474 research outputs found
Testing Closed String Field Theory with Marginal Fields
We study the feasibility of level expansion and test the quartic vertex of
closed string field theory by checking the flatness of the potential in
marginal directions. The tests, which work out correctly, require the
cancellation of two contributions: one from an infinite-level computation with
the cubic vertex and the other from a finite-level computation with the quartic
vertex. The numerical results suggest that the quartic vertex contributions are
comparable or smaller than those of level four fields.Comment: 14 pages, LaTeX. v2: New references to work of Beccaria and Rampino,
and Taylor. Improved numerical analysis at the end of section
Homotopy Lie Superalgebra in Yang-Mills Theory
The Yang-Mills equations are formulated in the form of generalized
Maurer-Cartan equations, such that the corresponding algebraic operations are
shown to satisfy the defining relations of homotopy Lie superalgebra.Comment: LaTeX2e, 10 page
Yang-Mills Action from Open Superstring Field Theory
We calculate the effective action for nonabelian gauge bosons up to quartic
order using WZW-like open superstring field theory. After including level zero
and level one contributions, we obtain with 75% accuracy the Yang-Mills quartic
term. We then prove that the complete effective action reproduces the exact
Yang-Mills quartic term by analytically performing a summation over the
intermediate massive states.Comment: 10 page
Field Redefinitions, T-duality and Solutions in Closed String Field Theories
We investigate classical solutions in closed bosonic string field theory and
heterotic string field theory that are obtained order by order starting from
solutions of the linearized equations of motion, and we discuss the ``field
redefinitions'' which relate massless fields in the string field theory side
and the low energy effective theory side. Massless components of the string
field theory solutions are not corrected and from them we can infer
corresponding solutions in the effective theory: the chiral null model and the
pp-wave solution with B-field, which have been known to be alpha'-exact. These
two sets of solutions in the two sides look slightly different because of the
field redefinitions. It turns out that T-duality is a useful tool to determine
them: We show that some part of the field redefinitions can be determined by
using the correspondence between T-duality rules in the two sides, irrespective
of the detail of the interaction terms and the integrating-out procedure.
Applying the field redefinitions, we see that the solutions in the effective
theory side are reproduced from the string field theory solutions.Comment: LaTeX, 40 pages, no figure v2: minor corrections v3: minor correctio
Tibial tuberosity derotation: a surgical procedure for realignment of the patellofemoral mechanism
We retrospectively reviewed the clinical outcomes of 22 patients (9 men and 13 women) aged 17–42 years, and affected with anterior knee pain. These patients underwent surgical derotation of the tibial tuberosity in the period between September 1992 and December 1993. We describe the details of this new surgical technique to correct a torsional abnormality that has perhaps been underestimated in the past, as a possible cause of anterior knee pain. Follow-up clinical and radiographic controls (average follow-up, 78 months; range 72–87 months) allowed us to document the efficacy of this new procedure as a treatment for anterior knee pain resistant to conservative therapy, in young patients with external hypertorsion of the proximal tibial metaphysis and without significant chondropathology
Linear conduction in N-type organic field effect transistors with nanometric channel lengths and graphene as electrodes
In this work, we test graphene electrodes in nanometric channel n-type Organic Field Effect Transistors (OFETs) based on thermally evaporated thin films of the perylene-3,4,9,10-tetracarboxylic acid diimide derivative. By a thorough comparison with short channel transistors made with reference gold electrodes, we found that the output characteristics of the graphene-based devices respond linearly to the applied bias, in contrast with the supralinear trend of gold-based transistors. Moreover, short channel effects are considerably suppressed in graphene electrode devices. More specifically, current on/off ratios independent of the channel length (L) and enhanced response for high longitudinal biases are demonstrated for L down to 3c140 nm. These results are rationalized taking into account the morphological and electronic characteristics of graphene, showing that the use of graphene electrodes may help to overcome the problem of Space Charge Limited Current in short channel OFETs
Invariant Measures and Decay of Correlations for a Class of Ergodic Probabilistic Cellular Automata
We give new sufficient ergodicity conditions for two-state probabilistic
cellular automata (PCA) of any dimension and any radius. The proof of this
result is based on an extended version of the duality concept. Under these
assumptions, in the one dimensional case, we study some properties of the
unique invariant measure and show that it is shift-mixing. Also, the decay of
correlation is studied in detail. In this sense, the extended concept of
duality gives exponential decay of correlation and allows to compute
explicitily all the constants involved
A solution to the 4-tachyon off-shell amplitude in cubic string field theory
We derive an analytic series solution of the elliptic equations providing the
4-tachyon off-shell amplitude in cubic string field theory (CSFT). From such a
solution we compute the exact coefficient of the quartic effective action
relevant for time dependent solutions and we derive the exact coefficient of
the quartic tachyon coupling. The rolling tachyon solution expressed as a
series of exponentials is studied both using level-truncation
computations and the exact 4-tachyon amplitude. The results for the level
truncated coefficients are shown to converge to those derived using the exact
string amplitude. The agreement with previous work on the subject, both on the
quartic tachyon coupling and on the CSFT rolling tachyon, is an excellent test
for the accuracy of our off-shell solution.Comment: 26 pages, 5 figure
Evaluating the use of graphene electrodes in sub-micrometric, high-frequency n-type organic transistors
In this work we report on fully operational sub-micrometric low voltage OFETs by using graphene as the source-drain electrodes pair and a high-Îş ultra-thin dielectric in a local gate architecture. The impact of the graphene electrodes on the miniaturization of the organic devices has been assessed, with particular attention to the influence of the contact resistances as well as the parasitic overlap gate capacitance on the device bandwidth. By the use of a modified Transmission-Line-Method, contact resistances have been analyzed as function of the applied voltages, revealing characteristic functional trends that follow the doping state of graphene electrodes. Through impedance spectroscopy of the electrodes, cut-off frequencies as high as 105 Hz have been estimated, highlighting the peculiar role of quantum capacitance of graphene in such architectures
Cosmological tachyon from cubic string field theory
The classical dynamics of the tachyon scalar field of cubic string field
theory is considered on a cosmological background. Starting from a nonlocal
action with arbitrary tachyon potential, which encodes the bosonic and several
supersymmetric cases, we study the equations of motion in the Hamilton-Jacobi
formalism and with a generalized Friedmann equation, appliable in braneworld or
modified gravity models. The cases of cubic (bosonic) and quartic
(supersymmetric) tachyon potential in general relativity are automatically
included. We comment the validity of the slow-roll approximation, the stability
of the cosmological perturbations, and the relation between this tachyon and
the Dirac-Born-Infeld one.Comment: 20 pages JHEP style, 1 figure; v4: misprints corrected, matches the
published versio
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