973 research outputs found
Multipole moments in Kaluza-Klein theories
This paper contains discussion of the problem of motion of extended i.e. non
point test bodies in multidimensional space. Extended bodies are described in
terms of so called multipole moments. Using approximated form of equations of
motion for extended bodies deviation from geodesic motion is derived. Results
are applied to special form of space-time.Comment: 11 pages, AMS-TeX, few misprints corrected, to appear in Classical
and Quantum Gravit
Effects of Initial Flow on Close-In Planet Atmospheric Circulation
We use a general circulation model to study the three-dimensional (3-D) flow
and temperature distributions of atmospheres on tidally synchronized extrasolar
planets. In this work, we focus on the sensitivity of the evolution to the
initial flow state, which has not received much attention in 3-D modeling
studies. We find that different initial states lead to markedly different
distributions-even under the application of strong forcing (large day-night
temperature difference with a short "thermal drag time") that may be
representative of close-in planets. This is in contrast with the results or
assumptions of many published studies. In general, coherent jets and vortices
(and their associated temperature distributions) characterize the flow, and
they evolve differently in time, depending on the initial condition. If the
coherent structures reach a quasi- stationary state, their spatial locations
still vary. The result underlines the fact that circulation models are
currently unsuitable for making quantitative predictions (e.g., location and
size of a "hot spot") without better constrained, and well posed, initial
conditions.Comment: Accepted for publication in the Astrophysical Journal; 23 pages, 9
figures
Changes in trabecular bone, hematopoiesis and bone marrow vessels in aplastic anemia, primary osteoporosis, and old age
Retrospective histologic analyses of bone biopsies and of post mortem samples from normal persons of different age groups, and of bone biopsies of age- and sex-matched groups of patients with primary osteoporosis and aplastic anemia show characteristic age dependent as well as pathologic changes including atrophy of osseous trabeculae and of hematopoiesis, and changes in the sinusoidal and arterial capillary compartments. These results indicate the possible role of a microvascular defect in the pathogenesis of osteoporosis and aplastic anemia
T-duality and closed string non-commutative (doubled) geometry
We provide some evidence that closed string coordinates will become
non-commutative turning on H-field flux background in closed string
compactifications. This is in analogy to open string non-commutativity on the
world volume of D-branes with B- and F-field background. The class of
3-dimensional backgrounds we are studying are twisted tori (fibrations of a
2-torus over a circle) and the their T-dual H-field, 3-form flux backgrounds
(T-folds). The spatial non-commutativity arises due to the non-trivial
monodromies of the toroidal Kahler resp. complex structure moduli fields, when
going around the closed string along the circle direction. In addition we study
closed string non-commutativity in the context of doubled geometry, where we
argue that in general a non-commutative closed string background is T-dual to a
commutative closed string background and vice versa. Finally, in analogy to
open string boundary conditions, we also argue that closed string momentum and
winding modes define in some sense D-branes in closed string doubled geometry.Comment: 31 pages, references added, extended version contains new sections
3.3., 3.4 and
Susceptibility functions for slow relaxation processes in supercooled liquids and the search for universal relaxation patterns
In order to describe the slow response of a glass former we discuss some
distribution of correlation times, e.g., the generalized gamma distribution
(GG) and an extension thereof (GGE), the latter allowing to reproduce a simple
peak susceptibility such as of Cole-Davidson type as well as a susceptibility
exhibiting an additional high frequency power law contribution (excess wing).
Applying the GGE distribution to the dielectric spectra of glass formers
exhibiting no beta-process peak (glycerol, propylene carbonate and picoline) we
are able to reproduce the salient features of the slow response (1e-6 Hz - 1e9
Hz). A line shape analysis is carried out either in the time or frequency
domain and in both cases an excess wing can be identified. The latter evolves
in a universal way while cooling and shows up for correlation times tau_alpha >
1e-8 s. It appears that its first emergence marks the break down of the high
temperature scenario of mode coupling theory. - In order to describe a glass
former exhibiting a beta-process peak we have introduced a distribution
function which is compatible with assuming a thermally activated process in
contrast to some commonly used fit functions. Together with the GGE
distribution this function allows in the frame of the Williams-Watts approach
to completely interpolate the spectra, e.g. of fluoro aniline (1e-6 Hz - 1e9
Hz). The parameters obtained indicate an emergence of both the excess wing and
the beta-process again at tau_alpha > 1e-8s.Comment: 22 pages, 12 figure
Factorization Properties of Soft Graviton Amplitudes
We apply recently developed path integral resummation methods to perturbative
quantum gravity. In particular, we provide supporting evidence that eikonal
graviton amplitudes factorize into hard and soft parts, and confirm a recent
hypothesis that soft gravitons are modelled by vacuum expectation values of
products of certain Wilson line operators, which differ for massless and
massive particles. We also investigate terms which break this factorization,
and find that they are subleading with respect to the eikonal amplitude. The
results may help in understanding the connections between gravity and gauge
theories in more detail, as well as in studying gravitational radiation beyond
the eikonal approximation.Comment: 35 pages, 5 figure
Topological crystalline insulator states in Pb(1-x)Sn(x)Se
Topological insulators are a novel class of quantum materials in which
time-reversal symmetry, relativistic (spin-orbit) effects and an inverted band
structure result in electronic metallic states on the surfaces of bulk
crystals. These helical states exhibit a Dirac-like energy dispersion across
the bulk bandgap, and they are topologically protected. Recent theoretical
proposals have suggested the existence of topological crystalline insulators, a
novel class of topological insulators in which crystalline symmetry replaces
the role of time-reversal symmetry in topological protection [1,2]. In this
study, we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a
topological crystalline insulator for x=0.23. Temperature-dependent
magnetotransport measurements and angle-resolved photoelectron spectroscopy
demonstrate that the material undergoes a temperature-driven topological phase
transition from a trivial insulator to a topological crystalline insulator.
These experimental findings add a new class to the family of topological
insulators. We expect these results to be the beginning of both a considerable
body of additional research on topological crystalline insulators as well as
detailed studies of topological phase transitions.Comment: v2: published revised manuscript (6 pages, 3 figures) and
supplementary information (5 pages, 8 figures
Intertwinings for general β Laguerre and Jacobi processes
We show that, for β≥1, the semigroups of β-Laguerre and β-Jacobi processes of different dimensions are intertwined in analogy to a similar result for β-Dyson Brownian motion recently obtained in Ramanan and Shkolnikov (Intertwinings of β-Dyson Brownian motions of different dimensions, 2016. arXiv:1608.01597). These intertwining relations generalize to arbitrary β≥1 the ones obtained for β=2 in Assiotis et al. (Interlacing diffusions, 2016. arXiv:1607.07182) between h-transformed Karlin–McGregor semigroups. Moreover, they form the key step toward constructing a multilevel process in a Gelfand–Tsetlin pattern leaving certain Gibbs measures invariant. Finally, as a by-product, we obtain a relation between general β-Jacobi ensembles of different dimensions
Next-to-eikonal corrections to soft gluon radiation: a diagrammatic approach
We consider the problem of soft gluon resummation for gauge theory amplitudes
and cross sections, at next-to-eikonal order, using a Feynman diagram approach.
At the amplitude level, we prove exponentiation for the set of factorizable
contributions, and construct effective Feynman rules which can be used to
compute next-to-eikonal emissions directly in the logarithm of the amplitude,
finding agreement with earlier results obtained using path-integral methods.
For cross sections, we also consider sub-eikonal corrections to the phase space
for multiple soft-gluon emissions, which contribute to next-to-eikonal
logarithms. To clarify the discussion, we examine a class of log(1 - x) terms
in the Drell-Yan cross-section up to two loops. Our results are the first steps
towards a systematic generalization of threshold resummations to
next-to-leading power in the threshold expansion.Comment: 66 pages, 19 figure
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