8,206 research outputs found
How to identify a Strange Star
Contrary to young neutron stars, young strange stars are not subject to the
r-mode instability which slows rapidly rotating, hot neutron stars to rotation
periods near 10 ms via gravitational wave emission. Young millisecond pulsars
are therefore likely to be strange stars rather than neutron stars, or at least
to contain significant quantities of quark matter in the interior.Comment: 4 pages, 1 figur
Strong Orientation Effects in Ionization of H by Short, Intense, High-Frequency Light Sources
We present three dimensional time-dependent calculations of ionization of
arbitrarily spatially oriented H by attosecond, intense, high-frequency
laser fields. The ionization probability shows a strong dependence on both the
internuclear distance and the relative orientation between the laser field and
the internuclear axis.Comment: 4 pages, 4 figure
Ionization of oriented targets by intense circularly polarized laser pulses: Imprints of orbital angular nodes in the 2D momentum distribution
We solve the three-dimensional time-dependent Schr\"{o}dinger equation for a
few-cycle circularly polarized femtosecond laser pulse interacting with an
oriented target exemplified by an Argon atom, initially in a or
state. The photoelectron momentum distributions show distinct
signatures of the orbital structure of the initial state as well as the
carrier-envelope phase of the applied pulse. Our \textit{ab initio} results are
compared with results obtained using the length-gauge strong-field
approximation, which allows for a clear interpretation of the results in terms
of classical physics. Furthermore, we show that ionization by a circularly
polarized pulse completely maps out the angular nodal structure of the initial
state, thus providing a potential tool for studying orbital symmetry in
individual systems or during chemical reactions
Control and femtosecond time-resolved imaging of torsion in a chiral molecule
We study how the combination of long and short laser pulses, can be used to
induce torsion in an axially chiral biphenyl derivative
(3,5-difluoro-3',5'-dibromo-4'-cyanobiphenyl). A long, with respect to the
molecular rotational periods, elliptically polarized laser pulse produces 3D
alignment of the molecules, and a linearly polarized short pulse initiates
torsion about the stereogenic axis. The torsional motion is monitored in
real-time by measuring the dihedral angle using femtosecond time-resolved
Coulomb explosion imaging. Within the first 4 picoseconds, torsion occurs with
a period of 1.25 picoseconds and an amplitude of 3 degrees in excellent
agreement with theoretical calculations. At larger times the quantum states of
the molecules describing the torsional motion dephase and an almost isotropic
distribution of the dihedral angle is measured. We demonstrate an original
application of covariance analysis of two-dimensional ion images to reveal
strong correlations between specific ejected ionic fragments from Coulomb
explosion. This technique strengthens our interpretation of the experimental
data.Comment: 11 pages, 9 figure
Second-order rotational effects on the r-modes of neutron stars
Techniques are developed here for evaluating the r-modes of rotating neutron
stars through second order in the angular velocity of the star. Second-order
corrections to the frequencies and eigenfunctions for these modes are evaluated
for neutron star models. The second-order eigenfunctions for these modes are
determined here by solving an unusual inhomogeneous hyperbolic boundary-value
problem. The numerical techniques developed to solve this unusual problem are
somewhat non-standard and may well be of interest beyond the particular
application here. The bulk-viscosity coupling to the r-modes, which appears
first at second order, is evaluated. The bulk-viscosity timescales are found
here to be longer than previous estimates for normal neutron stars, but shorter
than previous estimates for strange stars. These new timescales do not
substantially affect the current picture of the gravitational radiation driven
instability of the r-modes either for neutron stars or for strange stars.Comment: 13 pages, 5 figures, revte
WHAM Observations of H-alpha from High-Velocity Clouds: Are They Galactic or Extragalactic?
It has been suggested that high velocity clouds may be distributed throughout
the Local Group and are therefore not in general associated with the Milky Way
galaxy. With the aim of testing this hypothesis, we have made observations in
the H-alpha line of high velocity clouds selected as the most likely candidates
for being at larger than average distances. We have found H-alpha emission from
4 out of 5 of the observed clouds, suggesting that the clouds under study are
being illuminated by a Lyman continuum flux greater than that of the
metagalactic ionizing radiation. Therefore, it appears likely that these clouds
are in the Galactic halo and not distributed throughout the Local Group.Comment: 12 pages, 5 eps figures, accepted for publication in ApJ Letter
Physics and Astrophysics of Strange Quark Matter
3-flavor quark matter (strange quark matter; SQM) can be stable or metastable
for a wide range of strong interaction parameters. If so, SQM can play an
important role in cosmology, neutron stars, cosmic ray physics, and
relativistic heavy-ion collisions. As an example of the intimate connections
between astrophysics and heavy-ion collision physics, this Chapter gives an
overview of the physical properties of SQM in bulk and of small-baryon number
strangelets; discusses the possible formation, destruction, and implications of
lumps of SQM (quark nuggets) in the early Universe; and describes the structure
and signature of strange stars, as well as formation and detection of
strangelets in cosmic rays. It is concluded, that astrophysical and laboratory
searches are complementary in many respects, and that both should be pursued to
test the intriguing possibility of a strange ground state for hadronic matter,
and (more generally) to improve our knowledge of the strong interactions.Comment: 45 pages incl. figures. To appear in "Hadrons in Dense Matter and
Hadrosynthesis", Lecture Notes in Physics, Springer Verlag (ed. J.Cleymans
Probabilistic state preparation of a single molecular ion by projection measurement
We show how to prepare a single molecular ion in a specific internal quantum
state in a situation where the molecule is trapped and sympathetically cooled
by an atomic ion and where its internal degrees of freedom are initially in
thermal equilibrium with the surroundings. The scheme is based on conditional
creation of correlation between the internal state of the molecule and the
translational state of the collective motion of the two ions, followed by a
projection measurement of this collective mode by atomic ion shelving
techniques. State preparation in a large number of internal states is possible.Comment: 4 pages, 2 figures, 2 table
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
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