47,126 research outputs found
A novel variational approach for Quantum Field Theory: example of study of the ground state and phase transition in Nonlinear Sigma Model
We discuss a novel form of the variational approach in Quantum Field Theory
in which the trial quantum configuration is represented directly in terms of
relevant expectation values rather than, e.g., increasingly complicated
structure from Fock space. The quantum algebra imposes constraints on such
expectation values so that the variational problem is formulated here as an
optimization under constraints. As an example of application of such approach
we consider the study of ground state and critical properties in a variant of
nonlinear sigma model.Comment: talk presented at DPF2004 meeting in Riverside, CA; to appear in a
supplement in International Journal of Modern Physics
Effective field theory description of halo nuclei
Nuclear halos emerge as new degrees of freedom near the neutron and proton
driplines. They consist of a core and one or a few nucleons which spend most of
their time in the classically-forbidden region outside the range of the
interaction. Individual nucleons inside the core are thus unresolved in the
halo configuration, and the low-energy effective interactions are short-range
forces between the core and the valence nucleons. Similar phenomena occur in
clusters of He atoms, cold atomic gases near a Feshbach resonance, and some
exotic hadrons. In these weakly-bound quantum systems universal scaling laws
for s-wave binding emerge that are independent of the details of the
interaction. Effective field theory (EFT) exposes these correlations and
permits the calculation of non-universal corrections to them due to
short-distance effects, as well as the extension of these ideas to systems
involving the Coulomb interaction and/or binding in higher angular-momentum
channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo
nuclei, has been used to compute the properties of single-neutron, two-neutron,
and single-proton halos of s-wave and p-wave type. This review summarizes these
results for halo binding energies, radii, Coulomb dissociation, and radiative
capture, as well as the connection of these properties to scattering
parameters, thereby elucidating the universal correlations between all these
observables. We also discuss how Halo EFT's encoding of the long-distance
physics of halo nuclei can be used to check and extend ab initio calculations
that include detailed modeling of their short-distance dynamics.Comment: 104 pages, 31 figures. Topical Review for Journal of Physics G. v2
incorporates several modifications, particularly to the Introduction, in
response to referee reports. It also corrects multiple typos in the original
submission. It corresponds to the published versio
Leading Chiral Contributions to the Spin Structure of the Proton
The leading chiral contributions to the quark and gluon components of the
proton spin are calculated using heavy-baryon chiral perturbation theory.
Similar calculations are done for the moments of the generalized parton
distributions relevant to the quark and gluon angular momentum densities. These
results provide useful insight about the role of pions in the spin structure of
the nucleon, and can serve as a guidance for extrapolating lattice QCD
calculations at large quark masses to the chiral limit.Comment: 8 pages, 2 figures; a typo in Ref. 7 correcte
Local cloning of two product states
Local quantum operations and classical communication (LOCC) put considerable
constraints on many quantum information processing tasks such as cloning and
discrimination. Surprisingly however, discrimination of any two pure states
survives such constraints in some sense. In this paper, we show that cloning is
not that lucky; namely, conclusive LOCC cloning of two product states is
strictly less efficient than global cloning.Comment: Totally rewritten with improved result
- …