118416634
Self-consistent Green's functions with three-body forces
The quantum many-body problem is an everlasting challenge for theoretical physics. The aim sought is to analyze, at the quantum level, the observables arising from a group formed by a certain number of interacting particles N. In the specific case of nuclear physics, the study and interpretation of interacting nuclear systems has spanned from the finite nuclei to the infinite nuclear matter case. In order to characterize such systems, the forces with which nucleons interact in their interior need to be sorted out. Once the Hamiltonian is chosen, the many-body problem for the group of interacting fermions, the nucleons, has to be solved. In the present thesis we focus our study on infinite nuclear matter, analyzing the properties of the two systems which stand at the extremes in terms of isospin asymmetry: symmetric nuclear matter (SNM), with an equal number on neutrons and protons, and pure neutron matter (PNM), with only neutrons. We base our approach in terms of realistic microscopic potentials, hence we need to choose a many-body technique in order to treat the potential. We choose to perform our calculations exploiting the formalism provided by the self-consistent Green's function's (SCGF) theory. This approach is based on a diagrammatic expansion of the single-particle (SP) Green's function, or propagator. This method was devised to treat the correlated, i.e. beyond mean-field, behavior of strongly interacting systems, such as nuclear matter. Unfortunately, it is a well established fact that whatever microscopic two-nucleon forces (2NFs) are used in the many-body calculation, empirical saturation properties of nuclear matter fail to be reproduced. Saturation densities appear at high values, presenting energies which are inconsistently too attractive, overbinding nuclear matter. This inconsistency bears some similarities to the case of light nuclei where, on the contrary, the 2NF-only based theory underbinds experimental data. The inclusion of three-nucleon forces (3NFs) has been the indispensable factor to cure this deficiency. Hence, microscopic 3NFs have been mostly devised to provide attraction in light finite systems, small densities, and repulsion in infinite systems, high densities. However, in modeling these 3NFs, the inclusion of phenomenological ingredients has often been the way followed. To bypass the need to adjust the potential with ad hoc contributions, an alternative has been provided by chiral effective field theory (EFT). Featuring the consistent Hamiltonian at the 2N and 3N level provided by EFT, in this thesis we present calculations including both chiral 2NFs and 3NFs. This is dealt within an extended SCGF formalism, specifically formulated to include consistently 3B forces by means of effective interactions. We observe the striking effect of the inclusion of 3N forces for the total energy of the many-body ground state. Exploiting the extended SCGF approach presented in this thesis, we see how the modifications induced by the 3B force are larger as the density increases. This increasing with density is what provides the saturation mechanism for nuclear matter. In pure neutron matter, 3NFs are the main cause for the stiffening of the equation of state. In view of astrophysical studies for neutron star masses, this stiffening is a major ingredient for the achievement of theoretical results which can better match recent astrophysical observations. The idea, on which the development of this thesis was based, has been all the way the quest to introduce consistently three-body forces in the formalism of the SCGF theory. While the main motivation of this study has been nuclear systems, the extended SCGF formalism can be easily applied to other many-body systems, of either atomic or molecular nature.
14762623
Correlated density-dependent chiral forces for infinite-matter calculations within the Green's function approach
The properties of symmetric nuclear and pure neutron matter are investigated within an extended self-consistent Green's function method that includes the effects of three-body forces. We use the ladder approximation for the study of infinite nuclear matter and incorporate the three-body interaction by means of a density-dependent two-body force. This force is obtained via a correlated average over the third particle, with an in-medium propagator consistent with the many-body calculation we perform. We analyze different prescriptions in the construction of the average and conclude that correlations provide small modifications at the level of the density-dependent force. Microscopic as well as bulk properties are studied, focusing on the changes introduced by the density dependent two-body force. The total energy of the system is obtained by means of a modified Galitskii-Migdal-Koltun sum rule. Our results validate previously used uncorrelated averages and extend the availability of chirally motivated forces to a larger density regime.
118709020
Symmetric nuclear matter with chiral three-nucleon forces in the self-consistent Green's functions approach
We present calculations for symmetric nuclear matter using chiral nuclear interactions within the self-consistent Green's functions approach in the ladder approximation. Three-body forces are included via effective one-body and two-body interactions, computed from an uncorrelated average over a third particle. We discuss the effect of the three-body forces on the total energy, computed with an extended Galitskii-Migdal-Koltun sum-rule, as well as on single-particle properties. Saturation properties are substantially improved when three-body forces are included, but there is still some underlying dependence on the similarity renormalization group evolution scale.
17099587
Self-consistent Green's functions formalism with three-body interactions
We extend the self-consistent Green's functions formalism to take into account three-body interactions. We analyze the perturbative expansion in terms of Feynman diagrams and define effective one- and two-body interactions, which allows for a substantial reduction of the number of diagrams. The procedure can be taken as a generalization of the normal ordering of the Hamiltonian to fully correlated density matrices. We give examples up to third order in perturbation theory. To define nonperturbative approximations, we extend the equation of motion method in the presence of three-body interactions. We propose schemes that can provide nonperturbative resummation of three-body interactions. We also discuss two different extensions of the Koltun sum rule to compute the ground state of a many-body system.
11870428
High-momentum components in the nuclear symmetry energy
The short-range and tensor correlations associated to realistic nucleon-nucleon interactions induce a population of high-momentum components in the many-body nuclear wave function. We study the impact of such high-momentum components on bulk observables associated to isospin asymmetric matter. The kinetic part of the symmetry energy is strongly reduced by correlations when compared to the non-interacting case. The origin of this behaviour is elucidated using realistic interactions with different short-range and tensor structures.
120314857
Latent heat of nuclear matter
We study the latent heat of the liquid-gas phase transition in symmetric nuclear matter using self-consistent mean-field calculations with a few Skyrme forces. The temperature dependence of the latent heat is rather independent of the mean-field parametrization and it can be characterized by a few parameters. At low temperatures, the latent heat tends to the saturation energy. Near the critical point, the latent heat goes to zero with a well-determined mean-field critical exponent. A maximum value of the latent heat in the range l similar to 25-30 MeV is found at intermediate temperatures, which might have experimental relevance. All these features can be explained from very basic principles.
118666057
Tensor force effects and high-momentum components in the nuclear symmetry energy
We analyze microscopic many-body calculations of the nuclear symmetry energy and its density dependence. The calculations are performed in the framework of the Brueckner-Hartree-Fock and the self-consistent Green’s functions methods. Within Brueckner-Hartree-Fock, the Hellmann-Feynman theorem gives access to the kinetic energy contribution as well as the contributions of the different components of the nucleon-nucleon interaction. The tensor component gives the largest contribution to the symmetry energy. The decomposition of the symmetry energy in a kinetic part and a potential energy part provides physical insight on the correlated nature of the system, indicating that neutron matter is less correlated than symmetric nuclear matter. Within the self-consistent Green’s function approach, we compute the momentum distributions and we identify the effects of the high momentum components in the symmetry energy. The results are obtained for the realistic interaction Argonne V18 potential, supplemented by the Urbana IX three-body force in the Brueckner-Hartree-Fock calculations.
9108097
Performance Studies of the StoRM Storage Resource Manager
High performance disk-storage solutions based on parallel file systems are becoming increasingly important to fulfill the large I/O throughput required by high-energy physics applications. Storage area networks (SAN) are commonly employed at the Large Hadron Collider data centres, and SAN-oriented parallel file systems such as GPFS and Lustre provide high scalability and availability by aggregating many data volumes served by multiple disk-servers into a single POSIX file system hierarchy. Since these file systems do not come with a storage resource manager (SRM) interface, necessary to access and manage the data volumes in a grid environment, a specific project called StoRM has been developed for providing them with the necessary SRM capabilities. In this paper we describe the deployment of a StoRM instance, configured to manage a GPFS file system. A software suite has been realized in order to perform stress tests of functionality and throughput on StoRM. We present the results of these tests.
62765062
LHCb experience with LFC replication
Database replication is a key topic in the framework of the LHC Computing Grid to allow processing of data in a distributed environment. In particular, the LHCb computing model relies on the LHC File Catalog, i.e. a database which stores information about files spread across the GRID, their logical names and the physical locations of all the replicas. The LHCb computing model requires the LFC to be replicated at Tier-1s. The LCG 3D project deals with the database replication issue and provides a replication service based on Oracle Streams technology. This paper describes the deployment of the LHC File Catalog replication to the INFN National Center for Telematics and Informatics (CNAF) and to other LHCb Tier-1 sites. We performed stress tests designed to evaluate any delay in the propagation of the streams and the scalability of the system. The tests show the robustness of the replica implementation with performance going much beyond the LHCb requirements.
35523068
The LHCb Farm Monitoring and Control System
The LHCb experiment at CERN will have an online trigger farm composed of up to 2000 PCs. In order to monitor and control each PC and to supervise the overall status of the farm, a Farm Monitoring and Control System (FMC) was developed. The FMC is based on DIM (Distributed Information Management System) as network communication layer, it is accessible both through a command line interface and through the PVSS (Prozessvisualisierung und Steuerung) graphical interface, and it is interfaced to the Finite State Machine (FSM) of the LHCb Experiment Control System (ECS) in order to manage anomalous farm conditions. The FMC is an integral part of the ECS, which is in charge of monitoring and controlling all on-line components; it uses the same tools (DIM, PVSS, FSM, etc.) to guarantee its complete integration and a coherent look and feel throughout the whole control system.
39676478
High rate packets transmission on ethernet LAN using commodity hardware
We report on measurements performed to test the reliability of high rate data transmission over copper Gigabit Ethernet for the LHCb online system. High reliability of such transmissions will be crucial for the functioning of the software trigger layers of the LHCb experiment, at the CERN's LHC accelerator. The technological challenge in the system implementation consists of handling the expected high data throughput of event fragments using, to a large extent, commodity equipment. We report on performance evaluations (throughput, error rates and frame drop) of the main components involved in data transmission: the Ethernet cable, the PCI bus and the operating system (the latest kernel versions of Linux). Three different platforms have been used.