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I. V. Vancea

Publications and source records attributed to I. V. Vancea.

36 records · Page 2Linked to original sources
arXiv2003

TFD Approach to Bosonic Strings and $D_{P}$-branes

In this work we explain the construction of the thermal vacuum for the bosonic string, as well that of the thermal boundary state interpreted as a $D_{p}$-brane at finite temperature. In both case we calculate the respective entropy using the entropy operator of the Thermo Field Dynamics Theory. We show that the contribution of the thermal string entropy is explicitly present in the $D_{p}$-brane entropy. Furthermore, we show that the Thermo Field approach is suitable to introduce temperature in boundary states.

hep-th↗
arXiv2002

On The Symplectic Two-Form of Gravity in Terms of Dirac Eigenvalues

The Dirac eigenvalues form a subset of observables of the Euclidean gravity. The symplectic two-form in the covariant phase space could be expressed, in principle, in terms of the Dirac eigenvalues. We discuss the existence of the formal solution of the equations defining the components of the symplectic form in this framework.

gr-qc↗
arXiv2002

On the SU(1,1) Thermal Group of Bosonic Strings and D-Branes

All possible Bogoliubov operators that generate the thermal transformations in the Thermo Field Dynamics (TFD) form a SU(1,1) group. We discuss this contruction in the bosonic string theory. In particular, the transformation of the Fock space and string operators generated by the most general SU(1,1) unitary Bogoliubov transformation and the entropy of the corresponding thermal string are computed. Also, we construct the thermal $D$-brane solution generated by the SU(1,1) transformation in a constant Kalb-Ramond field and compute its entropy.

hep-th↗
arXiv2002

Entropy of Bosonic Open String and Boundary Conditions

The entropy of the states associated to the solutions of the equations of motion of the bosonic open string with combinations of Neumann and Dirichlet boundary conditions is given. Also, the entropy of the string in the states $| A^i > = α^{i}_{-1} |0>$ and $| ϕ^a > = α^{a}_{-1} |0>$ that describe the massless fields on the world-volume of the Dp-brane is computed.

hep-th↗
arXiv2001

Introductory Lectures on D-Branes

This is a pedagogical introduction to D-branes, addressed to graduate students in field theory and particle physics and to other beginners in string theory. I am not going to review the most recent results since there are already many good papers on web devoted to that. Instead, I will present some old techniques in some detail in order to show how some basic properties of strinfs and branes as the massless spectrum of string, the effective action of D-branes and their tension can be computed using QFT techniques. Also, I will present shortly the boundary state description of D-branes. The details are exposed for bosonic branes since I do not assume any previous knowledge of supersymmetry which is not a requirement for this school. However, for completeness and to provide basic notions for other lectures, I will discuss some properties of supersymemtric branes. The present lectures were delivered at Jorge André Swieca School on Particle and Fields, 2001, Campos do Jordão, Brazil.

hep-th↗
arXiv2001

Local Physical Coodinates from Symplectic Projector Method

The basic arguments underlying the symplectic projector method are presented. By this method, local free coordinates on the constrait surface can be obtained for a broader class of constrained systems. Some interesting examples are analyzed.

hep-th↗
arXiv2001

Bosonic D-branes at finite temperature with an external field

Bosonic boundary states at finite temperature are constructed as solutions of boundary conditions at $T\neq 0$ for bosonic open strings with a constant gauge field $F_{ab}$ coupled to the boundary. The construction is done in the framework of thermo field dynamics where a thermal Bogoliubov transformation maps states and operators to finite temperature. Boundary states are given in terms of states from the direct product space between the Fock space of the closed string and another identical copy of it. By analogy with zero temperature, the boundary states heve the interpretation of $Dp$-brane at finite temperature. The boundary conditions admit two different solutions. The entropy of the closed string in a $Dp$-brane state is computed and analysed. It is interpreted as the entropy of the $Dp$-brane at finite temperature.

hep-th↗
arXiv2001

Unconstrained Variables of Non-Commutative Open Strings

The boundary conditions of the bosonic string theory in non-zero $B$-field background are equivalent to the second class constraints of a discretized version of the theory. By projecting the original canonical coordinates onto the constraint surface we derive a set of coordinates of string that are unconstrained.These coordinates represent a natural framework for the quantization of the theory.

hep-th↗
arXiv2000

Bosonic D-Branes at Finite Temperature

We derive the finite temperature description of bosonic D-branes in the thermo field approach. The results might be relevant to the study of thermical properties of D-brane systems.

hep-th↗
arXiv2000

Duality between coordinates and Dirac field

The duality between the Cartesian coordinates on the Minkowski space-time and the Dirac field is investigated. Two distinct possibilities to define this duality are shown to exist. In both cases, the equations satisfied by prepotentials are of second order.

hep-th↗
arXiv2000

Gravity and Duality between Coordinates and Matter Fields

We use the duality between the local Cartezian coordinates and the solutions of the Klein-Gordon equation to parametrize locally the spacetime in terms of wave functions and prepotentials. The components of metric, metric connection, curvature as well as the Einstein equation are given in this parametrization. We also discuss the local duality between coordinates and quantum fields and the metric in this later reparametrization.

gr-qc↗
arXiv2000

Duality of Coordinates and Matter Fields in Curved Spacetime

We show that there exists a duality between the local coordinates and the solutions of the Klein-Gordon equation in curved spacetime in the same sense as in the Minkowski spacetime. However, the duality in curved spacetime does not have the same generality as in flat spacetime and it holds only if the system satisfies certain constraints. We derive these constraints and the basic equations of duality and discuss the implications in the quantum theory.

gr-qc↗
arXiv1998

On Local Constraints of D=4 Supergravity in Terms of Dirac Eigenvalues

It has been recently shown that in order to have Dirac eigenvalues as observables of Euclidean supergravity, certain constraints should be imposed on the covariant phase space as well as on Dirac eigenspinors. We investigate the relationships among the constraints in the first set and argue that these relationships are not linear. We also derive a set of equations expressing the linear dependency of the constraints in order that the second set of constraints be linearly independent.

gr-qc↗
arXiv1998

Euclidean Supergravity in Terms of Dirac Eigenvalues

It has been recently shown that the eigenvalues of the Dirac operator can be considered as dynamical variables of Euclidean gravity. The purpose of this paper is to explore the possiblity that the eigenvalues of the Dirac operator might play the same role in the case of supergravity. It is shown that for this purpose some primary constraints on covariant phase space as well as secondary constraints on the eigenspinors must be imposed. The validity of primary constraints under covariant transport is further analyzed. It is show that in the this case restrictions on the tanget bundle and on the spinor bundle of spacetime arise. The form of these restrictions is determined under some simplifying assumptions. It is also shown that manifolds with flat curvature of tangent bundle and spinor bundle and spinor bundle satisfy these restrictons and thus they support the Dirac eigenvalues as global observables.

gr-qc↗