5,374 research outputs found

### Possible Effects of the Existence of the 4th Generation Neutrino

The 4th generation of fermions predicted by the phenomenology of heterotic
string models can possess new strictly conserved charge, which leads, in
particular, to the hypothesis of the existence of the 4th generation massive
stable neutrino. The compatibility of this hypothesis with the results of
underground experiment DAMA searching for weakly interactive particles of dark
matter and with the EGRET measurements of galactic gamma--background at
energies above 1 GeV fixes the possible mass of the 4th neutrino at the value
about 50 GeV. The possibility to test the hypothesis in accelerator experiments
is considered. Positron signal from the annihilation of relic massive neutrinos
in the galactic halo is calculated and is shown to be accessible for planned
cosmic ray experiments.Comment: 10 pages, 4 PostScript figure, Latex2

### Galactic Gamma Halo by Heavy Neutrino annihilations?

The diffused gamma halo around our Galaxy recently discovered by EGRET could
be produced by annihilations of relic neutrinos N (of fourth generation), whose
mass is within a narrow range (Mz /2 < M < Mz). Neutrino annihilations in the
halo may lead to either ultrarelativistic electron pairs whose inverse Compton
Scattering on infrared or optical galactic photons could be the source of the
observed GeV gamma rays, or to prompt 100 MeV- 1 GeV photons (due to neutral
pion secondaries) born by N - anti N --> Z--> quark pairs reactions. The
consequent gamma flux (10 ^(-7)- 10^(-6) cm ^(-2) s^(-1) sr^(-1)) is well
comparable to the EGRET observed one and it is also compatible with the narrow
window of neutrino mass : 45 GeV < M < 50 GeV recently required to explain the
underground DAMA signals. The presence of heavy neutrinos of fourth generation
do not contribute much to solve the dark matter problem of the Universe, but it
may be easily detectable by outcoming LEP II data.Comment: 16 pages, Latex text,in press in Astroparticle Physics 199

### Antimatter Bounds by Anti-Asteroids annihilations on Planets and Sun

The existence of antimatter stars in the Galaxy as possible signature for
inflationary models with non-homogeneous baryo-synthesis may leave the trace by
antimatter cosmic rays as well as by their secondaries (anti-planets and
anti-meteorites) diffused bodies in our galactic halo. The anti-meteorite flux
may leave its explosive gamma signature by colliding on lunar soil as well as
on terrestrial, jovian and solar atmospheres. However the propagation in galaxy
and the consequent evaporation in galactic matter gas suppress the lightest (m
< 10^(-2)g) anti-meteorites. Anisotropic annihilation of larger anti-meteorites
within a narrow mass window, maybe rarely deflected, bounced by the galactic
gas disk, escaping detection in our solar system. Nevertheless heaviest
anti-meteorites (m > 10^(-1)g up to 10^(6)g) are unable to be deflected by the
thin galactic gas surface annihilation; they might hit the Sun (or rarely
Jupiter) leading to an explosive gamma event and a spectacular track with a
bouncing and even a propelling annihilation on cromosphere and photosphere.
Their anti-nuclei annihilation in pions and their final hard gammas showering
may be observabe as a "solar flare" at a rate nearly comparable to the observed
ones. From their absence we may infer bounds on antimatter-matter ratio near or
below 10^(-9) limit: already recorded data in BATSE catalog might be applied.Comment: 6 pages, more accurate estimate and minor correction

### A Self-consistent DFT+DMFT scheme in the Projector Augmented Wave : Applications to Cerium, Ce2O3 and Pu2O3 with the Hubbard I solver and comparison to DFT+U

An implementation of full self-consistency over the electronic density in the
DFT+DMFT framework on the basis of a plane wave-projector augmented wave (PAW)
DFT code is presented. It allows for an accurate calculation of the total
energy in DFT+DMFT within a plane wave approach. In contrast to frameworks
based on the maximally localized Wannier function, the method is easily applied
to f electron systems, such as cerium, cerium oxide (Ce2O3) and plutonium oxide
(Pu2O3). In order to have a correct and physical calculation of the energy
terms, we find that the calculation of the self-consistent density is
mandatory. The formalism is general and does not depend on the method used to
solve the impurity model. Calculations are carried out within the Hubbard I
approximation, which is fast to solve, and gives a good description of strongly
correlated insulators. We compare the DFT+DMFT and DFT+U solutions, and
underline the qualitative differences of their converged densities. We
emphasize that in contrast to DFT+U, DFT+DMFT does not break the spin and
orbital symmetry. As a consequence, DFT+DMFT implies, on top of a better
physical description of correlated metals and insulators, a reduced occurrence
of unphysical metastable solutions in correlated insulators in comparison to
DFT+U.Comment: 19 pages, 9 figures. This is an author-created, un-copyedited version
of an article accepted for publication in Journal of Physics: Condensed
Matter. IOP Publishing Ltd is not responsible for any errors or omissions in
this version of the manuscript or any version derived from it. The Version of
Record is available online at doi: 10.1088/0953-8984/24/7/07560

### Invisible Higgs Boson Decay into Massive Neutrinos of 4th Generation

Results from several recent experiments provide inderect evidences in the
favor of existence of a 4th generation neutrino. Such a neutrino of mass about
50 GeV is compatible with current physical and astrophysical constraints and
well motivated in the framework of superstring phenomenology. If sufficiently
stable the existence of such a neutrino leads to the drastic change of Higgs
boson physics: for a wide range of Higgs boson masses the dominant mode of
Higgs boson decay is invisible and the branching ratios for the most promising
modes of Higgs boson search are significantly reduced. The proper strategy of
Higgs boson searches in such a framework is discussed. It is shown that in the
same framework the absence of a signal in the search for invisible Higgs boson
decay at LEP means either that the mass of Higgs is greater than 113.5 GeV or
that the mass difference between the Higgs mass and doubled neutrino mass is
small.Comment: 8 pages, 2 figure

### Size-dependent bandgap and particle size distribution of colloidal semiconductor nanocrystals

A new analytical expression for the size-dependent bandgap of colloidal
semiconductor nanocrystals is proposed within the framework of the finite-depth
square-well effective mass approximation in order to provide a quantitative
description of the quantum confinement effect. This allows one to convert
optical spectroscopic data (photoluminescence spectrum and absorbance edge)
into accurate estimates for the particle size distributions of colloidal
systems even if the traditional effective mass model is expected to fail, which
occurs typically for very small particles belonging to the so-called strong
confinement limit. By applying the reported theoretical methodologies to CdTe
nanocrystals synthesized through wet chemical routes, size distributions are
inferred and compared directly to those obtained from atomic force microscopy
and transmission electron microscopy. This analysis can be used as a
complementary tool for the characterization of nanocrystal samples of many
other systems such as the II-VI and III-V semiconductor materials.Comment: 9 pages, 5 figure

### Antiprotons Annihilation in the Galaxy As A Source of Diffuse Gamma Background

The existence of antimatter domains in baryon asymmetrical Universe can
appear as the cosmological consequence of particle theory in inflationary
models with non-homogeneous baryosynthesis. Such a domain can survive in the
early Universe and form globular cluster of antimatter stars in our Galaxy. The
model of antimatter pollution of Galaxy and annihilation with matter gas is
developed. The proton-antiproton annihilation gamma flux is shown to reproduce
the observed galactic gamma background measured by EGRET. From comparison with
observational data the estimation on the maximally allowed amount of antimatter
stars, possibly present in our Galaxy, is found.Comment: LaTeX2e, 18 pages, 3 PostScript figures. Submitted to Yad.Fi

### Tensor polarizability of the vector mesons from $SU(3)$ lattice gauge theory

The magnetic dipole polarizabilities of the vector $\rho^0$ and $\rho^{\pm}$
mesons in $SU(3)$ pure gauge theory are calculated in the article. Based on
this the authors explore the contribution of the dipole magnetic
polarizabilities to the tensor polarization of the vector mesons in external
abelian magnetic field. The tensor polarization leads to the dilepton asymmetry
observed in non-central heavy ion collisions and can be also estimated in
lattice gauge theory.Comment: 18 pages, 7 figures, 6 table

### Self-consistency over the charge-density in dynamical mean-field theory: a linear muffin-tin implementation and some physical implications

We present a simple implementation of the dynamical mean-field theory
approach to the electronic structure of strongly correlated materials. This
implementation achieves full self-consistency over the charge density, taking
into account correlation-induced changes to the total charge density and
effective Kohn-Sham Hamiltonian. A linear muffin-tin orbital basis-set is used,
and the charge density is computed from moments of the many body
momentum-distribution matrix. The calculation of the total energy is also
considered, with a proper treatment of high-frequency tails of the Green's
function and self-energy. The method is illustrated on two materials with
well-localized 4f electrons, insulating cerium sesquioxide Ce2O3 and the
gamma-phase of metallic cerium, using the Hubbard-I approximation to the
dynamical mean-field self-energy. The momentum-integrated spectral function and
momentum-resolved dispersion of the Hubbard bands are calculated, as well as
the volume-dependence of the total energy. We show that full self-consistency
over the charge density, taking into account its modification by strong
correlations, can be important for the computation of both thermodynamical and
spectral properties, particularly in the case of the oxide material.Comment: 20 pages, 6 figures (submitted in The Physical Review B

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