65,275 research outputs found
The Hydrodynamic Chaplygin Sleigh
We consider the motion of rigid bodies in a potential fluid subject to
certain nonholonomic constraints and show that it is described by
Euler--Poincar\'e--Suslov equations.
In the 2-dimensional case, when the constraint is realized by a blade
attached to the body, the system provides a hydrodynamic generalization of the
Chaplygin sleigh, whose dynamics are studied in detail. Namely, the equations
of motion are integrated explicitly and the asymptotic behavior of the system
is determined. It is shown how the presence of the fluid brings new features to
such a behavior.Comment: 20 pages, 7 figure
Does the Sun Shine by pp or CNO Fusion Reactions?
We show that solar neutrino experiments set an upper limit of 7.8% (7.3%
including the recent KamLAND measurements) to the fraction of energy that the
Sun produces via the CNO fusion cycle, which is an order of magnitude
improvement upon the previous limit. New experiments are required to detect CNO
neutrinos corresponding to the 1.5% of the solar luminosity that the standard
solar model predicts is generated by the CNO cycle.Comment: Background information at http://www.sns.ias.edu/~jn
The State of the Circumstellar Medium Surrounding Gamma-Ray Burst Sources and its Effect on the Afterglow Appearance
We present a numerical investigation of the contribution of the presupernova
ejecta of Wolf-Rayet stars to the environment surrounding gamma-ray bursts
(GRBs), and describe how this external matter can affect the observable
afterglow characteristics. An implicit hydrodynamic calculation for massive
stellar evolution is used here to provide the inner boundary conditions for an
explicit hydrodynamical code to model the circumstellar gas dynamics. The
resulting properties of the circumstellar medium are then used to calculate the
deceleration of a relativistic, gas-dynamic jet and the corresponding afterglow
light curve produced as the shock wave propagates through the shocked-wind
medium. We find that variations in the stellar wind drive instabilities that
may produce radial filaments in the shocked-wind region. These comet-like tails
of clumps could give rise to strong temporal variations in the early afterglow
lightcurve. Afterglows may be expected to differ widely among themselves,
depending on the angular anisotropy of the jet and the properties of the
stellar progenitor; a wide diversity of behaviors may be the rule, rather than
the exception.Comment: 17 pages, 7 figures, ApJ in pres
On the Interpretation of the Atmospheric Neutrino Data in Terms of Flavor Changing Neutrino Interactions
Flavour changing (FC) neutrino-matter interactions have been proposed as a
solution to the atmospheric neutrino anomaly. Here we perform the analysis of
the full set of the recent 52 kTy Super-Kamiokande atmospheric neutrino data,
including the zenith angle distribution of the contained events as well as the
higher energy upward-going stopping and through-going muon events. Our results
show that the FC mechanism can describe the full data sample with a
chi^2_{min}=44/(33 d.o.f) which is acceptable at the 90% confidence level. The
combined analysis confines the amount of FC to be either close to maximal or to
the level of about (10-50)%.Comment: 15 pages, 4 Postscript figures, uses ReVTeX. Updated analysis to 52
kTy Super-Kamiokande data. A new figure for the up-down asymmetry is
included. Some comments and references are adde
Solar Neutrinos Before and After Neutrino 2004
We compare, using a three neutrino analysis, the allowed neutrino oscillation
parameters and solar neutrino fluxes determined by the experimental data
available Before and After Neutrino 2004. New data available after Neutrino2004
include refined KamLAND and gallium measurements. We use six different
approaches to analyzing the KamLAND data. We present detailed results using all
the available neutrino and anti-neutrino data for Delta m^2_{12}, tan^2
theta_{12}, sin^2 theta_{13}, and sin^2 eta (sterile fraction). Using the same
complete data sets, we also present Before and After determinations of all the
solar neutrino fluxes, which are treated as free parameters, an upper limit to
the luminosity fraction associated with CNO neutrinos, and the predicted rate
for a 7Be solar neutrino experiment. The 1 sigma (3 sigma) allowed range of
Delta m^2_{21} = (8.2 +- 0.3) (^+1.0_-0.8)times 10^{-5} eV^2 is decreased by a
factor of 1.7 (5), but the allowed ranges of all other neutrino oscillation
parameters and neutrino fluxes are not significantly changed. Maximal mixing is
disfavored at 5.8 sigma and the bound on the mixing angle theta_{13} is
slightly improved to sin^2 theta_{13}<0.048 at 3 sigma. The predicted rate in a
7Be neutrino-electron scattering experiment is (0.665 +-0.015) of the rate
implied by the BP04 solar model in the absence of neutrino oscillations. The
corresponding predictions for p-p and pep experiments are, respectively, 0.707
{+0.011}{-0.013} and 0.644 {+0.011}{-0.013}. We derive upper limits to CPT
violation in the weak sector by comparing reactor anti-neutrino oscillation
parameters with neutrino oscillation parameters. We also show that the recent
data disfavor at 91 % CL a proposed non-standard interaction description of
solar neutrino oscillations.Comment: Added predictions for p-p and pep neutrino-electron scattering rate;
publishe
Global Analysis of Solar Neutrino Oscillations Including SNO CC Measurement
For active and sterile neutrinos, we present the globally allowed solutions
for two neutrino oscillations. We include the SNO CC measurement and all other
relevant solar neutrino and reactor data. Five active neutrino oscillation
solutions (LMA, LOW, SMA, VAC, and Just So2) are currently allowed at 3 sigma;
three sterile neutrino solutions (Just So2, SMA, and VAC) are allowed at 3
sigma. The goodness of fit is satisfactory for all eight solutions. We also
investigate the robustness of the allowed solutions by carrying out global
analyses with and without: 1) imposing solar model constraints on the 8B
neutrino flux, 2) including the Super-Kamiokande spectral energy distribution
and day-night data, 3) including a continuous mixture of active and sterile
neutrinos, 4) using an enhanced CC cross section for deuterium (due to
radiative corrections), and 5) a optimistic, hypothetical reduction by a factor
of three of the error of the SNO CC rate. For every analysis strategy used in
this paper, the most favored solutions all involve large mixing angles: LMA,
LOW, or VAC. The favored solutions are robust, but the presence at 3 sigma of
individual sterile solutions and the active Just So2 solution is sensitive to
the analysis assumptions.Comment: 9 figures, higher resolution versions at http://www.sns.ias.edu/~jnb,
added references and clarification
An outburst scenario for the X-ray spectral variability in 3C 111
We present a combined Suzaku and Swift BAT broad-band E=0.6-200keV spectral
analysis of three 3C 111 observations obtained in 2010. The data are well
described with an absorbed power-law continuum and a weak (R~0.2) cold
reflection component from distant material. We constrain the continuum cutoff
at E_c~150-200keV, which is in accordance with X-ray Comptonization corona
models and supports claims that the jet emission is only dominant at much
higher energies. Fe XXVI Ly\alpha emission and absorption lines are also
present in the first and second observations, respectively. The modelling and
interpretation of the emission line is complex and we explore three
possibilities. If originating from ionized disc reflection, this should be
emitted at r_in> 50r_g or, in the lamp-post configuration, the illuminating
source should be at a height of h> 30r_g over the black hole. Alternatively,
the line could be modeled with a hot collisionally ionized plasma with
temperature kT = 22.0^{+6.1}_{-3.2} keV or a photo-ionized plasma with
log\xi=4.52^{+0.10}_{-0.16} erg s^{-1} cm and column density N_H > 3x10^23
cm^{-2}. However, the first and second scenarios are less favored on
statistical and physical grounds, respectively. The blue-shifted absorption
line in the second observation can be modelled as an ultra-fast outflow (UFO)
with ionization parameter log\xi=4.47^{+0.76}_{-0.04} erg s^{-1} cm, column
density N_H=(5.3^{+1.8}_{-1.3})x 10^{22} cm^{-2} and outflow velocity v_out =
0.104+/-0.006 c. Interestingly, the parameters of the photo-ionized emission
model remarkably match those of the absorbing UFO. We suggest an outburst
scenario in which an accretion disc wind, initially lying out of the line of
sight and observed in emission, then crosses our view to the source and it is
observed in absorption as a mildly-relativistic UFO.Comment: Accepted for publication in MNARS on July 1st 201
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