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, $\Lambda_q$, and one for gluons, $\Lambda_g$. 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 $\Lambda_q$ and $\Lambda_g$, 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 $\rho_f$ 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