1,297 research outputs found
Shock Breakout in Type II Plateau Supernovae: Prospects for High Redshift Supernova Surveys
Shock breakout is the brightest radiative phenomenon in a supernova (SN) but
is difficult to be observed owing to the short duration and X-ray/ultraviolet
(UV)-peaked spectra. After the first observation from the rising phase reported
in 2008, its observability at high redshift is attracting enormous attention.
We perform multigroup radiation hydrodynamics calculations of explosions for
evolutionary presupernova models with various main-sequence masses , metallicities , and explosion energies . We present multicolor
light curves of shock breakout in Type II plateau SNe, being the most frequent
core-collapse SNe, and predict apparent multicolor light curves of shock
breakout at various redshifts . We derive the observable SN rate and
reachable redshift as functions of filter and limiting magnitude by taking into account an initial mass function, cosmic star formation
history, intergalactic absorption, and host galaxy extinction. We propose a
realistic survey strategy optimized for shock breakout. For example, the
-band observable SN rate for mag is 3.3 SNe
degree day and a half of them locates at . It is clear
that the shock breakout is a beneficial clue to probe high- core-collapse
SNe. We also establish ways to identify shock breakout and constrain SN
properties from the observations of shock breakout, brightness, time scale, and
color. We emphasize that the multicolor observations in blue optical bands with
hour intervals, preferably over continuous nights, are essential
to efficiently detect, identify, and interpret shock breakout.Comment: 26 pages, 23 figures. Accepted for publication in the Astrophysical
Journal Supplement Serie
B^0-\bar{B}^0 mixing with quenched lattice NRQCD
We present our recent results for the B-parameters, which parameterize the
\Delta B=2 transition amplitudes. Calculations are made in quenched QCD at
\beta=5.7, 5.9, and 6.1, using NRQCD for heavy quark and the -improved
action for light quark. The operators are perturbatively renormalized including
corrections of O(\alpha_s/am_Q). We examine scaling behavior of the
B-parameters in detail, and discuss the systematic uncertainties using scatter
of results with different analysis procedures adopted. As a result, we find
B_{B_d}(m_b)=0.84(2)(8), B_{B_s}/B_{B_d}=1.017(10)(^{+4}_{-0}) and
B_{S_s}(m_b)=0.87(1)(9)(^{+1}_{-0}) in the quenched approximation.Comment: Lattice 2000 (Heavy Quark Physics), 4 pages, 4 eps-figures, Latex,
typo correcte
Heavy quark expansion parameters from lattice NRQCD
Using the lattice NRQCD action for heavy quark, we calculate the heavy quark
expansion parameters and for heavy-light mesons and
heavy-light-light baryons. The results are compared with the mass differences
among heavy hadrons to test the validity of HQET relations on the lattice.Comment: Lattice2001(heavyquark), 3 pages, 4 figure
Exploration of sea quark effects in two-flavor QCD with the O(a)-improved Wilson quark action
We explore sea quark effects in the light hadron mass spectrum in a
simulation of two-flavor QCD using the nonperturbatively O(a)-improved Wilson
fermion action. In order to identify finite-size effects, light meson masses
are measured on 12^3x48, 16^3x48 and 20^3x48 lattices with a~0.1 fm. On the
largest lattice, where the finite-size effect is negligible, we find a
significant increase of the strange vector meson mass compared to the quenched
approximation. We also investigate the quark mass dependence of pseudoscalar
meson masses and decay constants and test the consistency with (partially
quenched) chiral perturbation theory.Comment: 3 pages, 3 figures, Lattice2001(spectrum
An exact algorithm for three-flavor QCD with -improved Wilson fermions
We present an exact dynamical QCD simulation algorithm for the
-improved Wilson fermion with odd number of flavors. Our algorithm is an
extension of the non-Hermitian polynomials HMC algorithm proposed by Takaishi
and de Forcrand previously. In our algorithm, the systematic errors caused by
the polynomial approximation of the inverse of Dirac operator is removed by a
noisy-Metropolis test. For one flavor quark it is achieved by taking the square
root of the correction matrix explicitly. We test our algorithm for the case of
on a moderately large lattice size (). The
case is also investigated.Comment: Lattice 2001 (algorithm), 3 pages, LaTeX2e with espcrc2.st
Non-trivial phase structure of QCD with -improved Wilson fermion at zero temperature
JLQCD collaboration recently started the QCD simulations with the
-improved Wilson fermion action employing an exact fermion algorithm
developed for odd number of quark flavors. It is found that this theory has an
unexpected non-trivial phase structure in the plane even at
zero temperature. A detailed study is made to understand the nature of the
observed phase transitions and to find the way of avoiding untolerably large
lattice artifacts associated with the phase transition.Comment: 3 pages, 5 figures, Lattice2001(spectrum
Differential decay rate for semileptonic decays
We present our study on semileptonic decay form factors
with NRQCD action for heavy quark from a quenched lattice QCD simulation at
=5.9 on a lattice. We obtain form factors defined in the
context of heavy quark effective theory by Burdman et al. and find that their
correction is small. The limit of physical heavy and light quark masses
can be performed without introducing any model function, and we obtain a
prediction for the differential decay rate . We also discuss the
soft pion limit of the form factors.Comment: Lattice 2000, 4 pages, 4 figures, Late
A possible mechanism of ultrafast amorphization in phase-change memory alloys: an ion slingshot from the crystalline to amorphous position
We propose that the driving force of an ultrafast crystalline-to-amorphous
transition in phase-change memory alloys are strained bonds existing in the
(metastable) crystalline phase. For the prototypical example of GST, we
demonstrate that upon breaking of long Ge-Te bond by photoexcitation Ge ion
shot from an octahedral crystalline to a tetrahedral amorphous position by the
uncompensated force of strained short bonds. Subsequent lattice relaxation
stabilizes the tetrahedral surroundings of the Ge atoms and ensures the
long-term stability of the optically induced phase.Comment: 6 pages, 3 figure
Non-perturbative renormalization factors of bilinear quark operators for Kogut-Susskind fermions and light quark masses in quenched QCD
Light quark masses are computed for Kogut-Susskind fermions by evaluating
non-perturbatively the renormalization factor for bilinear quark operators.
Calculations are carried out in the quenched approximation at \beta=6.0, 6.2,
and 6.4. For the average up and down quark mass we find in the continuum limit, which is significantly larger than
() or () obtained with the
one-loop perturbative renormalization factor.Comment: LATTICE98(matrixelement), 3 pages, 4 eps figure
The Peculiar Type Ib Supernova 2006jc: A WCO Wolf-Rayet Star Explosion
We present a theoretical model for Type Ib supernova (SN) 2006jc. We
calculate the evolution of the progenitor star, hydrodynamics and
nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC).
The synthetic bolometric LC is compared with the observed bolometric LC
constructed by integrating the UV, optical, near-infrared (NIR), and
mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as
on the zero-age main-sequence. The star undergoes extensive mass
loss to reduce its mass down to as small as , thus becoming a WCO
Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which
amorphous carbon grains can be formed. This could explain the NIR brightening
and the dust feature seen in the MIR spectrum. We suggest that the progenitor
of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and
such massive stars are the important sites of dust formation. We derive the
parameters of the explosion model in order to reproduce the bolometric LC of SN
2006jc by the radioactive decays: the ejecta mass , hypernova-like
explosion energy ergs, and ejected Ni mass . We
also calculate the circumstellar interaction and find that a CSM with a flat
density structure is required to reproduce the X-ray LC of SN 2006jc. This
suggests a drastic change of the mass-loss rate and/or the wind velocity that
is consistent with the past luminous blue variable (LBV)-like event.Comment: 12 pages, 11 figures. Accepted for publication in the Astrophysical
Journa
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