13,209 research outputs found
Low-emissivity impact craters on Venus
An analysis of 144 impact craters on Venus has shown that 11 of these have floors with average emissivities lower than 0.8. The remaining craters have emissivities between 0.8 and 0.9, independent of the specific backscatter cross section of the crater floors. These 144 impact craters were chosen from a possible 164 craters with diameters greater than 30 km as identified by researchers for 89 percent of the surface of Venus. We have only looked at craters below 6053.5 km altitude because a mineralogical change causes high reflectivity/low emissivity above the altitude. We have also excluded all craters with diameters smaller than 30 km because the emissivity footprint at periapsis is 16 x 24 km and becomes larger at the poles
Self-consistent Approach to Off-Shell Transport
The properties of two forms of the gradient expanded Kadanoff--Baym
equations, i.e. the Kadanoff--Baym and Botermans-Malfliet forms, suitable to
describe the transport dynamics of particles and resonances with broad spectral
widths, are discussed in context of conservation laws, the definition of a
kinetic entropy and the possibility of numerical realization. Recent results on
exact conservations of charge and energy-momentum within Kadanoff-Baym form of
quantum kinetics based on local coupling schemes are extended to two cases
relevant in many applications. These concern the interaction via a finite range
potential, and, relevant in nuclear and hadron physics, e.g. for the
pion--nucleon interaction, the case of derivative coupling.Comment: 35 pages, submitted to issue of Phys. Atom. Nucl. dedicated to S.T.
Belyaev on the occasion of his 80th birthday. Few references are adde
Renormalization of Self-consistent Approximation schemes Finite Temperature II: Applications to the Sunset Diagram
The theoretical concepts for the renormalization of self-consistent Dyson
resummations, deviced in the first paper of this series, are applied to first
example cases for the -theory. Besides the tadpole (Hartree)
approximation as a novel part the numerical solutions are presented which
includes the sunset self-energy diagram into the self-consistent scheme based
on the -derivable approximation or 2PI effective action concept.Comment: 18 pages, 7 figures Changes in version 2: Adapted title to the first
paper of the series, added one figure and some references. This version was
submitted to Phys. Rev. D; Changes in version 3: added one more reference
Changes in version 4 (accepted for publication by Phys. Rev. D): Added a
paragraph about the massless case and some remarks in the introductio
Similar zone-center gaps in the low-energy spin-wave spectra of NaFeAs and BaFe2As2
We report results of inelastic-neutron-scattering measurements of low-energy
spin-wave excitations in two structurally distinct families of iron-pnictide
parent compounds: Na(1-{\delta})FeAs and BaFe2As2. Despite their very different
values of the ordered magnetic moment and N\'eel temperatures, T_N, in the
antiferromagnetic state both compounds exhibit similar spin gaps of the order
of 10 meV at the magnetic Brillouin-zone center. The gap opens sharply below
T_N, with no signatures of a precursor gap at temperatures between the
orthorhombic and magnetic phase transitions in Na(1-{\delta})FeAs. We also find
a relatively weak dispersion of the spin-wave gap in BaFe2As2 along the
out-of-plane momentum component, q_z. At the magnetic zone boundary (q_z = 0),
spin excitations in the ordered state persist down to 20 meV, which implies a
much smaller value of the effective out-of-plane exchange interaction, J_c, as
compared to previous estimates based on fitting the high-energy spin-wave
dispersion to a Heisenberg-type model.Comment: 5 pages, 4 figures, 1 tabl
Higgs mode and its decay in a two dimensional antiferromagnet
Condensed-matter analogs of the Higgs boson in particle physics allow
insights into its behavior in different symmetries and dimensionalities.
Evidence for the Higgs mode has been reported in a number of different
settings, including ultracold atomic gases, disordered superconductors, and
dimerized quantum magnets. However, decay processes of the Higgs mode (which
are eminently important in particle physics) have not yet been studied in
condensed matter due to the lack of a suitable material system coupled to a
direct experimental probe. A quantitative understanding of these processes is
particularly important for low-dimensional systems where the Higgs mode decays
rapidly and has remained elusive to most experimental probes. Here, we discover
and study the Higgs mode in a two-dimensional antiferromagnet using
spin-polarized inelastic neutron scattering. Our spin-wave spectra of
CaRuO directly reveal a well-defined, dispersive Higgs mode, which
quickly decays into transverse Goldstone modes at the antiferromagnetic
ordering wavevector. Through a complete mapping of the transverse modes in the
reciprocal space, we uniquely specify the minimal model Hamiltonian and
describe the decay process. We thus establish a novel condensed matter platform
for research on the dynamics of the Higgs mode.Comment: original submitted version, Nature Physics (2017). arXiv admin note:
substantial text overlap with arXiv:1510.0701
sl(N) Onsager's Algebra and Integrability
We define an analog of Onsager's Algebra through a finite set of
relations that generalize the Dolan Grady defining relations for the original
Onsager's Algebra. This infinite-dimensional Lie Algebra is shown to be
isomorphic to a fixed point subalgebra of Loop Algebra with respect
to a certain involution. As the consequence of the generalized Dolan Grady
relations a Hamiltonian linear in the generators of Onsager's Algebra
is shown to posses an infinite number of mutually commuting integrals of
motion
On the polarization properties of the charmed baryon Lambda^+_c in the Lambda^+_c -> p + K^- + pi^+ + pi^0 decay
The polarization properties of the charmed Lambda^+_c baryon are investigated
in weak non-leptonic four-body Lambda^+_c -> p + K^- + pi^+ + pi^0 decay. The
probability of this decay and the angular distribution of the probability are
calculated in the effective quark model with chiral U(3)XU(3) symmetry
incorporating Heavy Quark Effective theory (HQET) and the extended
Nambu-Jona-Lasinio model with a linear realization of chiral U(3)XU(3)
symmetry. The theoretical value of the probability of the decay Lambda^+_c -> p
+ K^- + pi^+ + pi^0 relative to the probability of the decay Lambda^+_c -> p +
K^- + pi^+ does not contain free parameters and fits well experimental data.
The application of the obtained results to the analysis of the polarization of
the Lambda^+_c produced in the processes of photo and hadroproduction is
discussed.Comment: 10 pages, no figures, Late
Magnetic Resonant Mode in the Low-Energy Spin-Excitation Spectrum of Superconducting Rb2Fe4Se5 Single Crystals
We have studied the low-energy spin-excitation spectrum of the
single-crystalline Rb2Fe4Se5 superconductor (Tc = 32 K) by means of inelastic
neutron scattering. In the superconducting state, we observe a magnetic
resonant mode centered at an energy of 14 meV and at the (0.5 0.25 0.5) wave
vector (unfolded Fe-sublattice notation), which differs from the ones
characterizing magnetic resonant modes in other iron-based superconductors. Our
finding suggests that the 245-iron-selenides are unconventional superconductors
with a sign-changing order parameter, in which bulk superconductivity coexists
with the sqrt(5) x sqrt(5) magnetic superstructure. The estimated ratios of the
resonance energy to Tc and the superconducting gap indicate moderate pairing
strength in this compound, similar to that in optimally doped 1111- and
122-pnictides.Comment: To be published in Phys. Rev. Lett. Figures and references have been
updated in v
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