From meson-nucleon scattering to vector mesons in nuclear matter

We employ meson-nucleon scattering data to deduce the properties of the low-mass vector mesons in nuclear matter, and present results for the $\rho$ and $\omega$ in-medium spectral functions. The corresponding thermal emission rate for lepton pairs is also discussed.Comment: Talk given at 28th International Workshop on Gross Properties of Nuclei and Nuclear Excitations, Hirschegg, Austria, 16-22 Jan. 200

Analysis of the ΣQ\Sigma_Q baryons in the nuclear matter with the QCD sum rules

In this article, we extend our previous work to study the $\Sigma$-type heavy baryons $\Sigma_c$ and $\Sigma_b$ in the nuclear matter using the QCD sum rules, and obtain three coupled QCD sum rules for the masses $M_{\Sigma_Q}^*$, vector self-energies $\Sigma_v$ and pole residues $\lambda^*_{\Sigma_Q}$ in the nuclear matter. Then we take into account the effects of the unequal pole residues from different spinor structures, and normalize the masses from the QCD sum rules in the vacuum to the experimental data, and obtain the mass-shifts $\delta M_{\Sigma_c}=-123\,\rm{MeV}$ and $\delta M_{\Sigma_b}=-375\,\rm{MeV}$ in the nuclear matter.Comment: 7 pages, 2 figures, revised versio

Plant pathogenic bacterium Ralstonia solanacearum can rapidly evolve tolerance to antimicrobials produced by Pseudomonas biocontrol bacteria.

Soil-borne plant pathogens significantly threaten crop production due to lack of effective control methods. One alternative to traditional agrochemicals is microbial biocontrol, where pathogen growth is suppressed by naturally occurring bacteria that produce antimicrobial chemicals. However, it is still unclear if pathogenic bacteria can evolve tolerance to biocontrol antimicrobials and if this could constrain the long-term efficacy of biocontrol strategies. Here we used an in vitro experimental evolution approach to investigate if the phytopathogenic Ralstonia solanacearum bacterium, which causes bacterial wilt disease, can evolve tolerance to antimicrobials produced by Pseudomonas bacteria. We further asked if tolerance was specific to pairs of R. solanacearum and Pseudomonas strains and certain antimicrobial compounds produced by Pseudomonas. We found that while all R. solanacearum strains could initially be inhibited by Pseudomonas strains, this inhibition decreased following successive subculturing with or without Pseudomonas supernatants. Using separate tolerance assays, we show that the majority of R. solanacearum strains evolved increased tolerance to multiple Pseudomonas strains. Mechanistically, evolved tolerance was most likely linked to reduced susceptibility to orfamide lipopeptide antimicrobials secreted by Pseudomonas strains in our experimental conditions. Some levels of tolerance also evolved in the control treatments, which was likely correlated response due to adaptations to the culture media. Together, these results suggest that plant-pathogenic bacteria can rapidly evolve increased tolerance to bacterial antimicrobial compounds, which could reduce the long-term efficacy of microbial biocontrol. [Abstract copyright: © The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology.

Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter

The bulk viscosity of the neutron star matter due to the direct Urca processes involving nucleons, electrons and muons is studied taking into account possible superfluidity of nucleons in the neutron star cores. The cases of singlet-state pairing or triplet-state pairing (without and with nodes of the superfluid gap at the Fermi surface) of nucleons are considered. It is shown that the superfluidity may strongly reduce the bulk viscosity. The practical expressions for the superfluid reduction factors are obtained. For illustration, the bulk viscosity is calculated for two models of dense matter composed of neutrons, protons,electrons and muons. The presence of muons affects the bulk viscosity due to the direct Urca reactions involving electrons and produces additional comparable contribution due to the direct Urca reactions involving muons. The results can be useful for studying damping of vibrations of neutron stars with superfluid cores.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy and Astrophysic

Low-momentum interactions for nuclei

We show how the renormalization group is used to construct a low-momentum nucleon-nucleon interaction V_{low k}, which unifies all potential models used in nuclear structure calculations. V_{low k} can be directly applied to the nuclear shell model or to nucleonic matter without a G matrix resummation. It is argued that V_{low k} parameterizes a high-order chiral effective field theory two-nucleon force. We use cutoff dependence as a tool to assess the error in the truncation of nuclear forces to two-nucleon interactions and introduce a low-momentum three-nucleon force, which regulates A=3,4 binding energies. The adjusted three-nucleon interaction is perturbative for small cutoffs. In contrast to other precision interactions, the error due to missing many-body forces can be estimated, when V_{low k} and the corresponding three-nucleon force are used in nuclear structure calculations and the cutoff is varied.Comment: 10 pages, 5 figures, talk at INT workshop on Nuclear Forces and the Quantum Many-Body Problem, Seattle, October 200

Nuclear Effects on Bremsstrahlung Neutrino Rates of Astrophysical Interest

We calculate in this work the rates for the neutrino pair production by nucleon-nucleon bremsstrahlung taking into account the full contribution from a nuclear one-pion-exchange potential. It is shown that if the temperatures are low enough ($T \leq 20 MeV$), the integration over the nuclear part can be done for the general case, ranging from the completely degenerate (D) to the non-degenerate (ND) regime. We find that the inclusion of the full nuclear contribution enhances the neutrino pair production by $nn$ and $pp$ bremsstrahlung by a factor of about two in both the D and ND limits when compared with previous calculations. This result may be relevant for the physical conditions of interest in the semitransparent regions near the neutrinosphere in type II supernovae, cooling of neutron stars and other astrophysical situations.Comment: 11 pages, no figures, LaTex file. submitted to PR

Saxion Emission from SN1987A

We study the possibility of emission of the saxion, a superpartner of the axion, from SN1987A. The fact that the observed neutrino pulse from SN1987A is in excellent agreement with the current theory of supernovae places a strong bound on the energy loss into any non-standard model channel, therefore enabling bounds to be placed on the decay constant, f_a, of a light saxion. The low-energy coupling of the saxion, which couples at high energies to the QCD gauge field strength, is expected to be enhanced from QCD scaling, making it interesting to investigate if the saxion could place stronger bounds on f_a than the axion itself. Moreover, since the properties of the saxion are determined by f_a, a constraint on this parameter can be translated into a constraint on the supersymmetry breaking scale. We find that the bound on f_a from saxion emission is comparable with the one derived from axion emission due to a cancellation of leading-order terms in the soft-radiation expansion.Comment: 18 pages, 2 figures; minor changes, typos corrected, version to appear in JHE