41 research outputs found
A generalized bag-like boundary condition for fields with arbitrary spin
Boundary conditions (BCs) for the Maxwell and Dirac fields at material surfaces are widely-used and physically well-motivated, but do not appear to have been generalized to deal with higher spin fields. As a result there is no clear prescription as to which BCs should be selected in order to obtain physically-relevant results pertaining to confined higher spin fields. This lack of understanding is significant given that boundary-dependent phenomena are ubiquitous across physics, a prominent example being the Casimir effect. Here, we use the two-spinor calculus formalism to present a unified treatment of BCs routinely employed in the treatment of spin-1/2 and spin-1 fields. We then use this unification to obtain a BC that can be applied to massless fields of any spin, including the spin-2 graviton, and its supersymmetric partner the spin-3/2 gravitino
The paradigm of the area law and the structure of transversal and longitudinal lightfront degrees of freedom
It is shown that an algebraically defined holographic projection of a QFT
onto the lightfront changes the local quantum properties in a very drastic way.
The expected ubiquitous vacuum polarization characteristic of QFT is confined
to the lightray (longitudinal) direction, whereas operators whose localization
is transversely separated are completely free of vacuum correlations. This
unexpected ''transverse return to QM'' combined with the rather universal
nature of the strongly longitudinal correlated vacuum correlations (which turn
out to be described by rather kinematical chiral theories) leads to a d-2
dimensional area structure of the d-1 dimensional lightfront theory. An
additive transcription in terms of an appropriately defined entropy related to
the vacuum restricted to the horizon is proposed and its model independent
universality aspects which permit its interpretation as a quantum candidate for
Bekenstein's area law are discussed. The transverse tensor product foliation
structure of lightfront degrees of freedom is essential for the simplifying
aspects of the algebraic lightcone holography. Key-words: Quantum field theory;
Mathematical physics, Quantum gravityComment: 16 pages latex, identical to version published in JPA: Math. Gen. 35
(2002) 9165-918
Quantum chromodynamics with advanced computing
We survey results in lattice quantum chromodynamics from groups in the USQCD
Collaboration. The main focus is on physics, but many aspects of the discussion
are aimed at an audience of computational physicists.Comment: 17 pp. Featured presentation at Scientific Discovery with Advanced
Computing, July 13-17, Seattl
Heuristic Models of Two-Fermion Relativistic Systems with Field-Type Interaction
We use the chain of simple heuristic expedients to obtain perturbative and
exactly solvable relativistic spectra for a family of two-fermionic bound
systems with Coulomb-like interaction. In the case of electromagnetic
interaction the spectrum coincides up to the second order in a coupling
constant with that following from the quantum electrodynamics. Discrepancy
occurs only for S-states which is the well-known difficulty in the bound-state
problem. The confinement interaction is considered too.
PACS number(s): 03.65.Pm, 03.65.Ge, 12.39.PnComment: 16 pages, LaTeX 2.0
Consistent histories of systems and measurements in spacetime
Traditional interpretations of quantum theory in terms of wave function
collapse are particularly unappealing when considering the universe as a whole,
where there is no clean separation between classical observer and quantum
system and where the description is inherently relativistic. As an alternative,
the consistent histories approach provides an attractive "no collapse"
interpretation of quantum physics. Consistent histories can also be linked to
path-integral formulations that may be readily generalized to the relativistic
case. A previous paper described how, in such a relativistic spacetime path
formalism, the quantum history of the universe could be considered to be an
eignestate of the measurements made within it. However, two important topics
were not addressed in detail there: a model of measurement processes in the
context of quantum histories in spacetime and a justification for why the
probabilities for each possible cosmological eigenstate should follow Born's
rule. The present paper addresses these topics by showing how Zurek's concepts
of einselection and envariance can be applied in the context of relativistic
spacetime and quantum histories. The result is a model of systems and
subsystems within the universe and their interaction with each other and their
environment.Comment: RevTeX 4; 37 pages; v2 is a revision in response to reviewer
comments, connecting the discussion in the paper more closely to consistent
history concepts; v3 has minor editorial corrections; accepted for
publication in Foundations of Physics; v4 has a couple minor typographical
correction
Signatures of Quark-Gluon-Plasma formation in high energy heavy-ion collisions: A critical review
A critical review on signatures of Quark-Gluon-Plasma formation is given and
the current (1998) experimental status is discussed. After giving an
introduction to the properties of QCD matter in both, equilibrium- and
non-equilibrium theories, we focus on observables which may yield experimental
evidence for QGP formation. For each individual observable the discussion is
divided into three sections: first the connection between the respective
observable and QGP formation in terms of the underlying theoretical concepts is
given, then the relevant experimental results are reviewed and finally the
current status concerning the interpretation of both, theory and experiment, is
discussed. A comprehensive summary including an outlook towards RHIC is given
in the final section.Comment: Topical review, submitted to Journal of Physics G: 68 pages,
including 39 figures (revised version: only minor modifications, some
references added
Confined quantum fields under the influence of a uniform magnetic field
We investigate the influence of a uniform magnetic field on the zero-point
energy of charged fields of two types, namely, a massive charged scalar field
under Dirichlet boundary conditions and a massive fermion field under MIT
boundary conditions. For the first, exact results are obtained, in terms of
exponentially convergent functions, and for the second, the limits for small
and for large mass are analytically obtained too. Coincidence with previously
known, partial result serves as a check of the procedure. For the general case
in the second situation --a rather involved one-- a precise numerical analysis
is performed.Comment: 17 pages, 5 figure
New Developments in the Casimir Effect
We provide a review of both new experimental and theoretical developments in
the Casimir effect. The Casimir effect results from the alteration by the
boundaries of the zero-point electromagnetic energy. Unique to the Casimir
force is its strong dependence on shape, switching from attractive to repulsive
as function of the size, geometry and topology of the boundary. Thus the
Casimir force is a direct manifestation of the boundary dependence of quantum
vacuum.
We discuss in depth the general structure of the infinities in the field
theory which are removed by a combination of zeta-functional regularization and
heat kernel expansion. Different representations for the regularized vacuum
energy are given. The Casimir energies and forces in a number of configurations
of interest to applications are calculated. We stress the development of the
Casimir force for real media including effects of nonzero temperature, finite
conductivity of the boundary metal and surface roughness. Also the combined
effect of these important factors is investigated in detail on the basis of
condensed matter physics and quantum field theory at nonzero temperature.
The experiments on measuring the Casimir force are also reviewed, starting
first with the older measurements and finishing with a detailed presentation of
modern precision experiments. The latter are accurately compared with the
theoretical results for real media.
At the end of the review we provide the most recent constraints on the
corrections to Newtonian gravitational law and other hypothetical long-range
interactions at submillimeter range obtained from the Casimir force
measurements.Comment: 275 pages,29 figures, to appear in Physics Report