3,776 research outputs found
Neutron beta decay in effective field theory
Radiative corrections to the lifetime and angular correlation coefficients of
neutron beta-decay are evaluated in effecitive field theory. We also evaluate
the lowest order nucleon recoil corrections, including weak-magnetism. Our
results agree with those of the long-range and model-independent part of
previous calculations. In an effective theory the model-dependent radiative
corrections are replaced by well-defined low-energy constants. The effective
field theory allows a systematic evaluation of higher order corrections to our
results to the extent that the relevant low-energy constants are known.Comment: 13 pages, 1 figure; two references added, minor correctio
Chiral Perturbation Theory and Nucleon Polarizabilities
Compton scattering offers in principle an intriguing new window on nucleon
structure. Existing experiments and future programs are discussed and the state
of theoretical understanding of such measurements is explored.Comment: 15 page standard Latex file---invited talk at Chiral Dynamics
Workshop, Mainz, Germany---typos correcte
A Search for Early Optical Emission at Gamma-Ray Burst Locations by the Solar Mass Ejection Imager (SMEI)
The Solar Mass Ejection Imager (SMEI) views nearly every point on the sky
once every 102 minutes and can detect point sources as faint as R~10th
magnitude. Therefore, SMEI can detect or provide upper limits for the optical
afterglow from gamma-ray bursts in the tens of minutes after the burst when
different shocked regions may emit optically. Here we provide upper limits for
58 bursts between 2003 February and 2005 April.Comment: accepted for publication in ApJ, 17 pages, 8 figure
Outburst of Comet 17P/Holmes Observed With The Solar Mass Ejection Imager
We present time-resolved photometric observations of Jupiter family comet
17P/Holmes during its dramatic outburst of 2007. The observations, from the
orbiting Solar Mass Ejection Imager (SMEI), provide the most complete measure
of the whole-coma brightness, free from the effects of instrumental saturation
and with a time-resolution well-matched to the rapid brightening of the comet.
The lightcurve is divided into two distinct parts. A rapid rise between the
first SMEI observation on UT 2007 October 24 06h 37m (mid-integration) and UT
2007 October 25, is followed by a slow decline until the last SMEI observation
on UT 2008 April 6 22h 16m (mid-integration). We find that the rate of change
of the brightness is reasonably well-described by a Gaussian function having a
central time of UT 2007 October 24.54+/-0.01 and a full-width-at-half-maximum
0.44+/-0.02 days. The maximum rate of brightening occurs some 1.2 days after
the onset of activity. At the peak the scattering cross-section grows at
1070+/-40 km^2/s while the (model-dependent) mass loss rates inferred from the
lightcurve reach a maximum at 3+/-10^5 kg/s. The integrated mass in the coma
lies in the range (2 to 90)x10^10 kg, corresponding to 0.2% to 10% of the
nucleus mass, while the kinetic energy of the ejecta is (0.6 to 30) MTonnes
TNT. The particulate coma mass could be contained within a shell on the nucleus
of thickness ~1.5 to 60 m. This is comparable to the distance traveled by
conducted heat in the century since the previous outburst of 17P/Holmes. This
coincidence is consistent with, but does not prove, the idea that the outburst
was triggered by the action of conducted heat, possibly through the
crystallization of buried amorphous ice.Comment: 27 pages, 8 figures;
http://www2.ess.ucla.edu/~jingli/Holmes_SMEI/17P_Holmes.htm
Optical precursors in transparent media
We theoretically study the linear propagation of a stepwise pulse through a
dilute dispersive medium when the frequency of the optical carrier coincides
with the center of a natural or electromagnetically induced transparency window
of the medium (slow-light systems). We obtain fully analytical expressions of
the entirety of the step response and show that, for parameters representative
of real experiments, Sommerfeld-Brillouin precursors, main field and second
precursors "postcursors" can be distinctly observed, all with amplitudes
comparable to that of the incident step. This behavior strongly contrasts with
that of the systems generally considered up to now
Slim Epistemology with a Thick Skin
The distinction between âthickâ and âthinâ value concepts, and its importance to ethical theory, has been an active topic in recent meta-ethics. This paper defends three claims regarding the parallel issue about thick and thin epistemic concepts. (1) Analogy with ethics offers no straightforward way to establish a good, clear distinction between thick and thin epistemic concepts. (2) Assuming there is such a distinction, there are no semantic grounds for assigning thick epistemic concepts priority over the thin. (3) Nor does the structure of substantive epistemological theory establish that thick epistemic concepts enjoy systematic theoretical priority over the thin. In sum, a good case has yet to be made for any radical theoretical turn to thicker epistemology
Solar Polar Sail mission: report of a study to put a scientific spacecraft in a circular polar orbit about the sun
The Solar Polar Sail Mission uses solar-sail propulsion to place a spacecraft in a circular orbit 0.48 Au from the Sun with an inclination of 90 degrees. The spacecraft's orbit around the Sun is in 3:1 resonance with Earth phased such that the Earth-Sun-spacecraft angle range from 30 degrees to 150 degrees. The polar view will further our understanding of: (1) the global structure and evolution of the corona, (2) the initiation, evolution, and propagation of coronal mass ejections; (3) the acceleration of the solar wind; (4) the interactions of rotation, magnetic fields, and convection within the Sun; (5) the acceleration and propagation of energetic particles; and (6) the rate of angular momentum loss by the Sun. Candidate imaging instruments are a coronagraph, an all-sky imager for following mass ejections and interaction regions from the Sun to 1 AU, and a disk imager. A lightweight package of fields and particle instruments is included. A mission using a 158 m square sail with an effective areal density of 6 g/m^2 would cost approximately $250-300M (FY97) for all mission phases, including the launch vehicle. This mission depends on the successful development and demonstration of solar-sail propulsion
Equilibrium long-ranged charge correlations at the interface between media coupled to the electromagnetic radiation
We continue studying long-ranged quantum correlations of surface charge
densities on the interface between two media of distinct dielectric functions
which are in thermal equilibrium with the radiated electromagnetic field. Two
regimes are considered: the non-retarded one with the speed of light taken
to be infinitely large and the retarded one with finite value of . The
analysis is based on results obtained by using fluctuational electrodynamics in
[L. \v{S}amaj and B. Jancovici, Phys. Rev. E {\bf 78}, 051119 (2008)]. Using an
integration method in the complex plane and the general analytic properties of
dielectric functions in the frequency upper half-plane, we derive explicit
forms of prefactors to the long-range decay of the surface charge correlation
functions for all possible media (conductor, dielectric, vacuum)
configurations. The main result is that the time-dependent quantum prefactor in
the retarded regime takes its static classical form, for any temperature.Comment: 9 pages, 3 figure
Building light nuclei from neutrons, protons, and pions
In these lectures I first explain, in a rather basic fashion, the
construction of effective field theories. I then discuss some recent
developments in the application of such theories to two- and three-nucleon
systems.Comment: 54 pages, uses czjphys.cls. Lectures given at 14th Summer School
"Understanding the Structure of Hadrons", Prague, July 2001. To appear in
Czechoslovak Journal of Physic
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