65 research outputs found
Quantum Gravity Without Ghosts
An outline is given of a recently discovered technique for building a quantum
effective action that is completely independent of gauge-fixing choices and
ghost determinants. One makes maximum use of the geometry and fibre-bundle
structure of the space of field histories and introduces a set of nonlocal
composite fields: the geodesic normal fields based on Vilkovisky's connection
on the space of histories. The closed-time-path formalism of Schwinger, Bakshi,
Mahantappa {\it et al} can be adapted for these fields, and a set of
gauge-fixing-independent dynamical equations for their expectation values
(starting from given initial conditions) can be computed. An obvious
application for such equations is to the study of the formation and radiative
decay of black holes, and to other back-reaction problems.Comment: This is a paper submitted to the Gravity Research Foundation Essay
Competition of 1998 that received Honorable Mentio
Wheeler-DeWitt Quantization of Gravity Models of Unified Dark Energy and Dark Matter
First, we describe the construction of a new type of gravity-matter models
based on the formalism of non-Riemannian space-time volume forms - alternative
generally covariant integration measure densities (volume elements) defined in
terms of auxiliary antisymmetric tensor gauge fields. Here gravity couples in a
non-conventional way to two distinct scalar fields providing a unified
Lagrangian action principle description of: (i) the evolution of both "early"
and "late" Universe - by the "inflaton" scalar field; (ii) dark energy and dark
matter as a unified manifestation of a single material entity - the "darkon"
scalar field. A physically very interesting phenomenon occurs when including in
addition interactions with the electro-weak model bosonic sector - we obtain a
gravity-assisted dynamical generation of electro-weak spontaneous gauge
symmetry breaking in the post-inflationary "late" Universe, while the
Higgs-like scalar remains massless in the "early" Universe. Next, we proceed to
the Wheeler-DeWitt minisuperspace quantization of the above models. The
"darkon" field plays here the role of cosmological "time". In particular, we
show the absence of cosmological space-time singularities.Comment: 15 pages, to be published in the Proceedings of QTS10 - 10th
International Symposium "Quantum Theory and Symmetries" (Varna, 2017),
Springer Proceedings in Mathematics and Statistics, V. Dobrev (ed.). arXiv
admin note: text overlap with arXiv:1609.0691
An introduction to quantum gravity
After an overview of the physical motivations for studying quantum gravity,
we reprint THE FORMAL STRUCTURE OF QUANTUM GRAVITY, i.e. the 1978 Cargese
Lectures by Professor B.S. DeWitt, with kind permission of Springer. The reader
is therefore introduced, in a pedagogical way, to the functional integral
quantization of gravitation and Yang-Mills theory. It is hoped that such a
paper will remain useful for all lecturers or Ph.D. students who face the task
of introducing (resp. learning) some basic concepts in quantum gravity in a
relatively short time. In the second part, we outline selected topics such as
the braneworld picture with the same covariant formalism of the first part, and
spectral asymptotics of Euclidean quantum gravity with diffeomorphism-invariant
boundary conditions. The latter might have implications for singularity
avoidance in quantum cosmology.Comment: 68 pages, Latex file. Sections from 2 to 17 are published thanks to
kind permission of Springe
The Research on Public Participation in Local Legislation ——Take Xiamen as an Example
1997年,党的十五大提出依法治国、建设社会主义法治国家的基本方略;1999年,“依法治国”正式写入宪法,明确规定“中华人民共和国实行依法治国,建设社会主义法治国家”;2007年,党的十七大做出“全面落实依法治国基本方略,加快建设社会主义法治国家”的战略部署。民主是法治国家必备的政治基础,完善的民主是法治国家的重要标志,立法并不必然是符合所有人意志的决定,但却应该是所有人参与立法决策过程的结果。2007年9月到2009年6月,西北政法大学教授王周户就“公众参与”项目在陕西西安、宝鸡进行了问卷调查。982份调查问卷结果显示:绝大多数人(78%)认为公民应该参与人大立法和政府决策;77%的被调查者...In the year of 1997, the 15th CCP congress raised the basic strategy of manage the state according to the rule of law and develop socialism law-based government; In the year of 1999, “running the country according to law” was formally written into the constitution law, “The People’s Republic of China governs the country according to law and makes it socialist country ruled by law.” was clearly dec...学位:法律硕士院系专业:法学院法律系_法律硕士(JM)学号:X200812013
The Quantized Sigma Model Has No Continuum Limit in Four Dimensions. I. Theoretical Framework
The nonlinear sigma model for which the field takes its values in the coset
space is similar to quantum gravity in being
perturbatively nonrenormalizable and having a noncompact curved configuration
space. It is therefore a good model for testing nonperturbative methods that
may be useful in quantum gravity, especially methods based on lattice field
theory. In this paper we develop the theoretical framework necessary for
recognizing and studying a consistent nonperturbative quantum field theory of
the model. We describe the action, the geometry of the
configuration space, the conserved Noether currents, and the current algebra,
and we construct a version of the Ward-Slavnov identity that makes it easy to
switch from a given field to a nonlinearly related one. Renormalization of the
model is defined via the effective action and via current algebra. The two
definitions are shown to be equivalent. In a companion paper we develop a
lattice formulation of the theory that is particularly well suited to the sigma
model, and we report the results of Monte Carlo simulations of this lattice
model. These simulations indicate that as the lattice cutoff is removed the
theory becomes that of a pair of massless free fields. Because the geometry and
symmetries of these fields differ from those of the original model we conclude
that a continuum limit of the model which preserves
these properties does not exist.Comment: 25 pages, no figure
Green's function for gravitational waves in FRW spacetimes
A method for calculating the retarded Green's function for the gravitational
wave equation in Friedmann-Roberson-Walker spacetimes, within the formalism of
linearized Einstein gravity is developed. Hadamard's general solution to
Cauchy's problem for second-order, linear partial differential equations is
applied to the FRW gravitational wave equation. The retarded Green's function
may be calculated for any FRW spacetime, with curved or flat spatial sections,
for which the functional form of the Ricci scalar curvature is known. The
retarded Green's function for gravitational waves propagating through a
cosmological fluid composed of both radiation and dust is calculated
analytically for the first time. It is also shown that for all FRW spacetimes
in which the Ricci scalar curvatures does not vanish, , the Green's
function violates Huygens' principle; the Green's function has support inside
the light-cone due to the scatter of gravitational waves off the background
curvature.Comment: 9 pages, FERMILAB-Pub-93/189-
Perfect Fluid Quantum Anisotropic Universe: Merits and Challenges
The present paper deals with quantization of perfect fluid anisotropic
cosmological models. Bianchi type V and IX models are discussed following
Schutz's method of expressing fluid velocities in terms of six potentials. The
wave functions are found for several examples of equations of state. In one
case a complete wave packet could be formed analytically. The initial
singularity of a zero proper volume can be avoided in this case, but it is
plagued by the usual problem of non-unitarity of anisotropic quantum
cosmological models. It is seen that a particular operator ordering alleviates
this problem.Comment: 13 pages, 4 figures; Accepted for publication in Gen Relativ Gravi
Feynman's interpretation of quantum theory
A historically important but little known debate regarding the necessity and
meaning of macroscopic superpositions, in particular those containing different
gravitational fields, is discussed from a modern perspective.Comment: Published version for Eur.Phys.J. H. 15 pages pdf. Final version
available at
http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1140/epjh/e2011-10035-
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