3,357 research outputs found
Instanton Dynamics in the Broken Phase of the Topological Sigma Model
The topological model with the black hole metric of the target space
is considered. It has been shown before that this model is in the phase with
BRST-symmetry broken. In particular, vacuum energy is non-\-zero and
correlation functions of observables show the coordinate dependence. However
these quantities turned out to be infrared (IR) divergent. It is shown here
that IR divergences disappear after the sum over an arbitrary number of
additional instanton-\-anti-\-instanton pairs is performed. The model appears
to be equivalent to Coulomb gas/Sine Gordon system.Comment: some references added
The Broken Phase of the Topological Sigma model
The topological sigma model with the semi-infinite cigar-like target space
(black hole geometry) is considered. The model is shown to possess unsuppressed
instantons. The noncompactness of the moduli space of these instantons is
responsible for an unusual physics. There is a stable vacuum state in which the
vacuum energy is zero, correlation functions are numbers thus the model is in
the topological phase. However, there are other vacuum states in which
correlation functions show the coordinate dependence. The estimation of the
vacuum energy indicates that it is nonzero. These states are interpreted as the
ones with broken BRST-symmetry.Comment: 30 pages, LATE
The Higgs and Coulomb/Confining Phases in "Twisted-Mass" Deformed CP(N-1) Model
We consider non-supersymmetric two-dimensional CP(N-1) model deformed by a
term presenting the bosonic part of the twisted mass deformation of N=2
supersymmetric version of the model. Our deformation has a special form
preserving a Z_N symmetry at the Lagrangian level. In the large mass limit the
model is weakly coupled. Its dynamics is described by the Higgs phase, with Z_N
spontaneously broken. At small masses it is in the strong coupling
Coulomb/confining phase. The Z_N symmetry is restored. Two phases are separated
by a phase transition. We find the phase transition point in the large-N limit.
It lies at strong coupling. As was expected, the phase transition is related to
broken versus unbroken Z_N symmetry in these two respective phases. The vacuum
energies for these phases are determined too.Comment: 20 pages, 3 figures, reference adde
Dynamical Electron Mass in a Strong Magnetic Field
Motivated by recent interest in understanding properties of strongly
magnetized matter, we study the dynamical electron mass generated through
approximate chiral symmetry breaking in QED in a strong magnetic field. We
reliably calculate the dynamical electron mass by numerically solving the
nonperturbative Schwinger-Dyson equations in a consistent truncation within the
lowest Landau level approximation. It is shown that the generation of dynamical
electron mass in a strong magnetic field is significantly enhanced by the
perturbative electron mass that explicitly breaks chiral symmetry in the
absence of a magnetic field.Comment: 5 pages, 1 figure, published versio
Introduction to Graphene Electronics -- A New Era of Digital Transistors and Devices
The speed of silicon-based transistors has reached an impasse in the recent
decade, primarily due to scaling techniques and the short-channel effect.
Conversely, graphene (a revolutionary new material possessing an atomic
thickness) has been shown to exhibit a promising value for electrical
conductivity. Graphene would thus appear to alleviate some of the drawbacks
associated with silicon-based transistors. It is for this reason why such a
material is considered one of the most prominent candidates to replace silicon
within nano-scale transistors. The major crux here, is that graphene is
intrinsically gapless, and yet, transistors require a band-gap pertaining to a
well-defined ON/OFF logical state. Therefore, exactly as to how one would
create this band-gap in graphene allotropes is an intensive area of growing
research. Existing methods include nano-ribbons, bilayer and multi-layer
structures, carbon nanotubes, as well as the usage of the graphene substrates.
Graphene transistors can generally be classified according to two working
principles. The first is that a single graphene layer, nanoribbon or carbon
nanotube can act as a transistor channel, with current being transported along
the horizontal axis. The second mechanism is regarded as tunneling, whether
this be band-to-band on a single graphene layer, or vertically between adjacent
graphene layers. The high-frequency graphene amplifier is another talking point
in recent research, since it does not require a clear ON/OFF state, as with
logical electronics. This paper reviews both the physical properties and
manufacturing methodologies of graphene, as well as graphene-based electronic
devices, transistors, and high-frequency amplifiers from past to present
studies. Finally, we provide possible perspectives with regards to future
developments.Comment: This is an updated version of our review article, due to be published
in Contemporary Physics (Sept 2013). Included are updated references, along
with a few minor corrections. (45 pages, 19 figures
Quantum Communication Through a Spin-Ring with Twisted Boundary Conditions
We investigate quantum communication between the sites of a spin-ring with
twisted boundary conditions. Such boundary conditions can be achieved by a flux
through the ring. We find that a non-zero twist can improve communication
through finite odd numbered rings and enable high fidelity multi-party quantum
communication through spin rings (working near perfectly for rings of 5 and 7
spins). We show that in certain cases, the twist results in the complete
blockage of quantum information flow to a certain site of the ring. This effect
can be exploited to interface and entangle a flux qubit and a spin qubit
without embedding the latter in a magnetic field.Comment: four pages two figure
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