101,887 research outputs found
A General Effective Theory for Dense Quark Matter
A general effective action for quark matter at nonzero temperature and/or
nonzero density is derived. Irrelevant quark modes are distinguished from
relevant quark modes, and hard from soft gluon modes, by introducing two
separate cut-offs in momentum space, one for quarks, , and one for
gluons, . Irrelevant quark modes and hard gluon modes are then
exactly integrated out in the functional integral representation of the QCD
partition function. Depending on the specific choice for and
, the resulting effective action contains well-known effective
actions for hot and/or dense quark matter, for instance the ``Hard Thermal
Loop'' (HTL) or the ``Hard Dense Loop'' (HDL) action, as well as the
high-density effective theory proposed by Hong and others.Comment: 10 pages, 6 figures, contribution to proceedings of SEWM 200
Excitation Energy as a Basic Variable to Control Nuclear Disassembly
Thermodynamical features of Xe system is investigated as functions of
temperature and freeze-out density in the frame of lattice gas model. The
calculation shows different temperature dependence of physical observables at
different freeze-out density. In this case, the critical temperature when the
phase transition takes place depends on the freeze-out density. However, a
unique critical excitation energy reveals regardless of freeze-out density when
the excitation energy is used as a variable insteading of temperature.
Moreover, the different behavior of other physical observables with temperature
due to different vanishes when excitation energy replaces temperature.
It indicates that the excitation energy can be seen as a more basic quantity to
control nuclear disassembly.Comment: 3 pages, 2 figures, Revte
Conduction mechanisms of epitaxial EuTiO3 thin films
To investigate leakage current density versus electric field characteristics,
epitaxial EuTiO3 thin films were deposited on (001) SrTiO3 substrates by pulsed
laser deposition and were post-annealed in a reducing atmosphere. This
investigation found that conduction mechanisms are strongly related to
temperature and voltage polarity. It was determined that from 50 to 150 K the
dominant conduction mechanism was a space-charge-limited current under both
negative and positive biases. From 200 to 300 K, the conduction mechanism shows
Schottky emission and Fowler-Nordheim tunneling behaviors for the negative and
positive biases, respectively. This work demonstrates that Eu3+ is one source
of leakage current in EuTiO3 thin films.Comment: 17 pages,4 figures, conferenc
Sub-Dominant Pairing Channels in Unconventional Superconductors: Ginzburg-Landau Theory
A Ginzburg-Landau theory is developed for unconventional superconductors with
the three relevant singlet pairing channels. Various consequences of the
sub-dominant channels (i.e., s- and d_{xy}-channels) are examined in detail.
(1) In the case of a d_{x^2-y^2}+is-wave superconductor, The structure of a
single vortex above and below T_{DS} is four-fold and two-fold symmetric,
respectively. (2) In the case of a d_{x^2-y^2}+id_{xy}-wave superconductor,
there is also a second order zero-field phase transition from the pure
d_{x^2-y^2}-phase to the Time-reversal-symmetry-breaking
d_{x^2-y^2}+id_{xy}-wave phase at the temperature T_{DD'}. But the subdominant
phase can (not) be induced by vortices above T_{DD'}. Below the time-reversal-
symmetry-breaking transition, the sub-dominant phase in the mixed state is
nontrivial: it survives at low fields, but may disappear above a field
(increasing with decreasing temperature) presumably via a first-order
transition. (3)By including the strong coupling effects, a
time-reversal-symmetry -breaking coupling term between the d_{x^2-y^2}- and
d_{xy}-waves is found to have significant effects on the low temperature
behavior of d_{x^2-y^2}+id_{xy} superconductors. In a magnetic field, a
d_{x^2-y^2}+id_{xy} state is always established, but the field-dependence of
d_{xy}-amplitude above T_{DD'} is different from that below T_{DD'}. Above but
not very close to T_{DD'}, the induced minimum gap Delta_0 proportional to
B/(T-T_{DD'}).Comment: updated, 7 two-column pages with one embedded figure, one formula
corrected, to appear in Phys. Rev. B 6
Detection of an X-ray Pulsar Wind Nebula and Tail in SNR N157B
We report Chandra X-ray observations of the supernova remnant N157B in the
Large Magellanic Cloud, which are presented together with an archival HST
optical image and a radio continuum map for comparison. This remnant contains
the recently discovered 16 ms X-ray pulsar PSR J0537-6910, the most rapidly
rotating young pulsar known.
Using phase-resolved Chandra imaging, we pinpoint the location of the pulsar
to within an uncertainty of less than 1 arcsec. PSR J0537-6910 is not detected
in any other wavelength band. The X-ray observations resolve three distinct
features: the pulsar itself, a surrounding compact wind nebula which is
strongly elongated and a feature of large-scale diffuse emission trailing from
the pulsar. This latter comet tail-shaped feature coexists with enhanced radio
emission and is oriented nearly perpendicular to the major axis of the pulsar
wind nebula. We propose the following scenario to explain these features. The
bright, compact nebula is likely powered by a toroidal pulsar wind of
relativistic particles which is partially confined by the ram-pressure from the
supersonic motion of the pulsar. The particles, after being forced out from the
compact nebula (the head of the ``comet''), are eventually dumped into a bubble
(the tail), which is primarily responsible for the extended diffuse X-ray and
radio emission. The ram-pressure confinement also allows a natural explanation
for the observed X-ray luminosity of the compact nebula and for the unusually
small X-ray to spin-down luminosity ratio, compared to similarly energetic
pulsars. We estimate the pulsar wind Lorentz factor of N157B as about 4 times
10^6 (with an uncertainty of a factor about 2, consistent with that inferred
from the modeling of the Crab Nebula.Comment: 15 pages plus 4 figures. The postscript file of the whole paper is
available at http://xray.astro.umass.edu/wqd/papers/n157b/n157b.ps. accepted
for publication in Ap
- …