13,410 research outputs found
Further search for a neutral boson with a mass around 9 MeV/c2
Two dedicated experiments on internal pair conversion (IPC) of isoscalar M1
transitions were carried out in order to test a 9 MeV/c2 X-boson scenario. In
the 7Li(p,e+e-)8Be reaction at 1.1 MeV proton energy to the predominantly T=0
level at 18.15 MeV, a significant deviation from IPC was observed at large pair
correlation angles. In the 11B(d,n e+e-)12C reaction at 1.6 MeV, leading to the
12.71 MeV 1+ level with pure T=0 character, an anomaly was observed at 9
MeV/c2. The compatibility of the results with the scenario is discussed.Comment: 12 pages, 5 figures, 2 table
Detecting Dark Matter Annihilation with CMB Polarization : Signatures and Experimental Prospects
Dark matter (DM) annihilation during hydrogen recombination (z ~ 1000) will
alter the recombination history of the Universe, and affect the observed CMB
temperature and polarization fluctuations. Unlike other astrophysical probes of
DM, this is free of the significant uncertainties in modelling galactic
physics, and provides a method to detect and constrain the cosmological
abundances of these particles. We parametrize the effect of DM annihilation as
an injection of ionizing energy at a rate e_{dm}, and argue that this simple
"on the spot'' modification is a good approximation to the complicated
interaction of the annihilation products with the photon-electron plasma.
Generic models of DM do not change the redshift of recombination, but change
the residual ionization after recombination. This broadens the surface of last
scattering, suppressing the temperature fluctuations and enhancing the
polarization fluctuations. We use the temperature and polarization angular
power spectra to measure these deviations from the standard recombination
history, and therefore, indirectly probe DM annihilation. (abridged)Comment: 13 pages, 8 figures, submitted to PR
Supersymmetry and LHC
The motivation for introduction of supersymmetry in high energy physics as
well as a possibility for supersymmetry discovery at LHC (Large Hadronic
Collider) are discussed. The main notions of the Minimal Supersymmetric
Standard Model (MSSM) are introduced. Different regions of parameter space are
analyzed and their phenomenological properties are compared. Discovery
potential of LHC for the planned luminosity is shown for different channels.
The properties of SUSY Higgs bosons are studied and perspectives of their
observation at LHC are briefly outlined.Comment: Lectures given at the 9th Moscow International School of Physics
(XXXIV ITEP Winter School of Physics
Device operation of organic tandem solar cells
A generalized methodology is developed to obtain the current-voltage characteristic of polymer tandem solar cells by knowing the electrical performance of both sub cells. We demonstrate that the electrical characteristics of polymer tandem solar cells are correctly predicted for both the series and parallel connection of the sub cells. The agreement with experiments allows us to investigate the effect of a reduced open-circuit voltage, short-circuit current or fill factor in one of the sub cells on the performance of the tandem cell. A low fill factor in one of the sub cells leads to a stronger reduction of the efficiency in a series configuration as compared to the parallel tandem device. (C) 2008 Elsevier B.V. All rights reserved
Dark matter from the scalar sector of 3-3-1 models without exotic electric charges
We show that three SU(2) singlet neutral scalars (two CP-even and one CP-odd)
in the spectrum of models based on the gauge symmetry SU(3)_c X SU(3)_L X
U(1)_X, which do not contain exotic electric charges, are realistic candidates
for thermally generated self-interacting dark matter in the Universe, a type of
dark matter that has been recently proposed in order to overcome some
difficulties of collisionless cold dark matter models at the galactic scale.
These candidates arise without introducing a new mass scale in the model and/or
without the need for a discrete symmetry to stabilize them, but at the expense
of tuning several combinations of parameters of the scalar potential.Comment: RevTeX, 11 pages. v2: typos corrected, one reference added. v3:
clarifications added, four more references added. To appear in Europhys. Let
Соціально-правова та етична природа мусульманської сім‘ї
Relative sea-level variations during the late Pleistocene can only be
reconstructed with the knowledge of ice-sheet history. On the other hand, the
knowledge of regional and global relative sea-level variations is necessary
to learn about the changes in ice volume. Overcoming this problem of
circularity demands a fully coupled system where ice sheets and sea level
vary consistently in space and time and dynamically affect each other. Here
we present results for the past 410 000 years (410 kyr) from the coupling
of a set of 3-D ice-sheet-shelf models to a global sea-level model, which is
based on the solution of the gravitationally self-consistent sea-level
equation. The sea-level model incorporates the glacial isostatic adjustment
feedbacks for a Maxwell viscoelastic and rotating Earth model with coastal
migration. Ice volume is computed with four 3-D ice-sheet-shelf models for
North America, Eurasia, Greenland and Antarctica. Using an inverse approach,
ice volume and temperature are derived from a benthic δ18O stacked
record. The derived surface-air temperature anomaly is added to the
present-day climatology to simulate glacial–interglacial changes in
temperature and hence ice volume. The ice-sheet thickness variations are then
forwarded to the sea-level model to compute the bedrock deformation, the
change in sea-surface height and thus the relative sea-level change. The
latter is then forwarded to the ice-sheet models. To quantify the impact of
relative sea-level variations on ice-volume evolution, we have performed
coupled and uncoupled simulations. The largest differences of ice-sheet
thickness change occur at the edges of the ice sheets, where relative sea-level
change significantly departs from the ocean-averaged sea-level variations
Trajectory Deflection of Spinning Magnetic Microparticles, the Magnus Effect at the Microscale
The deflection due to the Magnus force of magnetic particles with a diameter
of 80 micrometer dropping through fluids and rotating in a magnetic field was
measured. With Reynolds number for this experiment around 1, we found
trajectory deflections of the order of 1 degree, in agreement within
measurement error with theory. This method holds promise for the sorting and
analysis of the distribution in magnetic moment and particle diameter of
suspensions of microparticles, such as applied in catalysis, or objects loaded
with magnetic particles.Comment: 12 pages, 3 figures. Appendix with 6 figure
d_c=4 is the upper critical dimension for the Bak-Sneppen model
Numerical results are presented indicating d_c=4 as the upper critical
dimension for the Bak-Sneppen evolution model. This finding agrees with
previous theoretical arguments, but contradicts a recent Letter [Phys. Rev.
Lett. 80, 5746-5749 (1998)] that placed d_c as high as d=8. In particular, we
find that avalanches are compact for all dimensions d<=4, and are fractal for
d>4. Under those conditions, scaling arguments predict a d_c=4, where
hyperscaling relations hold for d<=4. Other properties of avalanches, studied
for 1<=d<=6, corroborate this result. To this end, an improved numerical
algorithm is presented that is based on the equivalent branching process.Comment: 4 pages, RevTex4, as to appear in Phys. Rev. Lett., related papers
available at http://userwww.service.emory.edu/~sboettc
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