2,399 research outputs found
Quantization of a relativistic particle on the SL(2,R) manifold based on Hamiltonian reduction
A quantum theory is constructed for the system of a relativistic particle
with mass m moving freely on the SL(2,R) group manifold. Applied to the
cotangent bundle of SL(2,R), the method of Hamiltonian reduction allows us to
split the reduced system into two coadjoint orbits of the group. We find that
the Hilbert space consists of states given by the discrete series of the
unitary irreducible representations of SL(2,R), and with a positive-definite,
discrete spectrum.Comment: 12 pages, INS-Rep.-104
Resonant Two-Magnon Raman Scattering and Photoexcited States in Two-Dimensional Mott Insulators
We investigate the resonant two-magnon Raman scattering in two-dimensional
(2D) Mott insulators by using a half-filled 2D Hubbard model in the strong
coupling limit. By performing numerical diagonalization calculations for small
clusters, we find that the Raman intensity is enhanced when the incoming photon
energy is not near the optical absorption edge but well above it, being
consistent with experimental data. The absence of resonance near the gap edge
is associated with the presence of background spins, while photoexcited states
for resonance are found to be characterized by the charge degree of freedom.
The resonance mechanism is different from those proposed previously.Comment: REVTeX4, 4 pages, 3 figures, to be published in Phys. Rev. Let
Electron-phonon coupling and spin-charge separation in one-dimensional Mott insulators
We examine the single-particle excitation spectrum in the one-dimensional
Hubbard-Holstein model at half-filling by performing the dynamical density
matrix renormalization group (DDMRG) calculation. The DDMRG results are
interpreted as superposition of spectra for a spinless carrier dressed with
phonons. The superposition is a consequence of robustness of the spin-charge
separation against electron-phonon coupling. The separation is in contrast to
the coupling between phonon and spin degrees of freedom in two-dimensional
systems. We discuss implication of the results of the recent angle-resolved
photoemission spectroscopy measurements on SrCuO.Comment: 5 pages, 4 figures. submitted to the Physical Review Letter
Temperature dependent band structure of the Kondo insulator
We present a Qantum Monte Carlo (QMC) study of the temperature dependent
dynamics of the Kondo insulator. Working at the so-called symmetrical point
allows to perform minus-sign free QMC simulations and thus reach temperatures
of less than 1% of the conduction electron bandwidth. Study of the temperature
dependence of the single particle Green's function and dynamical spin
correlation function shows a surprisingly intricate low temperature band
structure and gives evidence for two characteristic temperatures, which we
identify with the Kondo and coherence temperature, respectively. In particular,
the data show a temperature induced metal-insulator transition at the coherence
temperature.Comment: RevTex-file, 4 PRB pages with 4 eps figures. Hardcopies of figures
(or the entire manuscript) can be obtained by e-mail request to:
[email protected]
Nonlinear optical response and spin-charge separation in one-dimensional Mott insulators
We theoretically study the nonlinear optical response and photoexcited states
of the Mott insulators. The nonlinear optical susceptibility \chi^(3) is
calculated by using the exact diagonalization technique on small clusters. From
the systematic study of the dependence of \chi^(3) on dimensionality, we find
that the spin-charge separation plays a crucial role in enhancing \chi^(3) in
the one-dimensional (1D) Mott insulators. Based on this result, we propose a
holon-doublon model, which describes the nonlinear response in the 1D Mott
insulators. These findings show that the spin-charge separation will become a
key concept of optoelectronic devices.Comment: 5 pages with 3 figures, to appear in PRB RC, 15 August 200
Entanglement Measures for Intermediate Separability of Quantum States
We present a family of entanglement measures R_m which act as indicators for
separability of n-qubit quantum states into m subsystems for arbitrary 2 \leq m
\leq n. The measure R_m vanishes if the state is separable into m subsystems,
and for m = n it gives the Meyer-Wallach measure while for m = 2 it reduces, in
effect, to the one introduced recently by Love et al. The measures R_m are
evaluated explicitly for the GHZ state and the W state (and its modifications,
the W_k states) to show that these globally entangled states exhibit rather
distinct behaviors under the measures, indicating the utility of the measures
R_m for characterizing globally entangled states as well.Comment: 8 pages, 8 figure
Bcl-2 protein expression is associated with p27 and p53 protein expressions and MIB-1 counts in breast cancer
BACKGROUND: Recent experimental studies have shown that Bcl-2, which has been established as a key player in the control of apoptosis, plays a role in regulating the cell cycle and proliferation. The aim of this study was to investigate the relationship between Bcl-2 and p27 protein expression, p53 protein expression and the proliferation activity as defined by the MIB-1 counts. The prognostic implication of Bcl-2 protein expression in relation to p27 and p53 protein expressions and MIB-1 counts for breast cancer was also evaluated. METHODS: The immunohistochemical expression of Bcl-2 protein was evaluated in a series of 249 invasive ductal carcinomas of the breast, in which p27 and p53 protein expressions and MIB-1 counts had been determined previously. RESULTS: The Bcl-2 protein expression was found to be decreased in 105 (42%) cases. A decreased Bcl-2 protein expression was significantly correlated with a nuclear grade of III, a negative estrogen receptor, a decreased p27 protein expression, a positive p53 protein expression, positive MIB-1 counts and a positive HER2 protein expression. The incidence of a nuclear grade of III and positive MIB-1 counts increased as the number of abnormal findings of Bcl-2, p27 and p53 protein expressions increased. A univariate analysis indicated a decreased Bcl-2 protein expression to be significantly (p = 0.0089) associated with a worse disease free survival (DFS), while a multivariate analysis indicated the lymph node status and MIB-1 counts to be independently significant prognostic factors for the DFS. CONCLUSION: The Bcl-2 protein expression has a close correlation with p27 and p53 protein expressions and the proliferation activity determined by MIB-1 counts in invasive ductal carcinoma of the breast. The prognostic value of Bcl-2 as well as p27 and p53 protein expressions was dependent on the proliferation activity in breast cancer
Spectral properties on a circle with a singularity
We investigate the spectral and symmetry properties of a quantum particle
moving on a circle with a pointlike singularity (or point interaction). We find
that, within the U(2) family of the quantum mechanically allowed distinct
singularities, a U(1) equivalence (of duality-type) exists, and accordingly the
space of distinct spectra is U(1) x [SU(2)/U(1)], topologically a filled torus.
We explore the relationship of special subfamilies of the U(2) family to
corresponding symmetries, and identify the singularities that admit an N = 2
supersymmetry. Subfamilies that are distinguished in the spectral properties or
the WKB exactness are also pointed out. The spectral and symmetry properties
are also studied in the context of the circle with two singularities, which
provides a useful scheme to discuss the symmetry properties on a general basis.Comment: TeX, 26 pages. v2: one reference added and two update
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