2,415 research outputs found
Ground States for a Stationary Mean-Field Model for a Nucleon
In this paper we consider a variational problem related to a model for a
nucleon interacting with the and mesons in the atomic
nucleus. The model is relativistic, and we study it in a nuclear physics
nonrelativistic limit, which is of a very different nature than the
nonrelativistic limit in the atomic physics. Ground states are shown to exist
for a large class of values for the parameters of the problem, which are
determined by the values of some physical constants
Symmetric ground states for a stationary relativistic mean-field model for nucleons in the nonrelativistic limit
In this paper we consider a model for a nucleon interacting with the
and mesons in the atomic nucleus. The model is relativistic, but we
study it in the nuclear physics nonrelativistic limit, which is of a very
different nature from the one of the atomic physics. Ground states with a given
angular momentum are shown to exist for a large class of values for the
coupling constants and the mesons' masses. Moreover, we show that, for a good
choice of parameters, the very striking shapes of mesonic densities inside and
outside the nucleus are well described by the solutions of our model
High-order Time Expansion Path Integral Ground State
The feasibility of path integral Monte Carlo ground state calculations with
very few beads using a high-order short-time Green's function expansion is
discussed. An explicit expression of the evolution operator which provides
dramatic enhancements in the quality of ground-state wave-functions is
examined. The efficiency of the method makes possible to remove the trial wave
function and thus obtain completely model-independent results still with a very
small number of beads. If a single iteration of the method is used to improve a
given model wave function, the result is invariably a shadow-type wave
function, whose precise content is provided by the high-order algorithm
employed.Comment: 4 page
Superfluidity of metastable bulk glass para-hydrogen at low temperature
Molecular para-hydrogen has been proposed theoretically as a possible
candidate for superfluidity, but the eventual superfluid transition is hindered
by its crystallization. In this work, we study a metastable non crystalline
phase of bulk p-H2 by means of the Path Integral Monte Carlo method in order to
investigate at which temperature this system can support superfluidity. By
choosing accurately the initial configuration and using a non commensurate
simulation box, we have been able to frustrate the formation of the crystal in
the simulated system and to calculate the temperature dependence of the
one-body density matrix and of the superfluid fraction. We observe a transition
to a superfluid phase at temperatures around 1 K. The limit of zero temperature
is also studied using the diffusion Monte Carlo method. Results for the energy,
condensate fraction, and structure of the metastable liquid phase at T=0 are
reported and compared with the ones obtained for the stable solid phase.Comment: 10 pages, accepted for publication in Phys. Rev.
Condensate fraction in liquid 4He at zero temperature
We present results of the one-body density matrix (OBDM) and the condensate
fraction n_0 of liquid 4He calculated at zero temperature by means of the Path
Integral Ground State Monte Carlo method. This technique allows to generate a
highly accurate approximation for the ground state wave function Psi_0 in a
totally model-independent way, that depends only on the Hamiltonian of the
system and on the symmetry properties of Psi_0. With this unbiased estimation
of the OBDM, we obtain precise results for the condensate fraction n_0 and the
kinetic energy K of the system. The dependence of n_0 with the pressure shows
an excellent agreement of our results with recent experimental measurements.
Above the melting pressure, overpressurized liquid 4He shows a small condensate
fraction that has dropped to 0.8% at the highest pressure of p = 87 bar.Comment: 12 pages. 4 figures. Accepted for publication on "Journal of Low
Temperature Physics
Genetic diversity of wild-type measles viruses: implications for global measles elimination programs.
Wild-type measles viruses have been divided into distinct genetic groups according to the nucleotide sequences of their hemagglutinin and nucleoprotein genes. Most genetic groups have worldwide distribution; however, at least two of the groups appear to have a more limited circulation. To monitor the transmission pathways of measles virus, we observed the geographic distribution of genetic groups, as well as changes in them in a particular region over time. We found evidence of interruption of indigenous transmission of measles in the United States after 1993 and identified the sources of imported virus associated with cases and outbreaks after 1993. The pattern of measles genetic groups provided a means to describe measles outbreaks and assess the extent of virus circulation in a given area. We expect that molecular epidemiologic studies will become a powerful tool for evaluating strategies to control, eliminate, and eventually eradicate measles
Efficient Quantum Tensor Product Expanders and k-designs
Quantum expanders are a quantum analogue of expanders, and k-tensor product
expanders are a generalisation to graphs that randomise k correlated walkers.
Here we give an efficient construction of constant-degree, constant-gap quantum
k-tensor product expanders. The key ingredients are an efficient classical
tensor product expander and the quantum Fourier transform. Our construction
works whenever k=O(n/log n), where n is the number of qubits. An immediate
corollary of this result is an efficient construction of an approximate unitary
k-design, which is a quantum analogue of an approximate k-wise independent
function, on n qubits for any k=O(n/log n). Previously, no efficient
constructions were known for k>2, while state designs, of which unitary designs
are a generalisation, were constructed efficiently in [Ambainis, Emerson 2007].Comment: 16 pages, typo in references fixe
Spitzer's Identity and the Algebraic Birkhoff Decomposition in pQFT
In this article we continue to explore the notion of Rota-Baxter algebras in
the context of the Hopf algebraic approach to renormalization theory in
perturbative quantum field theory. We show in very simple algebraic terms that
the solutions of the recursively defined formulae for the Birkhoff
factorization of regularized Hopf algebra characters, i.e. Feynman rules,
naturally give a non-commutative generalization of the well-known Spitzer's
identity. The underlying abstract algebraic structure is analyzed in terms of
complete filtered Rota-Baxter algebras.Comment: 19 pages, 2 figure
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