72,742 research outputs found
A Time-Periodic Lyapunov Approach for Motion Planning of Controllable Driftless Systems on SU(n)
For a right-invariant and controllable driftless system on SU(n), we consider
a time-periodic reference trajectory along which the linearized control system
generates su(n): such trajectories always exist and constitute the basic
ingredient of Coron's Return Method. The open-loop controls that we propose,
which rely on a left-invariant tracking error dynamics and on a fidelity-like
Lyapunov function, are determined from a finite number of left-translations of
the tracking error and they assure global asymptotic convergence towards the
periodic reference trajectory. The role of these translations is to avoid being
trapped in the critical region of this Lyapunov-like function. The convergence
proof relies on a periodic version of LaSalle's invariance principle and the
control values are determined by numerical integration of the dynamics of the
system. Simulations illustrate the obtained controls for and the
generation of the C--NOT quantum gate.Comment: Submitte
Neutrino masses and mixing in A4 models with three Higgs doublets
We study neutrino masses and mixing in the context of flavor models with A4
symmetry, three scalar doublets in the triplet representation, and three lepton
families. We show that there is no representation assignment that yields a
dimension-five mass operator consistent with experiment. We then consider a
type-I seesaw with three heavy right-handed neutrinos, explaining in detail why
it fails, and showing with a numerical example that agreement with the present
neutrino oscillation data can be recovered with the inclusion of
dimension-three heavy neutrino mass terms that break softly the A4 symmetry.Comment: 10 pages, RevTex, 3 figures. v2: much expanded section on softly
broken A4; refs adde
Quantum Electro and Chromodynamics treated by Thompson's heuristic approach
In this work we apply Thompson's method (of the dimensions and scales) to
study some features of the Quantum Electro and Chromodynamics. This heuristic
method can be considered as a simple and alternative way to the Renormalisation
Group (R.G.) approach and when applied to QED-lagrangian is able to obtain in a
first approximation both the running coupling constant behavior of alpha(mu)
and the mass m(mu).The calculations are evaluated just at d_c=4, where d_c is
the upper critical dimension of the problem, so that we obtain the logarithmic
behavior both for the coupling alpha and the excess of mass Delta m on the
energy scale mu. Although our results are well-known in the vast literature of
field theories,it seems that one of the advantages of Thompson's method, beyond
its simplicity is that it is able to extract directly from QED-lagrangian the
physical (finite) behavior of alpha(mu) and m(mu), bypassing hard problems of
divergences which normally appear in the conventional renormalisation schemes
applied to field theories like QED. Quantum Chromodynamics (QCD) is also
treated by the present method in order to obtain the quark condensate value.
Besides this, the method is also able to evaluate the vacuum pressure at the
boundary of the nucleon. This is done by assumming a step function behavior for
the running coupling constant of the QCD, which fits nicely to some quantities
related to the strong interaction evaluated through the MIT-bag model.Comment: RevTex, 25 pages, no figure
Basis invariant conditions for supersymmetry in the two-Higgs-doublet model
The minimal supersymmetric standard model involves a rather restrictive Higgs
potential with two Higgs fields. Recently, the full set of classes of
symmetries allowed in the most general two Higgs doublet model was identified;
these classes do not include the supersymmetric limit as a particular class.
Thus, a physically meaningful definition of the supersymmetric limit must
involve the interaction of the Higgs sector with other sectors of the theory.
Here we show how one can construct basis invariant probes of supersymmetry
involving both the Higgs sector and the gaugino-higgsino Higgs interactions.Comment: RevTex, 11 pages, v2-small section adde
Semi-Automated SVG Programming via Direct Manipulation
Direct manipulation interfaces provide intuitive and interactive features to
a broad range of users, but they often exhibit two limitations: the built-in
features cannot possibly cover all use cases, and the internal representation
of the content is not readily exposed. We believe that if direct manipulation
interfaces were to (a) use general-purpose programs as the representation
format, and (b) expose those programs to the user, then experts could customize
these systems in powerful new ways and non-experts could enjoy some of the
benefits of programmable systems.
In recent work, we presented a prototype SVG editor called Sketch-n-Sketch
that offered a step towards this vision. In that system, the user wrote a
program in a general-purpose lambda-calculus to generate a graphic design and
could then directly manipulate the output to indirectly change design
parameters (i.e. constant literals) in the program in real-time during the
manipulation. Unfortunately, the burden of programming the desired
relationships rested entirely on the user.
In this paper, we design and implement new features for Sketch-n-Sketch that
assist in the programming process itself. Like typical direct manipulation
systems, our extended Sketch-n-Sketch now provides GUI-based tools for drawing
shapes, relating shapes to each other, and grouping shapes together. Unlike
typical systems, however, each tool carries out the user's intention by
transforming their general-purpose program. This novel, semi-automated
programming workflow allows the user to rapidly create high-level, reusable
abstractions in the program while at the same time retaining direct
manipulation capabilities. In future work, our approach may be extended with
more graphic design features or realized for other application domains.Comment: In 29th ACM User Interface Software and Technology Symposium (UIST
2016
Some properties of two Nambu--Jona-Lasinio -type models with inputs from lattice QCD
We investigate the phase diagram of the so-called
Polyakov--Nambu--Jona-Lasinio (PNJL) model at finite temperature and nonzero
chemical potential. The calculations are performed in the light and strange
quark sectors (, , ), which includes the 't Hooft instanton induced
interaction term that breaks the axial symmetry, and the quarks are coupled to
the (spatially constant) temporal background gauge field. On one hand, a
special attention is payed to the critical end point (CEP). The strength of the
flavor-mixing interaction alters the CEP location, since when it becomes weaker
the CEP moves to low temperatures and can even disappear. On the other hand, we
also explore the connection between QCD, a nonlocal Nambu--Jona-Lasinio type
model and the Landau gauge gluon propagator. Possible links between the
quenched gluon propagator and low energy hadronic phenomenology are
investigated.Comment: Contribution to the International Meeting "Excited QCD", Peniche,
Portugal, 06 - 12 May 201
Quark matter revisited with non extensive MIT bag model
In this work we revisit the MIT bag model to describe quark matter within
both the usual Fermi-Dirac and the Tsallis statistics. We verify the effects of
the non-additivity of the latter by analysing two different pictures: the first
order phase transition of the QCD phase diagram and stellar matter properties.
While, the QCD phase diagram is visually affected by the Tsallis statistics,
the resulting effects on quark star macroscopic properties are barely noticed.Comment: 10 pagens, 5 figure
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