72 research outputs found
Two-dimensional tetramer-cuprate Na5RbCu4(AsO4)4Cl2: phase transitions and AFMorder as seen by 87Rb NMR
We report the Rb nuclear magnetic resonance (NMR) results in a recently
synthesized Na5RbCu4(AsO4)Cl2. This complex novel two-dimensional (2D) cuprate
is an unique magnetic material, which contains layers of coupled Cu4O4
tetramers. In zero applied magnetic field, it orders antiferromagnetically via
a second-order low-entropy phase transition at TN = 15(1) K. We characterise
the ordered state by 87Rb NMR, and suggest for it a noncollinear rather than
collinear arrangement of spins. We discuss the properties of Rb nuclear site
and point out the new structural phase transition(s) around 74 K and 110 K.Comment: 2 pages, 2 figures, Proceedings of SCES'05, Vienna 200
RADTHYR: an open-label, single-arm, prospective multicenter phase II trial of Radium-223 for the treatment of bone metastases from radioactive iodine refractory differentiated thyroid cancer
Debye screening and Meissner effect in a two-flavor color superconductor
I compute the gluon self-energy in a color superconductor with two flavors of
massless quarks, where condensation of Cooper pairs breaks SU(3)_c to SU(2)_c.
At zero temperature, there is neither Debye screening nor a Meissner effect for
the three gluons of the unbroken SU(2)_c subgroup. The remaining five gluons
attain an electric as well as a magnetic mass. For temperatures approaching the
critical temperature for the onset of color superconductivity, or for gluon
momenta much larger than the color-superconducting gap, the self-energy assumes
the form given by the standard hard-dense loop approximation. The gluon
self-energy determines the coefficient of the kinetic term in the effective
low-energy theory for the condensate fields.Comment: 29 pages, RevTe
Chemical equilibration and thermal dilepton production from the quark gluon plasma at finite baryon density
The chemical equilibration of a highly unsaturated quark-gluon plasma has
been studied at finite baryon density. It is found that in the presence of
small amount of baryon density, the chemical equilibration for gluon becomes
slower and the temperature decreases less steeply as compared to the baryon
free plasma. As a result, the space time integrated yield of dilepton is
enhanced if the initial temperature of the plasma is held fixed. Even at a
fixed initial energy density, the suppression of the dilepton yields at higher
baryo-chemical potential is compensated, to a large extent, by the slow cooling
of the plasma.Comment: Latex, 19 pages, 8 postscript figures. To appear in Phys. Rev.
A first order transition and parity violation in a color superconductor
In cold, dense quark matter, quarks of different flavor can form Cooper pairs
which are anti-triplets under color and have total spin J=0. The transition to
a phase where strange quarks condense with either up or down quarks is driven
first order by the Coleman-Weinberg mechanism. At densities sufficiently high
to (effectively) restore the axial U(1) symmetry, then relative to the ordinary
vacuum, the condensation of up with down quarks (effectively) breaks parity
spontaneously.Comment: 4 pages, ReVTeX, final versio
Gluon self-energy in a two-flavor color superconductor
The energy and momentum dependence of the gluon self-energy is investigated
in a color superconductor with two flavors of massless quarks. The presence of
a color-superconducting quark-quark condensate modifies the gluon self-energy
for energies which are of the order of the gap parameter. For gluon energies
much larger than the gap, the self-energy assumes the form given by the
standard hard-dense loop approximation. It is shown that this modification of
the gluon self-energy does not affect the magnitude of the gap to leading and
subleading order in the weak-coupling limit.Comment: 21 pages, 6 figures, RevTeX, aps and epsfig style files require
Two lectures on color superconductivity
The first lecture provides an introduction to the physics of color
superconductivity in cold dense quark matter. The main color superconducting
phases are briefly described and their properties are listed. The second
lecture covers recent developments in studies of color superconducting phases
in neutral and beta-equilibrated matter. The properties of gapless color
superconducting phases are discussed.Comment: 56 pages, 9 figures. Minor corrections and references added. Lectures
delivered at the IARD 2004 conference, Saas Fee, Switzerland, June 12 - 19,
2004, and at the Helmholtz International Summer School and Workshop on Hot
points in Astrophysics and Cosmology, JINR, Dubna, Russia, August 2 - 13,
200
Color superconductivity in weak coupling
We derive perturbatively the gap equations for a color-superconducting
condensate with total spin J=0 in dense QCD. At zero temperature, we confirm
the results of Son for the dependence of the condensate on the coupling
constant, and compute the prefactor to leading logarithmic accuracy. At nonzero
temperature, we find that to leading order in weak coupling, the temperature
dependence of the condensate is identical to that in BCS-like theories. The
condensates for total spin J=1 are classified; to leading logarithmic accuracy
these condensates are of the same order as those of spin J=0.Comment: 30 pages, 3 figures, RevTeX, epsf and psfig style files require
Effect of baryon density on parton production, chemical equilibration and thermal photon emission from quark gluon plasma
The effect of baryon density on parton production processes of
and is studied
using full phase space distribution function and also with inclusion of quantum
statistics i.e. Pauli blocking and Bose enhancement factors, in the case of
both saturated and unsaturated quark gluon plasma. The rate for the process is found to be much less as compared to the most
commonly used factorized result obtained on the basis of classical
approximation. This discrepancy, which is found both at zero as well as at
finite baryon densities, however, is not due to the lack of quantum statistics
in the classical approximation, rather due to the use of Fermi-Dirac and
Bose-Einstein distribution functions for partons instead of Boltzmann
distribution which is appropriate under such approximation. Interestingly, the
rates of parton production are found to be insensitive to the baryo-chemical
potential particularly when the plasma is unsaturated although the process of
chemical equilibration strongly depends on it. The thermal photon yields, have
been calculated specifically from unsaturated plasma at finite baryon density.
The exact results obtained numerically are found to be in close agreement with
the analytic expression derived using factorized distribution functions
appropriate for unsaturated plasma. Further, it is shown that in the case of
unsaturated plasma, the thermal photon production is enhanced with increasing
baryon density both at fixed temperature and fixed energy density of the quark
gluon plasma.Comment: Latex, 24 pages, 6 postscript figures. Submitted to Phys. Rev.
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