8,443 research outputs found
A Faraway Quasar in the Direction of the Highest Energy Auger Event
The highest energy cosmic ray event reported by the Auger Observatory has an
energy of 148 EeV. It does not correlate with any nearby (z0.024) object
capable of originating such a high energy event. Intrigued by the fact that the
highest energy event ever recorded (by the Fly's Eye collaboration) points to a
faraway quasar with very high radio luminosity and large Faraday rotation
measurement, we have searched for a similar source for the Auger event. We find
that the Auger highest energy event points to a quasar with similar
characteristics to the one correlated to the Fly's Eye event. We also find the
same kind of correlation for one of the highest energy AGASA events. We
conclude that so far these types of quasars are the best source candidates for
both Auger and Fly's Eye highest energy events. We discuss a few exotic
candidates that could reach us from gigaparsec distances.Comment: 13 pages (version to be published in JCAP
Consequences of short range interactions between dark matter and protons in galaxy clusters
Protons gain energy in short range collisions with heavier dark matter
particles (DMPs) of comparable velocity dispersion. We examine the conditions
under which the heating of baryons by scattering off DMPs can offset radiative
cooling in the cores of galaxy clusters. Collisions with a constant cross
section independent of the relative velocity of the colliding particles, cannot
produce stable thermal balance. In this case, avoiding an unrealistic increase
of the central temperatures yields the upper bound on the cross-section,
\sigma_xp<10^-25 cm^2 (m_x/m_p), where m_x and m_p are the DMP and proton mass,
respectively. A stable balance, however, can be achieved for a power law
dependence on the relative velocity, V, of the form \sigma_xp \propto V^a with
a<-3. An advantage of this heating mechanism is that it preserves the metal
gradients observed in clusters.Comment: 7 pages, new calculations include
Closing the Window on Strongly Interacting Dark Matter with IceCube
We use the recent results on dark matter searches of the 22-string IceCube
detector to probe the remaining allowed window for strongly interacting dark
matter in the mass range 10^4<m_X<10^15 GeV. We calculate the expected signal
in the 22-string IceCube detector from the annihilation ofsuch particles
captured in the Sun and compare it to the detected background. As a result, the
remaining allowed region in the mass versus cross sectionparameter space is
ruled out. We also show the expected sensitivity of the complete IceCube
detector with 86 strings.Comment: 5 pages, 7 figures. Uppdated figures 2 and 3 (y-axis normalization
and label) . Version accepted for publication in PR
Heisenberg model in a random field: phase diagram and tricritical behavior
By using the differential operator technique and the effective field theory
scheme we study the tricritical behavior of Heisenberg classical model of
spin-1/2 in a random field. The phase diagram in the T-h plane on a square and
simple cubic lattice for a cluster with two spins is obtained when the random
field is bimodal distributed.Comment: 10 pages, 1 figur
Piper colubrinum Link. porta-enxêrto para Piper nigrum L. resistente às enfermidades causadas por Phytophthora palmivora Butl. e Fusarium solani f. piperi.
O sistema radicular da pimenta do reino (Piper nigrum L.) está sujeito ao ataque dos fungos do solo Fusarium solani f. piperi e Phytophthora palmivora (Butl.) Butl. Em testes de laboratório a espécie Piper colubrinum Link., compatível com a pimenta do reino, mostrou elevada resistência às enfermidades causadas pelos citados patógenos. Poderia ser utilizada como porta-enxêrto resistente em culturas extensas com fim lucrativo, desde que a produção venha a ser compensadora. A percentagem de pegamento dos enxêrtos feitos, foi elevada: acima de 98%. O desenvolvimento vegetativo das pimenteiras enxertadas, em áreas experimentais, no campo, vem sendo considerado bom. São relatados os processos de preparo dos porta-enxertos, métodos de enxertia e plantio no campo definitivo. A pimenteira enxertada só se desenvolve bem em áreas onde o solo possui umidade disponível constante.Separata da Pesquisa Agropecuária Brasileira, série agronomia, v. 3, p. 141-145, 1968
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