55,732 research outputs found
Sustained Acceleration of Over-dense Plasmas by Colliding Laser Pulses
We review recent PIC simulation results which show that double-sided
irradiaton of a thin overdense plasma slab by ultra-intense laser pulses from
both sides can lead to sustained comoving acceleration of surface electrons to
energies much higher than the conventional ponderomotive limit. The
acceleration stops only when the electrons drift transversely out of the laser
beam. We show results of parameter studies based on this concept and discuss
future laser experiments that can be used to test these computer results.Comment: 9 pages 6 figures. AIP Conference Proceedings for 2005 Varenna Conf.
on Superstrong Fields in Plasmas (AIP, NY 2006
Emission model of gamma-ray bursts
The emission mechanisms of cosmic gamma-ray bursts are reviewed. In particular, the thermal synchrotron model is discussed as the most viable mechanism for the majority of the continuum emission. Within this framework various information about the source region can be extracted. The picture that emerges is that of a hot (kT = .2 - 1.0 sq mc), thin sheet of dense pair-dominated plasma emitting via cyclo-synchrotron radiation in a strong magnetic field (B approximately one-hundred billion to one trillion gauss). Speculations on the origin and structure of this sheet are attempted. The problem of high-energy photons above pair production threshold escaping from the source is also considered
Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons
We have addressed the study of non-leptonic weak decays of heavy hadrons
( and ), with external and internal emission to
give two final hadrons, taking into account the spin-angular momentum structure
of the mesons and baryons produced.
A detailed angular momentum formulation is developed which leads to easy
final formulas. By means of them we have made predictions for a large amount of
reactions, up to a global factor, common to many of them, that we take from
some particular data. Comparing the theoretical predictions with the
experimental data, the agreement found is quite good in general and the
discrepancies should give valuable information on intrinsic form factors,
independent of the spin structure studied here. The formulas obtained are also
useful in order to evaluate meson-meson or meson-baryon loops, for instance of
decays, in which one has PP, PV, VP or VV intermediate states, with P for
pseudoscalar mesons and V for vector meson and lay the grounds for studies of
decays into three final particles.Comment: 54 pages, 7 figures, 13 tables; v2: 60 pages, 9 figures, 14 tables,
discussion added, references added, version to appear in Eur.Phys.J.
Theoretical description of the , and reactions
We have made a study of the (with
being and ) and assuming
the axial vector mesons to be dynamically generated from the
pseudoscalar-vector meson interaction. We have taken the needed input from
previous studies of the reactions.
We obtain fair agreement with experimental data and provide an explanation on
why the recent experiment on observed in the mode observes the peak of the
at a higher energy than its nominal mass.Comment: 21 pages, 6 figure
Baryon states with hidden charm in the extended local hidden gauge approach
The s-wave interaction of and , is studied within a unitary coupled channels scheme
with the extended local hidden gauge approach. In addition to the
Weinberg-Tomozawa term, several additional diagrams via the pion-exchange are
also taken into account as box potentials. Furthermore, in order to implement
the full coupled channels calculation, some of the box potentials which mix the
vector-baryon and pseudoscalar-baryon sectors are extended to construct the
effective transition potentials. As a result, we have observed six possible
states in several angular momenta. Four of them correspond to two pairs of
admixture states, two of - with , and two of - with . Moreover, we find a resonance which couples to
the channel and one spin degenerated bound state of
with .Comment: 24 pages, 6 figure
Confronting Synchrotron Shock and Inverse Comptonization Models with GRB Spectral Evolution
The time-resolved spectra of gamma-ray bursts (GRBs) remain in conflict with
many proposed models for these events. After proving that most of the bursts in
our sample show evidence for spectral "shape-shifting", we discuss what
restrictions that BATSE time-resolved burst spectra place on current models. We
find that the synchrotron shock model does not allow for the steep low-energy
spectral slope observed in many bursts, including GRB 970111. We also determine
that saturated Comptonization with only Thomson thinning fails to explain the
observed rise and fall of the low-energy spectral slope seen in GRB 970111 and
other bursts. This implies that saturated Comptonization models must include
some mechanism which can cause the Thomson depth to increase intially in
pulses.Comment: (5 pages, 3 figures, to appear in Proceedings of the Fourth
Huntsville Symposium on Gamma-Ray Bursts
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