8,506 research outputs found
Charge confinement and Klein tunneling from doping graphene
In the present work, we investigate how structural defects in graphene can
change its transport properties. In particular, we show that breaking of the
sublattice symmetry in a graphene monolayer overcomes the Klein effect, leading
to confined states of massless Dirac fermions. Experimentally, this corresponds
to chemical bonding of foreign atoms to carbon atoms, which attach themselves
to preferential positions on one of the two sublattices. In addition, we
consider the scattering off a tensor barrier, which describes the rotation of
the honeycomb cells of a given region around an axis perpendicular to the
graphene layer. We demonstrate that in this case the intervalley mixing between
the Dirac points emerges, and that Klein tunneling occurs.Comment: 11 pages, 5 figure
Hadrons in AdS/QCD models
We discuss applications of gauge/gravity duality to describe the spectrum of
light hadrons. We compare two particular 5-dimensional approaches: a model with
an infrared deformed Anti-de Sitter metric and another one based on a dynamical
AdS/QCD framework with back-reacted geometry in a dilaton/gravity background.
The models break softly the scale invariance in the infrared region and allow
mass gap for the field excitations in the gravity description, while keeping
the conformal property of the metric close to the four-dimensional boundary.
The models provide linear Regge trajectories for light mesons, associated with
specially designed infrared gravity properties. We also review the results for
the decay widths of the f0's into two pions, as overlap integrals between
mesonic string amplitudes, which are in qualitative agreement with data
Fermionic bound states in Minkowski-space: Light-cone singularities and structure
The Bethe-Salpeter equation for two-body bound system with spin
constituent is addressed directly in the Minkowski space. In order to
accomplish this aim we use the Nakanishi integral representation of the
Bethe-Salpeter amplitude and exploit the formal tool represented by the exact
projection onto the null-plane. This formal step allows one i) to deal with
end-point singularities one meets and ii) to find stable results, up to
strongly relativistic regimes, that settles in strongly bound systems. We apply
this technique to obtain the numerical dependence of the binding energies upon
the coupling constants and the light-front amplitudes for a fermion-fermion
state with interaction kernels, in ladder approximation, corresponding to
scalar-, pseudoscalar- and vector boson exchanges, respectively. After
completing the numerical survey of the previous cases, we extend our approach
to a quark-antiquark system in state, taking both constituent-fermion and
exchanged boson masses, from lattice calculations. Interestingly, the
calculated light-front amplitudes for such a mock pion show peculiar signatures
of the spin degrees of freedom.Comment: 22 pages, 7 figures, bst file include
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