366 research outputs found
Degenerations of LeBrun twistor spaces
We investigate various limits of the twistor spaces associated to the
self-dual metrics on n CP ^2, the connected sum of the complex projective
planes, constructed by C. LeBrun. In particular, we explicitly present the
following 3 kinds of degenerations whose limits of the metrics are: (a) LeBrun
metrics on (n-1) CP ^2$, (b) (Another) LeBrun metrics on the total space of the
line bundle O(-n) over CP ^1 (c) The hyper-Kaehler metrics on the small
resolution of rational double points of type A_{n-1}, constructed by Gibbons
and Hawking.Comment: 21 pages, 7 figures. V2: A new section added at the end of the
article. V3: Reference slightly update
Entropic force and its cosmological implications
We investigate a possibility of realizing the entropic force into the
cosmology. A main issue is how the holographic screen is implemented in the
Newtonian cosmology. Contrary to the relativistic realization of Friedmann
equations, we do not clarify the connection between Newtonian cosmology and
entropic force because there is no way of implementing the holographic screen
in the Newtonian cosmology.Comment: 16 pages, no figures, version "Accepted for publication in
Astrophysics & Space Science
Does entropic force always imply the Newtonian force law?
We study the entropic force by introducing a bound between
entropy and area which was derived by imposing the non-gravitational collapse
condition. In this case, applying a modified entropic force to this system does
not lead to the Newtonian force law.Comment: 11 pages, version to appear in EPJ
Continuous Percolation Phase Transitions of Two-dimensional Lattice Networks under a Generalized Achlioptas Process
The percolation phase transitions of two-dimensional lattice networks under a
generalized Achlioptas process (GAP) are investigated. During the GAP, two
edges are chosen randomly from the lattice and the edge with minimum product of
the two connecting cluster sizes is taken as the next occupied bond with a
probability . At , the GAP becomes the random growth model and leads
to the minority product rule at . Using the finite-size scaling analysis,
we find that the percolation phase transitions of these systems with are always continuous and their critical exponents depend on .
Therefore, the universality class of the critical phenomena in two-dimensional
lattice networks under the GAP is related to the probability parameter in
addition.Comment: 7 pages, 14 figures, accepted for publication in Eur. Phys. J.
Optimal control theory for unitary transformations
The dynamics of a quantum system driven by an external field is well
described by a unitary transformation generated by a time dependent
Hamiltonian. The inverse problem of finding the field that generates a specific
unitary transformation is the subject of study. The unitary transformation
which can represent an algorithm in a quantum computation is imposed on a
subset of quantum states embedded in a larger Hilbert space. Optimal control
theory (OCT) is used to solve the inversion problem irrespective of the initial
input state. A unified formalism, based on the Krotov method is developed
leading to a new scheme. The schemes are compared for the inversion of a
two-qubit Fourier transform using as registers the vibrational levels of the
electronic state of Na. Raman-like transitions through the
electronic state induce the transitions. Light fields are found
that are able to implement the Fourier transform within a picosecond time
scale. Such fields can be obtained by pulse-shaping techniques of a femtosecond
pulse. Out of the schemes studied the square modulus scheme converges fastest.
A study of the implementation of the qubit Fourier transform in the Na
molecule was carried out for up to 5 qubits. The classical computation effort
required to obtain the algorithm with a given fidelity is estimated to scale
exponentially with the number of levels. The observed moderate scaling of the
pulse intensity with the number of qubits in the transformation is
rationalized.Comment: 32 pages, 6 figure
Entropic Corrections to Coulomb's Law
Two well-known quantum corrections to the area law have been introduced in
the literatures, namely, logarithmic and power-law corrections. Logarithmic
corrections, arises from loop quantum gravity due to thermal equilibrium
fluctuations and quantum fluctuations, while, power-law correction appears in
dealing with the entanglement of quantum fields in and out the horizon.
Inspired by Verlinde's argument on the entropic force, and assuming the quantum
corrected relation for the entropy, we propose the entropic origin for the
Coulomb's law in this note. Also we investigate the Uehling potential as a
radiative correction to Coulomb potential in 1-loop order and show that for
some value of distance the entropic corrections of the Coulomb's law is
compatible with the vacuum-polarization correction in QED. So, we derive
modified Coulomb's law as well as the entropy corrected Poisson's equation
which governing the evolution of the scalar potential . Our study further
supports the unification of gravity and electromagnetic interactions based on
the holographic principle.Comment: 17 pages, 5 figures, accepted in IJT
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays
By analyzing about 33 data sample collected at and around 3.773
GeV with the BES-II detector at the BEPC collider, we directly measure the
branching fractions for the neutral and charged inclusive semimuonic decays
to be and , and determine the ratio of the two branching
fractions to be
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
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