327 research outputs found
Possible stimulation of nuclear alpha-decay by superfluid helium
It is suggested that superfluid helium (condensate of 4-He atoms) may
stimulate nuclear alpha-decay in a situation when an alpha-emitter moves
through superfluid helium with fine-tuned velocity, so that the
backward-emitted alpha-particle is at rest in the laboratory frame. It is shown
that the probability of stimulated alpha-decay in this case may be sizable
enough to be detected.Comment: 5 pages, LaTeX, final published version in Phys. Rev. Lett. 103
(2009
Dispersion of the dielectric function of a charge-transfer insulator
We study the problem of dielectric response in the strong coupling regime of
a charge transfer insulator. The frequency and wave number dependence of the
dielectric function and its inverse is the main object of consideration. We show that the
problem, in general, cannot be reduced to a calculation within the Hubbard
model, which takes into account only a restricted number of electronic states
near the Fermi energy. The contribution of the rest of the system to the
longitudinal response (i.e. to ) is essential
for the whole frequency range. With the use of the spectral representation of
the two-particle Green's function we show that the problem may be divided into
two parts: into the contributions of the weakly correlated and the Hubbard
subsystems. For the latter we propose an approach that starts from the
correlated paramagnetic ground state with strong antiferromagnetic
fluctuations. We obtain a set of coupled equations of motion for the
two-particle Green's function that may be solved by means of the projection
technique. The solution is expressed by a two particle basis that includes the
excitonic states with electron and hole separated at various distances. We
apply our method to the multiband Hubbard (Emery) model that describes layered
cuprates. We show that strongly dispersive branches exist in the excitonic
spectrum of the 'minimal' Emery model () and consider the
dependence of the spectrum on finite oxygen hopping and on-site
repulsion . The relationship of our calculations to electron energy loss
spectroscopy is discussed.Comment: 22 pages, 5 figure
Origin of spin-gap in CaVO: effect of frustration and lattice distortion
We study the origin of spin-gap in recently discovered material CaVO.
We analyze the spin- Heisenberg model on the depleted square lattice
with nearest neighbor (nn) and next nearest neighbor (nnn) interactions, in
terms of the singlet and triplet states of the 4-spin plaquettes and 2-spin
dimers. Phase diagram of the model is obtained within a linear
``spin-wave"-like approximation, and is shown to agree well with the earlier
results of QMC simulations for nn interactions. We further propose that the
special lattice structure of CaVO naturally leads to lattice
distortions, which enhances the spin-gap via a spin-Peierls mechanism.Comment: 4 pages, RevTex, 2 postscript figures. Latex file and figures have
been uuencode
Hole motion in the Ising antiferromagnet: an application of the recursion method
We study hole motion in the Ising antiferromagnet using the recursion method.
Using the retraceable path approximation we find the hole's Green's function as
well as its wavefunction for arbitrary values of . The effect of small
transverse interaction also is taken into account. Our results provide some
additional insight into the self-consistent Born approximation.Comment: 8 pages, RevTex, no figures. Accepted for publication in Phys.Rev.
Performances and stability of a 2.4 ton Gd organic liquid scintillator target for antineutrino detection
In this work we report the performances and the chemical and physical
properties of a (2 x 1.2) ton organic liquid scintillator target doped with Gd
up to ~0.1%, and the results of a 2 year long stability survey. In particular
we have monitored the amount of both Gd and primary fluor actually in solution,
the optical and fluorescent properties of the Gd-doped liquid scintillator
(GdLS) and its performances as a neutron detector, namely neutron capture
efficiency and average capture time. The experimental survey is ongoing, the
target being continuously monitored. After two years from the doping time the
performances of the Gd-doped liquid scintillator do not show any hint of
degradation and instability; this conclusion comes both from the laboratory
measurements and from the "in-tank" measurements. This is the largest stable
Gd-doped organic liquid scintillator target ever produced and continuously
operated for a long period
Searching for three-nucleon resonances
We search for three-neutron resonances which were predicted from pion double
charge exchange experiments on He-3. All partial waves up to J=5/2 are
nonresonant except the J=3/2^+ one, where we find a state at E=14 MeV energy
with 13 MeV width. The parameters of the mirror state in the three-proton
system are E=15 MeV and Gamma=14 MeV. The possible existence of an excited
state in the triton, which was predicted from a H(He-6,alpha) experiment, is
also discussed.Comment: LaTex with RevTe
Testing for new physics with low-energy anti-neutrino sources: LAMA as a case study
Some electroweak models with extended neutral currents, such as those based on the E6 group, lead to an increase of the ν¯−e scattering cross section at energies below 100 keV. We propose to search for the heavy Z' boson contribution in an experiment with a high-activity artificial neutrino source and with a large-mass detector. We present the case for the LAMA experiment with a large NaI(Tl) detector located at the Gran Sasso underground laboratory. The neutrino flux is known to within a one percent accuracy, in contrast to the reactor case and one can reach lower neutrino energies. Both features make our proposed experiment more sensitive to extended gauge models, such as the χ model. For a low enough background the sensitivity to the Zχ boson mass would reach 600 GeV for one year running of the experiment
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