1,932 research outputs found
Calabi-Yau Fourfolds with Flux and Supersymmetry Breaking
In Calabi-Yau fourfold compactifications of M-theory with flux, we
investigate the possibility of partial supersymmetry breaking in the
three-dimensional effective theory. To this end, we place the effective theory
in the framework of general N=2 gauged supergravities, in the special case
where only translational symmetries are gauged. This allows us to extract
supersymmetry-breaking conditions, and interpret them as conditions on the
4-form flux and Calabi-Yau geometry. For N=2 unbroken supersymmetry in three
dimensions we recover previously known results, and we find a new condition for
breaking supersymmetry from N=2 to N=1, i.e. from four to two supercharges. An
example of a Calabi-Yau hypersurface in a toric variety that satisfies this
condition is provided.Comment: 26 page
F-term uplifting via consistent D-terms
The issue of fine-tuning necessary to achieve satisfactory degree of
hierarchy between moduli masses, the gravitino mass and the scale of the
cosmological constant has been revisited in the context of supergravities with
consistent D-terms. We have studied (extended) racetrack models where
supersymmetry breaking and moduli stabilisation cannot be separated from each
other. We show that even in such cases the realistic hierarchy can be achieved
on the expense of a single fine-tuning. The presence of two condensates changes
the role of the constant term in the superpotential, W_0, and solutions with
small vacuum energy and large gravitino mass can be found even for very small
values of W_0. Models where D-terms are allowed to vanish at finite vevs of
moduli fields - denoted `cancellable' D-terms - and the ones where D-terms may
vanish only at infinite vevs of some moduli - denoted `non-cancellable' -
differ markedly in their properties. It turns out that the tuning with respect
to the Planck scale required in the case of cancellable D-terms is much weaker
than in the case of non-cancellable ones. We have shown that, against
intuition, a vanishing D-term can trigger F-term uplifting of the vacuum energy
due to the stringent constraint it imposes on vacuum expectation values of
charged fields. Finally we note that our models only rely on two dimensionful
parameters: M_P and W_0.Comment: 10 pages, 2 figures, plain Latex, references adde
A Note on Flux Induced Superpotentials in String Theory
Non-vanishing fluxes in M-theory and string theory compactifications induce a
superpotential in the lower dimensional theory. Gukov has conjectured the
explicit form of this superpotential. We check this conjecture for the
heterotic string compactified on a Calabi-Yau three-fold as well as for warped
M-theory compactifications on Spin(7) holonomy manifolds, by performing a
Kaluza-Klein reduction.Comment: 19 pages, no figure
Professionalism, golf coaching and a master of science degree
A distinction can be made between 'professionalisation', which is concerned with occupational status and standing, and 'professionalism,' which refers to matters of quality and standards of practice (especially specialized knowledge, ethics and altruism). The purpose of this stimulus article is to present key features of contemporary medical professionalism as a basis for critically reflecting on discourse associated with Tiger Woods' current coach, Sean Foley. It is suggested that that provision of a Master of Science degree in golf teaching/coaching would facilitate the development of 'professionalism' in golf coaches
Use of RIP to inactivate genes in Neurospora crassa.
About two years ago we suggested that a novel genetic mechanism, operating in the period between fertilization and nuclear fusion in Neurospora, scans the genome for sequence dupliations and alters them (Selker E. et al. 1987 Cell 51:741-752)
Supersymmetric codimension-two branes and U(1)_R mediation in 6D gauged supergravity
We construct a consistent supersymmetric action for brane chiral and vector
multiplets in a six-dimensional chiral gauged supergravity. A nonzero brane
tension can be accommodated by allowing for a brane-localized Fayet-Iliopoulos
term proportional to the brane tension. When the brane chiral multiplet is
charged under the bulk U(1)_R, we obtain a nontrivial coupling to the extra
component of the U(1)_R gauge field strength as well as a singular scalar
self-interaction term. Dimensionally reducing to 4D on a football
supersymmetric solution, we discuss the implication of such interactions for
obtaining the U(1)_R D-term in the 4D effective supergravity. By assuming the
bulk gaugino condensates and nonzero brane F- and/or D-term for the uplifting
potential, we have all the moduli stabilized with a vanishing cosmological
constant. The brane scalar with nonzero R charge then gets a soft mass of order
the gravitino mass. The overall sign of the soft mass squared depends on the
sign of the R charge as well as whether the brane F- or D-term dominates.Comment: 28 pages, no figures, version to appear in JHE
Observing Brane Inflation
Linking the slow-roll scenario and the Dirac-Born-Infeld scenario of
ultra-relativistic roll (where, thanks to the warp factor, the inflaton moves
slowly even with an ultra-relativistic Lorentz factor), we find that the KKLMMT
D3/anti-D3 brane inflation is robust, that is, enough e-folds of inflation is
quite generic in the parameter space of the model. We show that the
intermediate regime of relativistic roll can be quite interesting
observationally. Introducing appropriate inflationary parameters, we explore
the parameter space and give the constraints and predictions for the
cosmological observables in this scenario. Among other properties, this
scenario allows the saturation of the present observational bound of either the
tensor/scalar ratio r (in the intermediate regime) or the non-Gaussianity f_NL
(in the ultra-relativistic regime), but not both.Comment: 31 pages, 12 figures; typo correcte
Generalized geometry, calibrations and supersymmetry in diverse dimensions
We consider type II backgrounds of the form R^{1,d-1} x M^{10-d} for even d,
preserving 2^{d/2} real supercharges; for d = 4, 6, 8 this is minimal
supersymmetry in d dimensions, while for d = 2 it is N = (2,0) supersymmetry in
two dimensions. For d = 6 we prove, by explicitly solving the Killing-spinor
equations, that there is a one-to-one correspondence between background
supersymmetry equations in pure-spinor form and D-brane generalized
calibrations; this correspondence had been known to hold in the d = 4 case.
Assuming the correspondence to hold for all d, we list the calibration forms
for all admissible D-branes, as well as the background supersymmetry equations
in pure-spinor form. We find a number of general features, including the
following: The pattern of codimensions at which each calibration form appears
exhibits a (mod 4) periodicity. In all cases one of the pure-spinor equations
implies that the internal manifold is generalized Calabi-Yau. Our results are
manifestly invariant under generalized mirror symmetry.Comment: 28 pages, 1 tabl
Ion exchange membranes derived from sulfonated polyaramides
Homo- and both random and block copolyaramides of high molecular weights, with sulfonated moieties in the backbone, were obtained by low temperature polycondensation technique in a dipolar aprotic solvent (NMP) using (a) free aromatic diamines in the presence of pyridine as acid acceptor and (b) N,N ′-bis-trimethylsilyl derivatives of the diamines without additional acid acceptor. The addition of low molecular weight electrolytes (LiCl or CaCl2) and in some cases trimesoyl chloride to the reaction mixture was found to be favorable for the synthesis of high molecular weight polyamides. The materials had a theoretical ion exchange capacity of up to 3.14 meq/g. The membranes were characterized in terms of morphology, thermal stability, water-uptake, and ion exchange capacities.Fil: Taeger, A.. Institute of Polymer Research Dresden; AlemaniaFil: Vogel, C.. Institute of Polymer Research Dresden; AlemaniaFil: Lehmann, D.. Institute of Polymer Research Dresden; AlemaniaFil: Jehnichen, D.. Institute of Polymer Research Dresden; AlemaniaFil: Komber, H.. Institute of Polymer Research Dresden; AlemaniaFil: Meier Haack, J.. Institute of Polymer Research Dresden; AlemaniaFil: Ochoa, Nelio Ariel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - San Luis. Instituto de FÃsica Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias FÃsico Matemáticas y Naturales. Instituto de FÃsica Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Nunes, S.P.. GKSS Research Center; AlemaniaFil: Peinemann, K.-V.. GKSS Research Center; Alemani
The Gaugings of Maximal D=6 Supergravity
We construct the most general gaugings of the maximal D=6 supergravity. The
theory is (2,2) supersymmetric, and possesses an on-shell SO(5,5) duality
symmetry which plays a key role in determining its couplings. The field content
includes 16 vector fields that carry a chiral spinor representation of the
duality group. We utilize the embedding tensor method which determines the
appropriate combinations of these vectors that participate in gauging of a
suitable subgroup of SO(5,5). The construction also introduces the magnetic
duals of the 5 two-form potentials and 16 vector fields.Comment: 34 pages, latex, reference added, typo's corrected and minor
improvements mad
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