342 research outputs found
On the Structure of Noncommutative N=2 Super Yang-Mills Theory
We show that the recently proposed formulation of noncommutative N=2 Super
Yang-Mills theory implies that the commutative and noncommutative effective
coupling constants \tau(u) and \tau_{nc}(u) coincide. We then introduce a key
relation which allows to find a nontrivial solution of such equation, thus
fixing the form of the low-energy effective action. The dependence on the
noncommutative parameter arises from a rational function deforming the
Seiberg-Witten differential.Comment: 1+5 pages, LaTe
Multi - instantons, supersymmetry and topological field theories
In this letter we argue that instanton-dominated Green's functions in N=2 Super Yang-Mills theories can be equivalently computed either using the so-called constrained instanton method or making reference to the topological twisted version of the theory. Defining an appropriate BRST operator (as a supersymmetry plus a gauge variation), we also show that the expansion coefficients of the Seiberg-Witten effective action for the low-energy degrees of freedom can be written as integrals of total derivatives over the moduli space of self-dual gauge connections
Instanton Calculus, Topological Field Theories and N=2 Super Yang-Mills Theories
The results obtained by Seiberg and Witten for the low-energy Wilsonian
effective actions of N=2 supersymmetric theories with gauge group SU(2) are in
agreement with instanton computations carried out for winding numbers one and
two. This suggests that the instanton saddle point saturates the
non-perturbative contribution to the functional integral. A natural framework
in which corrections to this approximation are absent is given by the
topological field theory built out of the N=2 Super Yang-Mills theory. After
extending the standard construction of the Topological Yang-Mills theory to
encompass the case of a non-vanishing vacuum expectation value for the scalar
field, a BRST transformation is defined (as a supersymmetry plus a gauge
variation), which on the instanton moduli space is the exterior derivative. The
topological field theory approach makes the so-called "constrained instanton"
configurations and the instanton measure arise in a natural way. As a
consequence, instanton-dominated Green's functions in N=2 Super Yang-Mills can
be equivalently computed either using the constrained instanton method or
making reference to the topological twisted version of the theory. We
explicitly compute the instanton measure and the contribution to u=<\Tr
\phi^2> for winding numbers one and two. We then show that each
non-perturbative contribution to the N=2 low-energy effective action can be
written as the integral of a total derivative of a function of the instanton
moduli. Only instanton configurations of zero conformal size contribute to this
result. Finally, the 8k-dimensional instanton moduli space is built using the
hyperkahler quotient procedure, which clarifies the geometrical meaning of our
approach.Comment: latex, 66 page
Superspace Gauge Fixing of Topological Yang-Mills Theories
We revisit the construction of topological Yang-Mills theories of the Witten
type with arbitrary space-time dimension and number of ``shift supersymmetry''
generators, using a superspace formalism. The super-BF structure of these
theories is exploited in orderto determine their actions uniquely, up to the
ambiguities due to the fixing of the Yang-Mills and BF gauge invariance. UV
finiteness to all orders of perturbation theory is proved in a gauge of the
Landau type.Comment: 26 pages, no figures, Late
Accelerating D-branes
Higher derivative terms are computed in the one-loop effective action
governing the interactions of D3-branes, in two ways: (1) in a formalism with
N=2 supersymmetry preserved off-shell, and (2) in the standard background field
formalism, with only on-shell supersymmetry. It is shown that these
calculations only agree using tree-level equations of motion. The off-shell
supersymmetric calculation exhibits acceleration terms that appear in terms
with four derivatives. These may imply disagreement at two-loop order between
supergravity and Yang-Mills descriptions of D-brane dynamics.Comment: 11 pages, LaTeX. Minor wording change
Superlocalization formulas and supersymmetric Yang-Mills theories
By using supermanifold techniques we prove a generalization of the
localization formula in equivariant cohomology which is suitable for studying
supersymmetric Yang-Mills theories in terms of ADHM data. With these techniques
one can compute the reduced partition functions of topological super Yang-Mills
theory with 4, 8 or 16 supercharges. More generally, the superlocalization
formula can be applied to any topological field theory in any number of
dimensions.Comment: 22 pages, Latex2
On the Low-Energy Effective Action of N=2 Supersymmetric Yang-Mills Theory
We investigate the perturbative part of Seiberg's low-energy effective action
of N=2 supersymmetric Yang-Mills theory in Wess-Zumino gauge in the
conventional effective field theory technique. Using the method of constant
field approximation and restricting the effective action with at most two
derivatives and not more than four-fermion couplings, we show some features of
the low-energy effective action given by Seiberg based on anomaly and
non-perturbative -function arguments.Comment: 27 pages, RevTex, no figure
SPADAS: A high-speed 3D single-photon camera for advanced driver assistance systems
Advanced Driver Assistance Systems (ADAS) are the most advanced technologies to fight road accidents. Within ADAS, an important role is played by radar- and lidar-based sensors, which are mostly employed for collision avoidance and adaptive cruise control. Nonetheless, they have a narrow field-of-view and a limited ability to detect and differentiate objects. Standard camera-based technologies (e.g. stereovision) could balance these weaknesses, but they are currently not able to fulfill all automotive requirements (distance range, accuracy, acquisition speed, and frame-rate). To this purpose, we developed an automotive-oriented CMOS single-photon camera for optical 3D ranging based on indirect time-of-flight (iTOF) measurements. Imagers based on Single-photon avalanche diode (SPAD) arrays offer higher sensitivity with respect to CCD/CMOS rangefinders, have inherent better time resolution, higher accuracy and better linearity. Moreover, iTOF requires neither high bandwidth electronics nor short-pulsed lasers, hence allowing the development of cost-effective systems. The CMOS SPAD sensor is based on 64 × 32 pixels, each able to process both 2D intensity-data and 3D depth-ranging information, with background suppression. Pixel-level memories allow fully parallel imaging and prevents motion artefacts (skew, wobble, motion blur) and partial exposure effects, which otherwise would hinder the detection of fast moving objects. The camera is housed in an aluminum case supporting a 12 mm F/1.4 C-mount imaging lens, with a 40°×20° field-of-view. The whole system is very rugged and compact and a perfect solution for vehicle’s cockpit, with dimensions of 80 mm × 45 mm × 70 mm, and less that 1 W consumption. To provide the required optical power (1.5 W, eye safe) and to allow fast (up to 25 MHz) modulation of the active illumination, we developed a modular laser source, based on five laser driver cards, with three 808 nm lasers each. We present the full characterization of the 3D automotive system, operated both at night and during daytime, in both indoor and outdoor, in real traffic, scenario. The achieved long-range (up to 45m), high dynamic-range (118 dB), highspeed (over 200 fps) 3D depth measurement, and high precision (better than 90 cm at 45 m), highlight the excellent performance of this CMOS SPAD camera for automotive applications. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
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