4,285 research outputs found
The Master Ward Identity
In the framework of perturbative quantum field theory (QFT) we propose a new,
universal (re)normalization condition (called 'master Ward identity') which
expresses the symmetries of the underlying classical theory. It implies for
example the field equations, energy-momentum, charge- and ghost-number
conservation, renormalized equal-time commutation relations and BRST-symmetry.
It seems that the master Ward identity can nearly always be satisfied, the
only exceptions we know are the usual anomalies. We prove the compatibility of
the master Ward identity with the other (re)normalization conditions of causal
perturbation theory, and for pure massive theories we show that the 'central
solution' of Epstein and Glaser fulfills the master Ward identity, if the
UV-scaling behavior of its individual terms is not relatively lowered.
Application of the master Ward identity to the BRST-current of non-Abelian
gauge theories generates an identity (called 'master BRST-identity') which
contains the information which is needed for a local construction of the
algebra of observables, i.e. the elimination of the unphysical fields and the
construction of physical states in the presence of an adiabatically switched
off interaction.Comment: 73 pages, version to appear in Rev. Math. Phy
Effective polar potential in the central force Schrodinger equation
The angular part of the Schrodinger equation for a central potential is
brought to the one-dimensional 'Schrodinger form' where one has a kinetic
energy plus potential energy terms. The resulting polar potential is seen to be
a family of potentials characterized by the square of the magnetic quantum
number m. It is demonstrated that this potential can be viewed as a confining
potential that attempts to confine the particle to the xy-plane, with a
strength that increases with increasing m. Linking the solutions of the
equation to the conventional solutions of the angular equation, i.e. the
associated Legendre functions, we show that the variation in the spatial
distribution of the latter for different values of the orbital angular quantum
number l can be viewed as being a result of 'squeezing' with different
strengths by the introduced 'polar potential'.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in European Journal of Physic
Selective coherent destruction of tunneling in a quantum-dot array
The coherent manipulation of quantum states is one of the main tasks required
in quantum computation. In this paper we demonstrate that it is possible to
control coherently the electronic position of a particle in a quantum-dot
array. By tuning an external ac electric field we can selectively suppress the
tunneling between dots, trapping the particle in a determined region of the
array. The problem is treated non-perturbatively by a time-dependent
Hamiltonian in the effective mass approximation and using Floquet theory. We
find that the quasienergy spectrum exhibits crossings at certain field
intensities that result in the selective suppression of tunneling.Comment: 4 pages, 5 figures, submitted to PRB Rapid Com
Honey volatiles as a fingerprint for botanical origin: a review on their occurrence on monofloral honeys
Honeys have specific organoleptic characteristics, with nutritional and health benefits, being highly appreciated by consumers, not only in food but also in the pharmaceutical and cosmetic industries. Honey composition varies between regions according to the surrounding flora, enabling its characterization by source or type. Monofloral honeys may reach higher market values than multifloral ones. Honey's aroma is very specific, resulting from the combination of volatile compounds present in low concentrations. The authentication of honey's complex matrix, according to its botanical and/or geographical origin, represents a challenge nowadays, due to the different sorts of adulteration that may occur, leading to the search for reliable marker compounds for the different monofloral honeys. The existing information on the volatiles of monofloral honeys is scarce and disperse. In this review, twenty monofloral honeys and honeydews, from acacia, buckwheat, chestnut, clover, cotton, dandelion, eucalyptus, fir tree, heather, lavender, lime tree, orange, pine, rape, raspberry, rhododendron, rosemary, strawberry tree, sunflower and thyme, were selected for volatile comparison purposes. Taking into consideration the country of origin, the technique of isolation and analysis, the five main volatiles from each of the honeys are compared. Whereas some compounds were found in several types of monofloral honey, and thus not considered good volatile markers, some monofloral honeys revealed characteristic volatile compounds independently of their provenance.Funding: SFRH/BD/117013/2016, UID/AGR/00690/2019,
UID/AMB/50017/2019, MED (UIDB/05183/2020), FEDER, PT2020 PACompete 2020info:eu-repo/semantics/publishedVersio
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