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R. D. Amado

Publications and source records attributed to R. D. Amado.

At least 19 recordsLinked to original sources

Skyrmion-anti-Skyrmion Annihilation with Omega Mesons

We study numerically the annihilation of an omega-stabilized Skyrmion and an anti-Skyrmion in three spatial dimensions. To our knowledge this is a first successful simulation of Skyrmion-anti-Skyrmion annihilation which follows through to the point where the energy is carried by outgoing meson waves. We encounter instabilities similar to those encountered is earlier calculations, but in our case these are not fatal and we are able to simulate through this process with a global energy loss of less than 8%, and to identify robust features of the final radiation pattern. The system passes through a singular configuration at the time of half-annihilation. This is followed by the onset of fast oscillations which are superimposed on the smoother process which leads to the appearence of outgoing spherical waves. We investigate the two prominent features of this process, the proliferation of small, fast oscillations, and the singular intermediate configuration. We find that our equations of motion allow for a regime in which the amplitude of certain small perturbations increases exponentially. This regime is similar but not identical to the situation pointed out earlier regarding the original Skyrme model. We argue that the singularity may be seen as the result of a pinch effect similar to that encountered in plasmas.

hep-ph

Two Skyrmion Dynamics with Omega Mesons

We present our first results of numerical simulations of two skyrmion dynamics using an $ω$-meson stabilized effective Lagrangian. We consider skyrmion-skyrmion scattering with a fixed initial velocity of $β=0.5$, for various impact parameters and groomings. The physical picture that emerges is surprisingly rich, while consistent with previous results and general conservation laws. We find meson radiation, skyrmion scattering out of the scattering plane, orbiting and capture to bound states.

hep-ph

Nucleon-Antinucleon Interaction from the Skyrme Model: II. Beyond the Product Ansatz

We calculate the full static interaction of a Skyrmion and an anti-Skyrmion as a function of separation and relative grooming. From this, using projection methods and Born-Oppenheimer mixing, we obtain the nucleon antinucleon interaction. We find agreement with the major features of the empirical interaction including the strong central attraction and the sharp onset of annihilation at about 1 fm.

nucl-th

Domains of Disoriented Chiral Condensate

The probability distribution of neutral pion fraction from independent domains of disoriented chiral condensate is characterized. The signal for the condensate is clear for a small number of domains but is greatly reduced for more than three.

hep-ph

Nucleon-Antinucleon Interaction from the Skyrme Model

We calculate the nucleon-antinucleon static potential in the Skyrme model using the product ansatz and including some finite $N_C$ (number of colors) corrections. The mid and long range part of the spin-spin and tensor force are correctly given in both iso-spin channels while the central interaction has insufficient mid-range attraction. This is a well known problem of the product ansatz that should be repaired with better Skyrme dynamics.

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On the relationship of the scaled phase space and Skyrme-coherent state treatments of proton antiproton annihilation at rest

We discuss pion multiplicities and single pion momentum spectra from proton antiproton annihilation at rest. Both the scaled phase space model and the Skyrme-coherent state approach describe these observables well. In the coherent state approach the puzzling size of the scale parameter relating the phase space integrals for different multiplicities is replaced by a well defined weight function. The strength of this function is determined by the intensity of the classical pion field and its spatial extent is of order 1 fm.

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Pion correlation from Skyrmion-AntiSkyrmion annihilation

We study two pion correlations from Skyrmion and antiSkyrmion collision, using the product ansatz and an approximate random grooming method for nucleon projection. The spatial-isospin coupling inherent in the Skyrme model, along with empirical averages, leads to correlations not only among pions of like charges but also among unlike charge types.

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Nucleon-Antinucleon Annihilation in Large Nc QCD with rho and omega Mesons

We use classical/large Nc (number of colors) QCD to study nucleon--antinucleon annihilation at rest. We include pion, rho and omega fields in the classical dynamics, starting from the nonlinear sigma model. We begin with a spherical blob of pionic matter with zero baryon number and energy of twice the nucleon mass. This evolves according to the classical dynamics to pion and vector meson fields into the radiation zone. The radiation fields are quantized using the method of coherent states modified to include isospin and four momentum conservation. Empirical information is extracted from that coherent state. We find good agreement with data for single particle momentum and number spectra, and with branching ratios to many annihilation channels. All this emerges with nearly no free parameters.

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Quantum Phenomenology for the Disoriented Chiral Condensate

We consider the quantum state describing theDisoriented Chiral Condensate (DCC), which may be produced in high energy collisions. We show how a mean field treatment of the quantum equations corresponding to the classical linear sigma model leads to a squeezed state description of the pions emerging from the DCC. We examine various squeezed and coherent state descriptions of those pions with particular attention to charge and number fluctuations. We also study the phenomenology of multiple DCC domains.

hep-ph

Classical and Quantum Coherent State Description of Nucleon-Antinucleon Annihilation at Rest in the Skyrme Model with Omega Mesons

We model the $N\bar{N}$ system at rest as a baryon number zero lump in the Skyrme model including the $ω$ field. We integrate the classical equations of motion from the highly non-perturbative annihilation region into the non-interacting radiation zone. Subsequent coherent state quantization of the radiation field gives a good description of the pion spectrum from annihilation at rest.

hep-ph

Coherent state formulation of pion radiation from nucleon antinucleon annihilation

We assume that nucleon antinucleon annihilation is a fast process leading to a classical coherent pion pulse. We develop the quantum description of such pion waves based on the method of coherent states. We study the consequences of such a description for averages of charge types and moments of distributions of pion momenta with iso-spin and four-momentum conservation taken into account. We briefly discuss the applicability of our method to annihilation at rest, where we find agreement with experiment, and suggest other avenues for its use.

hep-ph

Coherent Pion Radiation From Nucleon Antinucleon Annihilation

A unified picture of nucleon antinucleon annihilation into pions emerges from a classical description of the pion wave produced in annihilation and the subsequent quantization of that wave as a coherent state. When the constraints of energy-momentum and iso-spin conservation are imposed on the coherent state, the pion number distribution and charge ratios are found to be in excellent agreement with experiment.

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The Skyrme model description of the spin-orbit force

We examine the derivation of the spin-orbit force from the Skyrme model. We find substantial agreement with phenomenological potentials. We show that a systematic and simultaneous treatment of all components of the kinetic energy introduces a minus sign relative to previous calculations for the iso-spin independent part of the interaction. We also explain the smallness of the iso-spin dependent part of the spin-orbit potential.

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Inertial parameters of the Skyrmion-Skyrmion system with the product ansatz

The kinetic energy of the Skyrmion-Skyrmion system is calculated in the product ansatz. The energy is expanded in a set of rotationally invariant quadratic functions of translational and iso-rotational velocities in the product ansatz and all inertial parameters are evaluated. Most of the iso-spin dependent parameters are small at separations larger than 1 fm. However, some parameters of the coupling between the iso-rotational velocities of the Skyrmions decay slowly, as $1/R$, when zero pion mass is used. Otherwise we find that the results are not sensitive to the addition of the pion mass term.

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Dynamics of antibaryon-baryon annihilation in the Skyrme model

We examine the dynamics of a baryon number zero lump in the Skyrme picture, as a model for annihilation in the $\bar{N}N$ system. We find that radiation propagates at the causal limit as a localized pulse and that the linearized theory gives a good approximation. Both of these results are contrary to findings in the Sine-Gordon model.

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Quartets of superdeformed bands and supersymmetry breaking

We examine the prediction of supersymmetric quantum mechanics that bands with identical gamma-ray energies occur in quartets. The experimental data suggest that this scenario is actually realized in nature. In the $A=150$ mass region, four known pairs of isospectral bands can be grouped in two quartets, while there are indications of such patterns around $A=190$. We introduce a small supersymmetry breaking, necessary to describe the details of the data. We derive relations among the transition rates that can be used to test our predictions. pacs: 21.10.Re, 11.30.Pb, 21.60.Fw, 23.20.Lv

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