69,360 research outputs found
An almost existence theorem for non-contractible periodic orbits in cotangent bundles
Assume M is a closed connected smooth manifold and H:T^*M->R a smooth proper
function bounded from below. Suppose the sublevel set {H<d} contains the zero
section and \alpha is a non-trivial homotopy class of free loops in M. Then for
almost every s>=d the level set {H=s} carries a periodic orbit z of the
Hamiltonian system (T^*M,\omega_0,H) representing \alpha.
Examples show that the condition that {H<d} contains M is necessary and
almost existence cannot be improved to everywhere existence.Comment: 9 pages, 4 figures. v2: corrected typo
Elucidating the multiplicity dependence of J/ production in proton-proton collisions with PYTHIA8
A study of prompt and non-prompt J/ production as a function of
charged-particle multiplicity in inelastic proton--proton (pp) collisions at a
centre-of-mass energy of = 13 TeV based on calculations using the
PYTHIA8 Monte Carlo is reported. Recent experimental data shows an intriguing
stronger-than-linear increase of the self-normalized J/ yield with
multiplicity; several models, based on initial or final state effects, have
been able to describe the observed behaviour. In this paper, the microscopic
reasons for this behaviour, like the role of multiple parton interactions,
colour reconnections and auto-correlations are investigated. It is observed
that the stronger-than-linear increase and the transverse momentum () dependence, contrary to what is predicted by the other available models,
can be attributed to auto-correlation effects only. In absence of
auto-correlation effects, the increase of the yield of J/ with
multiplicity -- and in general for all hard processes -- is weaker than linear
for multiplicities exceeding about three times the mean multiplicity. The
possibility of disentangling auto-correlation effects from other physical
phenomena by measuring the charged-particle multiplicity in different
pseudo-rapidity and azimuthal regions relative to the J/ direction is
investigated. In this regard, it is suggested to extend the experimental
measurements of J/ production as a function of the charged-particle
multiplicity by determining the multiplicity in several azimuthal regions and
in particular in the Transverse region with respect to the direction of the
J/ meson.Comment: 12 pages, 14 figures: accepted by EPJ
A Theory on the Convective Origins of Active Longitudes on Solar-like Stars
Using a thin flux tube model in a rotating spherical shell of turbulent,
solar-like convective flows, we find that the distribution of emerging flux
tubes in our simulation is inhomogeneous in longitude, with properties similar
to those of active longitudes on the Sun and other solar-like stars. The
large-scale pattern of flux emergence our simulations produce exhibits
preferred longitudinal modes of low order, drift with respect to a fixed
reference system, and alignment across the Equator at low latitudes between 15
degrees. We suggest that these active-longitude-like emergence patterns are the
result of columnar, rotationally aligned giant cells present in our convection
simulation at low latitudes. If giant convecting cells exist in the bulk of the
solar convection zone, this phenomenon, along with differential rotation, could
in part provide an explanation for the behavior of active longitudes.Comment: This paper was accepted to The Astrophysical Journal on May 6, 201
Morse homology for the heat flow
We use the heat flow on the loop space of a closed Riemannian manifold to
construct an algebraic chain complex. The chain groups are generated by
perturbed closed geodesics. The boundary operator is defined in the spirit of
Floer theory by counting, modulo time shift, heat flow trajectories that
converge asymptotically to nondegenerate closed geodesics of Morse index
difference one.Comment: 89 pages, 3 figure
Comparative study of the electron- and positron-atom bremsstrahlung
Fully relativistic treatment of the electron-atom and positron-atom
bremsstrahlung is reported. The calculation is based on the partial-wave
expansion of the Dirac scattering states in an external atomic field. A
comparison of the electron and positron bremsstrahlung is presented for the
single and double differential cross sections and the Stokes parameters of the
emitted photon. It is demonstrated that the electron-positron symmetry of the
bremsstrahlung spectra, which is nearly exact in the nonrelativistic regime, is
to a large extent removed by the relativistic effects
Performance characteristics of wind profiling radars
Doppler radars used to measure winds in the troposphere and lower stratosphere for weather analysis and forecasting are lower-sensitivity versions of mesosphere-stratosphere-troposphere radars widely used for research. The term wind profiler is used to denote these radars because measurements of vertical profiles of horizontal and vertical wind are their primary function. It is clear that wind profilers will be in widespread use within five years: procurement of a network of 30 wind profilers is underway. The Wave Propagation Laboratory (WPL) has operated a small research network of radar wind profilers in Colorado for about two and one-half years. The transmitted power and antenna aperture for these radars is given. Data archiving procedures have been in place for about one year, and this data base is used to evaluate the performance of the radars. One of the prime concerns of potential wind profilers users is how often and how long wind measurements are lacking at a given height. Since these outages constitute an important part of the performance of the wind profilers, they are calculated at three radar frequencies, 50-, 405-, and 915-MHz, (wavelengths of 6-, 0.74-, and 0.33-m) at monthly intervals to determine both the number of outages at each frequency and annual variations in outages
Electroweak corrections to e+ e- -> nu anti-nu H and e+ e- -> t anti-t H
The most interesting Higgs-production processes at future e+ e- colliders
belong to the process class e+ e- -> f anti-f H. We study the full O(alpha)
corrections to this reaction in the Standard Model for neutrinos and top quarks
in the final state. Leading higher-order corrections from initial-state
radiation and QCD corrections are also taken into account. Although
cancellations between the different kinds of corrections occur, the full
corrections are of the order of +/-10% and thus important ingredients in the
theoretical predictions for future e+ e- colliders.Comment: 3 pages, LaTeX, 4 postscript figures, talk given at the EPS
conference, Aachen, 200
Z Pole Observables in the MSSM
We present the currently most accurate prediction of Z pole observables such
as sin^2 theta_eff, Gamma_Z, R_b, R_l, and sigma^0_had in the Minimal
Supersymmetric Standard Model (MSSM). We take into account the complete
one-loop results including the full complex phase dependence, all available
MSSM two-loop corrections as well as the full SM results. We furthermore
include higher-order corrections in the MSSM Higgs boson sector, entering via
virtual Higgs boson contributions. For Gamma(Z -> neutralino{1} neutralino{1})
we present a full one-loop calculation. We analyse the impact of the different
sectors of the MSSM with particular emphasis on the effects of the complex
phases. The predictions for the Z boson observables and M_W are compared with
the current experimental values. Furthermore we provide an estimate of the
remaining higher-order uncertainties in the prediction of sin^2 theta_eff.Comment: 53 pages, 20 figures, journal versio
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