3,549 research outputs found
The degenerate gravitino scenario
In this work, we explore the "degenerate gravitino" scenario where the mass
difference between the gravitino and the lightest MSSM particle is much smaller
than the gravitino mass itself. In this case, the energy released in the decay
of the next to lightest sypersymmetric particle (NLSP) is reduced. Consequently
the cosmological and astrophysical constraints on the gravitino abundance, and
hence on the reheating temperature, become softer than in the usual case. On
the other hand, such small mass splittings generically imply a much longer
lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for
neutralino LSP or NLSP, reheating temperatures compatible with thermal
leptogenesis are reached for small splittings of order 10^{-2} GeV. While for
stau NLSP, temperatures of 4x10^9 GeV can be obtained even for splittings of
order of tens of GeVs. This "degenerate gravitino" scenario offers a possible
way out to the gravitino problem for thermal leptogenesis in supersymmetric
theories.Comment: 27 pages, 10 figures and 1 table. Minor typos and references fixed.
Matches published version in JCAP
Magneto-Optical Trap for Thulium Atoms
Thulium atoms are trapped in a magneto-optical trap using a strong transition
at 410 nm with a small branching ratio. We trap up to atoms at
a temperature of 0.8(2) mK after deceleration in a 40 cm long Zeeman slower.
Optical leaks from the cooling cycle influence the lifetime of atoms in the MOT
which varies between 0.3 -1.5 s in our experiments. The lower limit for the
leaking rate from the upper cooling level is measured to be 22(6) s. The
repumping laser transferring the atomic population out of the F=3 hyperfine
ground-state sublevel gives a 30% increase for the lifetime and the number of
atoms in the trap.Comment: 4 pages, 6 figure
Bulk Nanocrystalline Thermoelectrics Based on Bi-Sb-Te Solid Solution
A nanopowder from p-Bi-Sb-Te with particles ~ 10 nm were fabricated by the
ball milling using different technological modes. Cold and hot pressing at
different conditions and also SPS process were used for consolidation of the
powder into a bulk nanostructure and nanocomposites. The main factors allowing
slowing-down of the growth of nanograins as a result of recrystallization are
the reduction of the temperature and of the duration of the pressing, the
increase of the pressure, as well as addition of small value additives (like
MoS2, thermally expanded graphite or fullerenes). It was reached the
thermoelectric figure of merit ZT=1.22 (at 360 K) in the bulk nanostructure
Bi0,4Sb1,6Te3 fabricated by SPS method. Some mechanisms of the improvement of
the thermoelectric efficiency in bulk nanocrystalline semiconductors based on
BixSb2-xTe3 are studied theoretically. The reduction of nanograin size can lead
to improvement of the thermoelectric figure of merit. The theoretical
dependence of the electric and heat conductivities and the thermoelectric power
as the function of nanograins size in BixSb2-xTe3 bulk nanostructure are quite
accurately correlates with the experimental data.Comment: 35 pages, 24 figures, 4 tables, 52 reference
BRST Algebra Quantum Double and Quantization of the Proper Time Cotangent Bundle
The quantum double for the quantized BRST superalgebra is studied. The
corresponding R-matrix is explicitly constucted. The Hopf algebras of the
double form an analytical variety with coordinates described by the canonical
deformation parameters. This provides the possibility to construct the
nontrivial quantization of the proper time supergroup cotangent bundle. The
group-like classical limit for this quantization corresponds to the generic
super Lie bialgebra of the double.Comment: 11 pages, LaTe
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