8,696 research outputs found
Explosion of white dwarfs harboring hybrid CONe cores
Recently, it has been found that off-centre carbon burning in a subset of
intermediate-mass stars does not propagate all the way to the center, resulting
in a class of hybrid CONe cores. Here, we consider the possibility that stars
hosting these hybrid CONe cores might belong to a close binary system and,
eventually, become white dwarfs accreting from a non-degenerate companion at
rates leading to a supernova explosion. We have computed the hydrodynamical
phase of the explosion of Chandrasekhar-mass white dwarfs harboring hybrid
cores, assuming that the explosion starts at the center, either as a detonation
(as may be expected in some degenerate merging scenarios) or as a deflagration
(that afterwards transitions into a delayed detonation). We assume these hybrid
cores are made of a central CO volume, of mass M(CO), surrounded by an ONe
shell. We show that, in case of a pure detonation, a medium-sized CO-rich
region, M(CO)<0.4 Msun, results in the ejection of a small fraction of the
mantle while leaving a massive bound remnant. Part of this remnant is made of
the products of the detonation, Fe-group nuclei, but they are buried in its
inner regions, unless convection is activated during the ensuing cooling and
shrinking phase of the remnant. In contrast, and somehow paradoxically, delayed
detonations do not leave remnants but for the minimum M(CO) we have explored,
M(CO)=0.2 Msun, and even in this case the remnant is as small as 0.13 Msun. The
ejecta produced by these delayed detonations are characterized by slightly
smaller masses of 56Ni and substantially smaller kinetic energies than obtained
for a delayed detonation of a 'normal' CO white dwarf. The optical emission
expected from these explosions would hardly match the observational properties
of typical Type Ia supernovae, although they make interesting candidates for
the subluminous class of SN2002cx-like or SNIax.Comment: Accepted for Astronomy and Astrophysics, 11 pages, 4 figure
Anderson Localization in Disordered Vibrating Rods
We study, both experimentally and numerically, the Anderson localization
phenomenon in torsional waves of a disordered elastic rod, which consists of a
cylinder with randomly spaced notches. We find that the normal-mode wave
amplitudes are exponentially localized as occurs in disordered solids. The
localization length is measured using these wave amplitudes and it is shown to
decrease as a function of frequency. The normal-mode spectrum is also measured
as well as computed, so its level statistics can be analyzed. Fitting the
nearest-neighbor spacing distribution a level repulsion parameter is defined
that also varies with frequency. The localization length can then be expressed
as a function of the repulsion parameter. There exists a range in which the
localization length is a linear function of the repulsion parameter, which is
consistent with Random Matrix Theory. However, at low values of the repulsion
parameter the linear dependence does not hold.Comment: 10 pages, 6 figure
The Triple Higgs Boson Self-Coupling at Future Linear e+e- Colliders Energies: ILC and CLIC
We analyzed the triple Higgs boson self-coupling at future
colliders energies, with the reactions . We evaluate the total cross-sections for both and ,
and calculate the total number of events considering the complete set of
Feynman diagrams at tree-level. We vary the triple coupling
within the range and +2. The numerical
computation is done for the energies expected to be available at a possible
Future Linear Collider with a center-of-mass energy and a luminosity 1000 . Our analysis is also extended to a
center-of-mass energy 3 and luminosities of 1000 and 5000
. We found that for the process , the
complete calculation differs only by 3% from the approximate calculation
, while for the process , the expected number of events, considering the decay products of both
and , is not enough to obtain an accurate determination of the triple Higgs
boson self-coupling.Comment: 19 pages, 12 figure
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