arXiv subjects

Robert S. Plant

Publications and source records attributed to Robert S. Plant.

4 recordsLinked to original sources

arXiv2026

An observationally constrained probabilistic trigger for organized deep convection in an NWP ensemble

A novel stochastic parametrization scheme representing organized convection is described. The effects of mesoscale convective systems (MCSs) are represented in an observationally constrained manner, by probabilistically triggering an MCS scheme in regions of enhanced environmental total column water vapour. In combination with the probabilistic trigger, patterns with given spatiotemporal scales determine where and when the scheme is active. Our scheme builds on the multiscale coherent structure parametrization (MCSP), which represents the top-heavy heating structure associated with MCSs. The original and new MCSP schemes are tested in a numerical weather prediction (NWP) ensemble. Both MCSP schemes improve the spatiotemporal scales of tropical precipitation compared to a control. When the spread-error relationship of tropical precipitation is analysed, the new scheme successfully boosts spread compared to original MCSP, improving the underdispersion of the ensemble seen with the original MCSP.

physics.ao-ph↗

arXiv2001

Mesonic fluctuations in a nonlocal Nambu-Jona-Lasinio model

The effects of meson fluctuations are studied in a nonlocal generalization of the Nambu-Jona-Lasinio model, by including terms of next-to-leading order (NLO) in 1/N_c. In the model with only scalar and pseudoscalar interactions NLO contributions to the quark condensate are found to be very small. This is a result of cancellation between virtual mesons and Fock terms, which occurs for the parameter sets of most interest. In the quark self-energy, similar cancellations arise in the tadpole diagrams, although not in other NLO pieces which contribute at the \sim 25% level. The effects on pion properties are also found to be small. NLO contributions from real $ππ$ intermediate states increase the sigma meson mass by $\sim 30%$. In an extended model with vector and axial interactions, there are indications that NLO effects could be larger.

hep-ph↗

arXiv1997

Meson properties in an extended nonlocal NJL model

We consider a nonlocal version of the NJL model, based on a separable quark-quark interaction. The interaction is extended to include terms that bind vector and axial-vector mesons. The nonlocality means that no further regulator is required. Moreover the model is able to confine the quarks by generating a quark propagator without poles at real energies. Working in the ladder approximation, we calculate amplitudes in Euclidean space and discuss features of their continuation to Minkowski energies. Conserved currents are constructed and we demonstrate their consistency with various Ward identities. Various meson masses are calculated, along with their strong and electromagnetic decay amplitudes. We also calculate the electromagnetic form factor of the pion, as well as form factors associated with the processes gamma gamma^* to pi^0 and omega to pi^0 gamma^*. The results are found to lead to a satisfactory phenomenology and lend some dynamical support to the idea of vector-meson dominance.

hep-ph↗

arXiv1995

$ρ\to 4π$ in chirally symmetric models

The decays $ρ^0\to 2π^+2π^-$ and $ρ^0\to 2π^0π^+π^-$ are studied using various effective Lagrangians for $π$ and $ρ$ (and in some cases $a_1$) mesons, all of which respect the approximate chiral symmetry of the strong interaction. Partial widths of the order of 1 keV or less are found in all cases. These are an order of magnitude smaller than recent predictions based on non-chiral models.

hep-ph↗