2,823 research outputs found
On Neutrino Masses and Mixings from Extra Dimensions
In the framework of a Kaluza-Klein type theory with the Standard Model fields
localized on a 4-dimensional section while gravity propagates in a full
-dimensional space-time, we examine a mechanism of naturally small
neutrino mass generation through couplings of Standard Model singlet fermion(s)
living also in the full space-time. A numerical studies is carried out on the
charged current universality constraint from the ratio of pion decay partial
widths. The bounds obtained on the fundamental mass scale could be stringent.Comment: 16 pages latex, no figure; small modifications in discussions;
version to appear in Phys.Lett.
Strings, Matrix Models, and Meanders
I briefly review the present status of bosonic strings and discretized random
surfaces in D>1 which seem to be in a polymer rather than stringy phase. As an
explicit example of what happens, I consider the Kazakov-Migdal model with a
logarithmic potential which is exactly solvable for any D (at large D for an
arbitrary potential). I discuss also the meander problem and report some new
results on its representation via matrix models and the relation to the
Kazakov-Migdal model. A supersymmetric matrix model is especially useful for
describing the principal meanders.Comment: 12 pages, 4 Latex figures, uses espcrc2.sty Talk at the 29th
Ahrenshoop Symp., Buckow, Germany, Aug.29 - Sep.2, 199
Physics of Quantum Relativity through a Linear Realization
The idea of quantum relativity as a generalized, or rather deformed, version
of Einstein (special) relativity has been taking shape in recent years.
Following the perspective of deformations, while staying within the framework
of Lie algebra, we implement explicitly a simple linear realization of the
relativity symmetry, and explore systematically the resulting physical
interpretations. Some suggestions we make may sound radical, but are arguably
natural within the context of our formulation. Our work may provide a new
perspective on the subject matter, complementary to the previous approach(es),
and may lead to a better understanding of the physics.Comment: 27 pages in Revtex, no figure; proof-edited version to appear in
Phys.Rev.
Two and three-point functions in Liouville theory
Based on our generalization of the Goulian-Li continuation in the power of
the 2D cosmological term we construct the two and three-point correlation
functions for Liouville exponentials with generic real coefficients. As a
strong argument in favour of the procedure we prove the Liouville equation of
motion on the level of three-point functions. The analytical structure of the
correlation functions as well as some of its consequences for string theory are
discussed. This includes a conjecture on the mass shell condition for
excitations of noncritical strings. We also make a comment concerning the
correlation functions of the Liouville field itself.Comment: 15 pages, Latex, Revised version: A sign error in formula (50) is
correcte
The Multivalued Free-Field Maps of Liouville and Toda Gravities
Liouville and Toda gravity theories with non-vanishing interaction potentials
have spectra obtained by dividing the free-field spectra for these cases by the
Weyl group of the corresponding or Lie algebra. We study the
canonical transformations between interacting and free fields using the
technique of intertwining operators, giving explicit constructions for the
wavefunctions and showing that they are invariant under the corresponding Weyl
groups. These explicit constructions also permit a detailed analysis of the
operator-state maps and of the nature of the Seiberg bounds.Comment: 47 pages, plain Tex, 5 Postscript figures, uses epsf.tex. Repackaging
to permit Postscript generation, no changes to pape
Cycloadditions in mixed aqueous solvents: the role of the water concentration
We examined the kinetics of a series of cycloaddition reactions in mixtures of water with methanol, acetonitrile and poly(ethylene glycol) (MW 1000). The reactions include the Diels–Alder (DA) reaction between cyclopentadiene and N-n-butylmaleimide or acridizinium bromide, the retro-Diels-Alder (RDA) reaction of 1,4,4a,9a-tetrahydro-4a-methyl-(1α,4α,4aα,9aα)-1,4-methaneanthracene-9,10-dione and the 1,3-dipolar cycloaddition of benzonitrile oxide with N-n-butylmaleimide. Plots of logk vs the molar concentration or volume fraction of water are approximately linear, but with a characteristic break around 40 M water. This break, absent for the RDA reaction, is ascribed to hydrophobic effects. Comparison with aqueous mixtures of the more hydrophobic 1-propanol shows that these mixtures induce qualitatively similar effects on the rate, but that preferential solvation effects cause the mixtures of 1-propanol to exhibit a more complex behavior of logk on composition. The results are analyzed using the Abraham–Kamlett–Taft model. The solvent effects in aqueous mixtures are not satisfactorily described by this model. For some cycloadditions, small maxima in rate are observed in highly aqueous mixtures of alcohols. The origin of these maxima and the aforementioned breaks is most likely the same.
Situating Sexual Violence in Rwanda (1990–2001): Sexual Agency, Sexual Consent, and the Political Economy of War
This article situates the sexual violence associated with the Rwandan civil war and 1994 genocide within a local cultural history and political economy in which institutionalized gender violence shaped the choices of Rwandan women and girls. Based on ethnographic research, it argues that Western notions of sexual consent are not applicable to a culture in which colonialism, government policy, war, and scarcity of resources have limited women’s access to land ownership, economic security, and other means of survival. It examines emic cultural models of sexual consent and female sexual agency and proposes that sexual slavery, forced marriage, prostitution, transactional sex, nonmarital sex, informal marriage or cohabitation, and customary (bridewealth) marriages exist on a continuum on which female sexual agency becomes more and more constrained by material circumstance. Even when women’s choices are limited, sometimes impossibly limited, they still exercise their agency to survive. Conflating all forms of sex in conflict zones under the rubric of harm undermines women’s and children’s rights because it reinforces gendered hierarchies and diverts attention from the structural conditions of poverty in postconflict societies
Surface plasmons in metallic structures
Since the concept of a surface collective excitation was first introduced by
Ritchie, surface plasmons have played a significant role in a variety of areas
of fundamental and applied research, from surface dynamics to surface-plasmon
microscopy, surface-plasmon resonance technology, and a wide range of photonic
applications. Here we review the basic concepts underlying the existence of
surface plasmons in metallic structures, and introduce a new low-energy surface
collective excitation that has been recently predicted to exist.Comment: 14 pages, 14 figures, to appear in J. Opt. A: Pure Appl. Op
Dchs1-Fat4 regulation of osteogenic differentiation in mouse
In human, mutations of the protocadherins FAT4 and DCHS1 result in Van Maldergem syndrome, which is characterised, in part, by craniofacial abnormalities. Here, we analyse the role of Dchs1-Fat4 signalling during osteoblast differentiation in mouse. We show that Fat4 and Dchs1 mutants mimic the craniofacial phenotype of the human syndrome and that Dchs1-Fat4 signalling is essential for osteoblast differentiation. In Dchs1/Fat4 mutants, proliferation of osteoprogenitors is increased and osteoblast differentiation is delayed. We show that loss of Dchs1-Fat4 signalling is linked to increased Yap-Tead activity and that Yap is expressed and required for proliferation in osteoprogenitors. In contrast, Taz is expressed in more-committed Runx2-expressing osteoblasts, Taz does not regulate osteoblast proliferation and Taz-Tead activity is unaffected in Dchs1/Fat4 mutants. Finally, we show that Yap and Taz differentially regulate the transcriptional activity of Runx2, and that the activity of Yap-Runx2 and Taz-Runx2 complexes is altered in Dchs1/Fat4 mutant osteoblasts. In conclusion, these data identify Dchs1-Fat4 as a signalling pathway in osteoblast differentiation, reveal its crucial role within the early Runx2 progenitors, and identify distinct requirements for Yap and Taz during osteoblast differentiation
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