178,812 research outputs found
Are neutrino masses modular forms?
We explore a new class of supersymmetric models for lepton masses and mixing
angles where the role of flavour symmetry is played by modular invariance. The
building blocks are modular forms of level N and matter supermultiplets, both
transforming in representations of a finite discrete group Gamma_N. In the
simplest version of these models, Yukawa couplings are just modular forms and
the only source of flavour symmetry breaking is the vacuum expectation value of
a single complex field, the modulus. In the special case where modular forms
are constant functions the whole construction collapses to a supersymmetric
flavour model invariant under Gamma_N, the case treated so far in the
literature. The framework has a number of appealing features. Flavon fields
other than the modulus might not be needed. Neutrino masses and mixing angles
are simultaneously constrained by the modular symmetry. As long as
supersymmetry is exact, modular invariance determines all higher-dimensional
operators in the superpotential. We discuss the general framework and we
provide complete examples of the new construction. The most economical model
predicts neutrino mass ratios, lepton mixing angles, Dirac and Majorana phases
uniquely in terms of the modulus vacuum expectation value, with all the
parameters except one within the experimentally allowed range. As a byproduct
of the general formalism we extend the notion of non-linearly realised
symmetries to the discrete case.Comment: 40 pages, 3 figures; added comments and a new section with an example
of normal ordering of neutrino masses; to appear in the book "From my vast
repertoire: the legacy of Guido Altarelli", S. Forte, A. Levy and G. Ridolfi,
ed
Sigma Model BPS Lumps on Torus
We study doubly periodic Bogomol'nyi-Prasad-Sommerfield (BPS) lumps in
supersymmetric CP^{N-1} non-linear sigma models on a torus T^2. Following the
philosophy of the Harrington-Shepard construction of calorons in Yang-Mills
theory, we obtain the n-lump solutions on compact spaces by suitably arranging
the n-lumps on R^2 at equal intervals. We examine the modular invariance of the
solutions and find that there are no modular invariant solutions for n=1,2 in
this construction.Comment: 15 pages, 3 figures, published versio
Generalized string compactifications with spontaneously broken supersymmetry
The Narain lattice construction of string compactifications is generalized to
include spontaneously broken supersymmetry. Consistency conditions from modular
invariance and Lorentz symmetry are solved in full generality. This framework
incorporates models where supersymmetry breaking is inversely proportional to
the radii of compact dimensions. The enhanced lattice description, however,
might allow for models with a different geometrical or even non-geometrical
interpretation.Comment: 15 pages, LaTeX, no figure
Self-similar planar graphs as models for complex networks
In this paper we introduce a family of planar, modular and self-similar
graphs which have small-world and scale-free properties. The main parameters of
this family are comparable to those of networks associated to complex systems,
and therefore the graphs are of interest as mathematical models for these
systems. As the clustering coefficient of the graphs is zero, this family is an
explicit construction that does not match the usual characterization of
hierarchical modular networks, namely that vertices have clustering values
inversely proportional to their degrees.Comment: 10 pages, submitted to 19th International Workshop on Combinatorial
Algorithms (IWOCA 2008
Long life, low cost ball valve, with lifted seals and cartridge type construction
Ball valve design incorporates modular construction in easy-to-install, easy-to-replace cartridge housing, and a system of cams to lift upstream and downstream seals away from the ball during rotation. Tests conducted on nitrogen tetroxide prove new valve to be more efficient than previous models in preventing leakage
A Vision-based Scheme for Kinematic Model Construction of Re-configurable Modular Robots
Re-configurable modular robotic (RMR) systems are advantageous for their
reconfigurability and versatility. A new modular robot can be built for a
specific task by using modules as building blocks. However, constructing a
kinematic model for a newly conceived robot requires significant work. Due to
the finite size of module-types, models of all module-types can be built
individually and stored in a database beforehand. With this priori knowledge,
the model construction process can be automated by detecting the modules and
their corresponding interconnections. Previous literature proposed theoretical
frameworks for constructing kinematic models of modular robots, assuming that
such information was known a priori. While well-devised mechanisms and built-in
sensors can be employed to detect these parameters automatically, they
significantly complicate the module design and thus are expensive. In this
paper, we propose a vision-based method to identify kinematic chains and
automatically construct robot models for modular robots. Each module is affixed
with augmented reality (AR) tags that are encoded with unique IDs. An image of
a modular robot is taken and the detected modules are recognized by querying a
database that maintains all module information. The poses of detected modules
are used to compute: (i) the connection between modules and (ii) joint angles
of joint-modules. Finally, the robot serial-link chain is identified and the
kinematic model constructed and visualized. Our experimental results validate
the effectiveness of our approach. While implementation with only our RMR is
shown, our method can be applied to other RMRs where self-identification is not
possible
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