arXiv subjects

A. O. Barvinsky

Publications and source records attributed to A. O. Barvinsky.

At least 73 records · Page 4Linked to original sources

arXiv2002

Duality of boundary value problems and braneworld action in curved brane models

Braneworld effective action is constructed by two different methods based respectively on the Dirichlet and Neumann boundary value problems. The equivalence of these methods is shown due to nontrivial duality relations between special boundary operators of these two problems. Previously known braneworld action algorithms in two-brane Randall-Sundrum model are generalized to curved branes with deSitter and Anti-deSitter geometries.

hep-th↗

arXiv2002

New nonlocal effective action

We suggest a new method for the calculation of the nonlocal part of the effective action. It is based on resummation of perturbation series for the heat kernel and its functional trace at large values of the proper time parameter. We derive a new, essentially nonperturbative, nonlocal contribution to the effective action in spacetimes with dimensions $d>2$.

hep-th↗

arXiv2002

Braneworld effective action and origin of inflation

We construct braneworld effective action in two brane Randall-Sundrum model and show that the radion mode plays the role of a scalar field localizing essentially nonlocal part of this action. Non-minimal curvature coupling of this field reflects the violation of AdS/CFT-correspondence for finite values of brane separation. Under small detuning of the brane tension from the Randall-Sundrum flat brane value, the radion mode can play the role of inflaton. Inflationary dynamics corresponds to branes moving apart in the field of repelling interbrane inflaton-radion potential and implies the existence acceleration stage caused by remnant cosmological constant at late (large brane separation) stages of evolution. We discuss the possibility of fixing initial conditions in this model within the concept of braneworld creation from the tunneling or no-boundary cosmological state, which formally replaces the conventional moduli stabilization mechanism.

hep-th↗

arXiv2001

Quantum cosmology at the turn of Millennium

A brief review of the modern state of quantum cosmology is presented as a theory of quantum initial conditions for inflationary scenario. The no-boundary and tunneling states of the Universe are discussed as a possible source of probability peaks in the distribution of initial data for inflation. It is emphasized that in the tree-level approximation the existence of such peaks is in irreconcilable contradiction with the slow roll regime -- the difficulty that is likely to be solved only on account of quantum gravitational effects. The low-energy (typically GUT scale) mechanism of quantum origin of the inflationary Universe with observationally justified parameters is presented for closed and open inflation models with a strong non-minimal coupling.

gr-qc↗

arXiv2000

Geometry of the Dirac and reduced phase space quantization of constrained systems

Geometric properties of operators of quantum Dirac constraints and physical observables are studied in semiclassical theory of generic constrained systems. The invariance transformations of the classical theory -- contact canonical transformations and arbitrary changes of constraint basis -- are promoted to the quantum domain as unitary equivalence transformations. Geometry of the quantum reduction of the Dirac formalism to the physical sector of the theory is presented in the coordinate gauges and extended to unitary momentum-dependent gauges of a general type. The operators of physical observables are constructed satisfying one-loop quantum gauge invariance and Hermiticity with respect to a physical inner product. Abelianization procedure on Lagrangian constraint surfaces of phase space is discussed in the framework of the semiclassical expansion.

gr-qc↗

arXiv2000

Quantum Cauchy problem in cosmology

We develop a general framework for effective equations of expectation values in quantum cosmology and pose for them the quantum Cauchy problem with no-boundary and tunneling wavefunctions. We apply this framework in the model with a big negative non-minimal coupling, which incorporates a recently proposed low energy (GUT scale) mechanism of the quantum origin of the inflationary Universe and study the effects of the quantum inflaton mode.

hep-th↗

arXiv2000

Effective equations in quantum cosmology

We develop a general framework for effective equations of expectation values in quantum cosmology and pose for them the quantum Cauchy problem with no-boundary and tunneling wavefunctions. Cosmological configuration space is decomposed into two sectors that give qualitatively different contributions to the radiation currents in effective equations. The field-theoretical sector of inhomogeneous modes is treated by the method of Euclidean effective action, while the quantum mechanical sector of the spatially homogeneous inflaton is handled by the technique of manifest quantum reduction to gauge invariant cosmological perturbations. We apply this framework in the model with a big negative non-minimal coupling, which incorporates a recently proposed low energy (GUT scale) mechanism of the quantum origin of the inflationary Universe and study the effects of the quantum inflaton mode.

gr-qc↗

arXiv1998

Open inflation from quantum cosmology with a strong nonminimal coupling

We propose the mechanism of quantum creation of the open Universe in the observable range of values of $Ω$. This mechanism is based on the no-boundary quantum state with the Hawking-Turok instanton applied to the model with a strong nonminimal coupling of the inflaton field. We develop the slow roll perturbation expansion for the instanton solution and obtain a nontrivial contribution to the classical instanton action. The interplay of this classical contribution with the loop effects due to quantum effective action generates the probability distribution peak with necessary parameters of the inflation stage without invoking any anthropic considerations. In contrast with a similar mechanism for closed models, existing only for the tunneling quantum state of the Universe, the observationally justified open inflation originates from the no-boundary cosmological wavefunction.

gr-qc↗

arXiv1998

Open inflation without anthropic principle

We propose the mechanism of quantum creation of the open Universe in the observable range of values of $Ω$. This mechanism is based on the no-boundary quantum state with the Hawking-Turok instanton in the model with nonminimally coupled inflaton field and does not use any anthropic considerations. Rather, the probability distribution peak with necessary parameters of the inflation stage is generated on this instanton due to quantum loop effects. In contrast with a similar mechanism for closed models, existing only for the tunneling quantum state of the Universe, open inflation originates from the no-boundary cosmological wavefunction.

hep-th↗

arXiv1998

Effective equations of motion and initial conditions for inflation in quantum cosmology

We obtain effective equations of inflationary dynamics for the mean inflaton and metric fields in the no-boundary and tunneling quantum states of the Universe. In the slow roll approximation (taking the form of the local Schwiger-DeWitt expansion) effective equations follow from the Euclidean effective action on the DeSitter gravitational instanton. Effective equations are applied in the model of the inflaton scalar field coupled to the GUT sector of matter fields and also having a strong nonminimal coupling to the curvature. The inverse of its big negative nonminimal coupling constant, serves as a small parameter of the slow roll expansion and semiclassical expansion of quantum gravitational effects. As a source of initial conditions we use a sharp probability peak recently obtained in the one-loop approximation for the no-boundary and tunneling quantum states and belonging (in virtue of a strong nonminimal coupling) to the GUT energy scale much below the Planck scale. The obtained equations in the tunneling quantum state predict a finite duration of inflationary stage compatible with the observational status of inflation theory, whereas for the no-boundary state they lead to the infinite inflationary epoch with a constant inflaton field.

hep-th↗

arXiv1997

Quantum Dirac constraints, Ward identities and path integral in relativistic gauge

Quantum Dirac constraints in generic constrained system are solved by directly calculating in the one-loop approximation the path integral with relativistic gauge fixing procedure. The calculations are based on the reduction algorithms for functional determinants extended to gauge theories. Explicit mechanism of transition from relativistic gauge conditions to unitary gauges, participating in the construction of this solution, is revealed by the method of Ward identities.

hep-th↗

arXiv1997

Solution of quantum Dirac constraints via path integral

The semiclassical solution of quantum Dirac constraints in generic constrained system is obtained by directly calculating in the one-loop approximation the gauge field path integral with relativistic gauge fixing procedure. The gauge independence property of this path integral is analyzed by the method of Ward identities with a special emphasis on boundary conditions for gauge fields. The calculations are based on the known reduction algorithms for functional determinants extended to gauge theories. The mechanism of transition from relativistic gauge conditions to unitary gauges, participating in the construction of this solution, is explicitly revealed. Implications of this result in problems with spacetime boundaries, quantum gravity and cosmology are briefly discussed.

hep-th↗

arXiv1997

Wheeler-DeWitt equation and Feynman diagrams

We present a systematic expansion of all constraint equations in canonical quantum gravity up to the order of the inverse Planck mass squared. It is demonstrated that this method generates the conventional Feynman diagrammatic technique involving graviton loops and vertices. It also reveals explicitly the back reaction effects of quantized matter and graviton vacuum polarization. This provides an explicit correspondence between the frameworks of canonical and covariant quantum gravity in the semiclassical limit.

gr-qc↗

arXiv1996

Quantum origin of the early inflationary Universe

We give a detailed presentation of a recently proposed mechanism of generating the energy scale of inflation by loop effects in quantum cosmology. We discuss the quantum origin of the early inflationary Universe from the no-boundary and tunneling quantum states and present a universal effective action algorithm for the distribution function of chaotic inflationary cosmologies in both of these states. The energy scale of inflation is calculated by finding a sharp probability peak in this distribution function for a tunneling model driven by the inflaton field with large negative constant $ξ$ of non-minimal interaction. The sub-Planckian parameters of this peak (the mean value of the corresponding Hubble constant $H\simeq 10^{-5}m_P$, its quantum width $ΔH/H\simeq 10^{-5}$ and the number of inflationary e-foldings $N\geq 60$) are found to be in good correspondence with the observational status of inflation theory, provided the coupling constants of the theory are constrained by a condition which is likely to be enforced by the (quasi) supersymmetric nature of the sub-Planckian particle physics model.

gr-qc↗

arXiv1996

Non-minimal coupling, boundary terms and renormalization of the Einstein-Hilbert action

A consistent variational procedure applied to the gravitational action requires according to Gibbons and Hawking a certain balance between the volume and boundary parts of the action. We consider the problem of preserving this balance in the quantum effective action for the matter non-minimally coupled to metric. It is shown that one has to add a special boundary term to the matter action analogous to the Gibbons-Hawking one. This boundary term modifies the one-loop quantum corrections to give a correct balance for the effective action as well. This means that the boundary UV divergences do not require independent renormalization and are automatically renormalized simultaneously with their volume part. This result is derived for arbitrary non-minimally coupled matter. The example of 2D Maxwell field is considered in much detail. The relevance of the results obtained to the problem of the renormalization of the black hole entropy is discussed.

gr-qc↗

arXiv1995

Conformal Decomposition of the Effective Action and Covariant Curvature Expansion

The class of effective actions exactly reproducing the conformal anomaly in 4D is considered. It is demonstrated that the freedom within this class can be fixed by the choice of the conformal gauge. The conformal invariant part of the generic one-loop effective action expanded in the covariant series up to third order in the curvature is rewritten in the new conformal basis. The possible applications of the obtained results are discussed.

gr-qc↗

arXiv1995

Quantum Origin of the Early Universe and the Energy Scale of Inflation

Quantum origin of the early inflationary Universe from the no-boundary and tunnelling quantum states is considered in the one-loop approximation of quantum cosmology. A universal effective action algorithm for the distribution function of chaotic inflationary cosmologies is derived for both of these states.The energy scale of inflation is calculated by finding a sharp probability peak in this distribution function for a tunnelling model driven by the inflaton field with large negative constant $ξ$ of nonminimal interaction. The sub-Planckian parameters of this peak (the mean value of the corresponding Hubble constant ${\mbox{\boldmath $H$}}\simeq 10^{-5}m_P$, its quantum width $Δ{\mbox{\boldmath $H$}}/{\mbox{\boldmath $H$}}\simeq 10^{-5}$ and the number of inflationary e-foldings ${\mbox{\boldmath $N$}}\simeq 60$) are found to be in good correspondence with the observational status of inflation theory, provided the coupling constants of the theory are constrained by a condition which is likely to be enforced by the (quasi) supersymmetric nature of the sub-Planckian particle physics model.

gr-qc↗

arXiv1994

Quantum scale of inflation and particle physics of the early universe

The quantum gravitational scale of inflation is calculated by finding a sharp probability peak in the distribution function of chaotic inflationary cosmologies driven by a scalar field with large negative constant $ξ$ of nonminimal interaction. In the case of the no-boundary state of the universe this peak corresponds to the eternal inflation, while for the tunnelling quantum state it generates a standard inflationary scenario. The sub-Planckian parameters of this peak (the mean value of the corresponding Hubble constant ${\mbox{\boldmath $H$}}\simeq 10^{-5}m_P$, its quantum width $Δ{\mbox{\boldmath $H$}}/{\mbox{\boldmath $H$}}\simeq 10^{-5}$ and the number of inflationary e-foldings ${\mbox{\boldmath $N$}}\simeq 60$) are found to be in good correspondence with the observational status of inflation theory, provided the coupling constants of the theory are constrained by a condition which is likely to be enforced by the (quasi) supersymmetric nature of the sub-Planckian particle physics model.

gr-qc↗