Dissertations / Theses on the topic 'Relativistic mean field'
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Centelles, Aixalà Mario. "Semiclassical approach to relativistic nuclear mean field theory." Doctoral thesis, Universitat de Barcelona, 1992. http://hdl.handle.net/10803/1593.
Full textThe success of semi-classical models in non-relativistic nuclear physics provides a very strong motivation for investigating similar methods in the relativistic context, where only the pure Thomas-Fermi approximation had been studied. In this thesis we set up the semi-classical expansion in relativistic nuclear mean field theory, including gradient corrections of order h(2) to the Thomas-Fermi model, and investigate several applications to nuclear systems.
On the basis of Wigner transform techniques, a. recursive scheme to obtain the semi-classical h(2) expansion of the propagator associated with a time-independent single-particle Hamiltonian with matrix structure is presented. We focus our attention on the application of the method to a Dirac Hamiltonian related to relativistic nuclear mean field theory, i.e., including a position-dependent effective mass and the time-like component of a. four-vector field. Compared with the non-relativistic case, the procedure is considerably more complicated owing to the matrix structure of the Hamiltonian. For this reason the "h", expansion is pushed to order h(2) only. A detailed derivation is given of the h(2)-order Wigner-Kirkwood expansion of the relativistic density matrix, in terms of the gradients of the vector and the scalar field, as well as of the expansion of the particle and energy densities. The idempotency of the semi-classical density matrix to second order in "h" is proven. The Wigner-Kirkwood expressions, as they stand, are not suitable to be employed in a self-consistent problem. Therefore, we obtain the corresponding density functional results. In this case the energy densities are expressed as a functional of the local density, the effective mass and their gradients.
The accuracy of the Wigner-Kirkwood series is tested on a. relativistic harmonic oscillator and perfect agreement with the Strutinsky averaged observables is found even in the highly relativistic regime. The density functional version is shown to be slightly less accurate, a feature already known in the non-relativistic case. It turns out that the semi-classical expressions represent the different quantities on average, that is, quantum fluctuations are averaged out. This model study shows that, for positive energy states, the derived semi-classical expansions contain all the relativistic ingredients, the difference with quantal results being due mainly to shell effects.
Extended Thomas-Fermi calculations, which· include h(2)-order gradient corrections, are performed for relativistic non-linear "sigma"- "omega" models using two kinds of Lagrangians which differ in the form of the scalar coupling for the isoscalar sigma meson. Comparing the semi-classical results of order h(2) (TFh(2)) with the Hartree results, we find that the TFh(2) approximation yields some underbinding when the effective mass (mº) of the model is small, and some overbinding when mº is large. For a value around mº/m = 0.65, both TFh(2) and Hartree would roughly yield the same binding energy. However, since semi-classical and quantal results must differ in the so-called shell energy, this indicates that it is not properly estimated by the TFh(2) approximation.
When the h(2)-order gradient corrections are taken into account (TFh(2), we have found a numerical instability in the solution of the semi-classical Klein-Gordon equation obeyed by the scalar field in the case of parameterizations which have mº/m = 0.60, which can be eliminated if the q-meson mass mº is reduced (with the ratio g(2-0)/m(2-0) unaltered).
Second-order corrections in "h" to the TFh(0) approximation improve the agreement with Hartree solutions in a sensitive way, always yielding more bound nuclei than within the Hartree approach. The sign of the h(2) corrections depends on mº, and they are found to vanish around mº/m = 0.75 for the models of the type considered here. In several respects, the semi-classical relativistic phenomenology quite resembles the one met in the non-relativistic regime using Skyrme forces, in spite of the different origin of mº in both situations. Extending the so-called expectation value method to the relativistic problem, and using the TFh(2) semi-classical mean field as a starting point, perturbative quantal solutions are found which are in good agreement with the Hartree results.
The semi-classical TFh(0) and TFh(2) density distributions do not present oscillations due to the absence of shell effects, but they average the Hartree results. In the interior of the nucleus the TFh(0) and TF1i2 densities are very similar. However, in the surface and the outer region the TF1i2 densities come appreciably closer than TFh(0) to the Hartree results, due to the gradient corrections incorporated by the TF1i2 functionals, and show an exponential drop off.
Liquid drop model coefficients are calculated for some parameter sets of the "sygma-omega" model. We have found reasonable results for the surface thickness and for the surface and curvature energies, which are within the range of the values obtained in non-relativistic calculations using density-dependent Skyrme forces. Therefore, the relativistic effects do not seem to avoid the disagreement of the calculated value of the curvature energy with the empirical value.
In this work we also study the effects of the density-dependent Dirac spinor for the nucleons, as is determined microscopically in the DBHF approach, on various properties of the structure and scattering of finite nuclei. To enable this, we construct a relativistic energy density functional that contains the semi-classical kinetic energy density of order h(2). The effective mass and the volume term in the potential energy arise from a DBHF calculation of nuclear matter. This volume term is supplemented by some conventional correction terms and the few free parameters are suitably adjusted. It turns out that the radii of nuclei calculated with the present approach agree better with the experimental value than those obtained in similar studies using a potential energy derived from a non-relativistic G-matrix. This demonstrates that the Dirac effects improve the calculation of ground-state properties of finite nuclei also in our relativistic extended Thomas-Fermi (RETF) approximation.
However, this study of ground-state properties is not the main goal of our investigation.
The capabilities of our RETF functional are actually appraised in situations in which a full microscopic relativistic calculation, or even a phenomenological one, cannot be easily made, such as nuclear fission of rotating nuclei and heavy ion scattering. In these situations, the method constitutes a reliable tool. For the nuclear fission barriers, the present calculations are the first ones carried out with a relativistic model. We have shown that the model yields results comparable to the non-relativistic ones, with the conceptual-advantage of being relativistic and thus automatically incorporating the spin-orbit force. For the calculations of heavy ion elastic scattering cross sections, we have been able to improve previous results due to achieving a better description of the nuclear, densities.
Let us summarize the two apparent merits which the TFh(2) approximation has over the simple TFh(0) one. On the one hand, it provides fully variational densities that go exponential to zero. On the other hand, it takes into account non-local spin-orbit and effective mass contributions up to order h(2), yielding a more reliable average value.
Se establece el desarrollo semi-clásico hasta orden h(2) en la teoría nuclear relativista de campo medio. Así, se obtienen las densidades semi-clásicas relativistas de partículas y de energía para un conjunto de fermiones sometidos a un campo escalar y a un campo vector, en las teorías de campo medio de Wigner-Kirkwood y de Thomas-Fermi, incluyendo correcciones en gradientes hasta orden h(2). El método semi-clásico se aplica a un oscilador armónico relativista. Después se utiliza en modelos T-W no lineales, para los cuales se resuelven las ecuaciones variacionales en núcleos finitos y en materia nuclear semi-infinita. Los resultados semi-clásicos son comparados con los correspondientes resultados cuánticos Hartree.
Para estudiar los efectos de los espinores de Dirac para los nucleones sobre diversas propiedades de la estructura y de la dispersión de núcleos finitos, se construye un funcional de la densidad de energía relativista. El funcional contiene la densidad de energía cinética relativista de orden h(2). La masa efectiva y la parte potencial se obtienen a partir de cálculos Dirac-Brueckner de materia nuclear. Se presta especial atención al cálculo de barreras de fisión de núcleos en rotación y del potencial óptico para la dispersión de iones pesados a energías intermedias.
Ban, Shufang. "Investigation of effective interactions in relativistic mean field theory." Licentiate thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4074.
Full text姚昌銓 and Cheong-chuen Yao. "Properties of neutron stars in the relativistic mean field theory." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B30409135.
Full textYao, Cheong-chuen. "Properties of neutron stars in the relativistic mean field theory /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19668867.
Full textPaar, Nils. "Relativistic mean field description of exotic excitations in finite nuclei." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969358199.
Full textDiener, Jacobus Petrus Willem. "Relativistic mean-field theory applied to the study of neutron star properties." Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/760.
Full textAcar, Fatma. "Spinodal Instabilities In Symmetric Nuclear Matter Within A Nonlinear Relativistic Mean-field Approach." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613472/index.pdf.
Full textB = 0.4 &rho
0 , while most unstable behavior occurs in shorter wavelengths at lower baryon densities &rho
B = 0.2 &rho
0 . The unstable response of the system shifts towards longer wavelengths with the increasing temperature at both densities. The early growth of the density correlation functions are calculated, which provide valuable information about the initial size of the condensation and the average speed of condensing fragments. Furthermore, the relativistic results are compared with Skyrme type non-relativistic calculations. Qualitatively similar results are found in both non-relativistic and relativistic descriptions.
Danisman, Betul. "Spinodal Instabilities In Symmetric Nuclear Matter Within A Density-dependent Relativistic Mean-field Approach." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613473/index.pdf.
Full textb &asymp
&rho
0/4 (below the saturation density) and at low temperatures. We therefore present our results at low temperature T=1 MeV and at higher temperature T=5 MeV, and also at a lower initial baryon density &rho
b = 0.2 &rho
0 and a higher value &rho
b = 0.4 &rho
0 where unstable behavior is within them. Calculations in density-dependent model are compared with the other calculations obtained in a relativistic non-linear model and in a Skyrme type nonivrelativistic model. Our results are consistent with them. Qualitatively similar results show that the physics of the quantities are model-independent. The size of clusterization is estimated in two ways, by using half-wavelength of the most unstable mode and from the width of correlation function at half maximum. Furthermore, the average speed of condensing fragments during the initial phase of spinodal decomposition are determined by using the current density correlation functions.
Voskresenskaya, Maria Verfasser], Karlheinz [Akademischer Betreuer] [Langanke, and Robert [Akademischer Betreuer] Roth. "Correlations in nuclear matter at low densities in an extended relativistic mean-field model / Maria Voskresenskaya. Betreuer: Karlheinz Langanke ; Robert Roth." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2013. http://d-nb.info/1106454383/34.
Full textVoskresenskaya, Maria [Verfasser], Karlheinz [Akademischer Betreuer] Langanke, and Robert [Akademischer Betreuer] Roth. "Correlations in nuclear matter at low densities in an extended relativistic mean-field model / Maria Voskresenskaya. Betreuer: Karlheinz Langanke ; Robert Roth." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2013. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-33606.
Full textAntić, Sofija [Verfasser], Karlheinz [Akademischer Betreuer] Langanke, and Gabriel [Akademischer Betreuer] Martinez-Pinedo. "Generalized relativistic mean-field model with non-linear derivative nucleon-meson couplings for nuclear matter and finite nuclei / Sofija Antić ; Karlheinz Langanke, Gabriel Martinez-Pinedo." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1153546388/34.
Full textLiang, Haozhao. "Nuclear charge-exchange excitations in a self-consistent covariant approach." Paris 11, 2010. http://www.theses.fr/2010PA112178.
Full textNowadays, charge-exchange excitations in nuclei become one of the central topics in nuclear physics and astrophysics. Basically, a systematic pattern of the energy and collectivity of these excitations could provide direct information on the spin and isospin properties of the in-medium nuclear interaction, and the equation of state of asymmetric nuclear matter. Furthermore, a basic and critical quantity in nuclear structure, neutron skin thickness, can be determined indirectly by the sum rule of spin-dipole resonances (SOR) or the excitation energy spacing between the isobaric analog states (lAS) and Gamow-Teller resonances (GTR). More generally, charge-exchange excitations allow one to attack other kinds of problems outside the realm of nuclear structure, like the description of neutron star and supernova evolutions, the β-decay of nuclei which lie on the r-process path of stellar nucleosynthesis, and the neutrino-nucleus cross sections. They also play an essential role in extracting the value of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element Vud via the nuclear 0+→ 0 + superallowed Fermi β decays. For all these reasons, it is important to develop the microscopic theories of charge-exchange excitations and it is the main motivation of the present work. Ln this work, a fully self-consistent charge-exchange relativistic random phase approximation (RPA) based on the relativistic Hartree-Fock (RHF) approach is established. Its self-consistency is verified by the so-called lAS check. This approach is then applied to investigate the nuclear spin-isospin resonances, isospin symmetry-breaking corrections for the superallowed β decays, and the charged-current neutrino-nucleus cross sections. For two important spin-isospin resonances, GTR and SOR, it is shown that a very satisfactory agreement with the experimental data can be obtained without any readjustment of the energy functional. Furthermore, the isoscalar mesons are found to play an essential role in spin-isospin resonances via the exchange terms, which leads to a profound effect in the nuclear isovector properties, e. G. , the density dependence of the symmetry energy in nuclear matter. Ln the investigation of the isospin symmetry-breaking corrections for the superallowed β decays, it is found that the corrections δc are sensitive to the proper treatments of the Coulomb mean field, but not so much to specific effective interactions. With these corrections δc, the nucleus-independent Ft values are obtained in combination with the experimental ft values in the most recent survey and the improved radiative corrections. The values of Cabibbo-Kobayashi-Maskawa matrix element IVudI thus obtained weil agree with those obtained in neutron decay, pion decay, and nuclear mirror transitions, while the sum of squared top-row elements somehow deviates from the unitarity condition. Expressing the weak lepton-hadron interaction in the standard current-current form, the relevant transitions from the nuclear ground state to the excited states are calculated with RHF+RPA approach. Ln this way, the semileptonic weak interaction processes, e. G. , neutrino reactions, charged- lepton capture, β-decays, can be investigated microscopically and self-consistently. First illustrative calculations of the inclusive neutrino-nucleus cross section are performed for the 16 O(Ve ,e-)16 F reaction, and a good agreement with the previous theoretical studies is obtained. The main effort is dedicated to discussing the substantial influence of different recipes for the axial vector coupling strength and the theoretical low-Iying excited states of the daughter nucleus
Rebillard-Soulie, Alex. "Etendre nοs cοnnaissances sur la matière nucléaire chaude dans la régiοn de faible densité." Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMC244.
Full textLight clusters in nuclear matter appear at densities below nuclear saturation density. They can play an important role in astrophysical scenarios like core-collapse supernovae, where the properties of nuclear matter influence the shock wave propagation and the path of emitted neutrinos. At such densities, in-medium effects are present and modify the properties of the formed clusters, their abundance, and, consequently, the dynamics of supernovae. We used a relativistic mean field (RMF) model with clusters as explicit degrees of freedom and virtual meson exchanges. This model includes an empirical cluster-meson coupling that requires calibration with experimental observations. From heavy ion collisions, we selected events to construct different statistical ensembles corresponding to particular thermodynamic conditions. In these ensembles, we extracted the chemical compositions in terms of the mass fractions of hydrogen and helium isotopes. In parallel, we strengthened the use of the equilibrium hypothesis by studying isoscaling properties. Finally, in a Bayesian analysis, we compared the experimental ensembles with calculations from the RMF model, where density, temperature, and cluster-meson coupling are free parameters. We successfully reproduced the experimental mass fractions of the various clusters, considering a unique density for each ensemble. To explore the limitations of this analysis and extend it to other systems, a new experiment was conducted with the INDRA-FAZIA multidetector. Significant improvements were made to the device, which has considerably enhanced its performance, particularly in terms of isotopic identification. Consequently, nearly all of the data reduction work (energy calibration and identification) has been completed for this new experiment. In a preliminary study, the analysis began on vaporization-type events, but further efforts are required
Wasson, David Allan. "Relativistic mean field theory: methods and applications." Thesis, 1990. https://thesis.library.caltech.edu/8785/1/Wasson-da-1990.pdf.
Full textWe develop a method for performing one-loop calculations in finite systems that is based on using the WKB approximation for the high energy states. This approximation allows us to absorb all the counterterms analytically and thereby avoids the need for extreme numerical precision that was required by previous methods. In addition, the local approximation makes this method well suited for self-consistent calculations. We then discuss the application of relativistic mean field methods to the atomic nucleus. Self-consistent, one loop calculations in the Walecka model are performed and the role of the vacuum in this model is analyzed. This model predicts that vacuum polarization effects are responsible for up to five percent of the local nucleon density. Within this framework the possible role of strangeness degrees of freedom is studied. We find that strangeness polarization can increase the kaon-nucleus scattering cross section by ten percent. By introducing a cutoff into the model, the dependence of the model on short-distance physics, where its validity is doubtful, is calculated. The model is very sensitive to cutoffs around one GeV.
Rutel, Bonnie Gwen Piekarewicz Jorge. "Exotic nuclei and relativistic mean-field theory." 2004. http://etd.lib.fsu.edu/theses/available/etd-04092004-152402.
Full textAdvisor: Dr. Jorge Piekarewicz, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed June 15, 2004). Includes bibliographical references.
Paar, Nils [Verfasser]. "Relativistic mean field description of exotic excitations in finite nuclei / Nils Paar." 2003. http://d-nb.info/969358199/34.
Full textVoskresenskaya, Maria. "Correlations in nuclear matter at low densities in an extended relativistic mean-field model." Phd thesis, 2013. http://tuprints.ulb.tu-darmstadt.de/3360/1/Thesis_Voskresenskaya_Final.pdf.
Full textAntic, Sofija. "Generalized relativistic mean-field model with non-linear derivative nucleon-meson couplings for nuclear matter and finite nuclei." Phd thesis, 2018. https://tuprints.ulb.tu-darmstadt.de/7240/13/SAntic_dissertation_v2.pdf.
Full textTomei, Niccolò. "GRMHD simulations of thick accretion disks in the Event Horizon Telescope era: the role of the mean-field dynamo mechanism." Doctoral thesis, 2022. http://hdl.handle.net/2158/1264722.
Full textMalik, Tuhin. "Equation of state for dense matter from finite nuclei to neutron star mergers." Doctoral thesis, 2019. http://hdl.handle.net/10316/94981.
Full textEquation of state (EOS) of dense matter has been constrained from the experimental data available on the properties of finite nuclei and neutron stars. Towards this purpose, a diverse set of nuclear energy density functionals based on relativistic and non-relativistic mean field models have been employed. These EOSs are so chosen that they are consistent with the bulk properties of the finite nuclei. The values of various nuclear matter parameters which predominantly govern the behaviour of the EOS are determined through their correlations with the properties of the neutron stars such as radii, tidal deformability and maximum mass of the neutron stars. The nuclear matter parameters considered are incompressibility, symmetry energy and their density derivatives which appear in the expansion of the EOS around the saturation density. The radii and tidal deformability of the neutron star with the canonical mass display strong correlations with the linear combinations of slopes of the incompressibility and symmetry energy coefficients. Similar correlations with the curvature of the symmetry energy coefficient are also obsvered indicating that the properties of the neutron stars are sensitive to the high density behaviour of the symmetry energy. It is also shown that the giant resonances in nuclei are instrumental in limiting the tidal deformability parameter and the radius of a neutron star in somewhat narrower bounds. The outcomes of the present thesis is important in view of the fact that the accurate values of the various neutron star observables as considered are expected to be available in near future.
Custódio, Tiago Emanuel Anjo de Oliveira. "Low Density Warm Stellar Matter with Light Clusters and Hyperclusters, Hyperons and Delta Isobars." Master's thesis, 2021. http://hdl.handle.net/10316/97914.
Full textThe abundance of light nuclei, hyperons and $\Delta$ isobars that are produced in stellar environments such as supernova or binary neutron star mergers, is calculated within both Nonlinear and Density-Dependent relativistic mean-field models in low-density matter. Five purely nucleonic light nuclei ($ ^2 $H, $ ^3 $H, $ ^3 $He, $ ^4 $He, $ ^6 $He) are considered, together with three light hypernuclei ($^{3}_{\Lambda}\text{H}$, $^{4}_{\Lambda}\text{H}$, $^{4}_{\Lambda}\text{He}$). We show that the presence of hyperons and $\Delta$s shifts the dissolution of clusters to larger densities, and increases the amount of clusters. This effect is larger the smaller the charge fraction, and the higher the temperature. The abundance of hyperons and $\Delta$s is also affected by the cluster formation: neutral and positively charged hyperons and $\Delta$s suffer a reduction, and the negatively charged ones an increase. We also observe that the dissolution of the less-abundant clusters occurs at larger densities due to smaller Pauli-blocking effects. Overall, hypernuclei set in at temperatures above 25 MeV, and depending on the temperature and chemical composition, they may be more abundant than $^4$He, or even more abundant than other heavier clusters. It is also seen that for some values of the couplings of the $\Delta$s, the nucleon effective mass becomes zero at too low densities, preventing the corresponding EoS of reaching the maximum mass star, therefore not being adequate to describe neutron stars.
A abundância de agregados leves, hiperões e partículas $\Delta$ produzidas em ambientes estelares tais como supernovas e colisões de duas estrelas de neutrões é calculada a baixas densidades no âmbito de modelos relativistas de campo médio não lineares e com acoplamentos dependentes da densidade. Em relação aos agregados leves, consideraram-se cinco agregados puramente nucleónicos e três hiperagregados. Verifica-se que a introdução de hiperões e partículas $\Delta$ empurra a dissolução dos agregados leves para densidades mais altas, aumentando também a sua abundância. Este efeito é tanto maior quanto menor for a fração de carga do sistema e quanto maior a temperatura. Por outro lado, as abundâncias de hiperões e partículas $\Delta$ são também afetadas pela presença de agregados leves no sistema, fazendo com que os hiperões e $\Delta$s de carga positiva ou neutra diminuam de quantidade, enquanto que os de carga negativa aumentam. Também se observa que a dissolução dos agregados menos abundantes ocorre a densidades mais elevadas fruto da redução dos efeitos de Pauli-blocking. De um modo geral, os hiperagregados apenas se formam a temperaturas superiores a 25 MeV, sendo que dependendo da temperatura e composiçao química do sistema, podem chegar a ser mais abundantes que o $ ^4 $He ou mesmo mais abundantes que outros agregados mais pesados. Também se verifica que para alguns valores dos acoplamentos das partículas $\Delta$ aos mesões, a massa efetiva do nucleão torna-se zero a baixas densidades, impedindo a equação de estado correspondente de atingir a estrela de massa máxima. Quando tal acontece, a equação de estado correspondente a esses acoplamentos não serve para descrever estrelas de neutrões.
Outro - Bolsa de Investigação Licenciado, duração 14 meses, no âmbito do projeto POCI-01-0145-FEDER-029912.