Neutron density distribution and neutron skin thickness of 208^{208}Pb

We present and discuss numerical predictions for the neutron density distribution of $^{208}$Pb using various non-relativistic and relativistic mean-field models for the nuclear structure. Our results are compared with the very recent pion photoproduction data from Mainz. The parity-violating asymmetry parameter for elastic electron scattering at the kinematics of the PREX experiment at JLab and the neutron skin thickness are compared with the available data. We consider also the dependence between the neutron skin and the parameters of the expansion of the symmetry energy.Comment: 9 pages, 6 figures, latest MAMI data use

Effective Fluid Description of the Dark Universe

We propose an effective anisotropic fluid description for a generic infrared-modified theory of gravity. In our framework, the additional component of the acceleration, commonly attributed to dark matter, is explained as a radial pressure generated by the reaction of the dark energy fluid to the presence of baryonic matter. Using quite general assumptions, and a microscopic description of the fluid in terms of a Bose-Einstein condensate of gravitons, we find the static, spherically symmetric solution for the metric in terms of the Misner-Sharp mass function and the fluid pressure. At galactic scales, we correctly reproduce the leading MOND-like $\log(r)$ and subleading $(1/r)\,\log(r)$ terms in the weak-field expansion of the potential. Our description also predicts a tiny (of order $10^{-6}$ for a typical spiral galaxy) Machian modification of the Newtonian potential at galactic scales, which is controlled by the cosmological acceleration.Comment: 13 pages, no figures. Replaced version: major revisions in the introduction, microscopic derivation of Tully-Fisher relation using Bose-Einstein condensate of gravitons. Some typos correcte

Elastic and quasi-elastic electron scattering off nuclei with neutron excess

We present theoretical predictions for electron scattering on oxygen and calcium isotopic chains. The calculations are done within the framework of the distorted-wave Born approximation and the proton and neutron density distributions are evaluated adopting a relativistic Dirac-Hartree model. We present results for the elastic and quasi-elastic cross sections and for the parity-violating asymmetry. As a first step, the results of the models are tested in comparison with some of the data available for elastic and quasi-elastic scattering on 16O and 40Ca nuclei. Then, the evolution of some nuclear properties is investigated as a function of the neutron number. We also present a comparison with the parity-violating asymmetry parameter obtained by the PREX Collaboration on 208Pb and give a prediction for the future experiment CREX on 48Ca.Comment: 37 pages, 17 figures. version accepted for publication in the Physical Review C. arXiv admin note: text overlap with arXiv:0809.4124 by other author

Proton-Nucleus Elastic Scattering: Comparison between Phenomenological and Microscopic Optical Potentials

Elastic scattering is a very important process to understand nuclear interactions in finite nuclei. Despite decades of efforts, the goal of reaching a coherent description of this physical process in terms of microscopic forces is still far from being completed. In previous papers (Phys. Rev. C93, 034619 (2016), Phys. Rev. C96, 044001 (2017)) we derived a nonrelativistic theoretical optical potential from nucleon-nucleon chiral potentials at fourth (N3LO) and fifth order (N4LO). We checked convergence patterns and established theoretical error bands. With this work we study the performances of our optical potential in comparison with those of a successful nonrelativistic phenomenological optical potential in the description of elastic proton scattering data on several isotopic chains at energies around and above 200 MeV. We use the same framework and the same approximations of our previous papers, where the nonrelativistic optical potential is derived at the first-order term within the spectator expansion of the multiple scattering theory and adopting the impulse approximation and the optimum factorization approximation. The cross sections and analyzing powers for elastic proton scattering off calcium, nickel, tin, and lead isotopes are presented for several incident proton energies, exploring the range $156 \le E \le 333$ MeV, where experimental data are available. In addition, we provide theoretical predictions for Ni56 at 400 MeV, which is of interest for the future experiments at EXL. Our results indicate that microscopic optical potentials derived from nucleon-nucleon chiral potentials at N4LO can provide reliable predictions for the cross section and the analyzing power both of stable and exotic nuclei, even at energies where the reliability of the chiral expansion starts to be questionable.Comment: 26 pages, 10 figures, submitted to PR

Emergence of a Dark Force in Corpuscular Gravity

We investigate the emergent laws of gravity when Dark Energy and the de Sitter space-time are modelled as a critical Bose-Einstein condensate of a large number of soft gravitons $N_{\rm G}$. We argue that this scenario requires the presence of various regimes of gravity in which $N_{\rm G}$ scales in different ways. Moreover, the local gravitational interaction affecting baryonic matter can be naturally described in terms of gravitons pulled out from this Dark Energy condensate (DEC). We then explain the additional component of the acceleration at galactic scales, commonly attributed to dark matter, as the reaction of the DEC to the presence of baryonic matter. This additional dark force is also associated to gravitons pulled out from the DEC and correctly reproduces the MOND acceleration. It also allows for an effective description in terms of General Relativity sourced by an anisotropic fluid. We finally calculate the mass ratio between the contribution of the apparent dark matter and the baryonic matter in a region of size $r$ at galactic scales and show that it is consistent with the $\Lambda$CDM predictions.Comment: 20 pages, no figure

Thermal QCD for non-perturbative renormalization of composite operators

We present our progresses in the use of the non-perturbative renormalization framework based on considering QCD at finite temperature with shifted and twisted (for quarks only) boundary conditions in the compact direction. We report our final results in the application of this method for the non-perturbative renormalization of the flavor-singlet local vector current. We then discuss the more challenging case of the renormalization of the energy-momentum tensor, and show preliminary results on the relevant one-point functions for the computation of the renormalization constants of its non-singlet components.Comment: 9 pages, 2 figures, contribution to the 39th International Symposium on Lattice Field Theory, 8th-13th August, 2022, Bonn, German

Microscopic optical potentials for medium-mass isotopes derived at the first order of the Watson multiple scattering theory

We perform a first-principle calculation of optical potentials for nucleon elastic scattering off medium-mass isotopes. Fully based on a saturating chiral Hamiltonian, the optical potentials are derived by folding nuclear density distributions computed with ab initio self-consistent Green's function theory with a nucleon-nucleon $t$ matrix computed with a consistent chiral interaction. The dependence on the folding interaction as well as the convergence of the target densities are investigated. Numerical results are presented and discussed for differential cross sections and analyzing powers, with focus on elastic proton scattering off Calcium and Nickel isotopes. Our optical potentials generally show a remarkable agreement with the available experimental data for laboratory energies in the range 65-200 MeV. We study the evolution of the scattering observables with increasing proton-neutron asymmetry by computing theoretical predictions of the cross section and analyzing power over the Calcium and Nickel isotopic chains

Elastic Antiproton-Nucleus Scattering from Chiral Forces

Elastic scattering of antiprotons off $^4$He, $^{12}$C, and $^{16,18}$O is described for the first time with a totally microscopic approach based on the calculation of an optical potential (OP) describing the antiproton-target interaction. The OP is derived using the recent antiproton-nucleon ($\bar{p}N$) chiral interaction to calculate the $\bar{p}N$ $t$ matrix, while the target densities are computed with the ab initio no-core shell model using chiral interactions as well. Our results are in a good agreement with the existing experimental data and the results computed at different chiral orders of the $\bar{p}N$ interaction display the convergence pattern expected from the theory

Scientific note: varroa mite eradication, the strange case of Gorgona Island

Varroa mites are vectors for several bee viruses contributing also to their diffusion worldwide (Martin 2001; Di Prisco et al. 2011; Cersini et al. 2013). The tripartite relationship among bees, mites, and viruses is thought to be responsible for the loss of a large amount of colonies (Highfield et al. 2009; Berthoud et al. 2010; Francis et al. 2013). Before the arrival of Varroa destructor , virus prevalence was lower (Martin et al. 2012). The mites have contributed to spread the viruses which could be correlated to the high number of mite-infested honey bee colony losses (Berthoud et al. 2010; Francis et al. 2013). Since the varroa mite arrival, control of varroosis has become necessary (Moritz et al. 2010). Such control is focused on the coexistence between honeybees and mites. A trial to eradicate the mite from isolated areas has not been successful. Experiments carried out to eradicate varroa mite by use of several coordinated treatments in Jersey, an island in the English Channel, did not succeed, showing how difficult it is to eradicate this ecto-parasite from an infested area (Sampson and Martin 1999). The aim of this study is to report the disappearance of varroa mite from the island of Gorgona (43° 26′ N; 9° 54′ E) following several treatments in a single apiary kept in complete isolation. Furthermore, after the varroa disappearance, the honeybee viral load has been analyzed. Gorgona Island has been chosen because it provides suitable conditions to guarantee continuous monitoring and isolation to avoid new reintroduction of bee pathogens and pests

Engaging with the pragmatics of relational thinking, leverage points and transformations – Reply to West et al.

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