Search results for "Field Theory"
showing 10 items of 1188 documents
Depletion in Bose-Einstein condensates using quantum field theory in curved space
2007
5 pages.-- PACS nrs.: 03.75.Kk; 05.30.Jp; 04.62.+v; 04.70.Dy.-- ISI Article Identifier: 000246074600122.-- ArXiv pre-print available at: http://arxiv.org/abs/cond-mat/0610367
Scattering theory for a class of fermionic Pauli–Fierz models
2004
Abstract The scattering theory for a class of fermionic Pauli–Fierz models is considered. We give a proof of the asymptotic completeness of the dynamics in the case of massive fermions. The result applied to the Hamiltonian of a quantized spin- 1 2 Dirac particle interacting with an external field through a cutoff Yukawa interaction and to the Hamiltonian of a system of finitely many confined particles coupled to a fermionic field with a quadratic interaction.
The Elliptic Sunrise
2020
In this talk, we discuss our recent computation of the two-loop sunrise integral with arbitrary non-zero particle masses in the vicinity of the equal mass point. In two space-time dimensions, we arrive at a result in terms of elliptic dilogarithms. Near four space-time dimensions, we obtain a result which furthermore involves elliptic generalizations of Clausen and Glaisher functions.
Emergence of regional leadership – a field approach
2016
ABSTRACTEmergence of regional leadership – a field approach. Regional Studies. The complex processes associated with the emergence of regional leadership are interpreted in this paper through a field theoretical framework, and are discussed with example cases relating to green economy developments in four Nordic regions. It is argued that macro- and meso-level processes create opportunities and constraints for local agency, and how local agency can respond to this is discussed. Field theory offers a novel perspective on regional leadership because it helps one gain a deeper understanding of the various forms regional leadership can take.
Crystal field calculations of energy levels of the Ni2+ ions in MgO
2013
Abstract The electronic energy levels of six-fold coordinated Ni 2+ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni 2+ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited 3 T 2g state fine structure; however, it does not explain why out of four levels arising from the 3 T 2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn–Teller effect.
Large-N kinetic theory for highly occupied systems
2018
We consider an effective kinetic description for quantum many-body systems, which is not based on a weak-coupling or diluteness expansion. Instead, it employs an expansion in the number of field components N of the underlying scalar quantum field theory. Extending previous studies, we demonstrate that the large-N kinetic theory at next-to-leading order is able to describe important aspects of highly occupied systems, which are beyond standard perturbative kinetic approaches. We analyze the underlying quasiparticle dynamics by computing the effective scattering matrix elements analytically and solve numerically the large-N kinetic equation for a highly occupied system far from equilibrium. T…
Colloquium: The Shape of Hadrons
2012
This Colloquium addresses the issue of the shape of hadrons and, in particular, that of the proton. The concept of shape in the microcosm is critically examined. Special attention is devoted to properly define the meaning of shape for bound-state systems of near massless quarks. The ideas that lead to the expectation of nonsphericity in the shape of hadrons, the calculations that predict it, and the experimental information obtained from recent high-precision measurements are examined. Particular emphasis is given to the study of the electromagnetic transition between the nucleon and its first excited state, the Δ(1232) resonance. The experimental evidence is critically examined and compare…
Quasi-free electron scattering in a relativistic model of the nucleus
1989
Longitudinal and transverse response functions of quasi-free electron scattering have been calculated in mean field approximation for a relativisticσ-ω model, including non-linearities in theσ-field. As a consequence of the completely consistent and fully relativistic treatment of wave functions and current operators, gauge invariance is perfectly satisfied throughout the calculation. The results indicate that models with the same nuclear bulk properties lead to similar response functions within 10%. Our results agree with the experimental data for12C and238U, but cannot describe the longitudinal response in the Ca-Fe region. Predictions for208Pb are given for comparison with future experim…
An infinite family of counterexamples to a conjecture on positivity
2021
Recently, G. Mason has produced a counterexample of order 128 to a conjecture in conformal field theory and tensor category theory in [Ma]. Here we easily produce an infinite family of counterexamples, the smallest of which has order 72.
Spacetime curvature and Higgs stability after inflation
2015
We investigate the dynamics of the Higgs field at the end of inflation in the minimal scenario consisting of an inflaton field coupled to the Standard Model only through the non-minimal gravitational coupling $\xi$ of the Higgs field. Such a coupling is required by renormalisation of the Standard Model in curved space, and in the current scenario also by vacuum stability during high-scale inflation. We find that for $\xi\gtrsim 1$, rapidly changing spacetime curvature at the end of inflation leads to significant production of Higgs particles, potentially triggering a transition to a negative-energy Planck scale vacuum state and causing an immediate collapse of the Universe.