30,352 research outputs found
Entanglement and quantum phase transitions
We examine several well known quantum spin models and categorize behavior of
pairwise entanglement at quantum phase transitions. A unified picture on the
connection between the entanglement and quantum phase transition is given.Comment: 4 pages, 3 figure
Can an observer really catch up with light
Given a null geodesic with a point in
conjugate to along , there will be a variation of
which will give a time-like curve from to . This is
a well-known theory proved in the famous book\cite{2}. In the paper we prove
that the time-like curves coming from the above-mentioned variation have a
proper acceleration which approaches infinity as the time-like curve approaches
the null geodesic. This means no observer can be infinitesimally near the light
and begin at the same point with the light and finally catch the light. Only
separated from the light path finitely, does the observer can begin at the same
point with the light and finally catch the light.Comment: 6 pages, no figures, submited to Physical Review
Circuit QED and sudden phase switching in a superconducting qubit array
Superconducting qubits connected in an array can form quantum many-body
systems such as the quantum Ising model. By coupling the qubits to a
superconducting resonator, the combined system forms a circuit QED system.
Here, we study the nonlinear behavior in the many-body state of the qubit array
using a semiclassical approach. We show that sudden switchings as well as a
bistable regime between the ferromagnetic phase and the paramagnetic phase can
be observed in the qubit array. A superconducting circuit to implement this
system is presented with realistic parameters .Comment: 4 pages, 3 figures, submitted for publication
Consistent analysis of neutral- and charged-current neutrino scattering off carbon
Background: Good understanding of the cross sections for (anti)neutrino
scattering off nuclear targets in the few-GeV energy region is a prerequisite
for correct interpretation of results of ongoing and planned oscillation
experiments.
Purpose: Clarify possible source of disagreement between recent measurements
of the cross sections on carbon.
Method: Nuclear effects in (anti)neutrino scattering off carbon nucleus are
described using the spectral function approach. The effect of two- and
multi-nucleon final states is accounted for by applying an effective value of
the axial mass, fixed to 1.23 GeV. Neutral-current elastic (NCE) and
charged-current quasielastic (CCQE) processes are treated on equal footing.
Results: The differential and total cross sections for the energy ranging
from a few hundreds of MeV to 100 GeV are obtained and compared to the
available data from the BNL E734, MiniBooNE, and NOMAD experiments.
Conclusions: Nuclear effects in NCE and CCQE scattering seem to be very
similar. Within the spectral function approach, the axial mass from the shape
analysis of the MiniBooNE data is in good agreement with the results reported
by the BNL E734 and NOMAD Collaborations. However, the combined analysis of NCE
and CCQE data does not seem to support the contribution of multi-nucleon final
states being large enough to explain the normalization of the
MiniBooNE-reported cross sections.Comment: 14 pages, 9 figures, detailed discussion of the role of FSI is adde
The K\"ahler-Ricci flow with positive bisectional curvature
We show that the K\"ahler-Ricci flow on a manifold with positive first Chern
class converges to a K\"ahler-Einstein metric assuming positive bisectional
curvature and certain stability conditions.Comment: 15 page
The K\"ahler-Ricci flow on surfaces of positive Kodaira dimension
The existence of K\"ahler-Einstein metrics on a compact K\"ahler manifold has
been the subject of intensive study over the last few decades, following Yau's
solution to Calabi's conjecture. The Ricci flow, introduced by Richard Hamilton
has become one of the most powerful tools in geometric analysis.
We study the K\"ahler-Ricci flow on minimal surfaces of Kodaira dimension one
and show that the flow collapses and converges to a unique canonical metric on
its canonical model. Such a canonical is a generalized K\"ahler-Einstein
metric. Combining the results of Cao, Tsuji, Tian and Zhang, we give a metric
classification for K\"aher surfaces with a numerical effective canonical line
bundle by the K\"ahler-Ricci flow. In general, we propose a program of finding
canonical metrics on canonical models of projective varieties of positive
Kodaira dimension
Exceptional del Pezzo hypersurfaces
We compute global log canonical thresholds of a large class of quasismooth
well-formed del Pezzo weighted hypersurfaces in
. As a corollary we obtain the existence
of orbifold K\"ahler--Einstein metrics on many of them, and classify
exceptional and weakly exceptional quasismooth well-formed del Pezzo weighted
hypersurfaces in .Comment: 149 pages, one reference adde
Superconducting correlations in ultra-small metallic grains
To describe the crossover from the bulk BCS superconductivity to a
fluctuation-dominated regime in ultrasmall metallic grains, new order
parameters and correlation functions, such as ``parity gap'' and ``pair-mixing
correlation function'', have been recently introduced. In this paper, we
discuss the small-grain behaviour of the Penrose-Onsager-Yang off-diagonal
long-range order (ODLRO) parameter in a pseudo-spin representation. Relations
between the ODLRO parameter and those mentioned above are established through
analytical and numerical calculations.Comment: 7 pages, 1 figur
A Note on the Generalization of the GEMS Approach
This paper is a supplement of our earlier work JHEP 0410 (2004)
011[gr-qc/0409107].We map the vector potential of charged black holes into GEMS
and find that its effect on the thermal spectrum is the same as that on the
black hole side, i.e., it will induce a chemical potential in the thermal
spectrum which is the same as that in the charged black holes.We also argue
that the generalization of GEMS approach to non-stationary motions is not
possible.Comment: Latex file, 10 pages, no figure; v2: minor corrections; v3: revised
with title changed, one new section added and references adde
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