44,699 research outputs found
Gauge-invariant Formulation of the Second-order Cosmological Perturbations
Gauge invariant treatments of the second order cosmological perturbation in a
four dimensional homogeneous isotropic universe filled with the perfect fluid
are completely formulated without any gauge fixing. We derive all components of
the Einstein equations in the case where the first order vector and tensor
modes are negligible. These equations imply that the tensor and the vector mode
of the second order metric perturbations may be generated by the scalar-scalar
mode coupling of the linear order perturbations as the result of the non-linear
effects of the Einstein equations.Comment: 5 pages, no figure. RevTeX; short letter version of gr-qc/0605108;
some details of explanations are adde
Dimerization in a half-filled one-dimensional extended Hubbard model
We use a density matrix renormalization group method to study quantitatively
the phase diagram of a one-dimensional extended Hubbard model at half-filling
by investigating the correlation functions and structure factors. We confirm
the existence of a novel narrow region with long-rang bond-order-wave order
which is highly controversial recently between the charge-density-wave phase
and Mott insulator phase. We determined accurately the position of the
tricritical point , which is quite different
from previous studies
Toda Lattice and Tomimatsu-Sato Solutions
We discuss an analytic proof of a conjecture (Nakamura) that solutions of
Toda molecule equation give those of Ernst equation giving Tomimatsu-Sato
solutions of Einstein equation. Using Pfaffian identities it is shown for Weyl
solutions completely and for generic cases partially.Comment: LaTeX 8 page
Galaxy types in the Sloan Digital Sky Survey using supervised artificial neural networks
Supervised artificial neural networks are used to predict useful properties of galaxies in the Sloan Digital Sky Survey, in this instance morphological classifications, spectral types and redshifts. By giving the trained networks unseen data, it is found that correlations between predicted and actual properties are around 0.9 with rms errors of order ten per cent. Thus, given a representative training set, these properties may be reliably estimated for galaxies in the survey for which there are no spectra and without human intervention
D3/D7 holographic Gauge theory and Chemical potential
N=2 supersymmetric Yang-Mills theory with flavor hypermultiplets at finite
temperature and in the dS are studied for finite quark number density
() by a dual supergravity background with non-trivial dilaton and axion.
The quarks and its number density are introduced by embedding a probe D7
brane. We find a critical value of the chemical potential at the limit of
, and it coincides with the effective quark mass given in each theory
for . At this point, a transition of the D7 embedding configurations
occurs between their two typical ones. The phase diagrams of this transition
are shown in the plane of chemical potential versus temperature and
cosmological constant for YM theory at finite temperature and in dS
respectively. In this phase transition, the order parameter is considered as
. % and the critical value of the chemical potential This result seems to
be reasonable since both theories are in the quark deconfinement phase.Comment: 17 pages, 8 figure
Coherent Quantum Dynamics of a Superconducting Flux Qubit
We have observed coherent time evolution between two quantum states of a
superconducting flux qubit comprising three Josephson junctions in a loop. The
superposition of the two states carrying opposite macroscopic persistent
currents is manipulated by resonant microwave pulses. Readout by means of
switching-event measurement with an attached superconducting quantum
interference device revealed quantum-state oscillations with high fidelity.
Under strong microwave driving it was possible to induce hundreds of coherent
oscillations. Pulsed operations on this first sample yielded a relaxation time
of 900 nanoseconds and a free-induction dephasing time of 20 nanoseconds. These
results are promising for future solid-state quantum computing.Comment: submitted 2 December 2002; accepted 4 February 200
General formulation of general-relativistic higher-order gauge-invariant perturbation theory
Gauge-invariant treatments of general-relativistic higher-order perturbations
on generic background spacetime is proposed. After reviewing the general
framework of the second-order gauge-invariant perturbation theory, we show the
fact that the linear-order metric perturbation is decomposed into
gauge-invariant and gauge-variant parts, which was the important premis of this
general framework. This means that the development the higher-order
gauge-invariant perturbation theory on generic background spacetime is
possible. A remaining issue to be resolve is also disscussed.Comment: 4 pages, no figure. (v3) some explanations are added and a reference
is adde
Mechanism of CDW-SDW Transition in One Dimension
The phase transition between charge- and spin-density-wave (CDW, SDW) phases
is studied in the one-dimensional extended Hubbard model at half-filling. We
discuss whether the transition can be described by the Gaussian and the
spin-gap transitions under charge-spin separation, or by a direct CDW-SDW
transition. We determine these phase boundaries by level crossings of
excitation spectra which are identified according to discrete symmetries of
wave functions. We conclude that the Gaussian and the spin-gap transitions take
place separately from weak- to intermediate-coupling region. This means that
the third phase exists between the CDW and the SDW states. Our results are also
consistent with those of the strong-coupling perturbative expansion and of the
direct evaluation of order parameters.Comment: 5 pages(REVTeX), 5 figures(EPS), 1 table, also available from
http://wwwsoc.nacsis.ac.jp/jps/jpsj/1999/p68a/p68a42/p68a42h/p68a42h.htm
Mixings of 4-quark components in light non-singlet scalar mesons in QCD sum rules
Mixings of 4-quark components in the non-singlet scalar mesons are studied in
the QCD sum rules. We propose a formulation to evaluate the cross correlators
of q\bar q and qq\bar q \bar q operators and to define the mixings of different
Fock states in the sum rule. It is applied to the non-singlet scalar mesons,
a_0 and K_0^\ast. It is found that the 4-quark operators predict lower masses
than the q\bar q operators and that the 4-quark states occupy about 70-90% of
the lowest mass states.Comment: 8 pages, 9 figure
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