To see the other types of publications on this topic, follow the link: Relativistic mean field.

Dissertations / Theses on the topic 'Relativistic mean field'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 21 dissertations / theses for your research on the topic 'Relativistic mean field.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.

1

Centelles, Aixalà Mario. "Semiclassical approach to relativistic nuclear mean field theory." Doctoral thesis, Universitat de Barcelona, 1992. http://hdl.handle.net/10803/1593.

Full text
Abstract:
The nuclear many-body problem is nowadays being increasingly approached on the basis of a relativistic formalism. Microscopic Dirac-Brueckner-Hartree-Fock (DBHF) calculations starting from a realistic nucleon-nucleon interaction seem to be very promising. In the theory of quantum hadrodynamics, nucleons interact through the exchange of virtual mesons and the dynamics is specified by Lorentz covariant Lagrangian densities. In the simplest version, only a vector field (associated with the w meson) accounting for short-range repulsion and a scalar field ("sygma" meson) responsible for attraction are needed to describe saturation in nuclear matter. Calculations in mean field Hartree approximation, neglecting exchange terms and without including any contribution from antiparticles, give an accurate description of many of the features of nuclear systems.

The 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
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.
APA, Harvard, Vancouver, ISO, and other styles
2

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
APA, Harvard, Vancouver, ISO, and other styles
3

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 text
APA, Harvard, Vancouver, ISO, and other styles
4

Yao, 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 text
APA, Harvard, Vancouver, ISO, and other styles
5

Paar, 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 text
APA, Harvard, Vancouver, ISO, and other styles
6

Diener, 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 text
APA, Harvard, Vancouver, ISO, and other styles
7

Acar, 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 text
Abstract:
Spinodal instability mechanism and early development of density fluctuations for symmetric nuclear matter at finite temperature are studied. A stochastic extension of Walecka-type relativistic mean-field model including non-linear self-interactions of scalar mesons with NL3 parameter set is employed in the semi-classical approximation. The growth rates of unstable collective modes are investigated below the normal density and at low temperatures. The system exhibits most unstable behavior in longer wave lengths at baryon densities &rho
B = 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.
APA, Harvard, Vancouver, ISO, and other styles
8

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 text
Abstract:
The nuclear matter liquid-gas phase transition is expected to be a signal of nuclear spinodal instabilities as a result of density fluctuations. Nuclear spinodal instabilities in symmetric nuclear matter are studied within a stochastic relativistic density-dependent model in semi-classical approximation. We use two parameterization for the Lagrange density, DDME1 and TW sets. The early growth of density fluctuations is investigated by employing relativistic Vlasov equation based on QHD and discussed the cluster size of the condensations from the early growth of density correlation functions. Expectations are that hot nuclear matter behaves unstable around &rho
b &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.
APA, Harvard, Vancouver, ISO, and other styles
9

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 text
APA, Harvard, Vancouver, ISO, and other styles
10

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://nbn-resolving.de/urn:nbn:de:tuda-tuprints-33606.

Full text
APA, Harvard, Vancouver, ISO, and other styles
11

Antić, 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 text
APA, Harvard, Vancouver, ISO, and other styles
12

Liang, Haozhao. "Nuclear charge-exchange excitations in a self-consistent covariant approach." Paris 11, 2010. http://www.theses.fr/2010PA112178.

Full text
Abstract:
Les excitations d'échange de charge dans les noyaux constituent l'un des sujets importants et actuels en physique nucléaire et en astrophysique. En principe, une connaissance systématique de l'évolution du comportement de ces excitations à travers la table des éléments fournirait des informations directes sur les propriétés en spin et isospin de l'interaction entre nucléons dans le milieu nucléaire, et sur l'équation d'état de la matière nucléaire. Par ailleurs, une quantité d'importance essentielle pour la structure des noyaux, l'épaisseur de la peau de neutrons, peut être déterminée par la règle de somme de la résonance spin-dipolaire (RSD) ou par la séparation en énergie entre l'état isobarique analogue (ElA) et la résonance de Gamow-Teller (RGT). Plus généralement, les excitations d'échange de charge permettent d'aborder des probèmes d'inérêt général tels que l'étude de l'évolution des étoiles à neutrons et des supernovae, la décroissance des noyaux le long du processus r dans la nucléosynthèse stellaire, ou les interactions neutrino-noyau. Elles jouent aussi un rôle essentiel pour extraire la valeur de l'élément Vud de la matrice de Cabibbo-Kobayashi-Maskawa par le biais de la réaction de décroissance β super-permise 0 +→ 0+ dans les noyaux. Pour toutes ces raisons, il est important de d'evelopper des théories microscopiques des excitations d'échange de charge, et ceci constitue la principale motivation de notre recherche. Dans ce travail, nous établissons le formalisme et les méthodes numériques pour d' ecrire les excitations d'échange de charge dans le cadre de la Random Phase Approximation (RPA) self-consistante construite sur l'approximation de Hartree-Fock relativiste (RHF). Un test important de précision numérique est réalisé sur l'état isobarique analogue. La méthode est ensuite utilisée pour mener des applications numériques réalistes sur un certain nombre de questions physiques : les résonances de spin-isospin dans les noyaux proches des noyaux magiques, les corrections dûes aux mélanges d'isospin dans les transitions β super-permises, les interactions neutrino-noyau dans les voies de courants chargés. Pour les deux modes importants de spin-isospin que sont la RGT et la RSD nous trouvons qu'un excellent accord avec l'expérience est obtenu sans aucun réajustement des paramètres du modèle. De plus, les termes d'échange de l'interaction induite par les mésons isoscalaires jouent un rôle essentiel dans les excitations de spin-isospin, à la différence de la RPA construite sur l'approximation de Hartree relativiste. En ce qui concerne notre étude des transitions β 0+ → 0+ super-permises, l'une des conclusions est que les corrections δc dues aux violations de la symétrie d'isospin dépendent sensiblement du champ moyen d'échange produit par les interactions coulombiennes, mais ne changent pas sensiblement avec le modèle de Lagrangien utilisé. Nous utilisons ces valeurs de δc pour déduire des plus récentes valeurs expérimentales de ft dans les noyaux T = 1, et en tenant compte des corrections radiatives, les valeurs de Ft "indépendantes de noyaux". Nous obtenons ainsi des valeurs de l'élément de matrice ıVudı de Cabbibo-Kobayashi-Maskawa en bon accord avec les valeurs déduites des décroissances neutronique et pionique, et les transitions dans les noyaux miroirs, tandis que la somme des carrés des éléments de la première ligne dévie légèrement de la condition d'unitarité. Nous avons également utilisé nos fonctions d'onde RPA pour évaluer les amplitudes de transition correspondant à l'interaction faible lepton-hadron sous la forme standard courant-courant. Ainsi, les processus faibles semi-leptoniques tels que les réactions neutrino-noyau, capture leptonique chargée, désintégration β , peuvent être étudiés. Nos premières applications concernent la réaction 16 O(Ve , e - ) 16 F pour laquelle nous comparons nos prédictions avec celles d'autres auteurs. Dans la discussion des résultats nous nous efforçons en particulier de clarifier l'influence appréciable des différentes prescriptions que l'on peut adopter pour le choix de la constante de couplage vecteur axiale et l'inclusion ou non des états excités de basse énergie dans le noyau final
Nowadays, 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
APA, Harvard, Vancouver, ISO, and other styles
13

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 text
Abstract:
Les clusters légers dans la matière nucléaire apparaissent à des densités inférieures à la densité de saturation nucléaire. Ils peuvent jouer un rôle important dans des scénarios astrophysiques comme les supernovae à effondrement de cœur, où les propriétés de la matière nucléaire influence la propagation de l'onde de choc et le parcours des neutrinos émis. À de telles densités, des effets de milieu sont présents et modifient les propriétés des clusters formés, leur abondance et, par conséquent, la dynamique des supernovae. Nous avons utilisé un modèle champ moyen relativiste (RMF) avec des clusters comme degrés de liberté explicites et des échanges de mésons virtuels. Ce modèle possède un couplage clusters-méson empirique qui nécessite d’être calibré avec des observations expérimentales. À partir des collisions d'ions lourds, nous avons sélectionné des événements afin de construire différents ensembles statistiques correspondant à des conditions thermodynamiques particulières. Dans ces ensembles, nous avons extrait les compositions chimiques en terme de fractions massique des isotopes d’hydrogène et d’hélium. En parallèle, nous avons renforcé l’utilisation de l’hypothèse d’équilibre par l’étude des propriétés d’isoscaling. Enfin, dans une analyse bayésienne, nous avons comparé les ensembles expérimentaux avec des calculs issus du modèle RMF, où la densité, la température et le couplage clusters-méson sont libres. Nous avons réussi à reproduire les fractions massiques expérimentales des différents clusters, en considérant une densité unique pour chaque ensemble. Pour étudier les limites de cette analyse et l’étendre à d’autres systèmes, une nouvelle expérience a été réalisée avec le multidétecteur INDRA-FAZIA. D’importantes améliorations ont été apportées sur le dispositif, ce qui a permis d’améliorer significativement ses performances, notamment en termes d’identification isotopique. Ainsi, la quasi-totalité du travail de réduction des données (calibration en énergie et identification) a été achevée pour cette nouvelle expérience. Dans le cadre d'une étude préliminaire, l'analyse a été initiée sur les événements de type vaporisation, mais elle nécessite des efforts supplémentaires
Light 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
APA, Harvard, Vancouver, ISO, and other styles
14

Wasson, David Allan. "Relativistic mean field theory: methods and applications." Thesis, 1990. https://thesis.library.caltech.edu/8785/1/Wasson-da-1990.pdf.

Full text
Abstract:

We 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.

APA, Harvard, Vancouver, ISO, and other styles
15

Rutel, Bonnie Gwen Piekarewicz Jorge. "Exotic nuclei and relativistic mean-field theory." 2004. http://etd.lib.fsu.edu/theses/available/etd-04092004-152402.

Full text
Abstract:
Thesis (Ph. D.)--Florida State University, 2004.
Advisor: 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.
APA, Harvard, Vancouver, ISO, and other styles
16

Paar, Nils [Verfasser]. "Relativistic mean field description of exotic excitations in finite nuclei / Nils Paar." 2003. http://d-nb.info/969358199/34.

Full text
APA, Harvard, Vancouver, ISO, and other styles
17

Voskresenskaya, 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 text
Abstract:
Knowledge of the equation of state of strongly interacting matter is required for the description of the variety of nuclear matter phases in a wide range of densities, temperatures, and proton fractions. A specifically important problem is the construction of equations of state for astrophysical applications, e.g for the investigation of various stages of core-collapse supernova explosions and the structure of proto-neutron and neutron stars. For many years, a very small number of equation of state tables was available that have been used in simulations of dynamical astrophysical processes covering the full parameter space needed. These equations of state often do not supply sufficient information on the thermodynamic and compositional details and do not take into account all relevant phase transitions when multiple phases co-exist. In recent years, the appearance of new experimental data on atomic nuclei,heavy-ion-collisions and from astrophysical observations as well as the progress in the theoretical description of the nuclear matter properties and significant improvements of supercomputers have triggered new developments for constructing equations of state. Nevertheless, existing microscopic approaches still do not allow to construct a description in the whole range of densities and temperatures. Thus, approximations and simplifications are needed to develop practical schemes. Thereby, different phenomenological approaches to the equation of state continue to be developed. In this work we study the effect of two specific types of correlations on thermodynamic properties of nuclear matter within the framework of a generalized relativistic mean-field model with light clusters as additional degrees of freedom beyond nucleons. In particular, these correlations include two-body scattering contributions and pairing effects. They appear due to the short-range nucleon-nucleon interaction at low densities and modify the composition and thermodynamic properties of matter. These effects should be included in the equation of state since in this density regime they may strongly influence the structure of the proto-neutron star, the effectiveness of the neutrino re-heating of the shock wave in supernova simulations and the cooling history of neutron stars. This thesis is divided into two major parts. In the first major part we introduce a generalized relativistic mean-field model that includes clusters and two-nucleon scattering correlations in an effective way as explicit degrees of freedom in the thermodynamic potential. These bound and scattering states are represented by quasiparticles with density and temperature dependent properties. All relevant quantities are derived in a thermodynamically consistent way. The model reproduces relativistic mean field results around nuclear saturation density, where clusters are dissolved. The low-density behavior of nuclear matter at finite temperatures with nucleons and light nuclei is considered within a fugacity expansion of the grand canonical potential by comparing the virial equation of state with the generalized relativistic mean field approach. From the comparison of the expansions consistency relations are derived, which connect quasiparticle parameters with the meson-nucleon couplings of the relativistic mean-field model in the vacuum and the phase shifts or effective-range parameters of nucleon-nucleon scattering. The second major part of this thesis is devoted to the investigation of the effect of pairing correlations on the thermodynamic properties of pure neutron matter for densities up to saturation. Here we extend the relativistic mean field model by including pairing correlations in the 1S0 nn channel. Calculations are performed with a Yamaguchi separable potential. Pairing gaps are computed for various temperatures. The results for thermodynamic quantities are compared with relativistic Fermi gas calculations. An overall variation in the pressure of 10 % is observed for a given model due to pairing.
APA, Harvard, Vancouver, ISO, and other styles
18

Antic, 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 text
Abstract:
The equation of state (EOS) for highly compressed dense matter is one of the main concerns of nuclear astrophysics in recent years. It is essential for modeling compact astrophysical objects like neutron stars (NS), their mergers and core-collapse supernovae (CCSN). It also sets the conditions for the creation of chemical elements in the universe, in particular for the r-process whose astrophysical site is still under debate. Therefore, it is an active theoretical and experimental research topic. At present, a realistic and quantitative description of dense matter is not available from first principles using the basic theory of quantum chromodynamics (QCD). Hence, a large variety of phenomenological models has been developed for describing nuclear systems. These models depend on a number of adjustable parameters that have to be determined by data. It is essential for the further development of the field to determine the most realistic parameter sets and to use them consistently. New and more precise constraints on EOS parameters are becoming available with the advancement of technology and novel astrophysical observations and laboratory experiments conducted. As a consequence we are able to provide models that can be further used in many studies, both for nuclear structure and astrophysical applications. In this work an extended relativistic mean-field (RMF) model, the density-dependent (DD) non-linear derivative (NLD), or in short DD-NLD model, is developed. The novelty is combining density-dependent nucleon-meson couplings with the energy dependence introduced in the nucleon self-energies in order to reproduce the experimental behavior of the optical potential. The model is applied to the description of infinite nuclear matter, focusing on the high density region above nuclear saturation, and used to obtain the NS EOS at zero temperature. In order to determine the model parameters they are fitted to nuclear matter properties at saturation density as well as to selected properties of several finite nuclei among which are binding energies, charge and diffraction radii, surface thicknesses, etc. The obtained set of parameters is used in the calculation of the NS mass-radius relation by solving the Tolman-Oppenheimer-Volkoff equations. This was considered only for nuclear systems at vanishing temperature. For general astrophysical applications however, e.g. in order to provide EOS tables for simulations of CCSN, it is necessary to extend the theoretical description to finite temperatures. Since the developed DD-NLD model has a very general form, it can in principle be extended to temperature dependent cases. For the purpose of this work, the extended temperature dependent model for nuclear matter is developed, but in the limit of low temperatures, up to about 20 MeV. This allows to study the liquid-gas phase transition for nuclear matter expected at sub-saturation densities, covering the full range of isospin asymmetries. A study of the spinodal and binodal regions of instability and phase coexistence is performed. We discuss the influence of the energy-dependent self-energies in the EOS model with increasing temperature and the effects it has on the liquid-gas phase transition.
APA, Harvard, Vancouver, ISO, and other styles
19

Tomei, 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 text
Abstract:
The baryonic matter of the Universe is found almost entirely in the form of plasma, or ionized gas where the moving charges interact with each other through the self-generated currents and the related magnetic fields within a highly material conductive. The energy contained in the plasma in terms of the magnetic field is usually comparable to the kinetic and/or thermal energy of the plasma itself, and many violent observed phenomena are attributable to the sudden release of magnetic energy (e.g. flares and coronal mass ejection in the Sun, gamma ray bursts, gamma flare in magnetars, relativistic jets in active galactic nuclei). Since the Universe may not have formed magnetized, a natural question one needs to answer is what processes can lead to a weak magnetic field, from zero initial fields. Battery-like mechanisms are needed to create primordial extra- galactic fields, which may be amplified to higher values by plasma advection, rotation and collapse to values appropriate for stellar magnetism, up to B ∼ 1012 G, the field of a standard neutron star, a value required to power the surrounding young supernova remnant. Most of these batteries lead to field strengths much weaker than the observed field. So some way of amplifying the field is required. Magnetic fields of small scale and large scale components are observed in various astrophysical settings. This thesis work is focused on the investigation of the amplification mechanisms of magnetic fields in system of gas rotating around a supermassive black hole, following the renewed interest given by the recent imaging of the M87 black hole at millimetre wavelengths by the Event Horizon Telescope (EHT). In most cases an amplification of the magnetic fields may occur also by instabilities capable of converting kinetic energy into magnetic energy. A very efficient and ideal process is the magneto-rotational instability (MRI) that provided a local mechanism, effcient for a wide range of magnetic field strength, which leads to a growth on dynamical time-scales of linear perturbations and naturally develops MHD turbulence. The only necessary condition for its onset is the presence of a differentially rotating fluid threaded by a weak magnetic field. However, the amplification of the magnetic field is a non-ideal process due to the non-linear coupling of small-scale velocity and magnetic field fluctuations, possibly caused by the MRI. The result of this correlation leads to the creation of an electromotive force capable of amplifying magnetic fields. This process is known as mean-field dynamo and has been applied to a large number of astrophysical contexts. Currently, GRMHD simulations of MRI-induced accretion on to rotating black holes are being receiving considerable attention due to the success of the EHT collaboration, capable of imaging the emission and the shadow around the event horizon of a black hole for the very first time. The aim of this thesis work is to provide an alternative numerical accretion modelling to the ideal one in which the initial magnetic field has a well-defined poloidal structure and an intensity not exactly negligible. The mean-field dynamo allows us to investigate the possibility of producing poloidal field necessary for the development of MRI and the launch of jets even starting from the most unfavorable condition, that is an initial toroidal field with extremely lower magnetization than those used in ideal GRMHD simulations. In this work we have investigated, for the first time by means of non-ideal axisymmetric GRMHD simulations, the mean-field dynamo process operating in thick accretion disks around black holes, in the fully non-linear regime. Combined with the differential rotation of the disk, the dynamo process is able to produce an exponential growth of any initial seed magnetic field up to the values required to explain the observations,when the instability tends to saturate even in the absence of artificial quenching effects. Before reaching the final saturation stage we observe a secondary regime of exponential growing, where the magnetic field increases more slowly due to accretion, which is modifying the underlying equilibrium. In the stationary state characterized by the saturation of the magnetic field growth, the dynamo is able to remove the angular momentum and trigger the accretion. Finally, we show that it is possible to reproduce the main diagnostics present in the literature by starting from very unfavorable initial configurations, such as a purely toroidal magnetic field with negligible magnetization. In parallel, we present the contribution to the code Comparison Project that aims to compare ideal GRMHD solutions for the evolution of a magnetized accretion flow in two distinct regimes where turbulence is promoted by the magnetorotational instability.
APA, Harvard, Vancouver, ISO, and other styles
20

Malik, Tuhin. "Equation of state for dense matter from finite nuclei to neutron star mergers." Doctoral thesis, 2019. http://hdl.handle.net/10316/94981.

Full text
Abstract:
Documentos apresentados no âmbito do reconhecimento de graus e diplomas estrangeiros
Equation 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.
APA, Harvard, Vancouver, ISO, and other styles
21

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 text
Abstract:
Dissertação de Mestrado em Física apresentada à Faculdade de Ciências e Tecnologia
The 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.
APA, Harvard, Vancouver, ISO, and other styles
We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!

To the bibliography