Modifications of the Rho Meson from the Virtual Pion Cloud in Hot and Dense Matter

The modification of the rho-meson self-energy due to the coupling to in-medium pions is calculated consistently at finite baryon density and temperature, keeping the full 3-momentum dependence in a gauge invariant way. As a function of nucleon density, the rho-meson spectral function is strongly enhanced in the invariant mass region M < 650 MeV, while the maximum, i.e. the pole mass, is slightly shifted upwards. As a function of temperature, for fixed nucleon density, the imaginary part of the self-energy increases further due to Bose-enhancement. At the same time the mass shift from the real part becomes very large. As a consequence of these medium effects, the dilepton rate in the low-mass region M < 650 MeV increases strongly, while the peak at M = 770 MeV disappears.Comment: 18 pages, 9 figures; resonance contributions adde

Massive Yang-Mills for Vector and Axial-Vector Spectral Functions at Finite Temperature

The hadronic mechanism which leads to chiral symmetry restoration is explored in the context of the rho-pi-a_1 system using Massive Yang-Mills, a hadronic effective theory which governs their microscopic interactions. In this approach, vector and axial-vector mesons are implemented as gauge bosons of a local chiral gauge group. We have previously shown that this model can describe the experimentally measured vector and axial-vector spectral functions in vacuum. Here, we carry the analysis to finite temperatures by evaluating medium effects in a pion gas and calculating thermal spectral functions. We find that the spectral peaks in both channels broaden along with a noticeable downward mass shift in the a_1 spectral peak and negligible movement of the rho peak. The approach toward spectral function degeneracy is accompanied by a reduction of chiral order parameters, i.e., the pion decay constant and scalar condensate. Our findings suggest a mechanism where the chiral mass splitting induced in vacuum is burned off. We explore this mechanism and identify future investigations which can further test it.Comment: 28 pages, 24 figure

Momentum Dependence of the Pion Cloud for Rho Mesons in Nuclear Matter

We extend hadronic models for rho-meson propagation in cold nuclear matter via coupling to in-medium pions to include finite three-momentum. Special care is taken to preserve gauge invariance. Consequences for photoabsorption on the proton and on nuclei as well as for the dilepton production in relativistic heavy-ion collisions are discussed.Comment: 32 pages, 18 figures. Corrected version, accepted for publication in Nucl. Phys.

The Influence of Reaction Rates on the Final p-Abundances

The astrophysical p-process is responsible for the origin of the proton rich nuclei,which are heavier than iron. A huge network involving thousands of reaction rates is necessary to calculate the final p-abundances. But not all rates included in the network have a strong influence on the p-nuclei abundances. The p-process was investigated using a full nuclear reaction network for a type II supernovae explosion when the shock front passes through the O/Ne layer. Calculations were done with a multi-layer model adopting the seed of a pre-explosion evolution of a 25 mass star. In extensive simulations we investigated the impact of single reaction rates on the final p-abundances. The results are important for the strategy of future experiments in this field.Comment: 4 page

A Microscopic Calculation of Photoabsorption Cross Sections on Protons and Nuclei

A recently developed model for $\rho$-meson propagation in dense hadronic matter is applied to total photoabsorption cross sections in $\gamma$-proton and $\gamma$-nucleus reactions. Within the vector dominance model the photon coupling to the virtual pion cloud of the nucleon, two-body meson-exchange currents, as well as $\gamma$-nucleon resonances are included. Whereas the $\gamma p$ reaction is determined by the low-density limit of the model, higher orders in the nuclear density are important to correctly account for the experimental spectra observed on both light and heavy nuclei over a wide range of photon energies, including the region below the pion threshold. In connection with soft dilepton spectra in high-energy heavy-ion collisions we emphasize the importance of photoabsorption to further constrain the parameters of the model.Comment: 10 pages RevTeX, 2 eps-figure

Estimation from quantized Gaussian measurements: when and how to use dither

Subtractive dither is a powerful method for removing the signal dependence of quantization noise for coarsely quantized signals. However, estimation from dithered measurements often naively applies the sample mean or midrange, even when the total noise is not well described with a Gaussian or uniform distribution. We show that the generalized Gaussian distribution approximately describes subtractively dithered, quantized samples of a Gaussian signal. Furthermore, a generalized Gaussian fit leads to simple estimators based on order statistics that match the performance of more complicated maximum likelihood estimators requiring iterative solvers. The order statistics-based estimators outperform both the sample mean and midrange for nontrivial sums of Gaussian and uniform noise. Additional analysis of the generalized Gaussian approximation yields rules of thumb for determining when and how to apply dither to quantized measurements. Specifically, we find subtractive dither to be beneficial when the ratio between the Gaussian standard deviation and quantization interval length is roughly less than one-third. When that ratio is also greater than 0.822/K^0.930 for the number of measurements K > 20, estimators we present are more efficient than the midrange.https://arxiv.org/abs/1811.06856Accepted manuscrip

Legal medical consideration of alzheimer’s disease patients’ dysgraphia and cognitive dysfunction: a 6 month follow up

Background: The purpose of this study was to investigate the ability of Alzheimer’s disease (AD) patients to express intentions and desires, and their decision-making capacity. This study examines the findings from a 6-month follow-up of our previous results in which 30 patients participated. Materials and methods: The patient’s cognition was examined by conducting the tests of 14 questions and letter-writing ability over a period of 19 days, and it was repeated after 6 months. The difference between these two cognitive measures (PQ1 before–PQ2 before), tested previously and later the writing test, was designated DΔ before. The test was repeated after 6 months, and PQ1 after–PQ2 after was designated DΔ after. Results: Several markedly strong relationships between dysgraphia and other measures of cognitive performance in AD patients were observed. The most aged patients (over 86 years), despite less frequency, maintain the cognitive capacity manifested in the graphic expressions. A document, written by an AD patient presents an honest expression of the patient’s intention if that document is legible, clear, and comprehensive. Conclusion: The identification of impairment/deficits in writing and cognition during different phases of AD may facilitate the understanding of disease progression and identify the occasions during which the patient may be considered sufficiently lucid to make decisions. Keywords: cognition, intentions, unfit to plead, consen

Photon production in relativistic nuclear collisions at SPS and RHIC energies

Chiral Lagrangians are used to compute the production rate of photons from the hadronic phase of relativistic nuclear collisions. Special attention is paid to the role of the pseudovector a_1 meson. Calculations that include reactions with strange mesons, hadronic form factors and vector spectral densities consistent with dilepton production, as well as the emission from a quark-gluon plasma and primordial nucleon-nucleon collisions, reproduce the photon spectra measured at the Super Proton Synchrotron (SPS). Predictions for the Relativistic Heavy Ion Collider (RHIC) are made.Comment: Work presented at the 26th annual Montreal-Rochester-Syracuse-Toronto conference (MRST 2004) on high energy physics, Montreal, QC, Canada, 12-14 May 2004. 8 pages, 3 figure