577 research outputs found
Human Arm simulation for interactive constrained environment design
During the conceptual and prototype design stage of an industrial product, it
is crucial to take assembly/disassembly and maintenance operations in advance.
A well-designed system should enable relatively easy access of operating
manipulators in the constrained environment and reduce musculoskeletal disorder
risks for those manual handling operations. Trajectory planning comes up as an
important issue for those assembly and maintenance operations under a
constrained environment, since it determines the accessibility and the other
ergonomics issues, such as muscle effort and its related fatigue. In this
paper, a customer-oriented interactive approach is proposed to partially solve
ergonomic related issues encountered during the design stage under a
constrained system for the operator's convenience. Based on a single objective
optimization method, trajectory planning for different operators could be
generated automatically. Meanwhile, a motion capture based method assists the
operator to guide the trajectory planning interactively when either a local
minimum is encountered within the single objective optimization or the operator
prefers guiding the virtual human manually. Besides that, a physical engine is
integrated into this approach to provide physically realistic simulation in
real time manner, so that collision free path and related dynamic information
could be computed to determine further muscle fatigue and accessibility of a
product designComment: International Journal on Interactive Design and Manufacturing
(IJIDeM) (2012) 1-12. arXiv admin note: substantial text overlap with
arXiv:1012.432
On the possibility of a very light A^0 at low \tan\beta
The searches at LEP II for the processes e^+e^-\to h^0Z and e^+e^-\to h^0A^0
in the Minimal Supersymmetric Standard Model (MSSM) fail to exclude regions of
the m_h,m_A plane where \tan\beta <1, thus allowing a very light A^0 (m_A< 20
GeV). Such a parameter choice would predict a light H^\pm with m_{H^\pm}< m_W.
Although the potentially large branching ratio for H^\pm \to A^0 W^* would
ensure that H^\pm also escaped detection in direct searches at LEP II and the
Tevatron Run I, we show that this elusive parameter space is overwhelmingly
disfavoured by electroweak precision measurements.Comment: 11 pages, 2 figures, Revtex, references added, minor additions to
tex
The Problem of Large Leptonic Mixing
Unlike in the quark sector where simple permutation symmetries can
generate the general features of quark masses and mixings, we find it
impossible (under conditions of hierarchy for the charged leptons and without
considering the see-saw mechanism or a more elaborate extension of the SM) to
guarantee large leptonic mixing angles with any general symmetry or
transformation of only known particles. If such symmetries exist, they must be
realized in more extended scenarios.Comment: RevTeX, 4 pages, no figure
Possible Z-width probe of a "brane-world" scenario for neutrino masses
The possibility that the accurately known value of the Z width might furnish
information about the coupling of two neutrinos to the Majoron (Nambu-Goldstone
boson of spontaneous lepton number violation) is proposed and investigated in
detail. Both the "ordinary" case and the case in which one adopts a "brane"
world picture with the Majoron free to travel in extra dimensions are studied.
Bounds on the dimensionless coupling constants are obtained, allowing for any
number of extra dimensions and any intrinsic mass scale. These bounds may be
applied to a variety of different Majoron models. If a technically natural
see-saw model is adopted, the predicted coupling constants are far below these
upper bounds. In addition, for this natural model, the effect of extra
dimensions is to decrease the predicted partial Z width, the increase due to
many Kaluza-Klein excitations being compensated by the decrease of their common
coupling constant.Comment: RevTeX, 12 pages, 3 figure
The Symmetry behind Extended Flavour Democracy and Large Leptonic Mixing
We show that there is a minimal discrete symmetry which leads to the extended
flavour democracy scenario constraining the Dirac neutrino, the charged lepton
and the Majorana neutrino mass term () to be all proportional to the
democratic matrix, with all elements equal. In particular, this discreet
symmetry forbids other large contributions to , such as a term
proportional to the unit matrix, which would normally be allowed by a
permutation symmetry. This feature is crucial in order to
obtain large leptonic mixing, without violating 't Hooft's, naturalness
principle.Comment: 11 pages, LaTe
Low scale gravity as the source of neutrino masses?
We address the question whether low-scale gravity alone can generate the
neutrino mass matrix needed to accommodate the observed phenomenology. In
low-scale gravity the neutrino mass matrix in the flavor basis is characterized
by one parameter (the gravity scale M_X) and by an exact or approximate flavor
blindness (namely, all elements of the mass matrix are of comparable size).
Neutrino masses and mixings are consistent with the observational data for
certain values of the matrix elements, but only when the spectrum of mass is
inverted or degenerate. For the latter type of spectra the parameter M_{ee}
probed in double beta experiments and the mass parameter probed by cosmology
are close to existing upper limits.Comment: 10 pages, 1 figur
Neutrino Masses and Lepton Flavour Violation in Thick Brane Scenarios
We address the issue of lepton flavour violation and neutrino masses in the
``fat-brane'' paradigm, where flavour changing processes are suppressed by
localising different fermion field wave-functions at different positions (in
the extra dimensions) in a thick brane. We study the consequences of
suppressing lepton number violating charged lepton decays within this scenario
for lepton masses and mixing angles. In particular, we find that charged lepton
mass matrices are constrained to be quasi-diagonal. We further consider whether
the same paradigm can be used to naturally explain small Dirac neutrino masses
by considering the existence of three right-handed neutrinos in the brane, and
discuss the requirements to obtain phenomenologically viable neutrino masses
and mixing angles. Finally, we examine models where neutrinos obtain a small
Majorana mass by breaking lepton number in a far away brane and show that, if
the fat-brane paradigm is the solution to the absence of lepton number
violating charged lepton decays, such models predict, in the absence of flavour
symmetries, that charged lepton flavour violation will be observed in the next
round of rare muon/tau decay experiments.Comment: 33 pages, 9 eps figure
Neutrino masses and mixing with seesaw mechanism and universal breaking of extended democracy
In the framework of a minimal extension of the SM, where the only additional
fields are three right-handed neutrinos, we suggest that the charged lepton,
the Dirac neutrino and the right-handed Majorana neutrino mass matrices are
all, to leading approximation, proportional to the democratic matrix. With the
further assumption that the breaking of this extended democracy is universal
for all leptonic mass matrices, a large mixing in the 2-3 sector can be
obtained and is linked to the seesaw mechanism, together with the existence of
a strong hierarchy in the masses of right-handed neutrinos. The structure of
the resulting effective mass matrix of light neutrinos is stable against the
RGE evolution, and a good fit to all solar and atmospheric neutrino data is
obtained.Comment: LaTeX, 17 pages, 2 eps figures. A section on RGE evolution and a few
references added; minor typos correcte
Minimal Mass Matrices for Dirac Neutrinos
We consider the possibility of neutrinos being Dirac particles and study
minimal mass matrices with as much zero entries as possible. We find that up to
5 zero entries are allowed. Those matrices predict one vanishing mass state, CP
conservation and U_{e3} either zero or proportional to R, where R is the ratio
of the solar and atmospheric \Delta m^2. Matrices containing 4 zeros can be
classified in categories predicting U_{e3} = 0, U_{e3} \neq 0 but no CP
violation or |U_{e3}| \neq 0 and possible CP violation. Some cases allow to set
constraints on the neutrino masses. The characteristic value of U_{e3} capable
of distinguishing some of the cases with non-trivial phenomenological
consequences is about R/2 \sin 2 \theta_{12}. Matrices containing 3 and less
zero entries imply (with a few exceptions) no correlation for the observables.
We outline models leading to the textures based on the Froggatt-Nielsen
mechanism or the non-Abelian discrete symmetry D_4 \times Z_2.Comment: 32 pages, 3 figures. Comments and references added. To appear in JHE
- âŠ