327 research outputs found
Free Fermionic Heterotic Model Building and Root Systems
We consider an alternative derivation of the GSO Projection in the free
fermionic construction of the weakly coupled heterotic string in terms of root
systems, as well as the interpretation of the GSO Projection in this picture.
We then present an algorithm to systematically and efficiently generate input
sets (i.e. basis vectors) in order to study Landscape statistics with minimal
computational cost. For example, the improvement at order 6 is approximately
10^{-13} over a traditional brute force approach, and improvement increases
with order. We then consider an example of statistics on a relatively simple
class of models.Comment: Standard Latex, 12 page
Heterotic Weight Lifting
We describe a method for constructing genuinely asymmetric (2,0) heterotic
strings out of N=2 minimal models in the fermionic sector, whereas the bosonic
sector is only partly build out of N=2 minimal models. This is achieved by
replacing one minimal model plus the superfluous E_8 factor by a
non-supersymmetric CFT with identical modular properties. This CFT generically
lifts the weights in the bosonic sector, giving rise to a spectrum with fewer
massless states. We identify more than 30 such lifts, and we expect many more
to exist. This yields more than 450 different combinations. Remarkably, despite
the lifting of all Ramond states, it is still possible to get chiral spectra.
Even more surprisingly, these chiral spectra include examples with a certain
number of chiral families of SO(10), SU(5) or other subgroups, including just
SU(3) x SU(2) x U(1). The number of families and mirror families is typically
smaller than in standard Gepner models. Furthermore, in a large number of
different cases, spectra with three chiral families can be obtained. Based on a
first scan of about 10% of the lifted Gepner models we can construct, we have
collected more than 10.000 distinct spectra with three families, including
examples without mirror fermions. We present an example where the GUT group is
completely broken to the standard model, but the resulting and inevitable
fractionally charged particles are confined by an additional gauge group
factor.Comment: 19 pages, 1 figur
Seasonality in Major Depressive Disorder: Effect of Sex and Age
Background: Aside from the concept of seasonal affective disorder, the evidence for a seasonal pattern (SP) of major depressive disorder (MDD) is controversial. Furthermore, the effect of sex and age is still unclear. Methods: This is a nationwide, registry-based study assessing all inpatient admissions in mental health hospitals due to MDD episodes according to ICD-10 (moderate (F32/33.1), severe (F32/33.2) and severe with psychotic features (F32/33.3)) in Austria across 14 years. Calculations were based on deviations from expected monthly admissions. Results: The sample comprised 231,824 hospitalisations (36.8% men) for MDD. A significant SP (p=0.001) in moderate and severe depressive episodes in both women and men with decreased admission rates in the summer months and December was detected. In psychotic depression a significant SP was only evidenced in women (p = 0.002, men: p = 0.291). Patients older than 55 years had a reduced SP compared to those being younger. Limitations: Only anonymised admission data of inpatient treatments were available. Hospitalization rates cannot fully be equated to the occurrence of MDD. Conclusions: The current study indicates a seasonal variation in MDD symptoms that may go beyond seasonal affective disorder. Knowledge about the predictability of depressive symptoms in patients should encourage preventive strategies
Stakeholder views on the acceptability of human infection studies in Malawi.
BACKGROUND: Human infection studies (HIS) are valuable in vaccine development. Deliberate infection, however, creates challenging questions, particularly in low and middle-income countries (LMICs) where HIS are new and ethical challenges may be heightened. Consultation with stakeholders is needed to support contextually appropriate and acceptable study design. We examined stakeholder perceptions about the acceptability and ethics of HIS in Malawi, to inform decisions about planned pneumococcal challenge research and wider understanding of HIS ethics in LMICs. METHODS: We conducted 6 deliberative focus groups and 15 follow-up interviews with research staff, medical students, and community representatives from rural and urban Blantyre. We also conducted 5 key informant interviews with clinicians, ethics committee members, and district health government officials. RESULTS: Stakeholders perceived HIS research to have potential population health benefits, but they also had concerns, particularly related to the safety of volunteers and negative community reactions. Acceptability depended on a range of conditions related to procedures for voluntary and informed consent, inclusion criteria, medical care or support, compensation, regulation, and robust community engagement. These conditions largely mirror those in existing guidelines for HIS and biomedical research in LMICs. Stakeholder perceptions pointed to potential tensions, for example, balancing equity, safety, and relevance in inclusion criteria. CONCLUSIONS: Our findings suggest HIS research could be acceptable in Malawi, provided certain conditions are in place. Ongoing assessment of participant experiences and stakeholder perceptions will be required to strengthen HIS research during development and roll-out
Yukawa couplings and masses of non-chiral states for the Standard Model on D6-branes on T6/Z6'
The perturbative leading order open string three-point couplings for the
Standard Model with hidden USp(6) on fractional D6-branes on T6/Z6' from
arXiv:0806.3039 [hep-th], arXiv:0910.0843 [hep-th] are computed. Physical
Yukawa couplings consisting of holomorphic Wilsonian superpotential terms times
a non-holomorphic prefactor involving the corresponding classical open string
Kaehler metrics are given, and mass terms for all non-chiral matter states are
derived. The lepton Yukawa interactions are at leading order flavour diagonal,
while the quark sector displays a more intricate pattern of mixings. While N=2
supersymmetric sectors acquire masses via only two D6-brane displacements -
which also provide the hierarchies between up- and down-type Yukawas within one
quark or lepton generation -, the remaining vector-like states receive masses
via perturbative three-point couplings to some Standard Model singlet fields
with vevs along flat directions. Couplings to the hidden sector and messengers
for supersymmetry breaking are briefly discussed.Comment: 52 pages (including 8p. appendix); 5 figures; 14 tables; v2:
discussion in section 4.1.3 extended, footnote 5 added, typos corrected,
accepted by JHE
Asymmetric Gepner Models II. Heterotic Weight Lifting
A systematic study of "lifted" Gepner models is presented. Lifted Gepner
models are obtained from standard Gepner models by replacing one of the N=2
building blocks and the factor by a modular isomorphic model on the
bosonic side of the heterotic string. The main result is that after this change
three family models occur abundantly, in sharp contrast to ordinary Gepner
models. In particular, more than 250 new and unrelated moduli spaces of three
family models are identified. We discuss the occurrence of fractionally charged
particles in these spectra.Comment: 46 pages, 17 figure
Merging Heterotic Orbifolds and K3 Compactifications with Line Bundles
We clarify the relation between six-dimensional Abelian orbifold
compactifications of the heterotic string and smooth heterotic K3
compactifications with line bundles for both SO(32) and E_8 x E_8 gauge groups.
The T^4/Z_N cases for N=2,3,4 are treated exhaustively, and for N=6 some
examples are given. While all T^4/Z_2 and nearly all T^4/Z_3 models have a
simple smooth match involving one line bundle only, this is only true for some
T^4/Z_4 and T^4/Z_6 cases. We comment on possible matchings with more than one
line bundle for the remaining cases. The matching is provided by comparisons of
the massless spectra and their anomalies as well as a field theoretic analysis
of the blow-ups.Comment: 49 pages, 1 figure; v2: references adde
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