3,079 research outputs found
Active Mass Under Pressure
After a historical introduction to Poisson's equation for Newtonian gravity,
its analog for static gravitational fields in Einstein's theory is reviewed. It
appears that the pressure contribution to the active mass density in Einstein's
theory might also be noticeable at the Newtonian level. A form of its
surprising appearance, first noticed by Richard Chase Tolman, was discussed
half a century ago in the Hamburg Relativity Seminar and is resolved here.Comment: 28 pages, 4 figure
Mn local moments prevent superconductivity in iron-pnictides Ba(Fe 1-x Mn x)2As2
75As nuclear magnetic resonance (NMR) experiments were performed on
Ba(Fe1-xMnx)2As2 (xMn = 2.5%, 5% and 12%) single crystals. The Fe layer
magnetic susceptibility far from Mn atoms is probed by the75As NMR line shift
and is found similar to that of BaFe2As2, implying that Mn does not induce
charge doping. A satellite line associated with the Mn nearest neighbours
(n.n.) of 75As displays a Curie-Weiss shift which demonstrates that Mn carries
a local magnetic moment. This is confirmed by the main line broadening typical
of a RKKY-like Mn-induced staggered spin polarization. The Mn moment is due to
the localization of the additional Mn hole. These findings explain why Mn does
not induce superconductivity in the pnictides contrary to other dopants such as
Co, Ni, Ru or K.Comment: 6 pages, 7 figure
Yet another way to measure
We show that the CKM phase can be extracted from measurement
of the time dependent rates in the decays and
, where , , , , ,
. These channels have a large asymmetry between decays of
and into the same final state. Even though the branching ratios are
small, their sensitivity to can be competitive with decays into
and .Comment: 5 pages, some clarifications and references adde
Complete list of Darboux Integrable Chains of the form
We study differential-difference equation of the form with unknown
depending on continuous and discrete variables and . Equation
of such kind is called Darboux integrable, if there exist two functions and
of a finite number of arguments , ,
, such that and , where
is the operator of total differentiation with respect to , and is
the shift operator: . Reformulation of Darboux integrability in
terms of finiteness of two characteristic Lie algebras gives an effective tool
for classification of integrable equations. The complete list of Darboux
integrable equations is given in the case when the function is of the
special form
Black holes and information theory
During the past three decades investigators have unveiled a number of deep
connections between physical information and black holes whose consequences for
ordinary systems go beyond what has been deduced purely from the axioms of
information theory. After a self-contained introduction to black hole
thermodynamics, we review from its vantage point topics such as the information
conundrum that emerges from the ability of incipient black holes to radiate,
the various entropy bounds for non-black hole systems (holographic bound,
universal entropy bound, etc) which are most easily derived from black hole
thermodynamics, Bousso's covariant entropy bound, the holographic principle of
particle physics, and the subject of channel capacity of quantum communication
channels.Comment: RevTeX, 12 pages, 5 figures. To appear in Contemporary Physic
On the Geometry of Surface Stress
We present a fully general derivation of the Laplace--Young formula and
discuss the interplay between the intrinsic surface geometry and the extrinsic
one ensuing from the immersion of the surface in the ordinary euclidean
three-dimensional space. We prove that the (reversible) work done in a general
surface deformation can be expressed in terms of the surface stress tensor and
the variation of the intrinsic surface metric
Benchmark calculations for elastic fermion-dimer scattering
We present continuum and lattice calculations for elastic scattering between
a fermion and a bound dimer in the shallow binding limit. For the continuum
calculation we use the Skorniakov-Ter-Martirosian (STM) integral equation to
determine the scattering length and effective range parameter to high
precision. For the lattice calculation we use the finite-volume method of
L\"uscher. We take into account topological finite-volume corrections to the
dimer binding energy which depend on the momentum of the dimer. After
subtracting these effects, we find from the lattice calculation kappa a_fd =
1.174(9) and kappa r_fd = -0.029(13). These results agree well with the
continuum values kappa a_fd = 1.17907(1) and kappa r_fd = -0.0383(3) obtained
from the STM equation. We discuss applications to cold atomic Fermi gases,
deuteron-neutron scattering in the spin-quartet channel, and lattice
calculations of scattering for nuclei and hadronic molecules at finite volume.Comment: 16 pages, 5 figure
The Measure Problem in Cosmology
The Hamiltonian structure of general relativity provides a natural canonical
measure on the space of all classical universes, i.e., the multiverse. We
review this construction and show how one can visualize the measure in terms of
a "magnetic flux" of solutions through phase space. Previous studies identified
a divergence in the measure, which we observe to be due to the dilatation
invariance of flat FRW universes. We show that the divergence is removed if we
identify universes which are so flat they cannot be observationally
distinguished. The resulting measure is independent of time and of the choice
of coordinates on the space of fields. We further show that, for some
quantities of interest, the measure is very insensitive to the details of how
the identification is made. One such quantity is the probability of inflation
in simple scalar field models. We find that, according to our implementation of
the canonical measure, the probability for N e-folds of inflation in
single-field, slow-roll models is suppressed by of order exp(-3N) and we
discuss the implications of this result.Comment: 22 pages, 6 figures. Revised version with clarifying remarks on
meaning of adopted measure, extra references and minor typographical
correction
Crossover from commensurate to incommensurate antiferromagnetism in stoichiometric NaFeAs revealed by single-crystal 23Na,75As-NMR experiments
We report results of 23Na and 75As nuclear magnetic resonance (NMR)
experiments on a self-flux grown high-quality single crystal of stoichiometric
NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic
structural phase transition at T_O = 57 K and an antiferromagnetic (AF)
transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate
near T_AF shows significant anisotropy, indicating that the critical slowing
down of stripe-type AF fluctuations are strongly anisotropic in spin space. The
NMR spectra at low enough temperatures consist of sharp peaks showing a
commensurate stripe AF order with a small moment \sim 0.3 muB. However, the
spectra just below T_AF exhibits highly asymmetric broadening pointing to an
incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs
shows a certain similarity to the behavior of SrFe2As2 under high pressure.Comment: 5 pages, 5 figures, revised version to appear in J. Phys. Soc. Jp
Digitization of LAr calorimeter for CSC simulations
This note describes the digitization of the LAr signals, which is the step creating RDO from Geant4 Hits, as used during the production of the CSC simulated samples with athena release 12
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