1,217 research outputs found
Heavy Right-Handed Neutrinos and Dark Matter in the CMSSM
We perform a systematic study of the effects of the type-I seesaw mechanism
on the dark matter abundance in the constrained supersymmetric standard model
(CMSSM) which includes three right-handed neutrinos (the CMSSM). For large
values of , we exploit the effects of large neutrino Yukawa
couplings on the renormalization group (RG) evolution of the up-type Higgs. In
particular, we show that the focus point scale can greatly exceed the
electroweak scale resulting in the absence of a focus point region for which
the relic density of neutralinos is within the range determined by WMAP. We
also discuss the effects of the right-handed neutrinos on the so-called funnel
region, where the relic density is controlled by s-channel annihilations
through a heavy Higgs. For small values of , we discuss the
possibility of sneutrino coannihilation regions with an emphasis on the
suppression of the left-handed slepton doublet masses due to the neutrino
Yukawa coupling. We consider two types of toy models consistent with either the
normal or inverted hierarchy of neutrino masses.Comment: 18 pages, 7 figures, references and a footnote added, typos correcte
Synthesis of magnesium ZIF-8 from Mg(BH₄)₂.
Porous Mg(2-methyl imidazolate)2 (Mg-ZIF-8) was synthesised from Mg(BH4)2 as a precursor under an Ar atmosphere. It possesses an uncommon tetrahedral Mg(2+)-N coordination geometry that is stabilised by the formation of a framework, and it exhibits a Brunauer-Emmett-Teller surface area greater than 1800 m(2) g(-1)
Positrons in Cosmic Rays from Dark Matter Annihilations for Uplifted Higgs Regions in MSSM
We point out that there are regions in the MSSM parameter space which
successfully provide a dark matter (DM) annihilation explanation for observed
positron excess (e.g. PAMELA), while still remaining in agreement with all
other data sets. Such regions (e.g. the uplifted Higgs region) can realize an
enhanced neutralino DM annihilation dominantly into leptons via a Breit-Wigner
resonance through the CP-odd Higgs channel. Such regions can give the proper
thermal relic DM abundance, and the DM annihilation products are compatible
with current antiproton and gamma ray observations. This scenario can succeed
without introducing any additional degrees of freedom beyond those already in
the MSSM.Comment: 11 pages, 9 figure
Orbital-dependent modifications of electronic structure across magneto-structural transition in BaFe2As2
Laser angle-resolved photoemission spectroscopy (ARPES) is employed to
investigate the temperature (T) dependence of the electronic structure in
BaFe2As2 across the magneto-structural transition at TN ~ 140 K. A drastic
transformation in Fermi surface (FS) shape across TN is observed, as expected
by first-principles band calculations. Polarization-dependent ARPES and band
calculations consistently indicate that the observed FSs at kz ~ pi in the
low-T antiferromagnetic (AF) state are dominated by the Fe3dzx orbital, leading
to the two-fold electronic structure. These results indicate that
magneto-structural transition in BaFe2As2 accompanies orbital-dependent
modifications in the electronic structure.Comment: 13 pages, 4 figures. accepted by Physical Review Letter
Development of Optical Emission Spectroscopy for Measuring H? and D? Densities in Divertor Plasmas
Survival of technologies: an evolutionary game approach
This paper models technology adoption as an evolutionary and asymmetric game based on a pairwise contest involving two populations, firms and consumers. First, externalities are considered only on the supply side, leading to the usual results found in the recent economic literature on the subject: path dependence, lock-in, and the possibility ofselecting inferior technology. Next externalities are introduced on the demand side, which in Leibenstein's classic paper leads to bandwagon and snob effects, and interactions between supply and demand are examined
Scale and externalities in an evolutionary game model
Este artigo discute o processo de seleção de escalas de produção em um modelo de jogo evolucionário no qual os requisitos de racionalidade são muito limitados
Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights
The temperature dependence and anisotropy of optical spectral weights
associated with different multiplet transitions is determined by the spin and
orbital correlations. To provide a systematic basis to exploit this close
relationship between magnetism and optical spectra, we present and analyze the
spin-orbital superexchange models for a series of representative
orbital-degenerate transition metal oxides with different multiplet structure.
For each case we derive the magnetic exchange constants, which determine the
spin wave dispersions, as well as the partial optical sum rules. The magnetic
and optical properties of early transition metal oxides with degenerate
orbitals (titanates and vanadates with perovskite structure) are shown
to depend only on two parameters, viz. the superexchange energy and the
ratio of Hund's exchange to the intraorbital Coulomb interaction, and on
the actual orbital state. In systems important corrections follow from
charge transfer excitations, and we show that KCuF can be classified as a
charge transfer insulator, while LaMnO is a Mott insulator with moderate
charge transfer contributions. In some cases orbital fluctuations are quenched
and decoupling of spin and orbital degrees of freedom with static orbital order
gives satisfactory results for the optical weights. On the example of cubic
vanadates we describe a case where the full quantum spin-orbital physics must
be considered. Thus information on optical excitations, their energies,
temperature dependence and anisotropy, combined with the results of magnetic
neutron scattering experiments, provides an important consistency test of the
spin-orbital models, and indicates whether orbital and/or spin fluctuations are
important in a given compound.Comment: 34 pages, 16 figure
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