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This paper reviews the progress made over the last five years in studying boundary conditions and semiclassical properties of quantum fields about 4-real-dimensional Riemannian backgrounds. For massless spin-${1\over 2}$ fields one has a…

General Relativity and Quantum Cosmology · Physics 2007-05-23 Giampiero Esposito

When quantum fields are studied on manifolds with boundary, the corresponding one-loop quantum theory for bosonic gauge fields with linear covariant gauges needs the assignment of suitable boundary conditions for elliptic differential…

High Energy Physics - Theory · Physics 2017-08-23 Giampiero Esposito

We suggest a method of construction of general diffeomorphism invariant boundary conditions for metric fluctuations. The case of $d+1$ dimensional Euclidean disk is studied in detail. The eigenvalue problem for the Laplace operator on…

General Relativity and Quantum Cosmology · Physics 2009-10-28 Valeri Marachevsky , Dmitri Vassilevich

Quantum gravity is studied nonperturbatively in the case in which space has a boundary with finite area. A natural set of boundary conditions is studied in the Euclidean signature theory, in which the pullback of the curvature to the…

General Relativity and Quantum Cosmology · Physics 2010-04-06 Lee Smolin

A crucial problem in quantum cosmology is a careful analysis of the one-loop semiclassical approximation for the wave function of the universe, after an appropriate choice of mixed boundary conditions. The results for Euclidean quantum…

High Energy Physics - Theory · Physics 2007-05-23 Giampiero Esposito , Alexander Yu. Kamenshchik

The fundamental laws of physics can be derived from the requirement of invariance under suitable classes of transformations on the one hand, and from the need for a well-posed mathematical theory on the other hand. As a part of this…

High Energy Physics - Theory · Physics 2016-12-28 Giampiero Esposito

We perform the manifestly covariant quantization of a scale invariant gravity with a scalar field, which is equivalent to the well-known Brans-Dicke gravity via a field redefinition of the scalar field, in the de Donder gauge condition (or…

High Energy Physics - Theory · Physics 2022-03-14 Ichiro Oda

This paper studies a new set of mixed boundary conditions in Euclidean quantum gravity. These involve, in particular, Robin boundary conditions on the perturbed 3-metric and hence lead, by gauge invariance, to Robin conditions on the whole…

General Relativity and Quantum Cosmology · Physics 2009-10-28 Giampiero Esposito , Alexander Yu. Kamenshchik

This paper studies the semiclassical approximation of simple supergravity in Riemannian four-manifolds with boundary, within the framework of $\zeta$-function regularization. The massless nature of gravitinos, jointly with the presence of a…

High Energy Physics - Theory · Physics 2009-10-30 Giampiero Esposito , Alexander Yu. Kamenshchik

The boundary-value problem for Laplace-type operators acting on smooth sections of a vector bundle over a compact Riemannian manifold with generalized local boundary conditions including both normal and tangential derivatives is studied.…

High Energy Physics - Theory · Physics 2009-10-30 Ivan G. Avramidi , Giampiero Esposito

It is known that the action of Euclidean Einstein gravity is not bounded from below and that the metric of flat space does not correspond to a minimum of the action. Nevertheless, perturbation theory about flat space works well. The deep…

General Relativity and Quantum Cosmology · Physics 2009-10-31 G. Modanese

We review what is known about boundary conditions in General Relativity on a spacetime of Euclidean signature. The obvious Dirichlet boundary condition, in which one specifies the boundary geometry, is actually not elliptic and in general…

High Energy Physics - Theory · Physics 2023-07-18 Edward Witten

We consider the lagrangian of a self-interacting complex scalar field admitting generically Q-balls solutions. This model is extended by minimal coupling to electromagnetism and to gravity. A stationnary, axially-symmetric ansatz for the…

General Relativity and Quantum Cosmology · Physics 2009-07-07 Y. Brihaye , Th. Caebergs , T. Delsate

In this work we investigate the ultraviolet behavior of Euclidean four-derivative quantum gravity beyond perturbation theory. In addition to a perturbative fixed point, we find an ultraviolet fixed point that is non-trivial in all couplings…

High Energy Physics - Theory · Physics 2016-12-20 Nicolai Christiansen

In this article we are interested in studying regularity up to the boundary for one-phase singularly perturbed fully nonlinear elliptic problems, associated to high energy activation potentials, namely $$ F(X, \nabla u^{\varepsilon}, D^2…

Analysis of PDEs · Mathematics 2015-10-09 Gleydson C. Ricarte , João Vitor da Silva

We consider four-dimensional Euclidean gravity in a finite cavity. Dirichlet conditions do not yield a well-posed elliptic system, and Anderson has suggested boundary conditions that do. Here we point out that there exists a one-parameter…

High Energy Physics - Theory · Physics 2024-04-05 Xiaoyi Liu , Jorge E. Santos , Toby Wiseman

When quantum supergravity is studied on manifolds with boundary, one may consider local boundary conditions which fix on the initial surface the whole primed part of tangential components of gravitino perturbations, and fix on the final…

High Energy Physics - Theory · Physics 2009-10-30 Giampiero Esposito

A model for quantum gravity in one (time) dimension is discussed, based on Regge's discrete formulation of gravity. The nature of exact continuous lattice diffeomorphisms and the implications for a regularized gravitational measure are…

High Energy Physics - Theory · Physics 2009-10-28 Herbert W. Hamber , Ruth M. Williams

The character of quantum corrections to the gravitational action of a conformally invariant field theory for a self-interacting scalar field on a manifold with boundary is considered at third loop-order in the perturbative expansion of the…

High Energy Physics - Theory · Physics 2009-11-07 George Tsoupros

This work considers the Neumann eigenvalue problem for the weighted Laplacian on a Riemannian manifold $(M,g,\partial M)$ under the singular perturbation. This perturbation involves the imposition of vanishing Dirichlet boundary conditions…

Analysis of PDEs · Mathematics 2023-06-02 Medet Nursultanov , William Trad , Justin Tzou , Leo Tzou