248 research outputs found
Cultivo in vitro de batata-doce.
Dissertação (Mestrado em Fisiologia Vegetal) - Programa de Pós-Graduação em Fisiologia Vegetal, Departamento de Botânica, Instituto de Biologia, Universidade Federal de Pelotas, Pelotas, 2017. Orientador: Prof. Dr. José Antônio Peters, Coorientador: Dr. Leonardo Ferreira Dutra
Efeito da concentração de sais do meio na organogênese indireta de hipocótilos de pinhão-manso.
Tracker fields from nonminimally coupled theory
We extend the concept of quintessence to a flat nonminimally coupled scalar -
tensor theories of gravity. By means of Noether's symmetries for the
cosmological pointlike Lagrangian L, it is possible to exhibit exact solutions
for a class of models depending on a free parameter s. This parameter comes out
in the relationship existing between the coupling F(\phi) and the potential
V(\phi) because of such a symmetry for L. When inverse power law potentials are
taken in account, a whole family of exact solutions parametrized by such an s
is proposed as a class of tracker fields, and some considerations are made
about them.Comment: 17 pages, submitted to Physical Review
Nonthermal Supermassive Dark Matter
We discuss several cosmological production mechanisms for nonthermal
supermassive dark matter and argue that dark matter may be elementary particles
of mass much greater than the weak scale. Searches for dark matter should not
be limited to weakly interacting particles with mass of the order of the weak
scale, but should extend into the supermassive range as well.Comment: 11 page LaTeX file. No major changes. Version accepted by PR
Baryogenesis from Primordial Blackholes after Electroweak Phase Transition
Incorporating a realistic model for accretion of ultra-relativistic particles
by primordial blackholes (PBHs), we study the evolution of an Einstein-de
Sitter universe consisting of PBHs embedded in a thermal bath from the epoch
sec to sec. In this paper we use Barrow
et al's ansatz to model blackhole evaporation in which the modified Hawking
temperature goes to zero in the limit of the blackhole attaining a relic state
with mass . Both single mass PBH case as well as the case in which
blackhole masses are distributed in the range gm
have been considered in our analysis. Blackholes with mass larger than gm appear to survive beyond the electroweak phase transition and,
therefore, successfully manage to create baryon excess via
emissions, averting the baryon number wash-out due to sphalerons. In this
scenario, we find that the contribution to the baryon-to-entropy ratio by PBHs
of initial mass is given by , where
and are the CP-violating parameter and the initial mass
fraction of the PBHs, respectively. For larger than ,
the observed matter-antimatter asymmetry in the universe can be attributed to
the evaporation of PBHs.Comment: Latex2e file with seven figures included as postscript file
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