351 research outputs found
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
Observable/Hidden Broken Symmetry for Symmetric Boundary Conditions
A 4-dimensional heterotic string model of free fermionic construction is
presented wherein mirror symmetry breaking between observable and hidden sector
gauge groups occurs in spite of mirror symmetry between observable and hidden
sector worldsheet fermion boundary conditions. The differentiation is invoked
by an asymmetry in GSO projections necessarily resulting from the symmetry of
the free fermionic boundary conditions. In the specific examples shown, an
expected non-chiral Pati-Salam mirror universe model is transformed into a
chiral model with enhanced hidden sector gauge symmetry and reduced observable
sector gauge symmetry: [SU(4)_C x SU(2)_L x SU(2)_R]_{obs} x [SU(4)_C x SU(2)_L
x SU(2)_R]_{hid} is necessarily transformed into a chiral [SU(4)_C x
SU(2)_L]_{obs} x [SO(10) x SU(2)_R]_{hid} model because of an unavoidable
asymmetry in GSO projections.Comment: latex, 22 page
Surgical innovation revisited: A historical narrative of the minimally invasive "Agarwal sliding-clip renorrhaphy" technique for partial nephrectomy and its application to an Australian cohort.
Objective
To evaluate local clinical outcomes of sliding clip renorrhaphy, from inception to current utilization for open, laparoscopic, and robotically assisted partial nephrectomy.
Methods
We reviewed prospectively maintained databases of three surgeons performing partial nephrectomies with the sliding-clip technique at teaching hospitals between 2005 and 2019. Baseline characteristics, operative parameters, including surgical approach, RENAL Nephrometry Score, and post-operative outcomes, including Clavien-Dindo classification of complications, were recorded for 76 consecutive cases. We compared perioperative and 90-day events with patient and tumor characteristics, stratified by operative approach and case complexity, using Wilcoxon rank-sum test for continuous variables and the Chi-squared or Fisher's exact test, for binary and categorical variables, respectively.
Results
Open surgery (n = 15) reduced ischemia time and operative time, but increased hospital admission time. Pre- and post-operative estimated glomerular filtration rates did not change significantly by operative approach. Older patients (P = .007) and open surgery (P = .003) were associated with a higher rate of complications (any-grade). Six grade ≥3 complications occurred: these were associated with higher RENAL Nephrometry Score (P = .016) and higher pathological tumor stage (P = .045). Limits include smaller case volumes which incorporate the learning curve cases; therefore, these data are most applicable to lower volume teaching hospitals.
Conclusion
The sliding-clip technique for partial nephrectomy was first described by Agarwal et al and has low complication rates, acceptable operative time, and preserves renal function across open and minimally invasive surgeries. This series encompasses the initial learning curve with developing the technique through to present-day emergence as a routine standard of practice
Mannose-binding Lectin-deficient Mice Are Susceptible to Infection with Staphylococcus aureus
Gram-positive organisms like Staphylococcus aureus are a major cause of morbidity and mortality worldwide. Humoral response molecules together with phagocytes play a role in host responses to S. aureus. The mannose-binding lectin (MBL, also known as mannose-binding protein) is an oligomeric serum molecule that recognizes carbohydrates decorating a broad range of infectious agents including S. aureus. Circumstantial evidence in vitro and in vivo suggests that MBL plays a key role in first line host defense. We tested this contention directly in vivo by generating mice that were devoid of all MBL activity. We found that 100% of MBL-null mice died 48 h after exposure to an intravenous inoculation of S. aureus compared with 45% mortality in wild-type mice. Furthermore, we demonstrated that neutrophils and MBL are required to limit intraperitoneal infection with S. aureus. Our study provides direct evidence that MBL plays a key role in restricting the complications associated with S. aureus infection in mice and raises the idea that the MBL gene may act as a disease susceptibility gene against staphylococci infections in humans
A Global SU(5) F-theory model with Wilson line breaking
We engineer compact SU(5) Grand Unified Theories in F-theory in which
GUT-breaking is achieved by a discrete Wilson line. Because the internal gauge
field is flat, these models avoid the high scale threshold corrections
associated with hypercharge flux. Along the way, we exemplify the
`local-to-global' approach in F-theory model building and demonstrate how the
Tate divisor formalism can be used to address several challenges of extending
local models to global ones. These include in particular the construction of
G-fluxes that extend non-inherited bundles and the engineering of U(1)
symmetries. We go beyond chirality computations and determine the precise
(charged) massless spectrum, finding exactly three families of quarks and
leptons but excessive doublet and/or triplet pairs in the Higgs sector
(depending on the example) and vector-like exotics descending from the adjoint
of SU(5)_{GUT}. Understanding why vector-like pairs persist in the Higgs sector
without an obvious symmetry to protect them may shed light on new solutions to
the mu problem in F-theory GUTs.Comment: 95 pages (71 pages + 1 Appendix); v2 references added, minor
correction
Massless Spectra of Three Generation U(N) Heterotic String Vacua
We provide the methods to compute the complete massless spectra of a class of
recently introduced supersymmetric E8 x E8 heterotic string models which invoke
vector bundles with U(N) structure group on simply connected Calabi-Yau
manifolds and which yield flipped SU(5) and MSSM string vacua of potential
phenomenological interest. We apply Leray spectral sequences in order to derive
the localisation of the cohomology groups H^i(X,V_a \times V_b),
H^i(X,\bigwedge^2 V) and H^i(X,{\bf S}^2 V) for vector bundles defined via
Fourier-Mukai transforms on elliptically fibered Calabi-Yau manifolds. By the
method of bundle extensions we define a stable U(4) vector bundle leading to
the first flipped SU(5) model with just three generations, i.e. without any
vector-like matter. Along the way, we propose the notion of Lambda-stability
for heterotic bundles.Comment: 48 page
Searching for the Standard Model in the String Landscape : SUSY GUTs
The goal of the present review article is to describe the ingredients
necessary to find the Standard Model in the string landscape.Comment: 70 pages, 20 figures, this review article will be published in
Reports on Progress in Physic
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