7,056 research outputs found
How massless are massless fields in
Massless fields of generic Young symmetry type in space are analyzed.
It is demonstrated that in contrast to massless fields in Minkowski space whose
physical degrees of freedom transform in irreps of algebra,
massless mixed symmetry fields reduce to a number of irreps of
algebra. From the field theory perspective this means that not every massless
field in flat space admits a deformation to with the same number of
degrees of freedom, because it is impossible to keep all of the flat space
gauge symmetries unbroken in the AdS space. An equivalent statement is that,
generic irreducible AdS massless fields reduce to certain reducible sets of
massless fields in the flat limit. A conjecture on the general pattern of the
flat space limit of a general massless field is made. The example of
the three-cell ``hook'' Young diagram is discussed in detail. In particular, it
is shown that only a combination of the three-cell flat-space field with a
graviton-like field admits a smooth deformation to .Comment: 23 pages, LaTeX, a few typos correcte
Non conventional screening of the Coulomb interaction in low dimensional and finite size system
We study the screening of the Coulomb interaction in non polar systems by
polarizable atoms. We show that in low dimensions and small finite size systems
this screening deviates strongly from that conventionally assumed. In fact in
one dimension the short range interaction is strongly screened and the long
range interaction is anti-screened thereby strongly reducing the gradient of
the Coulomb interaction and therefore the correlation effects. We argue that
this effect explains the success of mean field single particle theories for
large molecules.Comment: 4 pages, 5 figure
Cyclic and constant temperature aging effects on magnetic materials for inverters and converters
Cyclic and constant temperature aging effects on magnetic materials for inverters and converter
Local Invariants and Pairwise Entanglement in Symmetric Multi-qubit System
Pairwise entanglement properties of a symmetric multi-qubit system are
analyzed through a complete set of two-qubit local invariants. Collective
features of entanglement, such as spin squeezing, are expressed in terms of
invariants and a classifcation scheme for pairwise entanglement is proposed.
The invariant criteria given here are shown to be related to the recently
proposed (Phys. Rev. Lett. 95, 120502 (2005)) generalized spin squeezing
inequalities for pairwise entanglement in symmetric multi-qubit states.Comment: 9 pages, 2 figures, REVTEX, Replaced with a published versio
Purely twistorial string with canonical twistor field quantization
We introduce new purely twistorial scale-invariant action describing the
composite bosonic D=4 Nambu-Goto string with target space parametrized by the
pair of D=4 twistors. We show that by suitable gauge fixing of local scaling
one gets the bilinear twistorial action and canonical quantization rules for
the two-dimensional twistor-string fields. We consider the Poisson brackets of
all constraints characterizing our model and we obtain four first class
constraints describing two Virasoro constraints and two U(1)xU(1) Kac-Moody
(KM) local phase transformations.Comment: v3: 6p.(extended version), in press in Physical Review
Analytical approximation for the sphere-sphere Coulomb potential
A simple analytical expression, which closely approximates the Coulomb
potential between two uniformly charged spheres, is presented. This expression
can be used in the optical potential semiclassical analyses which require that
the interaction be analytic on and near the real r-axis.Comment: 4 pages including 3 figures and 1 tabl
The Jacobi identity for Dirac-like brackets
For redundant second-class constraints the Dirac brackets cannot be defined
and new brackets must be introduced. We prove here that the Jacobi identity for
the new brackets must hold on the surface of the second-class constraints. In
order to illustrate our proof we work out explicitly the cases of a fractional
spin particle in 2+1 dimensions and the original Brink-Schwarz massless
superparticle in D=10 dimensions in a Lorentz covariant constraints separation.Comment: 14 pages, Latex. Final version to be published in Int. J. Mod. Phys.
A Potts model for the distortion transition in LaMnO
The Jahn-Teller distortive transition of \lmo is described by a modified
3-state Potts model. The interactions between the three possible orbits depends
both on the orbits and their relative orientation on the lattice. Values of the
two exchange parameters which are chosen to give the correct low temperature
phase and the correct value for the transition temperature are shown to be
consistent with microscopy theory. The model predicts a first order transitions
and also a value for the entropy above the transition in good agreement with
experiment. The theory with the same parameters also predicts the temperature
dependence of the order parameter of orbital ordering agreeing well with
published experimental results. Finally, the type of the transition is shown to
be close to one of the most disordered phases of the generalised Potts model.
The short range order found experimentally above the transition is investigated
by this model.Comment: 16 pages, 7 figures and no tables. Re-submitted to Phys. Rev.
Surface-enhanced pair transfer in quadrupole states of neutron-rich Sn isotopes
We investigate the neutron pair transfer modes associated with the low-lying
quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle
random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean
field model. The transition strength of the quadrupole pair-addition mode
feeding the state is enhanced in the Sn isotopes with . The
transition density of the pair-addition mode has a large spatial extension in
the exterior of nucleus, reaching far to fm. The quadrupole
pair-addition mode reflects sensitively a possible increase of the effective
pairing interaction strength in the surface and exterior regions of
neutron-rich nuclei.Comment: 14 page
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