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Aram A. Saharian

Publications and source records attributed to Aram A. Saharian.

At least 19 recordsLinked to original sources
arXiv2019

Finite temperature fermionic condensate in a conical space with a circular boundary and magnetic flux

We investigate the edge effects on the finite temperature fermionic condensate (FC) for a massive fermionic field in a (2+1)-dimensional conical spacetime with a magnetic flux located at the cone apex. The field obeys the bag boundary condition on a circle concentric with the apex. The analysis is presented for both the fields realizing two irreducible representations of the Clifford algebra and for general case of the chemical potential. In both the regions outside and inside the circular boundary, the FC is decomposed into the boundary-free and boundary-induced contributions. They are periodic functions of the magnetic flux with the period equal to the flux quantum and even functions under the simultaneous change of the signs for the magentic flux and the chemical potential. The dependence of the FC on the magnetic flux becomes weaker with decreasing planar angle deficit. For points near the boundary, the effects of finite temperature, of planar angle deficit and of magnetic flux are weak. For a fixed distance from the boundary and at high temperatures the FC is dominated by the Minkowskian part. The FC in parity and time-reversal symmetric (2+1)-dimensional fermionic models is discussed and applications are given to graphitic cones.

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arXiv2015

Induced fermionic current at finite temperature

Here we analyze the finite temperature expectation values of the charge and current densities for a massive fermionic quantum field with nonzero chemical potential, $μ$, induced by a magnetic flux running along the axis of an idealized cosmic string. These densities are decomposed into the vacuum expectation values and contributions coming from the particles and antiparticles. Specifically the charge density is an even periodic function of the magnetic flux with the period equal to the quantum flux and an odd function of the chemical potential. The only nonzero component of the current density corresponds to the azimuthal current and it is an odd periodic function of the magnetic flux and an even function of the chemical potential. Both analyzed are developed for the cases where $|μ|$ is smaller than the mass of the field quanta, $m$.

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arXiv2006

Generalized Abel-Plana formula as a renormalization tool in quantum field theory with boundaries

We apply the generalized Abel-Plana formula for the investigation of one-loop quantum effects on manifolds with boundaries. This allows to extract from the vacuum expectation values of local physical observables the parts corresponding to the geometry without boundaries and to present the boundary-induced parts in terms of integrals strongly convergent for the points away from the boundaries. As a result, the renormalization procedure for these observables is reduced to the corresponding procedure for the bulks without boundaries.

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arXiv2006

Surface Casimir densities and induced cosmological constant in higher dimensional braneworlds

We investigate the vacuum expectation value of the surface energy-momentum tensor for a massive scalar field with general curvature coupling parameter obeying the Robin boundary conditions on two codimension one parallel branes in a (D+1)-dimensional background spacetime $AdS_{D_{1}+1}\times Σ$ with a warped internal space $Σ$. These vacuum densities correspond to a gravitational source of the cosmological constant type for both subspaces of the branes. Using the generalized zeta function technique in combination with contour integral representations, the surface energies on the branes are presented in the form of the sum of single brane and second brane induced parts. For the geometry of a single brane both regions, on the left and on the right of the brane, are considered. At the physical point the corresponding zeta functions contain pole and finite contributions. For an infinitely thin brane taking these regions together, in odd spatial dimensions the pole parts cancel and the total zeta function is finite. The renormalization procedure for the surface energies and the structure of the corresponding counterterms are discussed. The parts in the surface densities generated by the presence of the second brane are finite for all nonzero values of the interbrane separation and are investigated in various asymptotic regions of the parameters. In particular, it is shown that for large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane. The total energy of the vacuum including the bulk and boundary contributions is evaluated by the zeta function technique and the energy balance between separate parts is discussed.

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arXiv2006

Wightman function and vacuum fluctuations in higher dimensional brane models

Wightman function and vacuum expectation value of the field square are evaluated for a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two codimension one parallel branes located on $(D+1)$-dimensional background spacetime $AdS_{D_1+1}\times Σ$ with a warped internal space $Σ$. The general case of different Robin coefficients on separate branes is considered. The application of the generalized Abel-Plana formula for the series over zeros of combinations of cylinder functions allows us to extract manifestly the part due to the bulk without boundaries. Unlike to the purely AdS bulk, the vacuum expectation value of the field square induced by a single brane, in addition to the distance from the brane, depends also on the position of the brane in the bulk. The brane induced part in this expectation value vanishes when the brane position tends to the AdS horizon or AdS boundary. The asymptotic behavior of the vacuum densities near the branes and at large distances is investigated. The contribution of Kaluza-Klein modes along $Σ$ is discussed in various limiting cases. As an example the case $Σ=S^1$ is considered, corresponding to the $AdS_{D+1}$ bulk with one compactified dimension. An application to the higher dimensional generalization of the Randall-Sundrum brane model with arbitrary mass terms on the branes is discussed.

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arXiv2005

Vacuum densities in braneworlds

We give a short review of the recent development in the investigation of the vacuum expectation values of the bulk and surface energy-momentum tensors generated by quantum fluctuations of a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two codimension one parallel branes located on $(D+1)$-dimensional anti-de Sitter (AdS) bulk. An application to the Randall-Sundrum braneworld with arbitrary mass terms on the branes is discussed.

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arXiv2005

Bulk Casimir densities and vacuum interaction forces in higher dimensional brane models

Vacuum expectation value of the energy-momentum tensor and the vacuum interaction forces are evaluated for a massive scalar field with general curvature coupling parameter satisfying Robin boundary conditions on two codimension one parallel branes embedded in background spacetime $AdS_{D_1+1}\times Σ$ with a warped internal space $Σ$. The vacuum energy-momentum tensor is presented as a sum of boundary-free, single brane induced, and interference parts. The latter is finite everywhere including the points on the branes and is exponentially small for large interbrane distances. Unlike to the purely AdS bulk, the part induced by a single brane, in addition to the distance from the brane, depends also on the position of the brane in the bulk. The asymptotic behavior of this part is investigated for the points near the brane and for the position of the brane close to the AdS horizon and AdS boundary. The vacuum forces acting on the branes are presented as a sum of the self-action and interaction terms. The interaction forces between the branes are finite for all nonzero interbrane distances and are investigated as functions of the brane positions and the length scale of the internal space. As an example the case $Σ=S^{D_2}$ is considered. An application to the higher dimensional generalization of the Randall-Sundrum brane model with arbitrary mass terms on the branes is discussed.

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arXiv2005

Wightman function and Casimir densities on AdS bulk with application to the Randall-Sundrum braneworld

Positive frequency Wightman function and vacuum expectation value of the energy-momentum tensor are computed for a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two parallel plates located on $D+1$ - dimensional AdS background. The general case of different Robin coefficients on separate plates is considered. The mode summation method is used with a combination of a variant of the generalized Abel-Plana formula for the series over zeros of combinations of cylinder functions. This allows us to extract manifestly the parts due to the AdS spacetime without boundaries and boundary induced parts. The asymptotic behavior of the vacuum densities near the plates and at large distances is investigated. The vacuum forces acting on the boundaries are presented as a sum of the self-action and interaction forces. The first one contains well-known surface divergences and needs further regularization. The interaction forces between the plates are attractive for Dirichlet scalar. We show that threre is a region in the space of parameters defining the boundary conditions in which the interaction forces are repulsive for small distances and attractive for large distances. An application to the Randall-Sundrum braneworld with arbitrary mass terms on the branes is discussed.

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arXiv2004

Surface Casimir densities and induced cosmological constant on parallel branes in AdS

Vacuum expectation value of the surface energy-momentum tensor is evaluated for a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two parallel branes located on (D+1)-dimensional AdS bulk. The general case of different Robin coefficients on separate branes is considered. As an regularization procedure the generalized zeta function technique is used, in combination with contour integral representations. The surface energies on the branes are presented in the form of the sums of single brane and second brane-induced parts. For the geometry of a single brane both regions, on the left (L-region) and on the right (R-region), of the brane are considered. The surface densities for separate L- and R-regions contain pole and finite contributions. For an infinitely thin brane taking these regions together, in odd spatial dimensions the pole parts cancel and the total surface energy is finite. The parts in the surface densities generated by the presence of the second brane are finite for all nonzero values of the interbrane separation. It is shown that for large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane. In the Randall-Sundrum braneworld model, for the interbrane distances solving the hierarchy problem between the gravitational and electroweak mass scales, the cosmological constant generated on the visible brane is of the right order of magnitude with the value suggested by the cosmological observations.

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arXiv2004

Radiation from an oscillator uniformly moving along the axis of a dielectric cylinder

The radiation generated by a charged longitudinal oscillator moving with a constant drift velocity along the axis of a dielectric cylinder immersed in a homogeneous medium is investigated. For an arbitrary oscillation law a formula is derived for the spectral-angular distribution of this radiation. Under the Cherenkov condition for the dielectric permittivity of the external medium and oscillator drift velocity this formula contains two summands. The first one corresponds to the radiation with a continuous spectrum which propagates at the Cherenkov angle of the external medium. The second one describes the radiation which has a discrete spectrum for a given angle of propagation. The corresponding frequencies are multiples of the Doppler-shifted oscillation frequency. The results of numerical calculations for the angular distribution of the radiated quanta are presented and they are compared with the corresponding quantities for the radiation in a homogeneous medium. It is shown that the presence of the cylinder can increase essentially the radiation intensity.

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arXiv2003

On the energy-momentum tensor for a scalar field on manifolds with boundaries

We argue that already at classical level the energy-momentum tensor for a scalar field on manifolds with boundaries in addition to the bulk part contains a contribution located on the boundary. Using the standard variational procedure for the action with the boundary term, the expression for the surface energy-momentum tensor is derived for arbitrary bulk and boundary geometries. Integral conservation laws are investigated. The corresponding conserved charges are constructed and their relation to the proper densities is discussed. Further we study the vacuum expectation value of the energy-momentum tensor in the corresponding quantum field theory. It is shown that the surface term in the energy-momentum tensor is essential to obtain the equality between the vacuum energy, evaluated as the sum of the zero-point energies for each normal mode of frequency, and the energy derived by the integration of the corresponding vacuum energy density. As an application, by using the zeta function technique, we evaluate the surface energy for a quantum scalar field confined inside a spherical shell.

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arXiv2002

Local Casimir Energy for a Wedge with circular outer boundary

The local Casimir energy is investigated for a wedge with and without a circular outer boundary due to the confinement of a massless scalar field with general curvature coupling parameter and satisfying the Dirichlet boundary conditions. Regularization procedure is carried out making use of a variant of the generalized Abel-Plana formula, previously established by one of the authors. The surface divergences in the vacuum expectation values of the energy density near the boundaries are considered. The corresponding results can be applied to the cosmic strings.

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arXiv2002

Radiation from a charge circulating inside a waveguide with dielectric filling

The emitted power of the radiation from a charged particle moving uniformly on a circle inside a cylindrical waveguide is considered. The expressions for the energy flux of the radiation passing through the waveguide cross-section are derived for both TE and TM waves. The results of the numerical evaluation are presented for the number of emitted quanta depending on the waveguide radius, the radius of the charge rotation orbit and dielectric permittivity of the filling medium. These results are compared with the corresponding quantities for the synchrotron radiation in a homogeneous medium.

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arXiv2001

Polarization of the Fulling-Rindler vacuum by uniformly accelerated mirror

Positive frequency Wightman function and vacuum expectation values of the energy-momentum tensor are computed for a massive scalar field with general curvature coupling parameter and satisfying Robin boundary condition on a uniformly accelerated infinite plate. The both regions of the right Rindler wedge, (i) on the right (RR region) and (ii) on the left (RL region) of the plate are investigated. For the case (ii) the electromagnetic field is considered as well. The mode summation method is used with combination of a variant of the generalized Abel-Plana formula. This allows to present the expectation values in the form of a sum of the purely Rindler and boundary parts. Near the plate surface the vacuum energy-momentum tensor is dominated by the boundary term. At large distances from the plate and near the Rindler horizon the main contribution comes from the purely Rindler part. In the RL region the vacuum energy density of the electromagnetic field is negative near the horizon and is positive near the plate.

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arXiv2001

Scalar Casimir effect for D-dimensional spherically symmetric Robin boundaries

The vacuum expectation values for the energy-momentum tensor of a massive scalar field with general curvature coupling and obeying the Robin boundary condition on spherically symmetric boundaries in D-dimensional space are investigated. The expressions are derived for the regularized vacuum energy density, radial and azimuthal stress components (i) inside and outside a single spherical surface and (ii) in the intermediate region between two concentric spheres. Regularization procedure is carried out by making use of the generalized Abel-Plana formula for the series over zeros of cylinder functions. Asymptotic behavior of the vacuum densities near the sphere and at large distances is investigated. A decomposition of the Casimir energy into volumic and surface parts is provided for both cases (i) and (ii). We show that the mode sum energy, evaluated as a sum of the zero-point energies for each normal mode of frequency, and the volume integral of the energy density in general are different, and argue that this difference is due to the existence of an additional surface energy contribution.

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arXiv2001

Vacuum densities and zero-point energy for fields obeying Robin conditions on cylindrical surfaces

The Casimir effect for general Robin conditions on the surface of a cylinder in $D$-spacetime dimensions is studied for massive scalar field with general curvature coupling. The energy distribution and vacuum stress are investigated. We separate volumic and superficial energy contributions, for both interior and exterior space regions. The possibility that some special conditions may be energetically singled out is indicated.

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arXiv1997

Higher Loop String Cosmology with Moduli and Antisymmetric Tensor Field

The classical evolution of a homogeneous cosmological model is investigated within the framework of low - energy effective string gravity with higher genus corrections. Various conformal frames are considered. For the general case of correction functions in the Lagrangian we give the cosmological solutions with arbitrary curvature and dilaton, modulus and Kalb-Ramond fields. They generalize previously known tree level solutions. The features of the solutions are discussed.

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