30,915 research outputs found
Tetravalent Colloids by Nematic Wetting
In an elegant paper, D. Nelson suggested a method to produce tetravalent
colloids based on a tetrahedral configuration created on the surface of a
spherical particle. It emerges from a two-dimensional nematic liquid crystal
placed on a sphere due to the presence of four 1/2 disclinations, i.e.,
topological defects in the orientational order. In this paper we show that such
a tetrahedral configuration also occurs in the wetting layers which form around
spheres dispersed in a liquid crystal above the nematic-isotropic phase
transition. Nematic wetting therefore offers an alternative route towards
tetravalent colloids.Comment: 7 pages, 4 figures, submitted to Europhys. Let
Topological Transitions for Lattice Bosons in a Magnetic Field
We study the Hall response of the Bose-Hubbard model subjected to a magnetic
field. We show that the Hall conductivity is proportional to the particle
density plus an integer. The phase diagram is intersected by topological
transitions between different integer values. These transitions originate from
points in the phase diagram with effective charge conjugation symmetry, and are
attributed to degeneracies in the many body spectrum which serve as sources for
the Berry curvature. We find that extensive regions in the phase diagram
exhibit a negative Hall conductivity, implying that flux flow is reversed in
these regions - vortices there flow upstream. We discuss experimental
implications of our findings.Comment: 11 pages, 7 figure
Hand-held self-maneuvering unit Patent
Hand-held maneuvering unit for propulsion and attitude control of astronauts in zero or reduced gravity environmen
Compatibility of neutron star masses and hyperon coupling constants
It is shown that the modern equations of state for neutron star matter based
on microscopic calculations of symmetric and asymmetric nuclear matter are
compatible with the lower bound on the maximum neutron-star mass for a certain
range of hyperon coupling constants, which are constrained by the binding
energies of hyperons in symmetric nuclear matter. The hyperons are included by
means of the relativistic Hartree-- or Hartree--Fock approximation. The
obtained couplings are also in satisfactory agreement with hypernuclei data in
the relativistic Hartree scheme. Within the relativistic Hartree--Fock
approximation hypernuclei have not been investigated so far.Comment: 12 pages, 3 figures. Dedicated to Prof. Georg Suessmann on the
occasion of his 70th birthday. To be published in Zeitschrift fuer
Naturforschung
Symmetric and asymmetric nuclear matter in the relativistic approach at finite temperatures
The properties of hot matter are studied in the frame of the relativistic
Brueckner-Hartree-Fock theory. The equations are solved self-consistently in
the full Dirac space. For the interaction we used the potentials given by
Brockmann and Machleidt. The obtained critical temperatures are smaller than in
most of the nonrelativistic investigations. We also calculated the
thermodynamic properties of hot matter in the relativistic Hartree--Fock
approximation, where the force parameters were adjusted to the outcome of the
relativistic Brueckner--Hartree--Fock calculations at zero temperature. Here,
one obtains higher critical temperatures, which are comparable with other
relativistic calculations in the Hartree scheme.Comment: 8 pages, 9 figures, submitted in a shorter version to Phys. Rev.
The nonplanar cusp and collinear anomalous dimension at four loops in SYM theory
We present numerical results for the nonplanar lightlike cusp and collinear
anomalous dimension at four loops in SYM theory, which we
infer from a calculation of the Sudakov form factor. The latter is expressed as
a rational linear combination of uniformly transcendental integrals for
arbitrary colour factor. Numerical integration in the nonplanar sector reveals
explicitly the breakdown of quadratic Casimir scaling at the four-loop order. A
thorough analysis of the reported numerical uncertainties is carried out.Comment: 10 pages, 2 figures, 1 table. Proceedings of the 13th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), 25-29 September, 2017, St. Gilgen, Austri
The Sudakov form factor at four loops in maximal super Yang-Mills theory
The four-loop Sudakov form factor in maximal super Yang-Mills theory is
analysed in detail. It is shown explicitly how to construct a basis of
integrals that have a uniformly transcendental expansion in the dimensional
regularisation parameter, further elucidating the number-theoretic properties
of Feynman integrals. The physical form factor is expressed in this basis for
arbitrary colour factor. In the nonplanar sector the required integrals are
integrated numerically using a mix of sector-decomposition and Mellin-Barnes
representation methods. Both the cusp as well as the collinear anomalous
dimension are computed. The results show explicitly the violation of quadratic
Casimir scaling at the four-loop order. A thorough analysis concerning the
reliability of reported numerical uncertainties is carried out.Comment: 47 pages, 17 figures; v4: fixed typo in eqs. (4.4) and (A.4), final
result unchange
On the determination of anti-neutrino spectra from nuclear reactors
In this paper we study the effect of, well-known, higher order corrections to
the allowed beta decay spectrum on the determination of anti-neutrino spectra
resulting from the decays of fission fragments. In particular, we try to
estimate the associated theory errors and find that induced currents like weak
magnetism may ultimately limit our ability to improve the current accuracy and
under certain circumstance could even largely increase the theoretical errors.
We also perform a critical evaluation of the errors associated with our method
to extract the anti-neutrino spectrum using synthetic beta spectra. It turns
out, that a fit using only virtual beta branches with a judicious choice of the
effective nuclear charge provides results with a minimal bias. We apply this
method to actual data for U235, Pu239 and Pu241 and confirm, within errors,
recent results, which indicate a net 3% upward shift in energy averaged
anti-neutrino fluxes. However, we also find significant shape differences which
can in principle be tested by high statistics anti-neutrino data samples.Comment: 20 pages, 5 figures, 9 tables, added references, version accepted for
publication in Phys. Rev. C. Corrected errors in tab. 1 and eqs. 18 and 19.
Results and conclusion unchange
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