5,555 research outputs found
Right-veering diffeomorphisms of compact surfaces with boundary II
We continue our study of the monoid of right-veering diffeomorphisms on a
compact oriented surface with nonempty boundary, introduced in [HKM2]. We
conduct a detailed study of the case when the surface is a punctured torus; in
particular, we exhibit the difference between the monoid of right-veering
diffeomorphisms and the monoid of products of positive Dehn twists, with the
help of the Rademacher function. We then generalize to the braid group B_n on n
strands by relating the signature and the Maslov index. Finally, we discuss the
symplectic fillability in the pseudo-Anosov case by comparing with the work of
Roberts [Ro1,Ro2].Comment: 25 pages, 5 figure
Half-ordered state in the anisotropic Haldane-gap antiferromagnet NDMAP
Neutron diffraction experiments performed on the Haldane gap material NDMAP
in high magnetic fields applied at an angle to the principal anisotropy axes
reveal two consecutive field-induced phase transitions. The low-field phase is
the gapped Haldane state, while at high fields the system exhibits
3-dimensional long-range Neel order. In a peculiar phase found at intermediate
fields only half of all the spin chains participate in the long-range ordering,
while the other half remains disordered and gapped.Comment: 4 pages, 2 figures, submitted to Phys. Rev.
Observation of a Transient Magnetization Plateau in a Quantum Antiferromagnet on the Kagome Lattice
The magnetization process of an S=1/2 antiferromagnet on the kagome lattice,
[Cu_3(titmb)_2(OCOCH_3)_6]H_2O {titmb= 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6
trimethylbenzene} has been measured at very low temperatures in both pulsed and
steady fields. We have found a new dynamical behavior in the magnetization
process: a plateau at one third of the saturation magnetization appears in the
pulsed field experiments for intermediate sweep rates of the magnetic field and
disappears in the steady field experiments. A theoretical analysis using exact
diagonalization yields J_1=-19K and J_2=6K, for the nearest neighbor and second
nearest neighbor interactions, respectively. This set of exchange parameters
explains the very low saturation field and the absence of the plateau in the
thermodynamic equilibrium as well as the two-peak feature in the magnetic heat
capacity. Supported by numerical results we argue that a dynamical order by
disorder phenomenon could explain the transient appearance of the 1/3 plateau
in pulsed field experiments.Comment: 7 pages, 5 figure
Quasi-elastic neutron scattering in the high-field phase of a Haldane antiferromagnet
Inelastic neutron scattering experiments on the Haldane-gap quantum
antiferromagnet NDMAP are performed in magnetic fields below and above the
critical field Hc at which the gap closes. Quasi-elastic neutron scattering is
found for H>Hc indicating topological excitations in the high field phase.Comment: Added to discussion section. v2: Updated figure
Electronic transport properties of quasicrystals: a Review
We present a review of some results concerning electronic transport
properties of quasicrystals. After a short introduction to the basic concepts
of quasiperiodicity, we consider the experimental transport properties of
electrical conductivity with particular focus on the effect of temperature,
magnetic field and defects. Then, we present some heuristic approaches that
tend to give a coherent view of different, and to some extent complementary,
transport mechanisms in quasicrystals. Numerical results are also presented and
in particular the evaluation of the linear response Kubo-Greenwood formula of
conductivity in quasiperiodic systems in presence of disorder.Comment: Latex, 28 pages, Journ. of Math. Phys., Vol38 April 199
What do experimental data "say" about growth of hadronic total cross-section?
We reanalyse and high energy data of the elastic scattering
above GeV on the total cross-section and on the
forward -ratio for various models of Pomeron, utilizing two methods. The
first one is based on analytic amplitudes, the other one relies on assumptions
for and on dispersion relation for . We argue that it is
not possible, from fitting only existing data for forward scattering, to select
a definite asymptotic growth with the energy of . We find
equivalent fits to the data together with a logarithmic Pomeron giving a
behavior , and with
a supercritical Pomeron giving a behavior ,
.Comment: LaTeX, 18 pages, 5 eps figures included, to be published in Il Nuovo
Ciment
Tight Beltrami fields with symmetry
Let be a compact orientable Seifered fibered 3-manifold without a
boundary, and an -invariant contact form on . In a suitable
adapted Riemannian metric to , we provide a bound for the volume
and the curvature, which implies the universal tightness of the
contact structure .Comment: 26 page
Flavor Symmetry Breaking in Strongly Coupled N=1 Supersymmetric SO(N_c) Gauge Theory with N_f=N_c-2
In the SO(N_c) gauge theory with N_f quarks for N_f=N_c-2, its instanton
effects indicate the signal of dynamical flavor symmetry breakdown of SU(N_f)
to SO(N_f), which is not described by the conventional "magnetic" degree's of
freedom. It is argued that this breaking is well described by our effective
superpotential consisting of "electric" quarks and gluons instead of monopoles
of SO(N_c). The low-energy particles include the Nambu-Goldstone superfields
associated with this breakdown. The proposed superpotential is found to exhibit
the holomorphic decoupling property and the anomaly-matching property on a
residual chiral U(1) symmetry.Comment: 6 pages, version to appear in Europhysics Letter
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