87 research outputs found
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
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
Analysis of Rail Yard and Terminal Performances
One of the latest trends in the transport field is the increasing interest for the rejuvenation of the railway. It is considered to be a logical consequence of the gradual switch towards a more sustainable future in transports. Terminals and stations are considered to be the junction points between the various lines that constitute the railway network and can simply be described as points of arrival, departure and interchange of passengers or commodities. The most commonly used indicators that measure the level of their performance are time and cost. This study aims at exploring possible improvements that could be implemented to the infrastructure and the operation of terminals and stations in order to increase the efficiency level. Firstly, drawing upon grounded theory, a description is conducted, followed by a comparative analysis of the different types of existing terminals and stations. Secondly, the suggested improvements are presented in accordance with their time frame completion. The main contribution of the study is to illustrate the high significance of terminals, stations and yards, given the fact that they are considered to be crucial parts of the railway network. In addition to this, great emphasis is given to the need of improving and developing the existing terminal infrastructure and operations
N=2 SYM Action as a BRST Exact Term, Topological Yang Mills and Instantons
By constructing a nilpotent extended BRST operator \bs that involves the
N=2 global supersymmetry transformations of one chirality, we show that the
standard N=2 off-shell Super Yang Mills Action can be represented as an exact
BRST term \bs \Psi, if the gauge fermion is allowed to depend on the
inverse powers of supersymmetry ghosts. By using this nonanalytical structure
of the gauge fermion (via inverse powers of supersymmetry ghosts), we give
field redefinitions in terms of composite fields of supersymmetry ghosts and
N=2 fields and we show that Witten's topological Yang Mills theory can be
obtained from the ordinary Euclidean N=2 Super Yang Mills theory directly by
using such field redefinitions. In other words, TYM theory is obtained as a
change of variables (without twisting). As a consequence it is found that
physical and topological interpretations of N=2 SYM are intertwined together
due to the requirement of analyticity of global SUSY ghosts. Moreover, when
after an instanton inspired truncation of the model is used, we show that the
given field redefinitions yield the Baulieu-Singer formulation of Topological
Yang Mills.Comment: Latex, 1+15 pages. Published versio
Microscopic quantum superpotential in N=1 gauge theories
We consider the N=1 super Yang-Mills theory with gauge group U(N), adjoint
chiral multiplet X and tree-level superpotential Tr W(X). We compute the
quantum effective superpotential W_mic as a function of arbitrary off-shell
boundary conditions at infinity for the scalar field X. This effective
superpotential has a remarkable property: its critical points are in one-to-one
correspondence with the full set of quantum vacua of the theory, providing in
particular a unified picture of solutions with different ranks for the low
energy gauge group. In this sense, W_mic is a good microscopic effective
quantum superpotential for the theory. This property is not shared by other
quantum effective superpotentials commonly used in the literature, like in the
strong coupling approach or the glueball superpotentials. The result of this
paper is a first step in extending Nekrasov's microscopic derivation of the
Seiberg-Witten solution of N=2 super Yang-Mills theories to the realm of N=1
gauge theories.Comment: 23 pages, 1 figure; typos corrected, version to appear in JHE
Matone's Relation in the Presence of Gravitational Couplings
The prepotential in N=2 SUSY Yang-Mills theories enjoys remarkable
properties. One of the most interesting is its relation to the coordinate on
the quantum moduli space that results into recursion
equations for the coefficients of the prepotential due to instantons. In this
work we show, with an explicit multi-instanton computation, that this relation
holds true at arbitrary winding numbers. Even more interestingly we show that
its validity extends to the case in which gravitational corrections are taken
into account if the correlators are suitably modified. These results apply also
to the cases in which matter in the fundamental and in the adjoint is included.
We also check that the expressions we find satisfy the chiral ring relations
for the gauge case and compute the first gravitational correction.Comment: 21 page
Instantons on Quivers and Orientifolds
We compute the prepotential for gauge theories descending from
SYM via quiver projections and mass deformations.
This accounts for gauge theories with product gauge groups and bifundamental
matter. The case of massive orientifold gauge theories with gauge group SO/Sp
is also described. In the case with no gravitational corrections the results
are shown to be in agreement with Seiberg-Witten analysis and previous results
in the literature.Comment: 28 pages, revised version, references added, some typos correcte
N=2 SYM RG Scale as Modulus for WDVV Equations
We derive a new set of WDVV equations for N=2 SYM in which the
renormalization scale is identified with the distinguished modulus
which naturally arises in topological field theories.Comment: 6 pages, LaTe
Calculating the Prepotential by Localization on the Moduli Space of Instantons
We describe a new technique for calculating instanton effects in
supersymmetric gauge theories applicable on the Higgs or Coulomb branches. In
these situations the instantons are constrained and a potential is generated on
the instanton moduli space. Due to existence of a nilpotent fermionic symmetry
the resulting integral over the instanton moduli space localizes on the
critical points of the potential. Using this technology we calculate the one-
and two-instanton contributions to the prepotential of SU(N) gauge theory with
N=2 supersymmetry and show how the localization approach yields the prediction
extracted from the Seiberg-Witten curve. The technique appears to extend to
arbitrary instanton number in a tractable way.Comment: 24 pages, JHEP.cls, more references and extra discussion on N_F=2N
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