18,638 research outputs found
Constraining heavy colored resonances from top-antitop quark events
Recent measurements of the top quark charge asymmetry at Tevatron disfavor
the existence of flavor universal axigluons and colorons at 2 sigmas. In this
letter we explore the possibility to reconcile the data with these models and
use the charge asymmetry and the invariant mass distribution of top-antitop
quark pair events to constrain the mass and couplings of massive color-octet
gauge bosons decaying to top quarks.Comment: 4 pages, 4 figures. References added, final version to appear in
Phys.Rev.
All-optical control of surface plasmons by second-harmonic generation
Light with light control of surface plasmon polaritons is theoretically
demonstrated. A barely simple and compact source of these waves consists in a
finite number of slits (evenly spaced) perforating a metal film. The system
scatters electromagnetic fields in one side of the metal film when it is
illuminated from the opposite side by a polarized light source. High intensity
light sources moreover efficiently generate light at second harmonic and higher
frequencies in the metal led by optical nonlinearities. It is shown how the
mixing of fields scattered by the slits from a weak beam at
wavelength, with the second harmonic fields generated by a high intensity beam, creates a destructive interference of surface plasmons in one of
the two possible directions of emission from the slits, while these are
enhanced along the opposite direction. The unidirectional launching of surface
plasmons is due to the different properties of symmetry at whether
they are linearly or nonlinearly generated. It is envisaged a nanodevice which
might allow sending digital information codified in the surface plasmon field
or be used to build ultra-narrow bandwidth surface plasmon frequency combs.Comment: 5 pages, 3 figures, Supplemental Materia
Spin-charge coupling in quantum wires at zero magnetic field
We discuss an approximation for the dynamic charge response of nonlinear
spin-1/2 Luttinger liquids in the limit of small momentum. Besides accounting
for the broadening of the charge peak due to two-holon excitations, the
nonlinearity of the dispersion gives rise to a two-spinon peak, which at zero
temperature has an asymmetric line shape. At finite temperature the spin peak
is broadened by diffusion. As an application, we discuss the density and
temperature dependence of the Coulomb drag resistivity due to long-wavelength
scattering between quantum wires.Comment: 16 pages, 5 figures. This is an extended version of "Coulomb drag
from spin-charge coupling at zero magnetic field
Arnold diffusion for a complete family of perturbations with two independent harmonics
We prove that for any non-trivial perturbation depending on any two
independent harmonics of a pendulum and a rotor there is global instability.
The proof is based on the geometrical method and relies on the concrete
computation of several scattering maps. A complete description of the different
kinds of scattering maps taking place as well as the existence of piecewise
smooth global scattering maps is also provided.Comment: 23 pages, 14 figure
Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders
Several models predict the existence of heavy colored resonances decaying to
top quarks in the TeV energy range that might be discovered at the LHC. In some
of those models, moreover, a sizable charge asymmetry of top versus antitop
quarks might be generated. The detection of these exotic resonances, however,
requires selecting data samples where the top and the antitop quarks are highly
boosted, which is experimentally very challenging. We asses that the
measurement of the top quark charge asymmetry at the LHC is very sensitive to
the existence of excited states of the gluon with axial-vector couplings to
quarks. We use a toy model with general flavour independent couplings, and show
that a signal can be detected with relatively not too energetic top and antitop
quarks. We also compare the results with the asymmetry predicted by QCD, and
show that its highest statistical significance is achieved with data samples of
top-antitop quark pairs of low invariant masses.Comment: 20 page
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