1,669 research outputs found
Updates of PDFs in the MSTW framework
I present results on updates on PDFs which are obtained within the general
framework which led to the MSTW2008 PDF sets. There are some theory and
procedural improvements and a variety of new data sets, including many relevant
up-to-date LHC data. A new set of PDFs is very close to being finalised, with
no significant changes expected to the preliminary PDFs shown here.Comment: 6 pages, 6 figures,Published in PoS DIS (2014
Instantons and Chern-Simons flows in 6, 7 and 8 dimensions
The existence of K-instantons on a cylinder M^7 = R_tau x K/H over a
homogeneous nearly K"ahler 6-manifold K/H requires a conformally parallel or a
cocalibrated G_2-structure on M^7. The generalized anti-self-duality on M^7
implies a Chern-Simons flow on K/H which runs between instantons on the coset.
For K-equivariant connections, the torsionful Yang-Mills equation reduces to a
particular quartic dynamics for a Newtonian particle on C. When the torsion
corresponds to one of the G_2-structures, this dynamics follows from a gradient
or hamiltonian flow equation, respectively. We present the analytic (kink-type)
solutions and plot numerical non-BPS solutions for general torsion values
interpolating between the instantonic ones.Comment: 1+8 pages, 14 figures; talk presented at SQS-11 during 18-23 July,
2011, at JINR, Dubna, Russia; v2: missing * in eq.(1) adde
reaction at high energies
We evaluate differential distributions for the four-body reaction at high energies which constitutes an irreducible background to
three-body processes , where , ,
, , . We consider central diffractive
contribution mediated by Pomeron and Reggeon exchanges as well as completely
new mechanism of emission of kaons from the proton lines. We include absorption
effects due to proton-proton interaction and kaon-kaon rescattering. We compare
our results with measured cross sections for the CERN ISR experiment. We make
predictions for future experiments at RHIC, Tevatron and LHC. Differential
distributions in invariant two-kaon mass, kaon rapidities and transverse
momenta of kaons are presented. Two-dimensional distribution in is particularly interesting. The higher the incident energy, the
higher preference for the same-hemisphere emission of kaons. We find that the
kaons from the new mechanism of emission directly from proton lines are
produced rather forward and backward but the corresponding cross section is
rather small. The processes considered here constitute a sizeable contribution
to the total proton-proton cross section as well as to kaon inclusive cross
section.
We consider a measurement of exclusive production of scalar meson
in the proton-proton collisions via decay. The
corresponding amplitude for exclusive central diffractive meson
production is calculated within the -factorization approach. The
influence of kinematical cuts on the signal-to-background ratio is discussed.Comment: 20 pages, 16 figures. text has been corrected and supplemented, cross
section for forward/backward mechanisms has been corrected. arXiv admin note:
substantial text overlap with arXiv:1103.564
Hyperbolic calorons, monopoles, and instantons
We construct families of SO(3)-symmetric charge 1 instantons and calorons on
the space H^3 x R. We show how the calorons include instantons and hyperbolic
monopoles as limiting cases. We show how Euclidean calorons are the flat space
limit of this family.Comment: 11 pages, no figures 1 reference added Published version available
at: http://www.springerlink.com/content/k0j4815u54303450
The impact of the final HERA combined data on PDFs obtained from a global fit.
We investigate the effect of including the HERA run I + II combined cross section data on the MMHT2014 PDFs. We present the fit quality within the context of the global fit and when only the HERA data are included. We examine the changes in both the central values and the uncertainties in the PDFs. We find that the prediction for the data is good, and only relatively small improvements in χ2χ2 and changes in the PDFs are obtained with a refit at both NLO and NNLO. PDF uncertainties are slightly reduced. There is a small dependence of the fit quality on the value of Q2minQmin2 . This can be improved by phenomenologically motived corrections to FL(x,Q2)FL(x,Q2) which parametrically are largely in the form of higher-twist type contributions
Measurement of exclusive production of scalar meson in proton-(anti)proton collisions via decay
We consider a measurement of exclusive production of scalar
meson in the proton-proton collisions at LHC and RHIC and in
the proton-antiproton collisions at the Tevatron via decay. The corresponding amplitude for exclusive
double-diffractive meson production was obtained within the
-factorization approach including virtualities of active gluons and the
corresponding cross section is calculated with unintegrated gluon distribution
functions (UGDFs) known from the literature. The four-body reaction constitutes an irreducible background to the exclusive
meson production. We calculate several differential distributions
for process including absorptive
corrections. The influence of kinematical cuts on the signal-to-background
ratio is investigated. Corresponding experimental consequences are discussed.Comment: 16 pages, 10 figures, 2 table
Signal specific electric potential sensors for operation in noisy environments
Limitations on the performance of electric potential sensors are due to saturation caused by environmental electromagnetic noise. The work described involves tailoring the response of the sensors to reject the main components of the noise, thereby enhancing both the effective dynamic range and signal to noise. We show that by using real-time analogue signal processing it is possible to detect a human heartbeat at a distance of 40 cm from the front of a subject in an unshielded laboratory. This result has significant implications both for security sensing and biometric measurements in addition to the more obvious safety related applications
Signatures of chaotic and non-chaotic-like behaviour in a non-linear quantum oscillator through photon detection
The driven non-linear duffing osillator is a very good, and standard, example
of a quantum mechanical system from which classical-like orbits can be
recovered from unravellings of the master equation. In order to generated such
trajectories in the phase space of this oscillator in this paper we use a the
quantum jumps unravelling together with a suitable application of the
correspondence principle. We analyse the measured readout by considering the
power spectra of photon counts produced by the quantum jumps. Here we show that
localisation of the wave packet from the measurement of the oscillator by the
photon detector produces a concomitant structure in the power spectra of the
measured output. Furthermore, we demonstrate that this spectral analysis can be
used to distinguish between different modes of the underlying dynamics of the
oscillator.Comment: 7 pages, 6 figure
Homogeneous nucleation of colloidal melts under the influence of shearing fields
We study the effect of shear flow on homogeneous crystal nucleation, using
Brownian Dynamics simulations in combination with an umbrella sampling like
technique. The symmetry breaking due to shear results in anisotropic radial
distribution functions. The homogeneous shear rate suppresses crystal
nucleation and leads to an increase of the size of the critical nucleus. These
observations can be described by a simple, phenomenological extension of
classical nucleation theory. In addition, we find that nuclei have a
preferential orientation with respect to the direction of shear. On average the
longest dimension of a nucleus is along the vorticity direction, while the
shortest dimension is preferably perpendicular to that and slightly tilted with
respect to the gradient direction.Comment: 10 pages, 8 figures, Submitted to J. Phys.: Condens. Matte
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