518 research outputs found
Quantisation without Gauge Fixing: Avoiding Gribov Ambiguities through the Physical Projector
The quantisation of gauge invariant systems usually proceeds through some
gauge fixing procedure of one type or another. Typically for most cases, such
gauge fixings are plagued by Gribov ambiguities, while it is only for an
admissible gauge fixing that the correct dynamical description of the system is
represented, especially with regards to non perturbative phenomena. However,
any gauge fixing procedure whatsoever may be avoided altogether, by using
rather a recently proposed new approach based on the projection operator onto
physical gauge invariant states only, which is necessarily free on any such
issues. These different aspects of gauge invariant systems are explicitely
analysed within a solvable U(1) gauge invariant quantum mechanical model
related to the dimensional reduction of Yang-Mills theory.Comment: 22 pages, no figures, plain LaTeX fil
The Physical Projector and Topological Quantum Field Theories: U(1) Chern-Simons Theory in 2+1 Dimensions
The recently proposed physical projector approach to the quantisation of
gauge invariant systems is applied to the U(1) Chern-Simons theory in 2+1
dimensions as one of the simplest examples of a topological quantum field
theory. The physical projector is explicitely demonstrated to be capable of
effecting the required projection from the initially infinite number of degrees
of freedom to the finite set of gauge invariant physical states whose
properties are determined by the topology of the underlying manifold.Comment: 24 pages, no figures, plain LaTeX file; one more reference added.
Final version to appear in Jour. Phys.
Hybrid States from Constituent Glue Model
The hybrid meson is one of the most interesting new hadron specie beyond the
naive quark model. It acquire a great attention both from the theoretical and
experimental efforts. Many good candidates have been claimed to be observed,
but there is no absolute confirmation about existence of hybrid mesons. In the
present work we propose new calculations of the masses and decay widths of the
hybrid mesons in the context of constituent gluon model.Comment: 19 pages, 11 Table
Hamiltonian Analysis of the Higgs Mechanism for Graviton
In this paper we perform the canonical description of the Higgs mechanism for
gravity and provide the Hamiltonian definition of the massive gravities.Comment: 18 page
Supersymmetric Quantum Mechanics, Engineered Hierarchies of Integrable Potentials, and the Generalised Laguerre Polynomials
Within the context of Supersymmetric Quantum Mechanics and its related
hierarchies of integrable quantum Hamiltonians and potentials, a general
programme is outlined and applied to its first two simplest illustrations.
Going beyond the usual restriction of shape invariance for intertwined
potentials, it is suggested to require a similar relation for Hamiltonians in
the hierarchy separated by an arbitrary number of levels, N. By requiring
further that these two Hamiltonians be in fact identical up to an overall shift
in energy, a periodic structure is installed in the hierarchy of quantum
systems which should allow for its solution. Specific classes of orthogonal
polynomials characteristic of such periodic hierarchies are thereby generated,
while the methods of Supersymmetric Quantum Mechanics then lead to generalised
Rodrigues formulae and recursion relations for such polynomials. The approach
also offers the practical prospect of quantum modelling through the engineering
of quantum potentials from experimental energy spectra. In this paper these
ideas are presented and solved explicitly for the cases N=1 and N=2. The latter
case is related to the generalised Laguerre polynomials, for which indeed new
results are thereby obtained. At the same time new classes of integrable
quantum potentials which generalise that of the harmonic oscillator and which
are characterised by two arbitrary energy gaps are identified, for which a
complete solution is achieved algebraically.Comment: 1+19 page
Light Hybrid Mesons in QCD
Including the radiative perturbative corrections and the short distance
tachyonic gluon mass effects which mimic the ones of UV renormalons, we
re-estimate the decay amplitudes, masses and widths of light hybrid mesons from
QCD spectral sum rules. We show that the effects are tiny and confirm the
previous lowest order results. We discuss the phenomenological impacts of our
results for the vector hybrids.Comment: Typos fixed, references updated; the final version version to appear
in Phys. Lett. B. 6 pages, Latex, espcrc1.sty is required (included). The
complete paper is also available via the www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints
Gauge Fixing and BFV Quantization
Nonsingularity conditions are established for the BFV gauge-fixing fermion
which are sufficient for it to lead to the correct path integral for a theory
with constraints canonically quantized in the BFV approach. The conditions
ensure that anticommutator of this fermion with the BRST charge regularises the
path integral by regularising the trace over non-physical states in each ghost
sector. The results are applied to the quantization of a system which has a
Gribov problem, using a non-standard form of the gauge-fixing fermion.Comment: 14 page
An Improved Limit on Invisible Decays of Positronium
The results of a new search for positronium decays into invisible final
states are reported. Convincing detection of this decay mode would be a strong
evid ence for new physics beyond the Standard Model (SM): for example the
existence of extra--dimensions, of milli-charged particles, of new light gauge
bosons or of mirror particles. Mirror matter could be a relevant dark matter
candidate.
In this paper the setup and the results of a new experiment are presented. In
a collected sample of about orthopositronium decay
s, no evidence for invisible decays in an energy window [0,80] keV was found
and an upper limit on the branching ratio of orthopositronium \invdecay could
be set: \binvdecay<4.2\times 10^{-7} (90% C.L.)
Our results provide a limit on the photon mirror-photon mixing strength
(90% C.L.) and rule out particles lighter
than the electron mass with a fraction of the
electron charge. Furthermore, upper limits on the branching ratios for the
decay of parapositronium (90%
C.L.) and the direct annihilation (90% C.L.) could be set.Comment: 17 pages, 7 figures, added references, fixed limit on millicharged
particles and changed two plots accordingl
Ostrogradsky's Hamilton formalism and quantum corrections
By means of a simple scalar field theory it is demonstrated that the Lagrange
formalism and Ostrogradsky's Hamilton formalism in the presence of higher
derivatives, in general, do not lead to the same results. While the two
approaches are equivalent at the classical level, differences appear due to the
quantum corrections.Comment: 10 pages, 1 figure, REVTeX
Covariant scalar representation of quantization of the scalar relativistic particle
A covariant scalar representation of is constructed and
analysed in comparison with existing methods for the quantization of the scalar
relativistic particle. It is found that, with appropriately defined
wavefunctions, this produced representation can be identified
with the state space arising from the canonical BFV-BRST quantization of the
modular invariant, unoriented scalar particle (or antiparticle) with admissible
gauge fixing conditions. For this model, the cohomological determination of
physical states can thus be obtained purely from the representation theory of
the algebra.Comment: 16 pages Late
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