43,209 research outputs found
E6 Models from F-theory
F-theory is a non-perturbative formulation of type IIB superstring theory
which allows for the decoupling of gravity and for the formulation of GUT
theories based on the gauge group E6. In this paper we explore F-theory models
in which the low energy supersymmetric theory contains the particle content of
three 27 dimensional representations of the underlying E6 gauge group, plus two
extra right-handed neutrinos predicted from F and D flatness. The resulting TeV
scale effective theory resembles either the E6SSM or the NMSSM+, depending on
whether an additional Abelian gauge group does or does not survive. However
there are novel features compared to both these models as follows: (i) If the
additional Abelian gauge group is unbroken then it can have a weaker gauge
coupling than in the E6SSM; (ii) If the additional Abelian gauge group is
broken then non-perturbative effects can violate the scale invariance of the
NMSSM+ leading to a generalised model; (iii) Unification is achieved not at the
field theory level but at the F-theory level since the gauge couplings are
split by flux effects, negating the need for any additional doublet states
which are usually required; (iv) Proton decay is suppressed by the geometric
coupling suppression of a singlet state, a mechanism peculiar to F-theory,
which effectively suppresses the coupling of the exotic charge -1/3 colour
triplet state D to quarks and leptons; (v) The D bar couples to left-handed
leptoquarks, providing characteristic and striking signatures at the LHC.Comment: 31 pages, 7 figure
Master/slave manipulator system
System capabilities are equivalent to mobility, dexterity, and strength of human arm. Arrangement of torque motor, harmonic drive, and potentiometer combination allows all power and control leads to pass through center of slave with position-transducer arrangement of master, and "stovepipe joint" is incorporated for manipulator applications
Anthropomorphic master/slave manipulator system
An anthropomorphic master/slave manipulator system including master arm apparatus with a plurality of master tubular articulated portions is outlined. Objectives of this investion were to provide a system that accurately and smoothly simulates human limb movement at a remote location. The system has a high frequency response, a high structural stiffness and a design that protects the components of the slave mechanism. Simulation of human movements is possible in outer space, underwater, and in a hazardous environment such as in a high radiation area. The equivalent ability, dexterity, and strength of a human arm are simulated
On the rooted Tutte polynomial
The Tutte polynomial is a generalization of the chromatic polynomial of graph
colorings. Here we present an extension called the rooted Tutte polynomial,
which is defined on a graph where one or more vertices are colored with
prescribed colors. We establish a number of results pertaining to the rooted
Tutte polynomial, including a duality relation in the case that all roots
reside around a single face of a planar graph. The connection with the Potts
model is also reviewed.Comment: plain latex, 14 pages, 2 figs., to appear in Annales de l'Institut
Fourier (1999
Gauge Coupling Unification in E6 F-Theory GUTs with Matter and Bulk Exotics from Flux Breaking
We consider gauge coupling unification in E6 F-Theory Grand Unified Theories
(GUTs) where E6 is broken to the Standard Model (SM) gauge group using fluxes.
In such models there are two types of exotics that can affect gauge coupling
unification, namely matter exotics from the matter curves in the 27 dimensional
representation of E6 and the bulk exotics from the adjoint 78 dimensional
representation of E6. We explore the conditions required for either the
complete or partial removal of bulk exotics from the low energy spectrum. In
the latter case we shall show that (miraculously) gauge coupling unification
may be possible even if there are bulk exotics at the TeV scale. Indeed in some
cases it is necessary for bulk exotics to survive to the TeV scale in order to
cancel the effects coming from other TeV scale matter exotics which would by
themselves spoil gauge coupling unification. The combination of matter and bulk
exotics in these cases can lead to precise gauge coupling unification which
would not be possible with either type of exotics considered by themselves. The
combination of matter and bulk exotics at the TeV scale represents a unique and
striking signature of E6 F-theory GUTs that can be tested at the LHC.Comment: 21 pages, 5 figure
Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number
Supercritical fluids near the critical point are characterized by liquid-like
densities and gas-like transport properties. These features are purposely
exploited in different contexts ranging from natural products
extraction/fractionation to aerospace propulsion. Large part of studies
concerns this last context, focusing on the dynamics of supercritical fluids at
high Mach number where compressibility and thermodynamics strictly interact.
Despite the widespread use also at low Mach number, the turbulent mixing
properties of slightly supercritical fluids have still not investigated in
detail in this regime. This topic is addressed here by dealing with Direct
Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van
der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number
conditions found in many industrial applications, the numerical model is based
on a suitable low-Mach number expansion of the governing equation. According to
experimental observations, the weakly supercritical regime is characterized by
the formation of finger-like structures-- the so-called ligaments --in the
shear layers separating the two streams. The mechanism of ligament formation at
vanishing Mach number is extracted from the simulations and a detailed
statistical characterization is provided. Ligaments always form whenever a high
density contrast occurs, independently of real or perfect gas behaviors. The
difference between real and perfect gas conditions is found in the ligament
small-scale structure. More intense density gradients and thinner interfaces
characterize the near critical fluid in comparison with the smoother behavior
of the perfect gas. A phenomenological interpretation is here provided on the
basis of the real gas thermodynamics properties.Comment: Published on Physics of Fluid
Invariant approach to CP in family symmetry models
We propose the use of basis invariants, valid for any choice of CP
transformation, as a powerful approach to studying specific models of CP
violation in the presence of discrete family symmetries. We illustrate the
virtues of this approach for examples based on and family
symmetries. For , we show how to elegantly obtain several known results in
the literature. In we use the invariant approach to identify how
explicit (rather than spontaneous) CP violation arises, which is geometrical in
nature, i.e. persisting for arbitrary couplings in the Lagrangian.Comment: 4 pages plus references. v2: to be published in PR
Invariant approach to CP in unbroken
The invariant approach is a powerful method for studying CP violation for
specific Lagrangians. The method is particularly useful for dealing with
discrete family symmetries. We focus on the CP properties of unbroken
invariant Lagrangians with Yukawa-like terms, which proves to be a
rich framework, with distinct aspects of CP, making it an ideal group to
investigate with the invariant approach. We classify Lagrangians depending on
the number of fields transforming as irreducible triplet representations of
. For each case, we construct CP-odd weak basis invariants and use
them to discuss the respective CP properties. We find that CP violation is
sensitive to the number and type of representations.Comment: 24 pages, 1 figure. v2: to be published in NP
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