586 research outputs found
Deuteron Electromagnetic Form Factors in the Intermediate Energy Region
Based on a Perturbative QCD analysis of the deuteron form factor, a model for
the reduced form factor is suggested. The numerical result is consistent with
the data in the intermediate energy region.Comment: 9 pages, to appear in Phys.Rev.
A note on Friedmann equation of FRW universe in deformed Horava-Lifshitz gravity from entropic force
With entropic interpretation of gravity proposed by Verlinde, we obtain the
Friedmann equation of the Friedmann-Robertson-Walker universe for the deformed
Ho\v{r}ava-Lifshitz gravity. It is shown that, when the parameter of
Ho\v{r}ava-Lifshitz gravity , the modified Friedmann
equation will go back to the one in Einstein gravity. This results may imply
that the entropic interpretation of gravity is effective for the deformed
Ho\v{r}ava-Lifshitz gravity.Comment: 9 pages, no figure
Subset feedback vertex set is fixed parameter tractable
The classical Feedback Vertex Set problem asks, for a given undirected graph
G and an integer k, to find a set of at most k vertices that hits all the
cycles in the graph G. Feedback Vertex Set has attracted a large amount of
research in the parameterized setting, and subsequent kernelization and
fixed-parameter algorithms have been a rich source of ideas in the field.
In this paper we consider a more general and difficult version of the
problem, named Subset Feedback Vertex Set (SUBSET-FVS in short) where an
instance comes additionally with a set S ? V of vertices, and we ask for a set
of at most k vertices that hits all simple cycles passing through S. Because of
its applications in circuit testing and genetic linkage analysis SUBSET-FVS was
studied from the approximation algorithms perspective by Even et al.
[SICOMP'00, SIDMA'00].
The question whether the SUBSET-FVS problem is fixed-parameter tractable was
posed independently by Kawarabayashi and Saurabh in 2009. We answer this
question affirmatively. We begin by showing that this problem is
fixed-parameter tractable when parametrized by |S|. Next we present an
algorithm which reduces the given instance to 2^k n^O(1) instances with the
size of S bounded by O(k^3), using kernelization techniques such as the
2-Expansion Lemma, Menger's theorem and Gallai's theorem. These two facts allow
us to give a 2^O(k log k) n^O(1) time algorithm solving the Subset Feedback
Vertex Set problem, proving that it is indeed fixed-parameter tractable.Comment: full version of a paper presented at ICALP'1
Energy-momentum/Cotton tensor duality for AdS4 black holes
We consider the theory of gravitational quasi-normal modes for general linear
perturbations of AdS4 black holes. Special emphasis is placed on the effective
Schrodinger problems for axial and polar perturbations that realize
supersymmetric partner potential barriers on the half-line. Using the
holographic renormalization method, we compute the energy-momentum tensor for
perturbations satisfying arbitrary boundary conditions at spatial infinity and
discuss some aspects of the problem in the hydrodynamic representation. It is
also observed in this general framework that the energy-momentum tensor of
black hole perturbations and the energy momentum tensor of the gravitational
Chern-Simons action (known as Cotton tensor) exhibit an axial-polar duality
with respect to appropriately chosen supersymmetric partner boundary conditions
on the effective Schrodinger wave-functions. This correspondence applies to
perturbations of very large AdS4 black holes with shear viscosity to entropy
density ratio equal to 1/4\pi, thus providing a dual graviton description of
their hydrodynamic modes. We also entertain the idea that the purely
dissipative modes of black hole hydrodynamics may admit Ricci flow description
in the non-linear regime.Comment: 38 pages; minor typos corrected, a few extra references and a note
adde
Resonance scattering and singularities of the scattering function
Recent studies of transport phenomena with complex potentials are explained
by generic square root singularities of spectrum and eigenfunctions of
non-Hermitian Hamiltonians. Using a two channel problem we demonstrate that
such singularities produce a significant effect upon the pole behaviour of the
scattering matrix, and more significantly upon the associated residues. This
mechanism explains why by proper choice of the system parameters the resonance
cross section is increased drastically in one channel and suppressed in the
other channel.Comment: 4 pages, 3 figure
Mechanisms for Decays
Exclusive decays of into are investigated in
the framework of perturbative quantum chromodynamics(pQCD) and \tpz quark
pair creation model. The results show that these two mechanisms exhibit a quite
different behavior in evaluating the decay width for the and
. In pQCD method with nonrelativistic(NR) approximation, while the
calculated \cxpp{2} decay width is comparable with measured one, the result
for the \cxpp{0} decay width is suppressed and much smaller than experimental
value. However, in \tpz quark pair creation model, the situation is reversed:
the decay width of \cxpp{0} is greatly enhanced and can reproduce the large
measured value, while the contribution to the \cxpp{2} decay width is small.
The results suggest that while the pQCD mechanism is the dominant mechanism for
\cxpp{2} decay, the \tpz quark pair creation mechanism is the dominant one
for \cxpp{0} decay.Comment: 10 pages, 2 figure
Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta
In previous studies on a number of under- and overdoped high temperature
superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta},
the transition temperature T_c has been found to change with time in a manner
which depends on the sample's detailed temperature and pressure history. This
relaxation behavior in T_c is believed to originate from rearrangements within
the oxygen sublattice. In the present high-pressure studies on
HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation
effects in strongly under- and overdoped samples () with
an activation energy . For overdoped
HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than
previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of
+11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an
anomalous result for high-T_c superconductors in the present pressure range,
giving evidence for a change in the electronic and/or structural properties
near 0.4 GPa
Asymptotic Expansions for Stationary Distributions of Perturbed Semi-Markov Processes
New algorithms for computing of asymptotic expansions for stationary
distributions of nonlinearly perturbed semi-Markov processes are presented. The
algorithms are based on special techniques of sequential phase space reduction,
which can be applied to processes with asymptotically coupled and uncoupled
finite phase spaces.Comment: 83 page
- …