7,539 research outputs found
Extended Bose-Hubbard model with incompressible states at fractional numbers
The Bose-Hubbard model is extended to include nearest and far neighbor
interactions and is related to the fractional quantum Hall effect (FQHE). Both
models may be studied in optical lattices with quantum gases. The ground state
is calculated for the extended Bose-Hubbard model with strong repulsive
interactions (weak hopping). Incompressible Mott insulator states are found at
rational filling fractions compatible with the principal and secondary FQHE
filling fractions of the lowest Landau levels observed experimentally. It is
discussed to which extent these states at fractional filling survive or
undergoes a Mott insulator transition to a superfluid as hopping terms are
included.Comment: Revised version, to appear in PR
Neutrino masses or new interactions
Recent proposals to study the mass of the "electron" neutrino at a
sensitivity of 0.3 eV can be used to place limits on the right handed and
scalar charged currents at a level which improves on the present experimental
limits. Indeed the neglect of the possibility of such interactions can lead to
the inference of an incorrect value for the mass, as we illustrate.Comment: 12 pages and 3 figures. Contributed to the XX International Symposium
on Lepton and Photon Interactions at High Energies, Rome, July 2001, and to
the International Europhysics Conference on High Energy Physics, Budapest,
July 2001. Preprint numbers added, misprints correcte
Neutrino clustering and the Z-burst model
The possibility that the observed Ultra High Energy Cosmic Rays are generated
by high energy neutrinos creating "Z-bursts" in resonant interactions with the
background neutrinos has been proposed, but there are difficulties in
generating enough events with reasonable incident neutrino fluxes.
We point out that this difficulty is overcome if the background neutrinos
have coalesced into "neutrino clouds" --- a possibility previously suggested by
some of us in another context. The limitations that this mechanism for the
generation of UHECRs places on the high energy neutrino flux, on the masses of
the background neutrinos and the characteristics of the neutrino clouds are
spelled out.Comment: 13 pages and 3 figures. Contributed to the XX International Symposium
on Lepton and Photon Interactions at High Energies, Rome, July 2001, and to
the International Europhysics Conference on High Energy Physics, Budapest,
July 2001. Preprint numbers added, misprints correcte
Gas of self-avoiding loops on the brickwork lattice
An exact calculation of the phase diagram for a loop gas model on the
brickwork lattice is presented. The model includes a bending energy. In the
dense limit, where all the lattice sites are occupied, a phase transition
occuring at an asymmetric Lifshitz tricritical point is observed as the
temperature associated with the bending energy is varied. Various critical
exponents are calculated. At lower densities, two lines of transitions (in the
Ising universality class) are observed, terminated by a tricritical point,
where there is a change in the modulation of the correlation function. To each
tricritical point an associated disorder line is found.Comment: 19 pages, 6 figures. to appear in J. Phys. A : Math. & Ge
Reactive Quenching Of Od A (2)ÎŁ(+) By H-2: Translational Energy Distributions For H- And D-Atom Product Channels
The H- and D-atom products from collisional quenching of OD A (2)Sigma(+) by H-2 are characterized through Doppler spectroscopy using two-photon (2 S-2 \u3c-\u3c- 1 S-2) laser-induced fluorescence. Partial deuteration enables separation of the channel forming H + HOD products, which accounts for 75% of reactive quenching events, from the D + H2O product channel. The Doppler profiles, along with those reported previously for other isotopic variants, are transformed into product translational energy distributions using a robust fitting procedure based on discrete velocity basis functions. The product translational energy distribution for the H- atom channel is strongly peaked at low energy (below 0.5 eV) with a long tail extending to the energetic limit. By contrast, the D-atom channel exhibits a small peak at low translational energy with a distinctive secondary peak at higher translational energy (approximately 1.8 eV) before falling off to higher energy. In both cases, most of the available energy flows into internal excitation of the water products. Similar distributions are obtained upon reanalysis of D- and H- atom Doppler profiles, respectively, from reactive quenching of OH A (2)Sigma(+) by D-2. The sum of the translational energy distributions for H- and D- atom channels is remarkably similar to that obtained for OH A (2)Sigma(+) + H-2, where the two channels cannot be distinguished from one another. The product translational energy distributions from reactive quenching are compared with those obtained from a previous experiment performed at higher collision energy, quasiclassical trajectory calculations of the post-quenching dynamics, and a statistical model. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3644763
Scaling of Non-Perturbatively O(a) Improved Wilson Fermions: Hadron Spectrum, Quark Masses and Decay Constants
We compute the hadron mass spectrum, the quark masses and the meson decay
constants in quenched lattice QCD with non-perturbatively improved
Wilson fermions. The calculations are done for two values of the coupling
constant, and 6.2, and the results are compared with the
predictions of ordinary Wilson fermions. We find that the improved action
reduces lattice artifacts as expected
First results with non-perturbative fermion improvement
We present initial results for light hadron masses and nucleon structure
functions using a recent proposal for eliminating all effects from
Wilson fermion simulations in the quenched approximation. With initially
limited statistics, we find a much more linear APE plot and a value of the
axial coupling nearer to the experimental point than with comparable runs
using unimproved Wilson fermions.Comment: 3 pages, 2 PostScript figures, LaTeX 2.09 with espcrc2.sty v2.6,
amstex and epsf, talk presented at LATTICE96(phenomenology) by P. Stephenso
Epoch Dependent Dark Energy
We present a model in which the equation of state parameter w approaches -1
near a particular value of z, and has significant negative values in a
restricted range of z. For example, one can have w ~ -1 near z = 1, and w >
-0.2 from z = 0 to z = 0.3, and for z > 9. The ingredients of the model are
neutral fermions (which may be neutrinos, neutralinos, etc) which are very
weakly coupled to a light scalar field. This model emphasises the importance of
the proposed studies of the properties of dark energy into the region z > 1.Comment: 7pp., 2 figs. Invited talk at the 5th Int'l. Wkshp. on the Dark Side
of the Universe, 1-5 June 2009 Melbourne, DSU09; to appear in the proceeding
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