1,374 research outputs found
Role of the Coulomb interaction in the flow and the azimuthal distribution of kaons from heavy ion reactions
Coulomb final-state interaction of positive charged kaons in heavy ion
reactions and its impact on the kaon transverse flow and the kaon azimuthal
distribution are investigated within the framework of QMD (Quantum Molecular
Dynamics) model. The Coulomb interaction is found to tend to draw the flow of
kaons away from that of nucleons and lead to a more isotropic azimuthal
distribution of kaons in the target rapidity region. The recent FOPI data have
been analyzed by taking into accout both the Coulomb interaction and a kaon
in-medium potential of the strong interaction. It is found that both the
calculated kaon flows with only the Coulomb interaction and with both the
Coulomb interaction and the strong potential agree within the error bars with
the data. The kaon azimuthal distribution exhibits asymmetries of similar
magnitude in both theoretical approaches. This means, the inclusion of the
Coulomb potential makes it more difficult to extract information of the kaon
mean field potential in nuclear matter from the kaon flow and azimuthal
distribution data.Comment: 14 pages Latex, 4 PS-file
Liouville integrability of a class of integrable spin Calogero-Moser systems and exponents of simple Lie algebras
In previous work, we introduced a class of integrable spin Calogero-Moser
systems associated with the classical dynamical r-matrices with spectral
parameter, as classified by Etingof and Varchenko for simple Lie algebras. Here
the main purpose is to establish the Liouville integrability of these systems
by a uniform method
QCD Loop Corrections to Top Production and Decay at e^+ e^- Colliders
We present a computation of QCD next-to-leading order virtual corrections to
the top production and decay process at linear colliders. The top quarks are
allowed to be off-shell and the production and decay subprocesses are treated
together, thus allowing for interference effects. The framework employed for
our computation is the double pole approximation (DPA). We describe the
implementation of this approximation for the top production and decay process
and compare it with the implementation of DPA for the evaluation of QED
corrections to the W pair production at LEP II. Similarities and differences
between the two cases are pointed out. One result of interest is the incomplete
cancelation of interference corrections. Other results include values for the
total NLO top production cross section, and the impact the nonfactorizable
(interference) corrections have on the top invariant mass distribution.Comment: 27 pages, 8 ps figures; reference added to introductio
Scaling of Aharonov-Bohm couplings and the dynamical vacuum in gauge theories
Recent results on the vacuum polarization induced by a thin string of
magnetic flux lead us to suggest an analogue of the Copenhagen `flux spaghetti'
QCD vacuum as a possible mechanism for avoiding the divergence of perturbative
QED, thus permitting consistent completion of the full, nonperturbative theory.
The mechanism appears to operate for spinor, but not scalar, QED.Comment: 11 pages, ITP-SB-92-40, (major conceptual evolution from original
Non-existence of stationary two-black-hole configurations: The degenerate case
In a preceding paper we examined the question whether the spin-spin repulsion
and the gravitational attraction of two aligned sub-extremal black holes can
balance each other. Based on the solution of a boundary value problem for two
separate (Killing-) horizons and a novel black hole criterion we were able to
prove the non-existence of the equilibrium configuration in question. In this
paper we extend the non-existence proof to extremal black holes.Comment: 18 pages, 2 figure
Charge-conjugation violating neutrino interactions in supernovae
The well known charge conjugation violating interactions in the Standard
Model increase neutrino- and decrease anti-neutrino- nucleon cross sections.
This impacts neutrino transport in core collapse supernovae through "recoil"
corrections of order the neutrino energy over the nucleon mass . All
corrections to neutrino transport deep inside a protoneutron star are
calculated from angular integrals of the Boltzmann equation. We find these
corrections significantly modify neutrino currents at high temperatures. This
produces a large mu and tau number for the protoneutron star and can change the
ratio of neutrons to protons. In addition, the relative size of neutrino mean
free paths changes. At high temperatures, the electron anti-neutrino mean free
path becomes {\it longer} than that for mu or tau neutrinos.Comment: 14 pages, 2 included ps figures, subm. to Phys. Rev.
Localized Random Lasing Modes and a New Path for Observing Localization
We demonstrate that a knowledge of the density-of-states and the eigenstates
of a random system without gain, in conjunction with the frequency profile of
the gain, can accurately predict the mode that will lase first. Its critical
pumping rate can be also obtained. It is found that the shape of the
wavefunction of the random system remains unchanged as gain is introduced.
These results were obtained by the time-independent transfer matrix method and
finite-difference-time-domain (FDTD) methods. They can be also analytically
understood by generalizing the semi-classical Lamb theory of lasing in random
systems. These findings provide a new path for observing the localization of
light, such as looking for mobility edge and studying the localized states.
%inside the random systems..Comment: Sent to PRL. 3 figure
ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions
We investigate ac Josephson effect in the resonant tunneling through
mesoscopic superconducting junctions. In the presence of microwave irradiation,
we show that the trajectory of multiple Andreev reflections can be closed by
emitting or absorbing photons. Consequently, photon-assisted Andreev states are
formed and play the role of carrying supercurrent. On the Shapiro steps, dc
component appears when the resonant level is near a series of positions with
spacing of half of the microwave frequency. Analytical result is derived in the
limit of infinite superconducting gap, based on which new features of ac
Josephson effect are revealed.Comment: 11 pages, 3 figure
Solution of the Fan Diagram Equation in 2+1 Dimensional QCD
We investigate the Balitsky-Kovchegov (BK) equation for D=3 space-time
dimensions, corresponding to one transverse coordinate, and we show that it can
be solved analytically. The explicit solutions are found in the linear
approximation and for the paricular cases when they do not depend on the impact
parameter of the dipole or on its rapidity. It is shown, that in a general case
different solutions are related by an infinite parameter group of
transformations. The key observation is that the equation has the
Kowalewskaya-Painlev\'{e} property, which gives the possibility of reducing the
non-linear problem to the solution of a linear integral equation.Comment: 23 page
Exotic smooth structures on 4-manifolds with zero signature
For every integer , we construct infinite families of mutually
nondiffeomorphic irreducible smooth structures on the topological -manifolds
and (2k-1)(\CP#\CPb), the connected sums of
copies of and \CP#\CPb.Comment: 6 page
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