1,720,959 research outputs found
Worldline path integral for the massive graviton
Full text linkWe compute the counterterms necessary for the renormalization of the one-loop
effective action of massive gravity from a worldline perspective. This is
achieved by employing the recently proposed massive spinning
particle model to describe the propagation of the massive graviton on those
backgrounds that solve the Einstein equations without cosmological constant,
namely on Ricci-flat manifolds, in four dimensions. The model is extended to be
consistent in spacetime dimensions by relaxing the gauging of the full
SO(4) R-symmetry group to a parabolic subgroup, together with the inclusion of
a suitable Chern-Simons term. Then, constructing the worldline path integral on
the one-dimensional torus allows for the correct calculation of the one-loop
divergencies in arbitrary dimensions. Our primary contribution is the
determination of the Seleey-DeWitt coefficients up to the fourth coefficient
, which to our knowledge has never been reported in the literature. Its
calculation is generally laborious on the quantum field theory side, as a
general formula for these coefficients is not available for operators that are
non-minimal in the heat kernel sense. This work illustrates the computational
efficiency of worldline methods in this regard. Heat kernel coefficients
characterize linearized massive gravity in a gauge-independent manner due to
the on-shell condition of the background on which the graviton propagates. They
could serve as a benchmark for verifying alternative approaches to massive
gravity, and, for this reason, their precise expression should be known
explicitly.Comment: 20 pages. Updated version accepted for publicatio
Path integral approach to heat kernel in massive gravity
Full text linkIn this thesis, we consider the Fierz-Pauli theory of linearized massive gravity in an Einstein spacetime. The aim is to study the one-loop effective action of this theory employing the heat kernel method, which consists in a variety of perturbation methods applied to minimal second order operators on manifolds, which allow us to study asymptotic expansions and singularities of Green functions. It is a powerful technique in mathematical physics, with applications ranging from black hole entropy to mathematical finance. In the Fierz-Pauli model of massive gravity, the operator entering the heat kernel is non-minimal, so we need ways to relate it to minimal operators in order to avoid a rather tedious treatment of the heat kernel expansion in the presence of non-minimal operators, which can be analyzed
either by means of covariant projectors or by employing the reduction method suggested by Barvinsky and Vilkovisky. Our approach is based on computing the path integral of the Fierz-Pauli action with the Faddeev-Popov procedure, using appropriate gauge-fixing functions. In fact, the addition of a mass term to the action for massless gravity breaks the
gauge symmetry of the theory, which is the general coordinate invariance. Because of this, the Fierz-Pauli theory of massive gravity is not a gauge theory and, of course, a gauge-fixing cannot be performed. Nevertheless, by first introducing new fields in the theory with the so-called Stückelberg trick, we can restore a gauge symmetry to the theory. These manipulations allow us to perform the computation of the path integral and the evaluation
of the heat kernel coefficients by using the well-known Seeley-DeWitt method
Massive gravity from a first-quantized perspective
Full text linkIn this work, we investigate the BRST quantization of the massive supersymmetric spinning particle, with a twofold purpose: exploring different approaches to give mass to spinning particle models and formulating a first-quantized theory for massive gravity on both flat and curved spacetime. The main contribution of this study is the development of a worldline formulation of the linear theory of massive gravity, namely of the Fierz–Pauli theory, on a curved spacetime; such a theory describes the propagation of massive spin 2 particle on a non-flat background. Our results suggest that achieving the nilpotency of the BRST charge requires an Einstein spacetime with vanishing cosmological constant as the only viable consistent background. In the course of the analysis, we take the supersymmetric worldline as an exemplificative model, correctly producing the Proca theory on curved spacetime. Our analysis shows that the associated BRST system uniquely selects the minimal coupling to the background curvature
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Massive gravity from a first-quantized perspective
Full text linkIn this work, we investigate the BRST quantization of the massive
supersymmetric spinning particle, with a twofold purpose:
exploring different approaches to give mass to spinning particle models and
formulating a first-quantized theory for linearized massive gravity on both
flat and curved spacetime. Our results suggest that achieving the nilpotency of
the BRST charge requires an Einstein spacetime with vanishing cosmological
constant as the only viable consistent background. In the course of the
analysis, we take the supersymmetric worldline as an
exemplificative model, correctly producing the Proca theory on curved
spacetime. Our analysis shows that the associated BRST system uniquely selects
the minimal coupling to the background curvature.Comment: 30 pages. v2: footnote and references added, minor corrections and
clarifications inserte
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The Fierz–Pauli theory on curved spacetime at one-loop and its counterterms
No full textWe compute the first four heat-kernel coefficients required for the renormalization of Linearized Massive Gravity. We focus on the Fierz–Pauli theory in a curved spacetime, describing the propagation of a massive spin 2 field in a non-flat background. The background must be on-shell, i.e. must be an Einstein space, in order to ensure a consistent extension of the Fierz–Pauli theory beyond Minkowski space. Starting from the Stückelberg formulation with restored gauge invariance, we apply suitable gauge-fixing procedures to simplify the complicated non-minimal kinetic operators of the scalar, vector, and tensor sectors of the theory, reducing them into manageable minimal forms. Using standard techniques, we then compute the Seeley–DeWitt coefficients, with particular emphasis on the fourth coefficient, , in arbitrary spacetime dimensions. This result constitutes our main contribution, as it has not been previously reported in full generality in the literature
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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