209 research outputs found
Eliashberg's proof of Cerf's theorem
Following a line of reasoning suggested by Eliashberg, we prove Cerf's
theorem that any diffeomorphism of the 3-sphere extends over the 4-ball. To
this end we develop a moduli-theoretic version of Eliashberg's
filling-with-holomorphic-discs method.Comment: 32 page
Algebraic Torsion in Contact Manifolds
We extract a nonnegative integer-valued invariant, which we call the "order
of algebraic torsion", from the Symplectic Field Theory of a closed contact
manifold, and show that its finiteness gives obstructions to the existence of
symplectic fillings and exact symplectic cobordisms. A contact manifold has
algebraic torsion of order zero if and only if it is algebraically overtwisted
(i.e. has trivial contact homology), and any contact 3-manifold with positive
Giroux torsion has algebraic torsion of order one (though the converse is not
true). We also construct examples for each nonnegative k of contact 3-manifolds
that have algebraic torsion of order k but not k - 1, and derive consequences
for contact surgeries on such manifolds. The appendix by Michael Hutchings
gives an alternative proof of our cobordism obstructions in dimension three
using a refinement of the contact invariant in Embedded Contact Homology.Comment: 53 pages, 4 figures, with an appendix by Michael Hutchings; v.3 is a
final update to agree with the published paper, and also corrects a minor
error that appeared in the published version of the appendi
Calabi-Yau cones from contact reduction
We consider a generalization of Einstein-Sasaki manifolds, which we
characterize in terms both of spinors and differential forms, that in the real
analytic case corresponds to contact manifolds whose symplectic cone is
Calabi-Yau. We construct solvable examples in seven dimensions. Then, we
consider circle actions that preserve the structure, and determine conditions
for the contact reduction to carry an induced structure of the same type. We
apply this construction to obtain a new hypo-contact structure on S^2\times
T^3.Comment: 30 pages; v2: typos corrected, presentation improved, one reference
added. To appear in Ann. Glob. Analysis and Geometr
The geometry of recursion operators
We study the fields of endomorphisms intertwining pairs of symplectic
structures. Using these endomorphisms we prove an analogue of Moser's theorem
for simultaneous isotopies of two families of symplectic forms. We also
consider the geometric structures defined by pairs and triples of symplectic
forms for which the squares of the intertwining endomorphisms are plus or minus
the identity. For pairs of forms we recover the notions of symplectic pairs and
of holomorphic symplectic structures. For triples we recover the notion of a
hypersymplectic structure, and we also find three new structures that have not
been considered before. One of these is the symplectic formulation of
hyper-Kaehler geometry, which turns out to be a strict generalization of the
usual definition in terms of differential or Kaehler geometry.Comment: cosmetic changes only; to appear in Comm. Math. Phy
The f_LT Response Function of D(e,e'p)n at Q^2=0.33(GeV/c)^2
The interference response function f_LT (R_LT) of the D(e,e'p)n reaction has
been determined at squared four-momentum transfer Q^2 = 0.33 (GeV/c)^2 and for
missing momenta up to p_miss= 0.29 (GeV/c). The results have been compared to
calculations that reproduce f_LT quite well but overestimate the cross sections
by 10 - 20% for missing momenta between 0.1 (GeV/c) and 0.2 (GeV/c) .Comment: 12 Pages, 10 figure
State business: gender, sex and marriage in Tajikistan
This article examines the relation of the state to masculinity and sexuality by way of an exploration of the sexual problems of a young man and his wife in Tajikistan at the end of the Soviet era. It suggests that the regime’s inattention to this kind of issue was bound up with the importance to the state of projecting appropriate versions of masculinity. It further posits the idea that the continued refusal of the independent Tajik state to offer appropriate treatments for sexual dysfunction is consistent with the image of modernity President Rahmon wishes to present to the world. The article shows that as masculinity discursively occupies the superior gender position, with men expected to dominate, the state is itself impotent to respond when they are, in fact, unable to do so in sexual practice. However, the myth of male dominance persists to the point that it may prevent women from seeing beyond their subordination and finding mutually beneficial solutions in their familial and sexual relationships
A measurement of the axial form factor of the nucleon by the p(e,e'pi+)n reaction at W=1125 MeV
The reaction p(e,e'pi+)n was measured at the Mainz Microtron MAMI at an
invariant mass of W=1125 MeV and four-momentum transfers of Q^2=0.117, 0.195
and 0.273 (GeV/c)^2. For each value of Q^2, a Rosenbluth separation of the
transverse and longitudinal cross sections was performed. An effective
Lagrangian model was used to extract the `axial mass' from experimental data.
We find a value of M_A=(1.077+-0.039) GeV which is (0.051+-0.044) GeV larger
than the axial mass known from neutrino scattering experiments. This is
consistent with recent calculations in chiral perturbation theory.Comment: 14 pages, 5 figures, uses elsart.cl
Measurement of Rlt and Atl in the 4He(e,e'p)3H Reaction at pmiss of 130-300 MeV/c
We have measured the 4He(e,e'p)3H reaction at missing momenta of 130-300
MeV/c using the three-spectrometer facility at the Mainz microtron MAMI. Data
were taken in perpendicular kinematics to allow us to determine the response
function Rlt and the asymmetry term Atl. The data are compared to both
relativistic and non-relativistic calculations.Comment: To be published in the European Physical Journal
High-precision Studies of the He(e,ep) Reaction at the Quasielastic Peak
Precision studies of the reaction He(e,ep) using the
three-spectrometer facility at the Mainz microtron MAMI are presented. All data
are for quasielastic kinematics at MeV/c. Absolute cross
sections were measured at three electron kinematics. For the measured missing
momenta range from 10 to 165 MeV/c, no strength is observed for missing
energies higher than 20 MeV. Distorted momentum distributions were extracted
for the two-body breakup and the continuum. The longitudinal and transverse
behavior was studied by measuring the cross section for three photon
polarizations. The longitudinal and transverse nature of the cross sections is
well described by a currently accepted and widely used prescription of the
off-shell electron-nucleon cross-section. The results are compared to modern
three-body calculations and to previous data.Comment: 4 pages, 3 figures. Submitted for publication in Phys. Rev. Let
Measurement of the recoil polarization in the p (\vec e, e' \vec p) pi^0 reaction at the \Delta(1232) resonance
The recoil proton polarization has been measured in the p (\vec e,e'\vec p)
pi^0 reaction in parallel kinematics around W = 1232 MeV, Q^2 = 0.121 (GeV/c)^2
and epsilon = 0.718 using the polarized c.w. electron beam of the Mainz
Microtron. Due to the spin precession in a magnetic spectrometer, all three
proton polarization components P_x/P_e = (-11.4 \pm 1.3 \pm 1.4) %, P_y =
(-43.1 \pm 1.3 \pm 2.2) %, and P_z/P_e = (56.2 \pm 1.5 \pm 2.6) % could be
measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio CMR =
(-6.4\pm 0.7_{stat}\pm 0.8_{syst}) % was determined from P_x in the framework
of the Mainz Unitary Isobar Model. The consistency among the reduced
polarizations and the extraction of the ratio of longitudinal to transverse
response is discussed.Comment: 5 pages LaTeX, 1 table, 2 eps figure
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