4,511 research outputs found
MC generator TAUOLA: implementation of Resonance Chiral Theory for two and three meson modes. Comparison with experiment
We present a partial upgrade of the Monte Carlo event generator TAUOLA with
the two and three hadron decay modes using the theoretical models based on
Resonance Chiral Theory. These modes account for 88% of total hadronic width of
the tau meson. First results of the model parameters have been obtained using
BaBar data for three pion mode.Comment: 5 pages, 1 figure, contribution to the Proceedings of the QCD@Work12
Conferenc
Theoretical inputs and errors in the new hadronic currents in TAUOLA
The new hadronic currents implemented in the TAUOLA library are obtained in
the unified and consistent framework of Resonance Chiral Theory: a Lagrangian
approach in which the resonances exchanged in the hadronic tau decays are
active degrees of freedom included in a way that reproduces the low-energy
results of Chiral Perturbation Theory. The short-distance QCD constraints on
the imaginary part of the spin-one correlators yield relations among the
couplings that render the theory predictive.
In this communication, the obtaining of the two- and three-meson form factors
is sketched. One of the criticisms to our framework is that the error may be as
large as 1/3, since it is a realization of the large-N_C limit of QCD in a
meson theory. A number of arguments are given which disfavor that claim
pointing to smaller errors, which would explain the phenomenological success of
our description in these decays. Finally, other minor sources of error and
current improvements of the code are discussed.Comment: 5 pages, no figures, contribution to the Proceedings of the
QCD@Work12 Conferenc
Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days
We present an optical nebular spectrum of the nearby Type Ia supernova
2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution
since the +593 day optical spectrum, but there are several curious aspects in
this new extremely late-time regime. We suggest that the persistence of the
~\AA\ feature is due to Na I D, and that a new emission feature at
~\AA\ may be [Ca II]. Also, we discuss whether the new emission
feature at ~\AA\ might be [Fe I] or the high-velocity hydrogen
predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear
velocity evolution of per 100 days from at least
+220 to +980 days, but the line's shape also changes in this time, suggesting
that line blending contributes to the evolution. At days after
explosion, flux from the SN has declined to a point where contribution from a
luminous secondary could be detected. In this work we make the first
observational tests for a post-impact remnant star and constrain its
temperature and luminosity to and
. Additionally, we do not see any evidence for narrow H
emission in our spectrum. We conclude that observations continue to strongly
exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA
Resonance Chiral Lagrangian Currents and Experimental Data for
In this paper we document the modifications introduced to the previous
version of the Resonance Chiral Lagrangian current ({\it Phys.Rev.} {\bf D86}
(2012) 113008) of the decay
which enable the one dimensional distributions measured by the BaBar
collaboration to be well modeled. The main change required to model the data is
the addition of the resonance. Systematic errors, theoretical and
experimental ones, limitations due to fits of one dimensional distributions
only, and resulting difficulties and statistical/systematic errors for fitted
parameters are addressed. The current and fitting environment is ready for
comparisons with the fully exclusive experimental data. The present result for
is encouraging for work on
other decay modes and Resonance Chiral Lagrangian based currents.Comment: 16 pages, 2 figure
Near-infrared observations of type Ia supernovae: The best known standard candle for cosmology
We present an analysis of the Hubble diagram for 12 Type Ia supernovae (SNe
Ia) observed in the near-infrared J and H bands. We select SNe exclusively from
the redshift range 0.03 < z < 0.09 to reduce uncertainties coming from peculiar
velocities while remaining in a cosmologically well-understood region. All of
the SNe in our sample exhibit no spectral or B-band light-curve peculiarities
and lie in the B-band stretch range of 0.8-1.15. Our results suggest that SNe
Ia observed in the near-infrared (NIR) are the best known standard candles. We
fit previously determined NIR light-curve templates to new high-precision data
to derive peak magnitudes and to determine the scatter about the Hubble line.
Photometry of the 12 SNe is presented in the natural system. Using a standard
cosmology of (H_0, Omega_m, Lambda) = (70,0.27,0.73) we find a median J-band
absolute magnitude of M_J = -18.39 with a scatter of 0.116 and a median H-band
absolute magnitude of M_H = -18.36 with a scatter of 0.085. The scatter in the
H band is the smallest yet measured. We search for correlations between
residuals in the J- and H-band Hubble diagrams and SN properties, such as SN
colour, B-band stretch and the projected distance from host-galaxy centre. The
only significant correlation is between the J-band Hubble residual and the J-H
pseudo-colour. We also examine how the scatter changes when fewer points in the
near-infrared are used to constrain the light curve. With a single point in the
H band taken anywhere from 10 days before to 15 days after B-band maximum light
and a prior on the date of H-band maximum set from the date of B-band maximum,
we find that we can measure distances to an accuracy of 6%. The precision of
SNe Ia in the NIR provides new opportunities for precision measurements of both
the expansion history of the universe and peculiar velocities of nearby
galaxies.Comment: 6 pages, 2 figures. Accepted for publication in MNRA
Spectral Models for Early Time SN 2011fe Observations
We use observed UV through near IR spectra to examine whether SN 2011fe can
be understood in the framework of Branch-normal SNe Ia and to examine its
individual peculiarities. As a benchmark, we use a delayed-detonation model
with a progenitor metallicity of Z_solar/20. We study the sensitivity of
features to variations in progenitor metallicity, the outer density profile,
and the distribution of radioactive nickel. The effect of metallicity
variations in the progenitor have a relatively small effect on the synthetic
spectra. We also find that the abundance stratification of SN 2011fe resembles
closely that of a delayed detonation model with a transition density that has
been fit to other Branch-normal Type Ia supernovae. At early times, the model
photosphere is formed in material with velocities that are too high, indicating
that the photosphere recedes too slowly or that SN 2011fe has a lower specific
energy in the outer ~0.1 M_sun than does the model. We discuss several
explanations for the discrepancies. Finally, we examine variations in both the
spectral energy distribution and in the colors due to variations in the
progenitor metallicity, which suggests that colors are only weak indicators for
the progenitor metallicity, in the particular explosion model that we have
studied. We do find that the flux in the U band is significantly higher at
maximum light in the solar metallicity model than in the lower metallicity
model and the lower metallicity model much better matches the observed
spectrum.Comment: 9 pages, 14 figures, MNRAS, in press, fixed typ
The Subluminous and Peculiar Type Ia Supernova PTF09dav
PTF09dav is a peculiar subluminous type Ia supernova (SN) discovered by the
Palomar Transient Factory (PTF). Spectroscopically, it appears superficially
similar to the class of subluminous SN1991bg-like SNe, but it has several
unusual features which make it stand out from this population. Its peak
luminosity is fainter than any previously discovered SN1991bg-like SN Ia (M_B
-15.5), but without the unusually red optical colors expected if the faint
luminosity were due to extinction. The photospheric optical spectra have very
unusual strong lines of Sc II and Mg I, with possible Sr II, together with
stronger than average Ti II and low velocities of ~6000 km/s. The host galaxy
of PTF09dav is ambiguous. The SN lies either on the extreme outskirts (~41kpc)
of a spiral galaxy, or in an very faint (M_R>-12.8) dwarf galaxy, unlike other
1991bg-like SNe which are invariably associated with massive, old stellar
populations. PTF09dav is also an outlier on the light-curve-width--luminosity
and color--luminosity relations derived for other sub-luminous SNe Ia. The
inferred 56Ni mass is small (0.019+/-0.003Msun), as is the estimated ejecta
mass of 0.36Msun. Taken together, these properties make PTF09dav a remarkable
event. We discuss various physical models that could explain PTF09dav. Helium
shell detonation or deflagration on the surface of a CO white-dwarf can explain
some of the features of PTF09dav, including the presence of Sc and the low
photospheric velocities, but the observed Si and Mg are not predicted to be
very abundant in these models. We conclude that no single model is currently
capable of explaining all of the observed signatures of PTF09dav.Comment: Accepted for publication in Ap
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