1,720,982 research outputs found
Unruh versus Tolman: on the heat of acceleration Dedicated to the memory of Rudolf Haag
No full textIt is shown that the Unruh effect, i.e. the increase in temperature indicated by a uniformly accelerated thermometer in an inertial vacuum state of a quantum field, cannot be interpreted as the result of an exchange of heat with a surrounding gas. Since the vacuum is spatially homogeneous in the accelerated system its temperature must be zero everywhere as a consequence of Tolman's law. In fact, the increase of temperature of accelerated thermometers is due to systematic quantum effects induced by the local coupling between the thermometer and the vacuum. This coupling inevitably creates excitations of the vacuum which transfer energy to the thermometer, gained by the acceleration, and thereby affect its readings. The temperature of the vacuum, however, remains to be zero for arbitrary accelerations
Macroscopic aspects of the Unruh effect
No full textMacroscopic concepts pertaining to the Unruh effect are elaborated and used to clarify its physical manifestations. Based on a description of the motion of accelerated, spatially extended laboratories in Minkowski space in terms of Poincare transformations, it is shown that, from a macroscopic perspective, an accelerated observer will not register with his measuring instruments any global thermal effects of acceleration in the inertial (Minkowskian) vacuum state. As is explained, this result is not in conflict with the well-known fact that microscopic probes used as thermometers respond non-trivially to acceleration if coupled to the vacuum. But this response cannot be interpreted as the effect of some exchange of thermal energy with a gas surrounding the observer; in fact, it is induced by the measuring process itself. It is also shown that genuine equilibrium states in a uniformly accelerated laboratory cannot be spatially homogeneous. In particular, these states coincide with the homogeneous inertial vacuum at sufficiently large distances from the horizon of the observer and consequently have the same (zero) temperature there. The analysis is carried out in the theory of a free massless scalar field; however the conclusion that the Unruh effect is not of a macroscopic thermal origin is generally valid
KMS-like properties of local equilibrium states in quantum field theory
No full textA new condition, called “Local KMS Condition”, characterizing states of a quantum field to which one can ascribe, at a given spacetime point, a temperature, is introduced in this article. It will be shown that the Local KMS Condition (LKMS condition) is equivalent to the Local Thermal Equilibrium (LTE) condition, proposed previously by Buchholz, Ojima and Roos, for states of the quantized scalar Klein–Gordon field that fulfill the analytic microlocal spectrum condition. Therefore, known examples of states fulfilling the LTE condition provide examples of states obeying the LKMS condition with a temperature distribution varying in space and time. The results extend to the generalized cases of mixed-temperature LKMS and LTE states. The LKMS condition therefore provides a promising generalization of the KMS condition, which characterizes global thermal equilibrium states with respect to an inertial time evolution, to states which are globally out of equilibrium but still possess a local temperature distribution
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
Higher spin fields on curved spacetimes
Full text linkThis is a diploma thesis on Buchdahl's equations for the description of massive particles of arbitrary spin s/2. On 4-dimensional, globally hyperbolic Lorentzian spacetime manifolds, existence of advanced and retarded Green's operators is proved, the Cauchy problem for Buchdahl's equations is solved globally and two possible constructions for quantizing Buchdahl fields using CAR algebras in the fashion of [Dimock 1982] are given
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
Local Thermal Equilibrium on Curved Spacetimes and Linear Cosmological Perturbation Theory
Full text linkIn this work the extension of the criterion for local thermal equilibrium by Buchholz, Ojima and Roos to curved spacetime as introduced by Schlemmer is investigated. Several problems are identified and especially the instability under time evolution which was already observed by Schlemmer is inspected. An alternative approach to local thermal equilibrium in quantum field theories on curved spacetimes is presented and discussed. In the following the dynamic system of the linear field and matter perturbations in the generic model of inflation is studied in the view of ambiguity of quantisation. In the last part the compatibility of the temperature fluctuations of the cosmic microwave background radiation with local thermal equilibrium is investigated.:1. Introduction 5
2. Technical Background 10
2.1. The Free Scalar Field on a Globally Hyperbolic Spacetime . . . . . . 10
2.1.1. Construction of the Scalar Field . . . . . . . . . . . . . . . . . 10
2.1.2. Algebra of Wick Products . . . . . . . . . . . . . . . . . . . . 13
2.1.3. Local Covariance Principle . . . . . . . . . . . . . . . . . . . . 17
2.2. Local Thermal Equilibirum . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1. Global Thermodynamic Equilibrium - KMS States . . . . . . 21
2.2.2. Local Thermal Observables . . . . . . . . . . . . . . . . . . . 24
2.2.3. LTE on Flat Spacetime . . . . . . . . . . . . . . . . . . . . . . 29
2.2.4. LTE in Cosmological Spacetimes . . . . . . . . . . . . . . . . 32
2.3. Linear Scalar Cosmological Perturbations . . . . . . . . . . . . . . . . 34
2.3.1. Robertson-Walker Cosmology . . . . . . . . . . . . . . . . . . 35
2.3.2. Mathematical Background . . . . . . . . . . . . . . . . . . . . 38
2.3.3. Technical Framework and Formulae . . . . . . . . . . . . . . . 40
2.3.4. The Boltzmann Equation . . . . . . . . . . . . . . . . . . . . 46
2.3.5. The Sachs-Wolfe Effect for Adiabatic Perturbations . . . . . . 49
3. Towards a Refinement of the LTE Condition on Curved Spacetimes 54
3.1. Non-Minimal Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.1.1. Commutator Distribution . . . . . . . . . . . . . . . . . . . . 55
3.1.2. KMS Two-Point Function . . . . . . . . . . . . . . . . . . . . 57
3.1.3. Balanced Derivatives . . . . . . . . . . . . . . . . . . . . . . . 61
3.2. Conformally Static Spacetimes . . . . . . . . . . . . . . . . . . . . . . 65
3.2.1. Conformal KMS States . . . . . . . . . . . . . . . . . . . . . . 66
3.2.2. Extrinsic LTE in de Sitter Spacetime . . . . . . . . . . . . . . 71
3.3. Massive Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.3.1. Properties of the Model . . . . . . . . . . . . . . . . . . . . . 78
3.3.2. Bogoliubov Transformation . . . . . . . . . . . . . . . . . . . 80
3.3.3. Thermal Observables . . . . . . . . . . . . . . . . . . . . . . . 82
3.4. Towards an Alternative Concept . . . . . . . . . . . . . . . . . . . . . 91
3.4.1. Problems and Open Questions Concerning LTE . . . . . . . . 92
3.4.2. Dynamic Equations . . . . . . . . . . . . . . . . . . . . . . . . 94
3.4.3. Positivity Inequalities . . . . . . . . . . . . . . . . . . . . . . . 96
3.4.4. Macroobservable Interpretation . . . . . . . . . . . . . . . . . 100
3.5. An Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4. Cosmological Perturbation Theory 105
4.1. Dynamics of Perturbations in Inflation . . . . . . . . . . . . . . . . . 106
4.1.1. CCR Quantisation is Ambiguous . . . . . . . . . . . . . . . . 106
4.1.2. Canonical Symplectic Form . . . . . . . . . . . . . . . . . . . 111
4.1.3. The Algebraic Point of View . . . . . . . . . . . . . . . . . . . 117
4.2. LTE States in Cosmology . . . . . . . . . . . . . . . . . . . . . . . . 120
4.2.1. The Link to Fluid Dynamics . . . . . . . . . . . . . . . . . . . 120
4.2.2. Incompatibility of LTE with Sachs-Wolfe Effect . . . . . . . . 125
5. Conclusion and Outlook 131
A. Technical proofs 136
A.1. Proof of Lemma 3.2.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
A.2. Proof of Lemma 3.2.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
A.3. Proof of Lemma 3.4.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
A.4. Idea of Proof for Conjecture 3.4.3 . . . . . . . . . . . . . . . . . . . . 144
B. Introduction to Probability Theory 146
Bibliography 150
Correction of Lemma 3.1.2 155In dieser Arbeit wird die von Schlemmer eingeführte Erweiterung des Kriteriums für lokales thermisches Gleichgewicht in Quantenfeldtheorien von Buchholz, Ojima und Roos auf gekrümmte Raumzeiten untersucht. Dabei werden verschiedene Probleme identifiziert und insbesondere die bereits von Schlemmer gezeigte Instabilität unter Zeitentwicklung untersucht. Es wird eine alternative Herangehensweise an lokales thermisches Gleichgewicht in Quantenfeldtheorien auf gekrümmten Raumzeiten vorgestellt und deren Probleme diskutiert. Es wird dann eine Untersuchung des dynamischen Systems der linearen Feld- und Metrikstörungen im üblichen Inflationsmodell mit Blick auf Uneindeutigkeit der Quantisierung durchgeführt. Zuletzt werden die Temperaturfluktuationen der kosmischen Hintergrundstrahlung auf Kompatibilität mit lokalem thermalem Gleichgewicht überprüft.:1. Introduction 5
2. Technical Background 10
2.1. The Free Scalar Field on a Globally Hyperbolic Spacetime . . . . . . 10
2.1.1. Construction of the Scalar Field . . . . . . . . . . . . . . . . . 10
2.1.2. Algebra of Wick Products . . . . . . . . . . . . . . . . . . . . 13
2.1.3. Local Covariance Principle . . . . . . . . . . . . . . . . . . . . 17
2.2. Local Thermal Equilibirum . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1. Global Thermodynamic Equilibrium - KMS States . . . . . . 21
2.2.2. Local Thermal Observables . . . . . . . . . . . . . . . . . . . 24
2.2.3. LTE on Flat Spacetime . . . . . . . . . . . . . . . . . . . . . . 29
2.2.4. LTE in Cosmological Spacetimes . . . . . . . . . . . . . . . . 32
2.3. Linear Scalar Cosmological Perturbations . . . . . . . . . . . . . . . . 34
2.3.1. Robertson-Walker Cosmology . . . . . . . . . . . . . . . . . . 35
2.3.2. Mathematical Background . . . . . . . . . . . . . . . . . . . . 38
2.3.3. Technical Framework and Formulae . . . . . . . . . . . . . . . 40
2.3.4. The Boltzmann Equation . . . . . . . . . . . . . . . . . . . . 46
2.3.5. The Sachs-Wolfe Effect for Adiabatic Perturbations . . . . . . 49
3. Towards a Refinement of the LTE Condition on Curved Spacetimes 54
3.1. Non-Minimal Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.1.1. Commutator Distribution . . . . . . . . . . . . . . . . . . . . 55
3.1.2. KMS Two-Point Function . . . . . . . . . . . . . . . . . . . . 57
3.1.3. Balanced Derivatives . . . . . . . . . . . . . . . . . . . . . . . 61
3.2. Conformally Static Spacetimes . . . . . . . . . . . . . . . . . . . . . . 65
3.2.1. Conformal KMS States . . . . . . . . . . . . . . . . . . . . . . 66
3.2.2. Extrinsic LTE in de Sitter Spacetime . . . . . . . . . . . . . . 71
3.3. Massive Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.3.1. Properties of the Model . . . . . . . . . . . . . . . . . . . . . 78
3.3.2. Bogoliubov Transformation . . . . . . . . . . . . . . . . . . . 80
3.3.3. Thermal Observables . . . . . . . . . . . . . . . . . . . . . . . 82
3.4. Towards an Alternative Concept . . . . . . . . . . . . . . . . . . . . . 91
3.4.1. Problems and Open Questions Concerning LTE . . . . . . . . 92
3.4.2. Dynamic Equations . . . . . . . . . . . . . . . . . . . . . . . . 94
3.4.3. Positivity Inequalities . . . . . . . . . . . . . . . . . . . . . . . 96
3.4.4. Macroobservable Interpretation . . . . . . . . . . . . . . . . . 100
3.5. An Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4. Cosmological Perturbation Theory 105
4.1. Dynamics of Perturbations in Inflation . . . . . . . . . . . . . . . . . 106
4.1.1. CCR Quantisation is Ambiguous . . . . . . . . . . . . . . . . 106
4.1.2. Canonical Symplectic Form . . . . . . . . . . . . . . . . . . . 111
4.1.3. The Algebraic Point of View . . . . . . . . . . . . . . . . . . . 117
4.2. LTE States in Cosmology . . . . . . . . . . . . . . . . . . . . . . . . 120
4.2.1. The Link to Fluid Dynamics . . . . . . . . . . . . . . . . . . . 120
4.2.2. Incompatibility of LTE with Sachs-Wolfe Effect . . . . . . . . 125
5. Conclusion and Outlook 131
A. Technical proofs 136
A.1. Proof of Lemma 3.2.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
A.2. Proof of Lemma 3.2.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
A.3. Proof of Lemma 3.4.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
A.4. Idea of Proof for Conjecture 3.4.3 . . . . . . . . . . . . . . . . . . . . 144
B. Introduction to Probability Theory 146
Bibliography 150
Correction of Lemma 3.1.2 15
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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