7,240 research outputs found
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
Dark/Visible Parallel Universes and Big Bang Nucleosynthesis
We develop a model for visible matter-dark matter interaction based on the
exchange of a massive gray boson called herein the Mulato. Our model hinges on
the assumption that all known particles in the visible matter have their
counterparts in the dark matter. We postulate six families of particles five of
which are dark. This leads to the unavoidable postulation of six parallel
worlds, the visible one and five invisible worlds. A close study of big bang
nucleosynthesis (BBN), baryon asymmetries, cosmic microwave background (CMB)
bounds, galaxy dynamics, together with the Standard Model assumptions, help us
to set a limit on the mass and width of the new gauge boson. Modification of
the statistics underlying the kinetic energy distribution of particles during
the BBN is also discussed. The changes in reaction rates during the BBN due to
a departure from the Debye-Hueckel electron screening model is also
investigated.Comment: Invited talk at the Workshops "CompStar: the physics and astrophysics
of compact stars", Tahiti, June 4-8, 2012, "New Directions in Nuclear
Astrophysics", Castiglion Fiorentino, Italy, June 18-22, 2012, and
"Carpathian Summer School of Physics", Sinaia, Romania, June 24 - July 7,
2012. To be published in AIP Proceeding
Generation of photons from vacuum in cavity via time-modulation of a qubit invisible to the field
We propose a scheme for generation of photons from vacuum due to
time-modulation of a quantum system coupled indirectly to the cavity field
through some ancilla quantum subsystem. We consider the simplest case when the
modulation is applied to an artificial 2-level atom (we call t-qubit), while
the ancilla is a stationary qubit coupled via the dipole interaction both to
the cavity and t-qubit. We find that tripartite entangled states with a small
number of photons can be generated from the system ground state under resonant
modulations, even when the t-qubit is far detuned from both the ancilla and the
cavity, provided its bare and modulation frequencies are properly adjusted as
function of other system parameters. We attest our approximate analytic results
by numeric simulations and show that photon generation from vacuum persists in
the presence of common dissipation mechanisms
Vortex and gap generation in gauge models of graphene
Effective quantum field theoretical continuum models for graphene are
investigated. The models include a complex scalar field and a vector gauge
field. Different gauge theories are considered and their gap patterns for the
scalar, vector, and fermion excitations are investigated. Different gauge
groups lead to different relations between the gaps, which can be used to
experimentally distinguish the gauge theories. In this class of models the
fermionic gap is a dynamic quantity. The finite-energy vortex solutions of the
gauge models have the flux of the "magnetic field" quantized, making the
Bohm-Aharonov effect active even when external electromagnetic fields are
absent. The flux comes proportional to the scalar field angular momentum
quantum number. The zero modes of the Dirac equation show that the gauge models
considered here are compatible with fractionalization
Efeito da omissão de nutrientes nos teores de macronutrientes em tecidos foliares do cafeeiro "Acaiá do Cerrado".
Fungos associados a podridão penduncular em mangueira irrigada no submedio São Francisco e eficiencia de fungicidas in vitro e in vivo.
Fungos associados à podridão peduncular foram identificados e a eficiência de fungicidas foi avaliada
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