236 research outputs found
The effective action of D6-branes in N=1 type IIA orientifolds
We use a Kaluza-Klein reduction to compute the low-energy effective action
for the massless modes of a spacetime-filling D6-brane wrapped on a special
Lagrangian 3-cycle of a type IIA Calabi-Yau orientifold. The modifications to
the characteristic data of the N=1 bulk orientifold theory in the presence of a
D6-brane are analysed by studying the underlying Type IIA supergravity coupled
to the brane worldvolume in the democratic formulation and performing a
detailed dualisation procedure. The N=1 chiral coordinates are found to be in
agreement with expectations from mirror symmetry. We work out the Kahler
potential for the chiral superfields as well as the gauge kinetic functions for
the bulk and the brane gauge multiplets including the kinetic mixing between
the two. The scalar potential resulting from the dualisation procedure can be
formally interpreted in terms of a superpotential. Finally, the gauging of the
Peccei-Quinn shift symmetries of the complex structure multiplets reproduces
the D-term potential enforcing the calibration condition for special Lagrangian
3-cycles.Comment: 48 pages, v2: typos corrected, references adde
Massive Abelian Gauge Symmetries and Fluxes in F-theory
F-theory compactified on a Calabi-Yau fourfold naturally describes
non-Abelian gauge symmetries through the singularity structure of the elliptic
fibration. In contrast Abelian symmetries are more difficult to study because
of their inherently global nature. We argue that in general F-theory
compactifications there are massive Abelian symmetries, such as the uplift of
the Abelian part of the U(N) gauge group on D7-branes, that arise from
non-Kahler resolutions of the dual M-theory setup. The four-dimensional
F-theory vacuum with vanishing expectation values for the gauge fields
corresponds to the Calabi-Yau limit. We propose that fluxes that are turned on
along these U(1)s are uplifted to non-harmonic four-form fluxes. We derive the
effective four-dimensional gauged supergravity resulting from F-theory
compactifications in the presence of the Abelian gauge factors including the
effects of possible fluxes on the gauging, tadpoles and matter spectrum.Comment: 49 page
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
Holomorphic variables in magnetized brane models with continuous Wilson lines
We analyze the action of the target-space modular group in toroidal type IIB
orientifold compactifications with magnetized D-branes and continuous Wilson
lines. The transformation of matter fields agree with that of twisted fields in
heterotic compactifications, constituting a check of type I/heterotic duality.
We identify the holomorphic N = 1 variables for these compactifications. Matter
fields and closed string moduli are both redefined by open string moduli. The
redefinition of matter fields can be read directly from the perturbative Yukawa
couplings, whereas closed string moduli redefinitions are obtained from D-brane
instanton superpotential couplings. The resulting expressions reproduce and
generalize, in the presence of internal magnetic fields, previous results in
the literature.Comment: 9 pages, no figures; v2: conventions for Wilson lines changed, major
simplifications in expressions, discussions extended, typos corrected, some
references adde
The Universal Plausibility Metric (UPM) & Principle (UPP)
<p>Abstract</p> <p>Background</p> <p>Mere possibility is not an adequate basis for asserting scientific plausibility. A precisely defined universal bound is needed beyond which the assertion of <it>plausibility</it>, particularly in life-origin models, can be considered operationally falsified. But can something so seemingly relative and subjective as plausibility ever be quantified? Amazingly, the answer is, "Yes." A method of objectively measuring the plausibility of any chance hypothesis (The Universal Plausibility Metric [UPM]) is presented. A numerical inequality is also provided whereby any chance hypothesis can be definitively falsified when its UPM metric of ξ is < 1 (The Universal Plausibility Principle [UPP]). Both UPM and UPP pre-exist and are independent of any experimental design and data set.</p> <p>Conclusion</p> <p>No low-probability hypothetical plausibility assertion should survive peer-review without subjection to the UPP inequality standard of formal falsification (ξ < 1).</p
Flux and Instanton Effects in Local F-theory Models and Hierarchical Fermion Masses
We study the deformation induced by fluxes and instanton effects on Yukawa
couplings involving 7-brane intersections in local F-theory constructions. In
the absence of non-perturbative effects, holomorphic Yukawa couplings do not
depend on open string fluxes. On the other hand instanton effects (or gaugino
condensation on distant 7-branes) do induce corrections to the Yukawas. The
leading order effect may also be captured by the presence of closed string
(1,2) IASD fluxes, which give rise to a non-commutative structure. We check
that even in the presence of these non-perturbative effects the holomorphic
Yukawas remain independent of magnetic fluxes. Although fermion mass
hierarchies may be obtained from these non-perturbative effects, they would
give identical Yukawa couplings for D-quark and Lepton masses in SU(5) F-theory
GUT's, in contradiction with experiment. We point out that this problem may be
solved by appropriately normalizing the wavefunctions. We show in a simple toy
model how the presence of hypercharge flux may then be responsible for the
difference between D-quarks and Lepton masses in local SU(5) GUT's.Comment: 84 pages, 1 figure. v2: minor corrections and references adde
Envelope Determinants of Equine Lentiviral Vaccine Protection
Lentiviral envelope (Env) antigenic variation and associated immune evasion present major obstacles to vaccine development. The concept that Env is a critical determinant for vaccine efficacy is well accepted, however defined correlates of protection associated with Env variation have yet to be determined. We reported an attenuated equine infectious anemia virus (EIAV) vaccine study that directly examined the effect of lentiviral Env sequence variation on vaccine efficacy. The study identified a significant, inverse, linear correlation between vaccine efficacy and increasing divergence of the challenge virus Env gp90 protein compared to the vaccine virus gp90. The report demonstrated approximately 100% protection of immunized ponies from disease after challenge by virus with a homologous gp90 (EV0), and roughly 40% protection against challenge by virus (EV13) with a gp90 13% divergent from the vaccine strain. In the current study we examine whether the protection observed when challenging with the EV0 strain could be conferred to animals via chimeric challenge viruses between the EV0 and EV13 strains, allowing for mapping of protection to specific Env sequences. Viruses containing the EV13 proviral backbone and selected domains of the EV0 gp90 were constructed and in vitro and in vivo infectivity examined. Vaccine efficacy studies indicated that homology between the vaccine strain gp90 and the N-terminus of the challenge strain gp90 was capable of inducing immunity that resulted in significantly lower levels of post-challenge virus and significantly delayed the onset of disease. However, a homologous N-terminal region alone inserted in the EV13 backbone could not impart the 100% protection observed with the EV0 strain. Data presented here denote the complicated and potentially contradictory relationship between in vitro virulence and in vivo pathogenicity. The study highlights the importance of structural conformation for immunogens and emphasizes the need for antibody binding, not neutralizing, assays that correlate with vaccine protection. © 2013 Craigo et al
Gravitational Waves from Gravitational Collapse
Gravitational wave emission from the gravitational collapse of massive stars
has been studied for more than three decades. Current state of the art
numerical investigations of collapse include those that use progenitors with
realistic angular momentum profiles, properly treat microphysics issues,
account for general relativity, and examine non--axisymmetric effects in three
dimensions. Such simulations predict that gravitational waves from various
phenomena associated with gravitational collapse could be detectable with
advanced ground--based and future space--based interferometric observatories.Comment: 68 pages including 13 figures; revised version accepted for
publication in Living Reviews in Relativity (http://www.livingreviews.org
Non-perturbative Vacuum Destabilization and D-brane Dynamics
We analyze the process of string vacuum destabilization due to instanton
induced superpotential couplings which depend linearly on charged fields. These
non-perturbative instabilities result in potentials for the D-brane moduli and
lead to processes of D-brane recombination, motion and partial moduli
stabilization at the non-perturbative vacuum. By using techniques of D-brane
instanton calculus, we explicitly compute this scalar potential in toroidal
orbifold compactifications with magnetized D-branes by summing over the
possible discrete instanton configurations. We illustrate explicitly the
resulting dynamics in globally consistent models. These instabilities can have
phenomenological applications to breaking hidden sector gauge groups, open
string moduli stabilization and supersymmetry breaking. Our results suggest
that breaking supersymmetry by Polonyi-like models in string theory is more
difficult than expected.Comment: 61 pages, 6 figures, 5 tables; Minor corrections, version published
in JHE
Unification and Phenomenology of F-Theory GUTs with U(1)_PQ
We undertake a phenomenological study of SU(5) F-theory GUT models with an
additional U(1)_{PQ} symmetry. In such models, breaking SU(5) with hypercharge
flux leads to the presence of non-GUT multiplets in the spectrum. We study the
effect these have on the unification of gauge couplings, including two-loop
running as well as low- and high-scale threshold corrections. We use the
requirement of unification to constrain the size of thresholds from KK modes of
SU(5) gauge and matter fields. Assuming the non-GUT multiplets play the role of
messengers of gauge mediation leads to controlled non-universalities in the
sparticle spectrum while maintaining grand unification, and we study the LHC
phenomenology of this scenario. We find that the MSSM spectrum may become
compressed or stretched out {by up to a factor of three} depending on the
distribution of hypercharge flux. We present a set of benchmark points whose
production cross-sections and decays we investigate, and argue that precision
kinematic edge measurements will allow the LHC to distinguish between our model
and mGMSB.Comment: 46 pages, 15 figure
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