16,474 research outputs found
Minimal Standard Heterotic String Models
Three generation heterotic-string vacua in the free fermionic formulation
gave rise to models with solely the MSSM states in the observable Standard
Model charged sector. The relation of these models to Z_2 x Z_2 orbifold
compactifications dictates that they produce three pairs of untwisted Higgs
multiplets. The reduction to one pair relies on the analysis of supersymmetric
flat directions, that give superheavy mass to the dispensable Higgs states. We
explore the removal of the extra Higgs representations by using the free
fermion boundary conditions and hence directly at the string level, rather than
in the effective low energy field theory. We present a general mechanism that
achieves this reduction by using asymmetric boundary conditions between the
left- and right-moving internal fermions. We incorporate this mechanism in
explicit string models containing three twisted generations and a single
untwisted Higgs doublet pair. We further demonstrate that an additional effect
of the asymmetric boundary conditions is to substantially reduce the
supersymmetric moduli space.Comment: 20 pages, LaTeX; added reference
Notes on entropic characteristics of quantum channels
One of most important issues in quantum information theory concerns
transmission of information through noisy quantum channels. We discuss few
channel characteristics expressed by means of generalized entropies. Such
characteristics can often be dealt in line with more usual treatment based on
the von Neumann entropies. For any channel, we show that the -average output
entropy of degree is bounded from above by the -entropy of the
input density matrix. Concavity properties of the -entropy exchange are
considered. Fano type quantum bounds on the -entropy exchange are
derived. We also give upper bounds on the map -entropies in terms of the
output entropy, corresponding to the completely mixed input.Comment: 10 pages, no figures. The statement of Proposition 1 is explicitly
illustrated with the depolarizing channel. The bibliography is extended and
updated. More explanations. To be published in Cent. Eur. J. Phy
Dynamic performance of detuned ridge waveguide AlInGaAs distributed feedback laser diodes
The dynamic behavior of AlInGaAs ridge waveguide distributed feedback lasers is reported in this work covering five detuned wavelengths between 1291 nm and 1326 nm for a laser active layer optical peak gain design centered at 1310 nm at room temperature. The detuning is achieved by modifying the laser grating pitch that performs the mode selection within the laser cavity simultaneously across a single processed wafer. The dynamic behavior is evaluated using the resonance frequencies of the detuned lasers measured at a range of injection currents for heatsink temperatures of 25°C and 85°C. The results confirm that a speed improvement can be achieved at 25°C by detuning the laser to shorter wavelengths. However, the results also show that a lower direct modulation bandwidth at 85°C makes the shorter wavelength design less attractive. For communications applications such as 10 Gbps uncooled operation, this trade-off between detuning and modulation bandwidth imply an optimum around â2 nm to +8 nm detuning (measured at 25°C)
On the Possibility of Optical Unification in Heterotic Strings
Recently J. Giedt discussed a mechanism, entitled optical unification,
whereby string scale unification is facilitated via exotic matter with
intermediate scale mass. This mechanism guarantees that a virtual MSSM
unification below the string scale is extrapolated from the running of gauge
couplings upward from M_Z^o when an intermediate scale desert is assumed. In
this letter we explore the possibility of optical unification within the
context of weakly coupled heterotic strings. In particular, we investigate this
for models of free fermionic construction containing the NAHE set of basis
vectors. This class is of particular interest for optical unification, because
it provides a standard hypercharge embedding within SO(10), giving the standard
k_Y = 5/3 hypercharge level, which was shown necessary for optical unification.
We present a NAHE model for which the set of exotic SU(3)_C
triplet/anti-triplet pairs, SU(2)_L doublets, and non-Abelian singlets with
hypercharge offers the possibility of optical unification. Whether this model
can realize optical unification is conditional upon these exotics not receiving
Fayet-Iliopoulos (FI) scale masses when a flat direction of scalar vacuum
expectation values is non-perturbatively chosen to cancel the FI D-term, xi,
generated by the anomalous U(1)-breaking Green-Schwarz-Dine-Seiberg-Wittten
mechanism. A study of perturbative flat directions and their phenomenological
implications for this model is underway.
This paper is a product of the NFS Research Experiences for Undergraduates
and the NSF High School Summer Science Research programs at Baylor University.Comment: 16 pages. Standard Late
Facteurs liés au diagnostic tardif du cancer du sein: expérience du CHU Mohammed VI Marrakech
Le cancer du sein est le premier cancer féminin en termes d'incidence et de mortalité. Au Maroc, il vient au premier rang des cancers de la femme avant celui du col utérin Il constitue un problÚme de santé publique. Son pronostic est étroitement lié au stade auquel le diagnostic est posé. Il s'agit d'une pathologie dont les moyens diagnostiques sont de nos jours développés, allant de la détection précoce à la mise en évidence de lésions infra-cliniques, ce qui a nettement amélioré le pronostic dans les pays développés. Ce travail que nous présentons a pour objectif d'identifier dans notre pratique quotidienne, les facteurs qui amÚnent les patientes à consulter à des stades tardifs. Une étude rétrospective a été menée de janvier 2012 à janvier 2013 portant sur 130 patientes porteuses d'un cancer du sein au sein du service d'onco-radiotherapie CHU Mohammed VI Marrakech. Un questionnaire a été élaboré et dument renseigné en ayant recours aux dossiers des malades. Ainsi 63,07% des patientes consultaient au-delà de six mois avec un délai moyen de consultation de 8,47 mois avec comme motif de consultation des lésions classées T4 dans 27,69%, et des tumeurs d'emblée métastatiques dans 13,84%. Les facteurs retrouvés à l'interrogatoire étaient le manque de moyens financiers 40%, l'éloignement des structures sanitaires dans 23%, les habitudes socioculturelles avec les traitements traditionnels en premiÚre intention 20%, et l'insuffisance de prise en charge thérapeutique 7%. Cependant, pris individuellement, aucune concordance significative n'était retrouvée entre ces facteurs et le long délai diagnostique. Dans notre pratique, c'est la conjonction de la triade ignorance, indigence et habitudes socioculturelles qui constituent le facteur essentiel du diagnostic tardif des cancers du sein
Heterotic orbifold models on Lie lattice with discrete torsion
We provide a new class of Z_N x Z_M heterotic orbifolds on non-factorisable
tori, whose boundary conditions are defined by Lie lattices. Generally, point
groups of these orbifolds are generated by Weyl reflections and outer
automorphisms of the lattices. We classify abelian orbifolds with and without
discrete torsion. Then we find that some of these models have smaller Euler
numbers than those of models on factorisable tori T^2 x T^2 x T^2. There is a
possibility that these orbifolds provide smaller generation numbers of N=1
chiral matter fields than factorisable models.Comment: 24 pages, 5 figures; v2: a few errors on tables are corrected, typos
corrected, version to appear in JHE
Renormalization Group Invariants in the MSSM and Its Extensions
We derive one-loop renormalization group (RG) invariant observables and
analyze their phenomenological implications in the MSSM and its \mu problem
solving extensions, U(1)' model and NMSSM. We show that there exist several RG
invariants in the gauge, Yukawa and soft-breaking sectors of each model. In
general, RG invariants are highly useful for projecting experimental data to
messenger scale, for revealing correlations among the model parameters, and for
probing the mechanism that breaks supersymmetry. The Yukawa couplings and
trilinear soft terms in U(1)' model and NMSSM do not form RG invariants though
there exist approximate invariants in low tan(beta). In the NMSSM, there are no
invariants that contain the Higgs mass-squareds. We provide a comparative
analysis of RG invariants in all three models and analyze their model-building
and phenomenological implications by a number of case studies.Comment: 32 pages, 5 tables; extended previous analysis to include U(1)'
models and NMSSM where a comparative discussion is give
Attractors for a class of semi-linear degenerate parabolic equations
We consider degenerate parabolic equations of the form âtu = Îλu + f(u) u{pipe}âΩ = 0, u{pipe}t=0 = u0 in a bounded domain Ω âN, where Îλ is a subelliptic operator of the type (Formula presented.) We prove global existence of solutions and characterize their longtime behavior. In particular, we show the existence and finite fractal dimension of the global attractor of the generated semigroup and the convergence of solutions to an equilibrium solution when time tends to infinity
Solitons, solitonic vortices, and vortex rings in a confined Bose-Einstein condensate
Quasi-one-dimensional solitons that may occur in an elongated Bose-Einstein
condensate become unstable at high particle density. We study two basic modes
of instability and the corresponding bifurcations to genuinely
three-dimensional solitary waves such as axisymmetric vortex rings and
non-axisymmetric solitonic vortices. We calculate the profiles of the above
structures and examine their dependence on the velocity of propagation along a
cylindrical trap. At sufficiently high velocity, both the vortex ring and the
solitonic vortex transform into an axisymmetric soliton. We also calculate the
energy-momentum dispersions and show that a Lieb-type mode appears in the
excitation spectrum for all particle densities.Comment: RevTeX 9 pages, 9 figure
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