1,809 research outputs found
Oscillating instanton solutions in curved space
We investigate oscillating instanton solutions of a self-gravitating scalar
field between degenerate vacua. We show that there exist O(4)-symmetric
oscillating solutions in a de Sitter background. The geometry of this solution
is finite and preserves the symmetry. The nontrivial solution
corresponding to tunneling is possible only if the effect of gravity is taken
into account. We present numerical solutions of this instanton, including the
phase diagram of solutions in terms of the parameters of the present work and
the variation of energy densities. Our solutions can be interpreted as
solutions describing an instanton-induced domain wall or braneworld-like object
rather than a kink-induced domain wall or braneworld. The oscillating instanton
solutions have a thick wall and the solutions can be interpreted as a mechanism
providing nucleation of the thick wall for topological inflation. We remark
that invariant solutions also exist in a flat and anti-de Sitter
background, though the physical significance is not clear.Comment: 25 pages, 11 figues. Some typos corrected, references added, and Ch3.
modified according to referee's comment
Observation of a multiferroic critical end point
The study of abrupt increases in magnetization with magnetic field known as
metamagnetic transitions has opened a rich vein of new physics in itinerant
electron systems, including the discovery of quantum critical end points with a
marked propensity to develop new kinds of order. However, the electric analogue
of the metamagnetic critical end point, a "metaelectric" critical end point has
not yet been realized. Multiferroic materials wherein magnetism and
ferroelectricity are cross-coupled are ideal candidates for the exploration of
this novel possibility using magnetic-field (\emph{H}) as a tuning parameter.
Herein, we report the discovery of a magnetic-field-induced metaelectric
transition in multiferroic BiMnO in which the electric polarization
(\emph{P}) switches polarity along with a concomitant Mn spin-flop transition
at a critical magnetic field \emph{H}. The simultaneous metaelectric
and spin-flop transitions become sharper upon cooling, but remain a continuous
crossover even down to 0.5 K. Near the \emph{P}=0 line realized at
\emph{H}18 T below 20 K, the dielectric constant
() increases significantly over wide field- and temperature
(\emph{T})-ranges. Furthermore, a characteristic power-law behavior is found in
the \emph{P}(\emph{H}) and (\emph{H}) curves at \emph{T}=0.66 K.
These findings indicate that a magnetic-field-induced metaelectric critical end
point is realized in BiMnO near zero temperature.Comment: 6 pages, 3 figure
Global monopole solutions in Horava gravity
In Horava's theory of gravity coupled to a global monopole source, we seek
for static, spherically symmetric spacetime solutions for general values of
. We obtain the explicit solutions with deficit solid angles, in the
IR modified Horava gravity model, at the IR fixed point and at the
conformal point . For the other values of we also
find special solutions to the inhomogenous equation of the gravity model with
detailed balance, and we discuss an possibility of astrophysical applications
of the solution that has a deficit angle for a finite range.Comment: 7 pages, added reference
One-way multigrid method in electronic structure calculations
We propose a simple and efficient one-way multigrid method for
self-consistent electronic structure calculations based on iterative
diagonalization. Total energy calculations are performed on several different
levels of grids starting from the coarsest grid, with wave functions
transferred to each finer level. The only changes compared to a single grid
calculation are interpolation and orthonormalization steps outside the original
total energy calculation and required only for transferring between grids. This
feature results in a minimal amount of code change, and enables us to employ a
sophisticated interpolation method and noninteger ratio of grid spacings.
Calculations employing a preconditioned conjugate gradient method are presented
for two examples, a quantum dot and a charged molecular system. Use of three
grid levels with grid spacings 2h, 1.5h, and h decreases the computer time by
about a factor of 5 compared to single level calculations.Comment: 10 pages, 2 figures, to appear in Phys. Rev. B, Rapid Communication
XMMU J100750.5+125818: A strong lensing cluster at z=1.082
We report on the discovery of the X-ray luminous cluster XMMU
J100750.5+125818 at redshift 1.082 based on 19 spectroscopic members, which
displays several strong lensing features. SED modeling of the lensed arc
features from multicolor imaging with the VLT and the LBT reveals likely
redshifts ~2.7 for the most prominent of the lensed background galaxies. Mass
estimates are derived for different radii from the velocity dispersion of the
cluster members, M_200 ~ 1.8 10^{14} Msun, from the X-ray spectral parameters,
M_500 ~ 1.0 10^{14} Msun, and the largest lensing arc, M_SL ~ 2.3 10^{13} Msun.
The projected spatial distribution of cluster galaxies appears to be elongated,
and the brightest galaxy lies off center with respect to the X-ray emission
indicating a not yet relaxed structure. XMMU J100750.5+125818 offers excellent
diagnostics of the inner mass distribution of a distant cluster with a
combination of strong and weak lensing, optical and X-ray spectroscopy.Comment: A&A, accepted for publicatio
Strong magnetoelastic effect on the magnetoelectric phenomena of TbMn2O5
Comparative studies of magnetoelectric susceptibility (??), magnetization (M), and magnetostriction (u) in TbMn2O5 reveal that the increment of M owing to the field-induced Tb3+ spin alignment produces a field-asymmetric line shape in the ??(H) curve, which is conspicuous in a low-temperature incommensurate phase but persistently subsists in the entire ferroelectric phase. Correlations among electric polarization, u, and M2 variation represent linear relationships, unambiguously showing the significant role of Tb magnetoelastic effects on the low-field magnetoelectric phenomena of TbMn2O5. An effective free energy capturing the observed experimental features is also suggested.open3
Anyonic physical observables and spin phase transition
The quantization of charged matter system coupled to Chern-Simons gauge
fields is analyzed in a covariant gauge fixing, and gauge invariant physical
anyon operators satisfying fractional statistics are constructed in a symmetric
phase, based on Dirac's recipe performed on QED. This method provides us a
definite way of identifying physical spectrums free from gauge ambiguity and
constructing physical anyon operators under a covariant gauge fixing. We then
analyze the statistical spin phase transition in a symmetry-broken phase and
show that the Higgs mechanism transmutes an anyon satisfying fractional
statistics into a canonical boson, a spin 0 Higgs boson or a topologically
massive photon.Comment: 14 pages, added references, a few improvement
Density-functional Study of Small Molecules within the Krieger-Li-Iafrate Approximation
We report density-functional studies of several small molecules (, and ) within the Krieger-Li-Iafrate (KLI)
approximation to the exact Kohn-Sham local exchange potential, using a
three-dimensional real-space finite-difference pseudopotential method. It is
found that exchange-only KLI leads to markedly improved eigenvalue spectra
compared to those obtained within the standard local-density approximation
(LDA), the generalized gradient approximation (GGA), and the Hartree-Fock (HF)
method. For structural properties, exchange-only KLI results are close to the
corresponding HF values. We find that the addition of LDA or GGA correlation
energy functionals to the KLI exact exchange energy functional does not lead to
systematic improvements.Comment: 16 pages including 1 fugure, to be published in Phys. Rev. A Nov. 1
'9
Band gap opening by two-dimensional manifestation of Peierls instability in graphene
Using first-principles calculations of graphene having high-symmetry
distortion or defects, we investigate band gap opening by chiral symmetry
breaking, or intervalley mixing, in graphene and show an intuitive picture of
understanding the gap opening in terms of local bonding and antibonding
hybridizations. We identify that the gap opening by chiral symmetry breaking in
honeycomb lattices is an ideal two-dimensional (2D) extension of the Peierls
metal-insulator transition in 1D linear lattices. We show that the spontaneous
Kekule distortion, a 2D version of the Peierls distortion, takes place in
biaxially strained graphene, leading to structural failure. We also show that
the gap opening in graphene antidots and armchair nanoribbons, which has been
attributed usually to quantum confinement effects, can be understood with the
chiral symmetry breaking
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