25 research outputs found
Higher-Derivative Boson Field Theories and Constrained Second-Order Theories
As an alternative to the covariant Ostrogradski method, we show that
higher-derivative relativistic Lagrangian field theories can be reduced to
second differential-order by writing them directly as covariant two-derivative
theories involving Lagrange multipliers and new fields. Despite the intrinsic
non-covariance of the Dirac's procedure used to deal with the constraints, the
explicit Lorentz invariance is recovered at the end. We develop this new
setting on the grounds of a simple scalar model and then its applications to
generalized electrodynamics and higher-derivative gravity are worked out. For a
wide class of field theories this method is better suited than Ostrogradski's
for a generalization to 2n-derivative theoriesComment: 31 pages, Plain Te
Magneto-plasmonic nanoparticles as theranostic platforms for magnetic resonance imaging, drug delivery and NIR hyperthermia applications
PEGylated magneto-plasmonic nanoparticles with a hollow or semi-hollow interior have been successfully synthesized and their physico-chemical characteristics have been investigated. The hollow interior space can be used to store drugs or other molecules of interest whereas magnetic characterization shows their potential as contrast agents in magnetic resonance imaging (MRI) applications. In addition, their plasmonic characteristics in the near infrared (NIR) region make them efficient in photothermal applications producing high temperature gradients after short irradiation times. We show that by controlling the etching conditions the inner silica shell can be selectively dissolved to achieve a hollow or semi-hollow interior without compromising the magnetic or plasmonic characteristics of the resulting nanoparticles. Magnetic measurements and transmission electron microscopy observations have been used to demonstrate the precise control during the etching process and to select an optimal concentration of the etching reagent and contact time to preserve the inner superparamagnetic iron oxide-based nanoparticles and the plasmonic properties of the constructs. Drug loading capabilities were also evaluated for both semi-hollow and as-synthesized nanoparticles using Rhodamine B isothiocyanate as a model compound. The nanoparticles produced could be potentially used as “theranostic” nanoparticles with both imaging capabilities and a dual therapeutic function (drug delivery and hyperthermia)
Gauge Fixing in Higher Derivative Gravity
Linearized four-derivative gravity with a general gauge fixing term is
considered. By a Legendre transform and a suitable diagonalization procedure it
is cast into a second-order equivalent form where the nature of the physical
degrees of freedom, the gauge ghosts, the Weyl ghosts, and the intriguing
"third ghosts", characteristic to higher-derivative theories, is made explicit.
The symmetries of the theory and the structure of the compensating
Faddeev-Popov ghost sector exhibit non-trivial peculiarities.Comment: 21 pages, LaTe
Higher Derivative Operators from Scherk-Schwarz Supersymmetry Breaking on T^2/Z_2
In orbifold compactifications on T^2/Z_2 with Scherk-Schwarz supersymmetry
breaking, it is shown that (brane-localised) superpotential interactions and
(bulk) gauge interactions generate at one-loop higher derivative counterterms
to the mass of the brane (or zero-mode of the bulk) scalar field. These
brane-localised operators are generated by integrating out the bulk modes of
the initial theory which, although supersymmetric, is nevertheless
non-renormalisable. It is argued that such operators, of non-perturbative
origin and not protected by non-renormalisation theorems, are generic in
orbifold compactifications and play a crucial role in the UV behaviour of the
two-point Green function of the scalar field self-energy. Their presence in the
action with unknown coefficients prevents one from making predictions about
physics at (momentum) scales close to/above the compactification scale(s). Our
results extend to the case of two dimensional orbifolds, previous findings for
S^1/Z_2 and S^1/(Z_2 x Z_2') compactifications where brane-localised higher
derivative operators are also dynamically generated at loop level, regardless
of the details of the supersymmetry breaking mechanism. We stress the
importance of these operators for the hierarchy and the cosmological constant
problems in compactified theories.Comment: 23 pages, LaTeX, one figure, published version in JHE
Ostrogradski Formalism for Higher-Derivative Scalar Field Theories
We carry out the extension of the Ostrogradski method to relativistic field
theories. Higher-derivative Lagrangians reduce to second differential-order
with one explicit independent field for each degree of freedom. We consider a
higher-derivative relativistic theory of a scalar field and validate a powerful
order-reducing covariant procedure by a rigorous phase-space analysis. The
physical and ghost fields appear explicitly. Our results strongly support the
formal covariant methods used in higher-derivative gravity.Comment: 22 page
Living with Ghosts and their Radiative Corrections
The role of higher derivative operators in 4D effective field theories is
discussed in both non-supersymmetric and supersymmetric contexts. The approach,
formulated in the Minkowski space-time, shows that theories with higher
derivative operators do not always have an improved UV behaviour, due to
subtleties related to the analytical continuation from the Minkowski to the
Euclidean metric. This continuation is further affected at the dynamical level
due to a field-dependence of the poles of the Green functions of the
particle-like states, for curvatures of the potential of order unity in ghost
mass units. The one-loop scalar potential in lambda*phi^4 theory with a single
higher derivative term is shown to have infinitely many counterterms, while for
a very large mass of the ghost the usual 4D renormalisation is recovered. In
the supersymmetric context of the O'Raifeartaigh model of spontaneous
supersymmetry breaking with a higher derivative (supersymmetric) operator, it
is found that quadratic divergences are present in the one-loop self-energy of
the scalar field. They arise with a coefficient proportional to the amount of
supersymmetry breaking and suppressed by the scale of the higher derivative
operator. This is also true in the Wess-Zumino model with higher derivatives
and explicit soft breaking of supersymmetry. In both models, the UV logarithmic
behaviour is restored in the decoupling limit of the ghost.Comment: 28 pages, 3 figures; added reference
A Superspace Formulation of The BV Action for Higher Derivative Theories
We first analyze the anti-BRST and double BRST structures of a certain higher
derivative theory that has been known to possess BRST symmetry associated with
its higher derivative structure. We discuss the invariance of this theory under
shift symmetry in the Batalin Vilkovisky (BV) formalism. We show that the
action for this theory can be written in a manifestly extended BRST invariant
manner in superspace formalism using one Grassmann coordinate.
It can also be written in a manifestly extended BRST invariant manner and
on-shell manifestly extended anti-BRST invariant manner in superspace formalism
using two Grassmann coordinates.Comment: accepted for publication in EPJ
Functional Lagrange formalism for time-non-local Lagrangians
We develop a time-non-local (TNL) formalism based on variational calculus,
which allows for the analysis of TNL Lagrangians. We derive the generalized
Euler-Lagrange equations starting from the Hamilton's principle and, by
defining a generalized momentum, we introduce the corresponding Hamiltonian
formalism. We apply the formalism to second order TNL Lagrangians and we show
that it reproduces standard results in the time-local limit. An example will
show how the formalism works, and will provide an interesting insight on the
non-standard features of TNL equations.Comment: 13 pages, 2 figure
Shell Model in the Complex Energy Plane
This work reviews foundations and applications of the complex-energy
continuum shell model that provides a consistent many-body description of bound
states, resonances, and scattering states. The model can be considered a
quasi-stationary open quantum system extension of the standard configuration
interaction approach for well-bound (closed) systems.Comment: Topical Review, J. Phys. G, Nucl. Part. Phys, in press (2008