6,393 research outputs found
Event-plane dependent di-hadron correlations with harmonic subtraction in a hydrodynamic model
In this work, a hydrodynamic study of the di-hadron azimuthal correlations
for the Au+Au collisions at 200 GeV is carried out. The correlations are
evaluated using the ZYAM method for the centrality windows as well as the
transverse momentum range in accordance with the existing data. Event-plane
dependence of the correlation is obtained after the subtraction of
contributions from the most dominant harmonic coefficients. In particular, the
contribution from the triangular flow, , is removed from the proper
correlations following the procedure implemented by the STAR collaboration. The
resultant structure observed in the correlations was sometimes attributed to
the mini-jet dynamics, but the present calculations show that a pure
hydrodynamic model gives a reasonable agreement with the main feature of the
published data. A brief discussion on the physical content of the present
findings is presented.Comment: 9 pages, 2 figure
Time variation of proton-electron mass ratio and fine structure constant with runaway dilaton
Recent astrophysical observations indicate that the proton-electron mass
ratio and the fine structure constant have gone through nontrivial time
evolution. We discuss their time variation in the context of a dilaton runaway
scenario with gauge coupling unification at the string scale . We
show that the choice of adjustable parameters allows them to fit the same order
magnitude of both variations and their (opposite) signs in such a scenario.Comment: 16 pages, 1 figure, to appear in Phys. Rev.
Coreless and singular vortex lattices in rotating spinor Bose-Einstein condensates
We theoretically investigate vortex-lattice phases of rotating spinor
Bose-Einstein condensates (BEC) with the ferromagnetic spin-interaction by
numerically solving the Gross-Pitaevskii equation. The spinor BEC under slow
rotation can sustain a rich variety of exotic vortices due to the
multi-component order parameters, such as the Mermin-Ho and Anderson-Toulouse
coreless vortices (the 2-dimensional skyrmion and meron) and the
non-axisymmetric vortices with the sifting vortex cores. Here, we present the
spin texture of various vortex-lattice states at higher rotation rates and in
the presence of the external magnetic field. In addition, the vortex phase
diagram is constructed in the plane by the total magnetization and the
external rotation frequency by comparing the free energies of possible
vortices. It is shown that the vortex phase diagram in a - plane may
be divided into two categories; (i) the coreless vortex lattice formed by the
several types of Mermin-Ho vortices and (ii) the vortex lattice filling in the
cores with the pure polar (antiferromagnetic) state. In particular, it is found
that the type-(ii) state forms the composite lattices of coreless and
polar-core vortices. The difference between the type-(i) and type-(ii) results
from the existence of the singularity of the spin textures, which may be
experimentally confirmed by the spin imaging within polarized light recently
proposed by Carusotto and Mueller. We also discussed on the stability of
triangular and square lattice states for rapidly rotating condensates.Comment: to be published in Phys. Rev.
Solving problems of 4D minimal SO(10) model in a warped extra dimension
The minimal renormalizable supersymmetric SO(10) model, an SO(10) framework
with only one 10 and one 126 Higgs multiplets in the Yukawa sector, is
attractive because of its high predictive power for the neutrino oscillation
data. However, this model suffers from problems related to running of gauge
couplings. The gauge coupling unification may be spoiled due to the presence of
Higgs multiplets much lighter than the grand unification (GUT) scale. In
addition, the gauge couplings blow up around the GUT scale because of the
presence of Higgs multiplets of large representations. We consider the minimal
SO(10) model in the warped extra dimension and find a possibility to solve
these problems.Comment: 12 pages, no figure; version to appear in Phys. Rev.
Ferroelectric Phase Transitions in Ultra-thin Films of BaTiO3
We present molecular dynamics simulations of a realistic model of an
ultrathin film of BaTiO sandwiched between short-circuited electrodes to
determine and understand effects of film thickness, epitaxial strain and the
nature of electrodes on its ferroelectric phase transitions as a function of
temperature. We determine a full epitaxial strain-temperature phase diagram in
the presence of perfect electrodes. Even with the vanishing depolarization
field, we find that ferroelectric phase transitions to states with in-plane and
out-of-plane components of polarization exhibit dependence on thickness; it
arises from the interactions of local dipoles with their electrostatic images
in the presence of electrodes. Secondly, in the presence of relatively bad
metal electrodes which only partly compensate the surface charges and
depolarization field, a qualitatively different phase with stripe-like domains
is stabilized at low temperature
First-principles accurate total-energy surfaces for polar structural distortions of BaTiO3, PbTiO3, and SrTiO3: consequences to structural transition temperatures
Specific forms of the exchange correlation energy functionals in
first-principles density functional theory-based calculations, such as the
local density approximation (LDA) and generalized-gradient approximations
(GGA), give rise to structural lattice parameters with typical errors of -2%
and 2%. Due to a strong coupling between structure and polarization, the order
parameter of ferroelectric transitions, they result in large errors in
estimation of temperature dependent ferroelectric structural transition
properties. Here, we employ a recently developed GGA functional of Wu and Cohen
[Phys. Rev. B 73, 235116 (2006)] and determine total-energy surfaces for
zone-center distortions of BaTiO3, PbTiO3, and SrTiO3, and compare them with
the ones obtained with calculations based on standard LDA and GGA. Confirming
that the Wu and Cohen functional allows better estimation of structural
properties at 0 K, we determine a new set of parameters defining the effective
Hamiltonian for ferroelectric transition in BaTiO3. Using the new set of
parameters, we perform molecular-dynamics (MD) simulations under effective
pressures p=0.0 GPa, p=-2.0 GPa, and p=-0.005T GPa. The simulations under
p=-0.005T GPa, which is for simulating thermal expansion, show a clear
improvement in the cubic to tetragonal transition temperature and c/a parameter
of its ferroelectric tetragonal phase, while the description of transitions at
lower temperatures to orthorhombic and rhombohedral phases is marginally
improved. Our findings augur well for use of Wu-Cohen functional in studies of
ferroelectrics at nano-scale, particularly in the form of epitaxial films where
the properties depend crucially on the lattice mismatch.Comment: 10 pages, 7 figures, 3 tables, resubmitted to PR
A simple SO(10) GUT in five dimensions
A simple supersymmetric SO(10) GUT in five dimensions is considered. The
fifth dimension is compactified on the orbifold
possessing two inequivalent fixed points. In our setup, all matter and Higgs
multiplets reside on one brane (PS brane) where the original SO(10) gauge group
is broken down to the Pati-Salam (PS) gauge group, SU(4)_c \timesSU(2)_L
\times SU(2), by the orbifold boundary condition, while only the SO(10)
gauge multiplet resides in the bulk. The further breaking of the PS symmetry to
the Standard Model gauge group is realized by Higgs multiplets on the PS brane
as usual in four dimensional models. Proton decay is fully suppressed. In our
simple setup, the gauge coupling unification is realized after incorporating
threshold corrections of Kaluza-Klein modes. When supersymmetry is assumed to
be broken on the other brane, supersymmetry breaking is transmitted to the PS
brane through the gaugino mediation with the bulk gauge multiplet.Comment: 12 pages, 1 figure, some errors have been corrected (no change in
conclusions
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