13,387 research outputs found
Stability of the Accretion Flows with Stalled Shocks in Core-Collapse Supernovae
Bearing in mind the application to the theory of core-collapse supernovae, we
performed a global linear analysis on the stability of spherically symmetric
accretion flows through a standing shock wave onto a proto neutron star. As
unperturbed flows, we adopted the spherically symmetric steady solutions to the
Euler equations obtained with realistic equation of state and formulae for
neutrino reaction rates taken into account. Then we solved the equations for
linear perturbations numerically, and obtained the eigen frequencies and eigen
functions. We found (1) the flows are stable for all modes if the neutrino
luminosity is lower than ergs/s for
. (2) For larger luminosities, the non-radial
instabilities are induced, probably via the advection-acoustic cycles.
Interestingly, the modes with and 3 become unstable at first for
relatively low neutrino luminosities, e.g. ergs/s
for the same accretion rate, whereas the mode is the most unstable for
higher luminosities, ergs/s. These are all oscillatory
modes. (3) For still larger luminosities, ergs/s for
, non-oscillatory modes, both radial and
non-radial, become unstable. These non-radial modes were identified as
convection. We confirmed the results obtained by numerical simulations that the
instabilities induced by the advection-acoustic cycles are more important than
the convection for lower neutrino luminosities.Comment: 46 pages, 19 figures, Accepted by Ap
Near-threshold -meson production in proton-proton collisions: With or without resonance excitations ?
We present results for the reaction studied by
considering two different scenarios: with and without the inclusion of nucleon
resonance excitations. The recently measured angular distribution by the
COSY-TOF Collaboration at an excess energy of MeV and the energy
dependence of the total cross section data for are used
to calibrate the model parameters. The inclusion of nucleon resonances improves
the theoretical prediction for the energy dependence of the total cross section
in at excess energies MeV. However, it still
underestimates the data by about a factor of two, and remains a problem in
understanding the reaction mechanism.Comment: Fig.5 and text modified, Latex, 4 pages, 8 embedded figures, uses
espcrc1.sty (included), talk presented at PANIC02, Osaka, Japan, 30 September
- 4 October 200
Low-scale Supersymmetry from Inflation
We investigate an inflation model with the inflaton being identified with a
Higgs boson responsible for the breaking of U(1)B-L symmetry. We show that
supersymmetry must remain a good symmetry at scales one order of magnitude
below the inflation scale, in order for the inflation model to solve the
horizon and flatness problems, as well as to account for the observed density
perturbation. The upper bound on the soft supersymmetry breaking mass lies
between 1TeV and 10^3TeV. Interestingly, our finding opens up a possibility
that universes with the low-scale supersymmetry are realized by the
inflationary selection. Our inflation model has rich implications; non-thermal
leptogenesis naturally works, and the gravitino and moduli problems as well as
the moduli destabilization problem can be solved or ameliorated; the
standard-model higgs boson receives a sizable radiative correction if the
supersymmertry breaking takes a value on the high side ~10^3TeV.Comment: 23pages, 3 figures. v2: references adde
Interacting Dipoles in Type-I Clathrates: Why Glass-like though Crystal?
Almost identical thermal properties of type-I clathrate compounds to those of
glasses follow naturally from the consideration that off-centered guest ions
possess electric dipole moments. Local fields from neighbor dipoles create many
potential minima in the configuration space. A theoretical analysis based on
two-level tunneling states demonstrates that interacting dipoles are a key to
quantitatively explain the glass-like behaviors of low-temperature thermal
properties of type-I clathrate compounds with off-centered guest ions.From this
analysis, we predict the existence of a glass transition
General Analysis of Inflation in the Jordan frame Supergravity
We study various inflation models in the Jordan frame supergravity with a
logarithmic Kahler potential. We find that, in a class of inflation models
containing an additional singlet in the superpotential, three types of
inflation can be realized: the Higgs-type inflation, power-law inflation, and
chaotic inflation with/without a running kinetic term. The former two are
possible if the holomorphic function dominates over the non-holomorphic one in
the frame function, while the chaotic inflation occurs when both are
comparable. Interestingly, the fractional-power potential can be realized by
the running kinetic term. We also discuss the implication for the Higgs
inflation in supergravity.Comment: 16 pages, 1 figur
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