267 research outputs found
D-branes Wrapped on Fuzzy del Pezzo Surfaces
We construct classical solutions in quiver gauge theories on D0-branes
probing toric del Pezzo singularities in Calabi-Yau manifolds. Our solutions
represent D4-branes wrapped around fuzzy del Pezzo surfaces. We study the
fluctuation spectrum around the fuzzy CP^2 solution in detail. We also comment
on possible applications of our fuzzy del Pezzo surfaces to the fuzzy version
of F-theory, dubbed F(uzz) theory.Comment: 1+42 pages, 9 figures v2: references added v3: statements on the
structure of the Yukawa couplings weakened. published versio
Emerging Non-Anomalous Baryonic Symmetries in the AdS_5/CFT_4 Correspondence
We study the breaking of baryonic symmetries in the AdS_5/CFT_4
correspondence for D3 branes at Calabi-Yau three-fold singularities. This
leads, for particular VEVs, to the emergence of non-anomalous baryonic
symmetries during the renormalization group flow. We claim that these VEVs
correspond to critical values of the B-field moduli in the dual supergravity
backgrounds. We study in detail the C^3/Z_3 orbifold, the cone over F_0 and the
C^3/Z_5 orbifold. For the first two examples, we study the dual supergravity
backgrounds that correspond to the breaking of the emerging baryonic symmetries
and identify the expected Goldstone bosons and global strings in the infra-red.
In doing so we confirm the claim that the emerging symmetries are indeed
non-anomalous baryonic symmetries.Comment: 65 pages, 15 figures;v2: minor changes, published versio
Symmetries of Abelian Orbifolds
Using the Polya Enumeration Theorem, we count with particular attention to
C^3/Gamma up to C^6/Gamma, abelian orbifolds in various dimensions which are
invariant under cycles of the permutation group S_D. This produces a collection
of multiplicative sequences, one for each cycle in the Cycle Index of the
permutation group. A multiplicative sequence is controlled by its values on
prime numbers and their pure powers. Therefore, we pay particular attention to
orbifolds of the form C^D/Gamma where the order of Gamma is p^alpha. We propose
a generalization of these sequences for any D and any p.Comment: 75 pages, 13 figures, 30 table
Adherence to the screening program for HBV infection in pregnant women delivering in Greece
BACKGROUND: Hepatitis B infection (HBV) is a major Public Health Problem. Perinatal transmission can be prevented with the identification of HBsAg(+) women and administration of immunoprophylaxis to their newborns. A national prevention programme for HBV with universal screening of pregnant women and vaccination of infants is in effect since 1998 in Greece. METHODS: To evaluate adherence to the national guidelines, all women delivering in Greece between 17–30/03/03 were included in the study. Trained health professionals completed a questionnaire on demographic data, prenatal or perinatal screening for HBsAg and the implementation of appropriate immunoprophylaxis. RESULTS: During the study period 3,760 women delivered. Prenatal screening for HBsAg was documented in 91.3%. Greek women were more likely to have had prenatal testing. HBsAg prevalence was 2.89% (95%CI 2.3–3.4%). Higher prevalence of HBV-infection was noted in immigrant women, especially those born in Albania (9.8%). Other risk factors associated with maternal HBsAg (+) included young maternal age and absence of prenatal testing. No prenatal or perinatal HBsAg testing was performed in 3.2% women. Delivering in public hospital and illiteracy were identifiable risk factors for never being tested. All newborns of identified HBsAg (+) mothers received appropriate immunoprophylaxis. CONCLUSION: The prevalence of HBsAg in Greek pregnant women is low and comparable to other European countries. However, immigrant women composing almost 20% of our childbearing population, have significant higher prevalence rates. There are still women who never get tested. Universal vaccination against HBV at birth and reinforcement of perinatal testing of all women not prenatally tested should be discussed with Public Health Authorities
Network and Seiberg Duality
We define and study a new class of 4d N=1 superconformal quiver gauge
theories associated with a planar bipartite network. While UV description is
not unique due to Seiberg duality, we can classify the IR fixed points of the
theory by a permutation, or equivalently a cell of the totally non-negative
Grassmannian. The story is similar to a bipartite network on the torus
classified by a Newton polygon. We then generalize the network to a general
bordered Riemann surface and define IR SCFT from the geometric data of a
Riemann surface. We also comment on IR R-charges and superconformal indices of
our theories.Comment: 28 pages, 28 figures; v2: minor correction
Integrability on the Master Space
It has been recently shown that every SCFT living on D3 branes at a toric
Calabi-Yau singularity surprisingly also describes a complete integrable
system. In this paper we use the Master Space as a bridge between the
integrable system and the underlying field theory and we reinterpret the
Poisson manifold of the integrable system in term of the geometry of the field
theory moduli space.Comment: 47 pages, 20 figures, using jheppub.st
D-branes at Toric Singularities: Model Building, Yukawa Couplings and Flavour Physics
We discuss general properties of D-brane model building at toric
singularities. Using dimer techniques to obtain the gauge theory from the
structure of the singularity, we extract results on the matter sector and
superpotential of the corresponding gauge theory. We show that the number of
families in toric phases is always less than or equal to three, with a unique
exception being the zeroth Hirzebruch surface. With the physical input of three
generations we find that the lightest family of quarks is massless and the
masses of the other two can be hierarchically separated. We compute the CKM
matrix for explicit models in this setting and find the singularities possess
sufficient structure to allow for realistic mixing between generations and CP
violation.Comment: 55 pages, v2: typos corrected, minor comments adde
F-theory and Neutrinos: Kaluza-Klein Dilution of Flavor Hierarchy
We study minimal implementations of Majorana and Dirac neutrino scenarios in
F-theory GUT models. In both cases the mass scale of the neutrinos m_nu ~
(M_weak)^2/M_UV arises from integrating out Kaluza-Klein modes, where M_UV is
close to the GUT scale. The participation of non-holomorphic Kaluza-Klein mode
wave functions dilutes the mass hierarchy in comparison to the quark and
charged lepton sectors, in agreement with experimentally measured mass
splittings. The neutrinos are predicted to exhibit a "normal" mass hierarchy,
with masses m_3,m_2,m_1 ~ .05*(1,(alpha_GUT)^(1/2),alpha_GUT) eV. When the
interactions of the neutrino and charged lepton sectors geometrically unify,
the neutrino mixing matrix exhibits a mild hierarchical structure such that the
mixing angles theta_23 and theta_12 are large and comparable, while theta_13 is
expected to be smaller and close to the Cabibbo angle: theta_13 ~ theta_C ~
(alpha_GUT)^(1/2) ~ 0.2. This suggests that theta_13 should be near the current
experimental upper bound.Comment: v2: 83 pages, 10 figures, references adde
Evidence for F(uzz) Theory
We show that in the decoupling limit of an F-theory compactification, the
internal directions of the seven-branes must wrap a non-commutative four-cycle
S. We introduce a general method for obtaining fuzzy geometric spaces via toric
geometry, and develop tools for engineering four-dimensional GUT models from
this non-commutative setup. We obtain the chiral matter content and Yukawa
couplings, and show that the theory has a finite Kaluza-Klein spectrum. The
value of 1/alpha_(GUT) is predicted to be equal to the number of fuzzy points
on the internal four-cycle S. This relation puts a non-trivial restriction on
the space of gauge theories that can arise as a limit of F-theory. By viewing
the seven-brane as tiled by D3-branes sitting at the N fuzzy points of the
geometry, we argue that this theory admits a holographic dual description in
the large N limit. We also entertain the possibility of constructing string
models with large fuzzy extra dimensions, but with a high scale for quantum
gravity.Comment: v2: 66 pages, 3 figures, references and clarifications adde
- …