6,182 research outputs found
Nanocrystal seeding: A low temperature route to polycrystalline Si films
A novel method is presented for growth of polycrystalline silicon films on amorphous substrates at temperatures of 540–575 °C. Grain nucleation and grain growth are performed in two steps, using Si nanocrystals as nuclei ("seeds"). The nanocrystal seeds are produced by excimer laser photolysis of disilane in a room temperature flow cell. Film (grain) growth occurs epitaxially on the seeds in a separate thermal chemical vapor deposition (CVD) step, with growth rates 10–100 times higher than similar CVD growth rates on crystal Si. Grain size and CVD growth rates are dependent on seed coverage, for seed coverage <0.2 monolayers
D=(2+1) O(N) Wess-Zumino model in a large N limit
Using the superfield formalism, the effective Kahlerian superpotential of the
massless \cal{N}=1 O(N) Wess-Zumino model is computed in the limit of large N,
in three spacetime dimensions. The effective Kahlerian superpotential is
evaluated at the subleading order in the 1/N expansion, which involves diagrams
up to two-loop order, for a small coupling constant. We show that the O(N)
symmetry of the model is preserved in this approximation and that no mass is
dynamically generated in the supersymmetric phase. We discuss why spontaneous
O(N) symmetry breaking cannot be induced by radiative corrections in such
model.Comment: 8 pages, 1 figur
Supersymmetric Fluid Dynamics
Recently Navier-Stokes (NS) equations have been derived from the duality
between the black branes and a conformal fluid on the boundary of AdS_5.
Nevertheless, the full correspondence has to be established between solutions
of supergravity in AdS_5 and supersymmetric field theories on the boundary.
That prompts the construction of NS equations for a supersymmetric fluid. In
the framework of rigid susy, there are several possibilities and we propose one
candidate. We deduce the equations of motion in two ways: both from the
divergenless condition on the energy-momentum tensor and by a suitable
parametrization of the auxiliary fields. We give the complete component
expansion and a very preliminary analysis of the physics of this supersymmetric
fluid.Comment: 24 pages, Latex2
Dynamical breaking of gauge symmetry in supersymmetric quantum electrodynamics in three-dimensional spacetime
The dynamical breaking of gauge symmetry in the supersymmetric quantum
electrodynamics in three-dimensional spacetime is studied at two-loop
approximation. At this level, the effective superpotential is evaluated in a
supersymmetric phase. At one-loop order, we observe a generation of the
Chern-Simons term due to a parity violating term present in the classical
action. At two-loop order, the scalar background superfield acquires a
nonvanishing vacuum expectation value, generating a mass term
through Coleman-Weinberg mechanism. It is observed that
the mass of gauge superfield is predominantly an effect of the topological
Chern-Simons term.Comment: 10 pages, 2 figures, PRD versio
Seeking the Loop Quantum Gravity Barbero-Immirzi Parameter and Field in 4D, = 1 Supergravity
We embed the Loop Quantum Gravity Barbero-Immirzi parameter and field within
an action describing 4D, = 1 supergravity and thus within a Low Energy
Effective Action of Superstring/M-Theory. We use the fully gauge-covariant
description of supergravity in (curved) superspace. The gravitational constant
is replaced with the vacuum expectation value of a scalar field, which in local
supersymmetry is promoted to a complex, covariantly chiral scalar superfield.
The imaginary part of this superfield couples to a supersymmetric Holst term.
The Holst term also serves as a starting point in the Loop Quantum Gravity
action. This suggest the possibility of a relation between Loop Quantum Gravity
and supersymmetric string theory, where the Barbero-Immirzi parameter and field
of the former play the role of the supersymmetric axion in the latter. Adding
matter fermions in Loop Quantum Gravity may require the extension of the Holst
action through the Nieh-Yan topological invariant, while in pure, matter-free
supergravity their supersymmetric extensions are the same. We show that, when
the Barbero-Immirzi parameter is promoted to a field in the context of 4D
supergravity, it is equivalent to adding a dynamical complex chiral
(dilaton-axion) superfield with a non-trivial kinetic term (or K\"ahler
potential), coupled to supergravity.Comment: 20 pages, 1 figure. Replaced with accepted version in Phys. Rev.
Perturbative finiteness of the three-dimensional Susy QED to all orders
Within the superfield formalism, we study the ultraviolet properties of the
three-dimensional supersymmetric quantum electrodynamics. The theory is shown
to be finite at all loops orders in a particular gauge.Comment: 8 pages, 3 figures, revtex
A Note on Embedding of M-Theory Corrections into Eleven-Dimensional Superspace
By analyzing eleven-dimensional superspace fourth-rank superfield strength
F-Bianchi identities, we show that M-theory corrections to eleven-dimensional
supergravity can not be embedded into the mass dimension zero constraints, such
as the (\g^{a b})_{\a\b} X_{a b}{}^c or i (\g^{a_1... a_5})_{\a\b} X_{a_1...
a_5}{}^c -terms in the supertorsion constraint T_{\a\b}{}^c. The only possible
modification of superspace constraint at dimension zero is found to be the
scaling of F_{\a\b c d} like F_{\a\b c d} = (1/2) \big(\g_{c d}\big)_{\a\b}
e^\Phi for some real scalar superfield \Phi, which alone is further shown not
enough to embed general M-theory corrections. This conclusion is based on the
dimension zero F-Bianchi identity under the two assumptions: (i) There are no
negative dimensional constraints on the F-superfield strength: F_{\a\b\g\d} =
F_{\a\b\g d} =0; (ii) The supertorsion T-Bianchi identities and F-Bianchi
identities are not modified by Chern-Simons terms. Our result can serve as a
powerful tool for future exploration of M-theory corrections embedded into
eleven-dimensional superspace supergravity.Comment: 14 pages, latex, some minor typos corrected, as well as old section 5
deleted, due to the subtlety about Chern-Simons term in F-Bianchi identitie
Identification of the orphan gene Prod 1 in basal and other salamander families.
The urodele amphibians (salamanders) are the only adult tetrapods able to regenerate the limb. It is unclear if this is an ancestral property that is retained in salamanders but lost in other tetrapods or if it evolved in salamanders. The three-finger protein Prod 1 is implicated in the mechanism of newt limb regeneration, and no orthologs have been found in other vertebrates, thus providing evidence for the second viewpoint. It has also been suggested that this protein could play a role in salamander-specific aspects of limb development. There are ten families of extant salamanders, and Prod 1 has only been identified in two of them to date. It is important to determine if it is present in other families and, particularly, the basal group of two families which diverged approximately 200 MYA
Supersymmetric K field theories and defect structures
We construct supersymmetric K field theories (i.e., theories with a
non-standard kinetic term) in 1+1 and 2+1 dimensions such that the bosonic
sector just consists of a nonstandard kinetic term plus a potential. Further,
we study the possibility of topological defect formation in these
supersymmetric models. Finally, we consider more general supersymmetric K field
theories where, again, topological defects exist in some cases.Comment: Latex, 6 figures, 27 page
Coleman-Weinberg mechanism in a three-dimensional supersymmetric Chern-Simons-matter model
Using the superfield formalism, we study the dynamical breaking of gauge
symmetry in the N=1 three-dimensional supersymmetric Chern-Simons model,
coupled to a complex scalar superfield with a quartic self-coupling. This is an
analogue of the conformally invariant Coleman-Weinberg model in four spacetime
dimensions. We show that a mass for the gauge and matter superfields are
dynamically generated after two-loop corrections to the effective
superpotential. We also discuss the N=2 extension of our work, showing that the
Coleman-Weinberg mechanism in such model is not feasible, because it is
incompatible with perturbation theory.Comment: 14 pages, 2 figures. Minor corrections, references added. Journal
versio
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