9 research outputs found
String dynamics and ejection along the axis of a spinning black hole
Relativistic current carrying strings moving axisymmetrically on the
background of a Kerr black hole are studied. The boundaries and possible types
of motion of a string with a given energy and current are found. Regions of
parameters for which the string falls into the black hole, or is trapped in a
toroidal volume, or can escape to infinity, are identified, and representative
trajectories are examined by numerical integration, illustrating various
interesting behaviors. In particular, we find that a string can start out at
rest near the equatorial plane and, after bouncing around, be ejected out along
the axis, some of its internal (elastic or rotational kinetic) energy having
been transformed into translational kinetic energy. The resulting velocity can
be an order unity fraction of the speed of light. This process results from the
presence of an outer tension barrier and an inner angular momentum barrier that
are deformed by the gravitational field. We speculatively discuss the possible
astrophysical significance of this mechanism as a means of launching a
collimated jet of MHD plasma flux tubes along the spin axis of a gravitating
system fed by an accretion disk.Comment: 14 pages, 11 figures; v.2: minor edits, references added, typos
corrected, published versio
Bounds on Cosmic Strings from WMAP and SDSS
We find the constraints from WMAP and SDSS data on the fraction of
cosmological fluctuations sourced by local cosmic strings using a Markov Chain
Monte Carlo (MCMC) analysis. In addition to varying the usual 6 cosmological
parameters and the string tension (), we also varied the amount of
small-scale structure on the strings. Our results indicate that cosmic strings
can account for up to 7 (14)% of the total power of the microwave anisotropy at
68 (95)% confidence level. The corresponding bound on the string mass per unit
length, within our string model, is at 68
(95)% c.l., where this constraint has been altered from what appears below
following the correction of errors in our cosmic string code outlined in a
recent erratum, astro-ph/0604141. We also calculate the B-type polarization
spectra sourced by cosmic strings and discuss the prospects of their detection.Comment: 11 pages, 7 figures. A few errors in the computer code used to
calculated CMB anistotropy from strings are fixed, resulting in a somewhat
tighter bound on G\mu and an enhanced B-mode polarization. Details of the
corrected errors and their implications can be found in astro-ph/0604141. Go
to http://physics.syr.edu/~lepogosi/cmbact.html for our now-corrected cosmic
string CMB and LSS cod
Signal of the pion string at high-energy collisions
We study the possible signals of a pion string associated with the QCD chiral
phase transition in LHC Pb - Pb collision at energy TeV. In
terms of the Kibble-Zurek mechanism we discuss the production and evolution of
the pion string. The pion string is not topologically stable, it decays into
neutral pions and sigma mesons which in turn decay into pions. Our results show
that all the neutral pions from the pion string are distributed at the low
momentum and the ratio of neutral to charged pions from the pion string
violates the isospin symmetry. For the momentum spectra of the total pions, the
signal from the sigma particle decay which is from the pion string will be
affected by the large decay width of the sigma significantly.Comment: 8 pages, 3 figures, one reference added, title changed, version
accepted for publication in Phys. Rev.