54,486 research outputs found
Lamellar phase separation and dynamic competition in La0.23Ca0.77MnO3
We report the coexistence of lamellar charge-ordered (CO) and
charge-disordered (CD) domains, and their dynamical behavior, in
La0.23Ca0.77MnO3. Using high resolution transmission electron microscopy (TEM),
we show that below Tcd~170K a CD-monoclinic phase forms within the established
CO-orthorhombic matrix. The CD phase has a sheet-like morphology, perpendicular
to the q vector of the CO superlattice (a axis of the Pnma structure). For
temperatures between 64K and 130K, both the TEM and resistivity experiments
show a dynamic competition between the two phases: at constant T, the CD phase
slowly advances over the CO one. This slow dynamics appears to be linked to the
magnetic transitions occurring in this compound, suggesting important
magnetoelastic effects.Comment: 4 pages, 4 figure
Thermodynamics of lattice QCD with 2 flavours of colour-sextet quarks: A model of walking/conformal Technicolor
QCD with two flavours of massless colour-sextet quarks is considered as a
model for conformal/walking Technicolor. If this theory possess an infrared
fixed point, as indicated by 2-loop perturbation theory, it is a
conformal(unparticle) field theory. If, on the other hand, a chiral condensate
forms on the weak-coupling side of this would-be fixed point, the theory
remains confining. The only difference between such a theory and regular QCD is
that there is a range of momentum scales over which the coupling constant runs
very slowly (walks). In this first analysis, we simulate the lattice version of
QCD with two flavours of staggered quarks at finite temperatures on lattices of
temporal extent and 6. The deconfinement and chiral-symmetry
restoration couplings give us a measure of the scales associated with
confinement and chiral-symmetry breaking. We find that, in contrast to what is
seen with fundamental quarks, these transition couplings are very different.
for each of these transitions increases significantly from
and as expected for the finite temperature transitions of an
asymptotically-free theory. This suggests a walking rather than a conformal
behaviour, in contrast to what is observed with Wilson quarks. In contrast to
what is found for fundamental quarks, the deconfined phase exhibits states in
which the Polyakov loop is oriented in the directions of all three cube roots
of unity. At very weak coupling the states with complex Polyakov loops undergo
a transition to a state with a real, negative Polyakov loop.Comment: 21 pages, 9 figures, Revtex with postscript figures. One extra
reference was added; text is unchanged. Corrected typographical erro
Nucleon Sigma Term and In-medium Quark Condensate in the Modified Quark-Meson Coupling Model
We evaluate the nucleon sigma term and in-medium quark condensate in the
modified quark-meson coupling model which features a density-dependent bag
constant. We obtain a nucleon sigma term consistent with its empirical value,
which requires a significant reduction of the bag constant in the nuclear
medium similar to those found in the previous works. The resulting in-medium
quark condensate at low densities agrees well with the model independent linear
order result. At higher densities, the magnitude of the in-medium quark
condensate tends to increase, indicating no tendency toward chiral symmetry
restoration.Comment: 9 pages, modified version to be publishe
SUSY Dark Matter In Light Of CDMS/XENON Limits
In this talk we briefly review the current CDMS/XENON constraints on the
neutralino dark matter in three popular supersymmetric models: the minimal
(MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). The
constraints from the dark matter relic density and various collider experiments
are also taken into account. The conclusion is that for each model the current
CDMS/XENON limits can readily exclude a large part of the parameter space
allowed by other constraints and the future SuperCDMS or XENON100 can cover
most of the allowed parameter space. The implication for the Higgs search at
the LHC is also discussed. It is found that in the currently allowed parameter
space the MSSM charged Higgs boson is quite unlikely to be discovered at the
LHC while the neutral Higgs bosons and may be accessible at the LHC in
the parameter space with a large parameter.Comment: talk given at 2nd International Workshop on Dark Matter, Dark Energy
and Matter-Antimatter Asymmetry, Nov 5-6, 2010, Hsinchu, Taiwan (to appear in
Int. J. Mod. Phys. D
Measurement of the interaction strength in a Bose-Fermi mixture with 87Rb and 40K
A quantum degenerate, dilute gas mixture of bosonic and fermionic atoms was
produced using 87Rb and 40K. The onset of degeneracy was confirmed by observing
the spatial distribution of the gases after time-of-flight expansion. Further,
the magnitude of the interspecies scattering length between the doubly spin
polarized states of 87Rb and 40K, |a_RbK|, was determined from
cross-dimensional thermal relaxation. The uncertainty in this collision
measurement was greatly reduced by taking the ratio of interspecies and
intraspecies relaxation rates, yielding |a_RbK| = 250 +/- 30 a_0, which is a
lower value than what was reported in [M. Modugno et al., Phys. Rev. A 68,
043626 (2003)]. Using the value for |a_RbK| reported here, current T=0 theory
would predict a threshold for mechanical instability that is inconsistent with
the experimentally observed onset for sudden loss of fermions in [G. Modugno et
al., Science 297, 2240 (2002)].Comment: RevTeX4 + 4 eps figures; Replaced with published versio
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