1,720,967 research outputs found
Gaussian effective potential for the standard model SU(2)×U(1) electroweak theory
No full textThe Gaussian effective potential is derived for the non-Abelian SU(2)×U(1) gauge theory of electroweak interactions. At variance with naive derivations, the Gaussian effective potential is proven to be a genuine variational tool in any gauge. The role of ghosts is discussed and the unitarity gauge is shown to be the only choice which allows calculability without insertion of further approximations. The full non-Abelian calculation confirms the existence of a light Higgs boson in the nonperturbative strong coupling regime of the Higgs sector
A Variational method from the variance of energy
Full text linkA variational method is studied based on the minimum of energy variance. The method is tested on exactly soluble problems in quantum mechanics, and is shown to be a useful tool whenever the properties of states are more relevant than the eigenvalues. In quantum field theory the method provides a consistent second order extension of the gaussian effective potential
Gaussian Effective Potential and antifferomagnetism in the Hubbard model
No full textThe Gaussian Effective Potential (GEP) is shown to be a useful variational tool for the study of the magnetic properties of strongly correlated electronic systems. The GEP is derived for a single band Hubbard model on a two-dimensional bi-partite square lattice in the strong coupling regime. At half-filling the antiferromagnetic order parameter emerges as the minimum of the effective potential with an accuracy which improves over RPA calculations and is very close to that achieved by Monte Carlo simulations. Extensions to other magnetic systems are discussed
Self-consistent variational approach to the minimal left-right symmetric model of electroweak interactions
No full textThe problem of mass generation is addressed by a Gaussian variational method for the minimal left-right symmetric model of electroweak interactions. Without any scalar bidoublet, the Gaussian effective potential is shown to have a minimum for a broken symmetry vacuum with a finite expectation value for both the scalar Higgs doublets. The symmetry is broken by the fermionic coupling that destabilizes the symmetric vacuum, yielding a self-consistent fermionic mass. In this framework a light Higgs is only compatible with the existence of a new high energy mass scale below 2 TeV
Nonperturbative effective model for the Higgs sector of the standard model
No full textA non-perturbative effective model is derived for the Higgs sector of the standard model, described by a simple scalar theory. The renormalized couplings are determined by the derivatives of the Gaussian Effective Potential that are known to be the sum of infinite bubble graphs contributing to the vertex functions. A good agreement has been found with strong coupling lattice simulations when a comparison can be made
General interpolation scheme for thermal fluctuations in superconductors
Full text linkWe present a general interpolation theory for the phenomenological effects of thermal fluctuations in superconductors. Fluctuations are described by a simple gauge invariant extension of the gaussian effective potential for the Ginzburg-Landau static model. The approach is shown to be a genuine variational method, and to be stationary for infinitesimal gauge variations around the Landau gauge. Correlation and penetration lengths are shown to depart from the mean field behaviour in a more or less wide range of temperature below the critical regime, depending on the class of material considered. The method is quite general and yields a very good interpolation of the experimental data for very different materials
Electroweak radiative corrections to Higgs production via vector boson fusion using soft-collinear effective theory: Numerical results
No full textElectroweak radiative corrections are computed for Higgs production through vector boson fusion, qq→qqH, which is one of the most promising channels for detecting and studying the Higgs boson at the LHC. Using soft-collinear effective theory, we obtain numerical results for the resummed logarithmic contributions to the hadronic cross section at next-to-leading logarithmic order. We compare our results to HAWK and find good agreement below 2 TeV where the logarithms do not dominate. The soft-collinear effective theory method is at its best in the high LHC energy domain where the corrections are found to be slightly larger than predicted by HAWK and by other one-loop fixed order approximations. This is one of the first tests of this formalism at the level of a hadronic cross section, and demonstrates the viability of obtaining electroweak corrections for generic processes without the need for difficult electroweak loop calculations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Trame di Sviluppo. Il volontariato e la ricerca psicologica per il cambiamento nei territori difficili
No full textIl testo, frutto della collaborazione tra il Centro di Servizi per il Volontariato di Palermo(Ce.S.Vo.P) e il gruppo di ricerca psicologico-clinica del Dipartimento di Psicologia dell''Università degli Studi di Palermo, presenta i risultati di una ricerca-intervento che mirava da un lato alla realizzazione di un''analisi approfondita della morfologia delle reti di volontariato nella Sicilia occidentale, del loro funzionamento, dei rapporti tra i membri delle reti e tra le diverse tipologie di reti esistenti, e dall''altro ad approfondire qual è l''effetto psichico (vissuti, emozioni, paure..) prodotto dalla mafia e dalla cultura mafiosa nel mondo del volontariato e dunque nei volontari. Il testo presenta, inoltre, uno studio specifico ed approfondito su una particolare associazione di volontariato: Addio Pizzo. Tale associazione basa la sua mission associativa su un''opera costante di sensibilizzazione rivolta a commercianti, imprenditori e comuni cittadini in relazione alle tematiche del racket e dell''usura. Il testo illustra i risultati dell''esplorazione dei vissuti, delle rappresentazioni, delle paure dei volontari che per una specifica mission associativa sono stati in contatto direttamente o indirettamente con il mondo della criminalità organizzata
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