1,120 research outputs found
Investigation of Quasi--Realistic Heterotic String Models with Reduced Higgs Spectrum
Quasi--realistic heterotic-string models in the free fermionic formulation
typically contain an anomalous U(1), which gives rise to a Fayet-Iliopolous
term that breaks supersymmetry at the one--loop level in string perturbation
theory. Supersymmetry is restored by imposing F- and D-flatness on the vacuum.
In Phys. Rev. D 78 (2008) 046009, we presented a three generation free
fermionic standard-like model which did not admit stringent F- and D-flat
directions, and argued that the all the moduli in the model are fixed. The
particular property of the model was the reduction of the untwisted Higgs
spectrum by a combination of symmetric and asymmetric boundary conditions with
respect to the internal fermions associated with the compactified dimensions.
In this paper we extend the analysis of free fermionic models with reduced
Higgs spectrum to the cases in which the SO(10) symmetry is left unbroken, or
is reduced to the flipped SU(5) subgroup. We show that all the models that we
study in this paper do admit stringent flat directions. The only examples of
models that do not admit stringent flat directions remain the strandard-like
models of reference Phys. Rev. D 78 (2008) 046009.Comment: 38 pages, 1 figur
Stringent Phenomenological Investigation into Heterotic String Optical Unification
For the weakly coupled heterotic string (WCHS) there is a well-known factor
of twenty conflict between the minimum string coupling unification scale,
Lambda_H ~5x10^(17) GeV, and the projected MSSM unification scale, Lambda_U ~
2.5x10^(16) GeV, assuming an intermediate scale desert (ISD). Renormalization
effects of intermediate scale MSSM-charged exotics (ISME) (endemic to
quasi-realistic string models) can resolve this issue, pushing the MSSM scale
up to the string scale. However, for a generic string model, this implies that
the projected Lambda_U unification under ISD is accidental. If the true
unification scale is 5.0x10^(17) GeV, is it possible that illusionary
unification at 2.5x10^(17) GeV in the ISD scenario is not accidental? If it is
not, then under what conditions would the assumption of ISME in a WCHS model
imply apparent unification at Lambda_U when ISD is falsely assumed? Geidt's
"optical unification" suggests that Lambda_U is not accidental, by offering a
mechanism whereby a generic MSSM scale Lambda_U < Lambda_H is guaranteed. A
WCHS model was constructed that offers the possibility of optical unification,
depending on the availability of anomaly-cancelling flat directions meeting
certain requirements. This paper reports on the systematic investigation of the
optical unification properties of the set of stringent flat directions of this
model. Stringent flat directions can be guaranteed to be F-flat to all finite
order (or to at least a given finite order consistent with electroweak scale
supersymmetry breaking) and can be viewed as the likely roots of more general
flat directions. Analysis of the phenomenology of stringent flat directions
gives an indication of the remaining optical unification phenomenology that
must be garnered by flat directions developed from them.Comment: standard latex, 18 pages of tex
Initial Systematic Investigations of the Landscape of Low Layer NAHE Extensions
The discovery that the number of physically consistent string vacua is on the
order of 10^500 has prompted several statistical studies of string
phenomenology. Contained here is one such study that focuses on the Weakly
Coupled Free Fermionic Heterotic String (WCFFHS) formalism. Presented are
systematic extensions of the well-known NAHE (Nanopoulos, Antoniadis, Hagelin,
Ellis) set of basis vectors, which have been shown to produce
phenomenologically realistic models. Statistics related to the number of
U(1)'s, gauge group factors, non-Abelian singlets, ST SUSYs, as well as the
gauge groups themselve are discussed for the full range of models produced as
well as models containing GUT groups only. Prior results of other large-scale
investigations are compared with these regarding the aforementioned quantities.
Statistical coupling between the gauge groups and the number of ST SUSYs is
also discussed, and it was found that for order-3 extensions there are more
models with enhanced ST SUSY when there is an exceptional group present. Also
discussed are some three-generation GUT models found in the data sets. These
models are unique because they come from basis vectors which still have a
geometric interpretation -- there are no "rank-cuts" in these models.Comment: 65 Pages, 31 Tables, 31 Figure
Indications for an Extra Neutral Gauge Boson in Electroweak Precision Data
A new analysis of the hadronic peak cross section at LEP 1 implies a small
amount of missing invisible width in Z decays, while the effective weak charge
in atomic parity violation has been determined recently to 0.6% accuracy,
indicating a significantly negative S parameter. As a consequence of these two
deviations, the data are described well if the presence of an additional Z'
boson, such as predicted in Grand Unified Theories, is assumed. Moreover, the
data are now rich enough to study an arbitrary extra Z' boson and to determine
its couplings in a model independent way. An excellent best fit to the data is
obtained in this case, suggesting the possibility of a family non-universal Z'
with properties similar to ones predicted in a class of superstring theories.Comment: 5 pages of ReVTeX, 2 figure
Dynamics and Energy Extraction of a Surging and Plunging Airfoil at Low Reynolds Number
We investigate the unsteady aerodynamic forces and energy transfer associated with harmonic surging (streamwise) and plunging (transverse) motion of a thin airfoil at low Reynolds number. Two-dimensional unsteady flows are simulated over a large range of amplitude and reduced-frequency of the oscillatory motion using the immersed boundary projection method, and the computational results are compared to inviscid flow models and experiments. At low angle of attack there is reasonable agreement with inviscid theory for the amplitude and phase of lift fluctuations, despite the low Reynolds number. At high angle of attack, the separated flow leads to larger lift and drag fluctuations not captured by inviscid models. At frequencies below the vortex shedding frequency, lift fluctuations are first enhanced and then attenuated depending on the phase between the freestream velocity and the forming leading-edge vortex. Resonance with the vortex shedding frequency also occurs. The time-averaged forces and power supplied by the oscillating airfoil are also evaluated to find frequency ranges that are favorable for the airfoil
Left-Right Symmetric Heterotic-String Derived Models
Recently it was demonstrated that free fermionic heterotic-strings can
produce models with solely the Minimal Supersymmetric Standard Model states in
the low energy spectrum. This unprecedented result provides further strong
evidence for the possibility that the true string vacuum shares some of the
properties of the free fermionic models. Past free fermionic models have
focused on several possible unbroken observable SO(10) subgroups at the string
scale, which include the flipped SU(5) (FSU5), the Pati-Salam (PS) string
models, and the string Standard-like Models (SLM). We extend this study to
include the case in which the SO(10) symmetry is broken to the Left-Right
Symmetric (LRS) gauge group, SO(10) -> SU(3)_C X U(1)_{B-L} X SU(2)_L X
SU(2)_R. We present several models of this type and discuss their
phenomenological features. The most striking new outcome of the LRS string
models, in contrast to the case of the FSU5, the PS, and the SLM string models,
is that they can produce effective field theories that are free of Abelian
anomalies. We discuss the distinction between the two types of free fermionic
models which result in the presence, or absence, of an anomalous U(1). As a
counter example we also present a LRS model that does contain an anomalous
U(1). Additionally, we discuss how in string models the Standard Model spectrum
may arise from the three \mbf 16 representations of SO(10), while the
weak-hypercharge does not have the canonical SO(10) embedding.Comment: 39 pages. Standard Latex. Version to appear in PR
The Hilbert basis method for D-flat directions and the superpotential
We discuss, using the Hilbert basis method, how to efficiently construct a
complete basis for D-flat directions in supersymmetric Abelian and non-Abelian
gauge theories. We extend the method to discrete (R and non-R) symmetries. This
facilitates the construction of a basis of all superpotential terms in a theory
with given symmetries.Comment: 11 pages; a related mathematica code can be found at
http://einrichtungen.ph.tum.de/T30e/codes/NonAbelianHilbert
A Mechanism for Ordinary-Sterile Neutrino Mixing
Efficient oscillations between ordinary (active) and sterile neutrinos can
occur only if Dirac and Majorana mass terms exist which are both small and
comparable. It is shown that this can occur naturally in a class of string
models, in which higher-dimensional operators in the superpotential lead to an
intermediate scale expectation value for a scalar field and to suppressed Dirac
and Majorana fermion masses.Comment: 12 page
External and intrinsic anchoring in nematic liquid crystals: A Monte Carlo study
We present a Monte Carlo study of external surface anchoring in nematic cells
with partially disordered solid substrates, as well as of intrinsic anchoring
at free nematic interfaces. The simulations are based on the simple hexagonal
lattice model with a spatially anisotropic intermolecular potential. We
estimate the corresponding extrapolation length by imposing an elastic
deformation in a hybrid cell-like nematic sample. Our estimates for
increase with increasing surface disorder and are essentially
temperature--independent. Experimental values of are approached only when
both the coupling of nematic molecules with the substrate and the anisotropy of
nematic--nematic interactions are weak.Comment: Revisions primarily in section I
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