74 research outputs found
Improved lower bounds for the ground-state energy of many-body systems
New lower bounds for the binding energy of a quantum-mechanical system of
interacting particles are presented. The new bounds are expressed in terms of
two-particle quantities and improve the conventional bounds of the Hall-Post
type. They are constructed by considering not only the energy in the
two-particle system, but also the structure of the pair wave function. We apply
the formal results to various numerical examples, and show that in some cases
dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.
Soft two-meson-exchange nucleon-nucleon potentials. I. Planar and crossed-box diagrams
Pion-meson-exchange nucleon-nucleon potentials are derived for two nucleons
in the intermediate states. The mesons we include are (i) pseudoscalar mesons:
; (ii) vector mesons: ; (iii) scalar
mesons: ; and (iv) the
contribution from the Pomeron. Strong dynamical pair suppression is assumed,
and at the nucleon-nucleon-meson vertices Gaussian form factors are
incorporated into the relativistic two-body framework using a dispersion
representation for the pion- and meson-exchange amplitudes. The Fourier
transformations are performed using factorization techniques for the energy
denominators. The potentials are first calculated in the adiabatic
approximation to all planar and crossed three-dimensional momentum-space
-meson diagrams. Next, we calculate the corrections.Comment: 28 pages RevTeX, 8 postscript figures; revised version as to appear
in Phys. Rev.
An Interactive EA for Multifractal Bayesian Denoising
International audienceWe present in this paper a multifractal bayesian denoising technique based on an interactive EA. The multifractal denoising algorithm that serves as a basis for this technique is adapted to complex images and signals, and depends on a set of parameters. As the tuning of these parameters is a difficult task, highly dependent on psychovisual and subjective factors, we propose to use an interactive EA to drive this process. Comparative denoising results are presented with automatic and interactive EA optimisation. The proposed technique yield efficient denoising in many cases, comparable to classical denoising techniques. The versatility of the interactive implementation is however a major advantage to handle difficult images like IR or medical images
"Dark energy" in the Local Void
The unexpected discovery of the accelerated cosmic expansion in 1998 has
filled the Universe with the embarrassing presence of an unidentified "dark
energy", or cosmological constant, devoid of any physical meaning. While this
standard cosmology seems to work well at the global level, improved knowledge
of the kinematics and other properties of our extragalactic neighborhood
indicates the need for a better theory. We investigate whether the recently
suggested repulsive-gravity scenario can account for some of the features that
are unexplained by the standard model. Through simple dynamical considerations,
we find that the Local Void could host an amount of antimatter
() roughly equivalent to the mass of a typical
supercluster, thus restoring the matter-antimatter symmetry. The antigravity
field produced by this "dark repulsor" can explain the anomalous motion of the
Local Sheet away from the Local Void, as well as several other properties of
nearby galaxies that seem to require void evacuation and structure formation
much faster than expected from the standard model. At the global cosmological
level, gravitational repulsion from antimatter hidden in voids can provide more
than enough potential energy to drive both the cosmic expansion and its
acceleration, with no need for an initial "explosion" and dark energy.
Moreover, the discrete distribution of these dark repulsors, in contrast to the
uniformly permeating dark energy, can also explain dark flows and other
recently observed excessive inhomogeneities and anisotropies of the Universe.Comment: 6 pages, accepted as a Letter to the Editor by Astrophysics and Space
Scienc
Scalar meson dynamics in Chiral Perturbation Theory
A comparison of the linear sigma model (LM) and Chiral Perturbation
Theory (ChPT) predictions for pion and kaon dynamics is presented. Lowest and
next-to-leading order terms in the ChPT amplitudes are reproduced if one
restricts to scalar resonance exchange. Some low energy constants of the order
ChPT Lagrangian are fixed in terms of scalar meson masses. Present values
of these low energy constants are compatible with the LM dynamics. We
conclude that more accurate values would be most useful either to falsify the
LM or to show its capability to shed some light on the controversial
scalar physics.Comment: 9 pages, REVTeX 4.0. Final version accepted for publicatio
Scalar sigma meson effects in rho and omega decays into pi0 pi0 gamma
The complementarity between Chiral Perturbation Theory and the Linear Sigma
Model in the scalar channel is exploited to study production in
and radiative decays, where the effects of a low mass scalar
resonance should manifest. The recently reported data on
seem to require the contribution of a low mass and
moderately narrow . The properties of this controversial state
could be fixed by improving the accuracy of these measurements. Data on
can also be accommodated in our framework, but are
much less sensitive to the properties.Comment: 17 pages, 4 figure
Charge asymmetries in e+e- -> pi+ pi- gamma at the phi resonance
We consider the forward-backward pion charge asymmetry for the
e^{+}e^{-}\to\pi^{+}\pi^{-}\gamma process. At tree level we consider
bremsstrahlung and double resonance contributions. Although the latter
contribution is formally sub-leading, it is enhanced at low dipion invariant
mass due to resonant effects. We consider also four alternative models
to describe the final state radiation at the loop level: Resonance Chiral
Perturbation Theory, Unitarized Chiral Perturbation Theory, Kaon Loop Model and
Linear Sigma Model. The last three models yield results compatible with
experimental data. The Kaon Loop Model requires an energy dependent phase to
achieve the agreement.Comment: Revised version, conclusions changed, 11 pages, 8 figs, version to
appear in PL
DES15E2mlf: a spectroscopically confirmed superluminous supernova that exploded 3.5 Gyr after the big bang
We present the Dark Energy Survey (DES) discovery of DES15E2mlf, the most distant superluminous supernova (SLSN) spectroscopically confirmed to date. The light curves and Gemini spectroscopy of DES15E2mlf indicate that it is a Type I superluminous supernova (SLSN-I) at z = 1.861 (a lookback time of ∼10 Gyr) and peaking at MAB = −22.3 ± 0.1 mag. Given the high redshift, our data probe the rest-frame ultraviolet (1400–3500 Å) properties of the SN, finding velocity of the C III feature changes by ∼5600 km s−1 over 14 d around maximum light. We find the host galaxy of DES15E2mlf has a stellar mass of 3.5+3.6 −2.4 × 109 M, which is more massive than the typical SLSN-I host galaxy
Effects of early-life stress on cognitive function and hippocampal structure in female rodents
Antiretroviral-naive and -treated HIV-1 patients can harbour more resistant viruses in CSF than in plasma
Objectives The neurological disorders in HIV-1-infected patients remain prevalent. The HIV-1 resistance in plasma and CSF was compared in patients with neurological disorders in a multicentre study. Methods Blood and CSF samples were collected at time of neurological disorders for 244 patients. The viral loads were >50 copies/mL in both compartments and bulk genotypic tests were realized. Results On 244 patients, 89 and 155 were antiretroviral (ARV) naive and ARV treated, respectively. In ARV-naive patients, detection of mutations in CSF and not in plasma were reported for the reverse transcriptase (RT) gene in 2/89 patients (2.2%) and for the protease gene in 1/89 patients (1.1%). In ARV-treated patients, 19/152 (12.5%) patients had HIV-1 mutations only in the CSF for the RT gene and 30/151 (19.8%) for the protease gene. Two mutations appeared statistically more prevalent in the CSF than in plasma: M41L (P = 0.0455) and T215Y (P = 0.0455). Conclusions In most cases, resistance mutations were present and similar in both studied compartments. However, in 3.4% of ARV-naive and 8.8% of ARV-treated patients, the virus was more resistant in CSF than in plasma. These results support the need for genotypic resistance testing when lumbar puncture is performe
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