622 research outputs found
Gauge fixing in higher derivative field theories
Higher Derivative (HD) Field Theories can be transformed into second order
equivalent theories with a direct particle interpretation. In a simple model
involving abelian gauge symmetries we examine the fate of the possible gauge
fixings throughout this process. This example is a useful test bed for HD
theories of gravity and provides a nice intuitive interpretation of the "third
ghost" occurring there and in HD gauge theories when a HD gauge fixing is
adopted.Comment: 16 pages, Latex,( Preprint imaff 93/10
Tri-hamiltonian vector fields, spectral curves and separation coordinates
We show that for a class of dynamical systems, Hamiltonian with respect to
three distinct Poisson brackets (P_0, P_1, P_2), separation coordinates are
provided by the common roots of a set of bivariate polynomials. These
polynomials, which generalise those considered by E. Sklyanin in his
algebro-geometric approach, are obtained from the knowledge of: (i) a common
Casimir function for the two Poisson pencils (P_1 - \lambda P_0) and (P_2 - \mu
P_0); (ii) a suitable set of vector fields, preserving P_0 but transversal to
its symplectic leaves. The frameworks is applied to Lax equations with spectral
parameter, for which not only it unifies the separation techniques of Sklyanin
and of Magri, but also provides a more efficient ``inverse'' procedure not
involving the extraction of roots.Comment: 49 pages Section on reduction revisite
Four-Dimensional Higher-Derivative Supergravity and Spontaneous Supersymmetry Breaking
We construct two classes of higher-derivative supergravity theories
generalizing Einstein supergravity. We explore their dynamical content as well
as their vacuum structure. The first class is found to be equivalent to
Einstein supergravity coupled to a single chiral superfield. It has a unique
stable vacuum solution except in a special case, when it becomes identical to a
simple no-scale theory. The second class is found to be equivalent to Einstein
supergravity coupled to two chiral superfields and has a richer vacuum
structure. It is demonstrated that theories of the second class can possess a
stable vacuum with vanishing cosmological constant that spontaneously breaks
supersymmetry. We present an explicit example of this phenomenon and compare
the result with the Polonyi model.Comment: 26 pages, LaTeX2e and AMS-LaTeX 1.2, 1 eps figur
Non-Trivial Vacua in Higher-Derivative Gravitation
A discussion of an extended class of higher-derivative classical theories of
gravity is presented. A procedure is given for exhibiting the new propagating
degrees of freedom, at the full non-linear level, by transforming the
higher-derivative action to a canonical second-order form. For general
fourth-order theories, described by actions which are general functions of the
scalar curvature, the Ricci tensor and the full Riemann tensor, it is shown
that the higher-derivative theories may have multiple stable vacua. The vacua
are shown to be, in general, non-trivial, corresponding to deSitter or
anti-deSitter solutions of the original theory. It is also shown that around
any vacuum the elementary excitations remain the massless graviton, a massive
scalar field and a massive ghost-like spin-two field. The analysis is extended
to actions which are arbitrary functions of terms of the form ,
and it is shown that such theories also have a non-trivial vacuum structure.Comment: 25 pages, LaTeX2e with AMS-LaTeX 1.2, 7 eps figure
The Role of Emotional Intelligence in Health Care Professionals Burnout
The purpose of this study is to explore the relationship between Emotional Intelligence (EI) and burnout in health care professionals. More specifically, this survey has the purpose of demonstrating the role of EI as a protective factor against the risk of burnout. Health professionals (doctors, nurses, and other caregivers) composed the sample. Data, collected during professional training, provided 148 employees. Major results of this survey underline the relationship between EI and burnout. As we expected, there is a negative and significant correlation between burnout and Emotional Intelligence. Moreover, burnout varies depending on length of service: burnout increases between 5 and 10 years of experience and decreases over 10 years. Indeed, burnout is differently expressed amongst healthcare professionals: more specifically, Psycho-physical exhaustion, Detriment of the relationships and Burnout (total score) has an impact on physician (doctors) more than other investigated health professionals. These findings seem to suggest the opportunity to improve Emotional Intelligence abilities through specific training programs, useful to promote the ability to cope with stress and to enrich the relationships in the workplace
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
Test-field limit of metric nonlinear gravity theories
In the framework of alternative metric gravity theories, it has been shown by
several authors that a generic Lagrangian depending on the Riemann tensor
describes a theory with 8 degrees of freedom (which reduce to 3 for f(R)
Lagrangians depending only on the curvature scalar). This result is often
related to a reformulation of the fourth-order equations for the metric into a
set of second-order equations for a multiplet of fields, including a massive
scalar field and a massive spin-2 field. In this article we investigate an
issue which does not seem to have been addressed so far: in ordinary
general-relativistic field theories, all fundamental fields (i.e. fields with
definite spin and mass) reduce to test fields in some appropriate limit of the
model, where they cease to act as sources for the metric curvature. In this
limit, each of the fundamental fields can be excited from its ground state
independently from the others. The question is: does higher-derivative gravity
admit a test-field limit for its fundamental fields? It is easy to show that
for a f(R) theory the test-field limit does exist; then, we consider the case
of Lagrangians quadratically depending on the full Ricci tensor. We show that
the constraint binding together the scalar field and the massive spin-2 field
does not disappear in the limit where they should be expected to act as test
fields, except for a particular choice of the Lagrangian, which cause the
scalar field to disappear (reducing to 7 DOF). We finally consider the addition
of an arbitrary function of the quadratic invariant of the Weyl tensor and show
that the resulting model still lacks a proper test-field limit. We argue that
the lack of a test-field limit for the fundamental fields may constitute a
serious drawback of the full 8 DOF higher-order gravity models, which is not
encountered in the restricted 7 DOF or 3 DOF cases.Comment: Title and abstract modified to make the content of the paper more
clear and readabl
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Intracardiac echocardiography in the diagnosis of prosthetic valve endocarditis
These images illustrate a new use of ICE as a diagnostic modality for prosthetic valve endocarditis. Although a few studies have examined the role of ICE in the evaluation of valvular pathology, its clinical role has primarily been within the electrophysiology laboratory to guide catheter placement. As this technology continues to evolve, ICE may supplement other imaging modalities and find new clinical applications
The Universality of Einstein Equations
It is shown that for a wide class of analytic Lagrangians which depend only
on the scalar curvature of a metric and a connection, the application of the
so--called ``Palatini formalism'', i.e., treating the metric and the connection
as independent variables, leads to ``universal'' equations. If the dimension
of space--time is greater than two these universal equations are Einstein
equations for a generic Lagrangian and are suitably replaced by other universal
equations at bifurcation points. We show that bifurcations take place in
particular for conformally invariant Lagrangians and prove
that their solutions are conformally equivalent to solutions of Einstein
equations. For 2--dimensional space--time we find instead that the universal
equation is always the equation of constant scalar curvature; the connection in
this case is a Weyl connection, containing the Levi--Civita connection of the
metric and an additional vectorfield ensuing from conformal invariance. As an
example, we investigate in detail some polynomial Lagrangians and discuss their
bifurcations.Comment: 15 pages, LaTeX, (Extended Version), TO-JLL-P1/9
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