782 research outputs found
Search for uncharged faster than light particles
Searching for uncharged particles with spacelike four momentum traveling faster than ligh
A Possible Origin of Dark Energy
We discuss the possibility that the existence of dark energy may be due to
the presence of a spin zero field , either elementary or composite. In
the presence of other matter field, the transformation
constant can generate a negative pressure, like the cosmological constant. In
this picture, our universe can be thought as a very large bag, similar to the
much smaller MIT bag model for a single nucleon.Comment: 4 pages, no figure, typos correcte
Initial Hubble Diagram Results from the Nearby Supernova Factory
The use of Type Ia supernovae as distance indicators led to the discovery of
the accelerating expansion of the universe a decade ago. Now that large second
generation surveys have significantly increased the size and quality of the
high-redshift sample, the cosmological constraints are limited by the currently
available sample of ~50 cosmologically useful nearby supernovae. The Nearby
Supernova Factory addresses this problem by discovering nearby supernovae and
observing their spectrophotometric time development. Our data sample includes
over 2400 spectra from spectral timeseries of 185 supernovae. This talk
presents results from a portion of this sample including a Hubble diagram
(relative distance vs. redshift) and a description of some analyses using this
rich dataset.Comment: Short version of proceedings for ICHEP08, Philadelphia PA, July 2008;
see v1 for full-length versio
The Rising Light Curves of Type Ia Supernovae
We present an analysis of the early, rising light curves of 18 Type Ia
supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the
La Silla-QUEST variability survey (LSQ). We fit these early data flux using a
simple power-law to determine the time of first
light , and hence the rise-time from first light to
peak luminosity, and the exponent of the power-law rise (). We find a mean
uncorrected rise time of days, with individual SN rise-times
ranging from to days. The exponent n shows significant
departures from the simple 'fireball model' of (or ) usually assumed in the literature. With a mean value of , our data also show significant diversity from event to event. This
deviation has implications for the distribution of 56Ni throughout the SN
ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The
range of n found also confirms that the 56Ni distribution is not standard
throughout the population of SNe Ia, in agreement with earlier work measuring
such abundances through spectral modelling. We also show that the duration of
the very early light curve, before the luminosity has reached half of its
maximal value, does not correlate with the light curve shape or stretch used to
standardise SNe Ia in cosmological applications. This has implications for the
cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA
A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw
We report on our findings based on the analysis of observations of the Type
II-L supernova LSQ13cuw within the framework of currently accepted physical
predictions of core-collapse supernova explosions. LSQ13cuw was discovered
within a day of explosion, hitherto unprecedented for Type II-L supernovae.
This motivated a comparative study of Type II-P and II-L supernovae with
relatively well-constrained explosion epochs and rise times to maximum
(optical) light. From our sample of twenty such events, we find evidence of a
positive correlation between the duration of the rise and the peak brightness.
On average, SNe II-L tend to have brighter peak magnitudes and longer rise
times than SNe II-P. However, this difference is clearest only at the extreme
ends of the rise time versus peak brightness relation. Using two different
analytical models, we performed a parameter study to investigate the physical
parameters that control the rise time behaviour. In general, the models
qualitatively reproduce aspects of the observed trends. We find that the
brightness of the optical peak increases for larger progenitor radii and
explosion energies, and decreases for larger masses. The dependence of the rise
time on mass and explosion energy is smaller than the dependence on the
progenitor radius. We find no evidence that the progenitors of SNe II-L have
significantly smaller radii than those of SNe II-P.Comment: 19 pages, 10 figures, accepted by A&
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