integrals over discrete groupoids. From this point of
view, basic combinatorial formulas of the theory of Feynman diagrams can be
interpreted as pull-back or push-forward formulas for integrals over suitable
groupoids.Comment: 27 pages, 4 eps figures; LaTeX2e; uses Xy-Pic. Some ambiguities
fixed, and several proofs simplifie
QCD Factorized Drell-Yan Cross Section at Large Transverse Momentum
We derive a new factorization formula in perturbative quantum chromodynamics
for the Drell-Yan massive lepton-pair cross section as a function of the
transverse momentum of the pair. When is much larger than the
pair's invariant mass , this factorization formula systematically resums the
logarithmic contributions of the type to all
orders in the strong coupling . When , our formula yields
the same Drell-Yan cross section as conventional fixed order QCD perturbation
theory. We show that resummation is important when the collision energy
is large enough and , and we argue that perturbative
expansions are more stable and reliable in terms of the modified factorization
formula.Comment: 36 pages, latex, including 16 figure
Relativistic description of electron scattering on the deuteron
Within a quasipotential framework a relativistic analysis is presented of the
deuteron current. Assuming that the singularities from the nucleon propagators
are important, a so-called equal time approximation of the current is
constructed. This is applied to both elastic and inelastic electron scattering.
As dynamical model the relativistic one boson exchange model is used.
Reasonable agreement is found with a previous relativistic calculation of the
elastic electromagnetic form factors of the deuteron. For the unpolarized
inelastic electron scattering effects of final state interactions and
relativistic corrections to the structure functions are considered in the
impulse approximation. Two specific kinematic situations are studied as
examples.Comment: (19 pages in revtex + 15 figures not included, available upon
request.) report THU-93-10
On the recurrence and robust properties of Lorenz'63 model
Lie-Poisson structure of the Lorenz'63 system gives a physical insight on its
dynamical and statistical behavior considering the evolution of the associated
Casimir functions. We study the invariant density and other recurrence features
of a Markov expanding Lorenz-like map of the interval arising in the analysis
of the predictability of the extreme values reached by particular physical
observables evolving in time under the Lorenz'63 dynamics with the classical
set of parameters. Moreover, we prove the statistical stability of such an
invariant measure. This will allow us to further characterize the SRB measure
of the system.Comment: 44 pages, 7 figures, revised version accepted for pubblicatio
Next-to-leading order QCD predictions for W+2j and Z+2j production at the CERN LHC
We present cross sections and differential distributions for QCD radiative
corrections to the QCD processes pp -> W+2j and pp -> Z+2j at the CERN LHC.
Calculations are performed with the Monte Carlo program MCFM. Cross section
dependence on the renormalization and factorization scales is greatly reduced,
except for the heavy-flavor case of Wbb~, which has new features at
next-to-leading order at the LHC. We also present cross sections for Wbb~ and
Z+2j in kinematic configurations relevant for Higgs boson searches.Comment: 24p, PRD version, ref's corrected, add. paragraph to explain pTmiss
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On operad structures of moduli spaces and string theory
Recent algebraic structures of string theory, including homotopy Lie
algebras, gravity algebras and Batalin-Vilkovisky algebras, are deduced from
the topology of the moduli spaces of punctured Riemann spheres. The principal
reason for these structures to appear is as simple as the following. A
conformal field theory is an algebra over the operad of punctured Riemann
surfaces, this operad gives rise to certain standard operads governing the
three kinds of algebras, and that yields the structures of such algebras on the
(physical) state space naturally.Comment: 33 pages (An elaboration of minimal area metrics and new references
are added
The molecular epidemiology of human immunodeficiency virus type 1 in six cities in Britain and Ireland
The authors sequenced the p17 coding regions of the gag gene from 211 patients infected either through injecting drug use (IDU) or by sexual intercourse between men from six cities in Scotland, N. England, N. Ireland, and the Republic of Ireland. All sequences were of subtype 5. Phylogenetic analysis revealed substantial heterogeneity in the sequences from homosexual men. In contrast, sequence from over 80% of IDUs formed a relatively tight cluster, distinct both from those of published isolates and of the gay men. There was no large-scale clustering of sequences by city in either risk group, although a number of close associations between pairs of individuals were observed. From the known date of the HIV-1 epidemic among IDUs in Edinburgh, the rate of sequence divergence at synonymous sites is estimated to be about 0.8%. On this basis it has been estimated that the date of divergence of the sequences among homosexual men to be about 1975, which may correspond to the origin of the B subtype epidemic
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