Space Time Foam: a ground state candidate for Quantum Gravity

A model of space-time foam, made by $N$ wormholes is considered. The Casimir energy leading to such a model is computed by means of the phase shift method which is in agreement with the variational approach used in Refs.[9-14]. The collection of Schwarzschild and Reissner-Nordstr\"{o}m wormholes are separately considered to represent the foam. The Casimir energy shows that the Reissner-Nordstr\"{o}m wormholes cannot be used to represent the foam.Comment: 6 pages.RevTeX with package epsf and two eps figures. To be submitted to the proceedings of the 4th Workshop of `Mysteries, Puzzles And Paradoxes In Quantum Mechanics' Gargnano (Italy), 27 August-1 September 200

The cosmological constant as an eigenvalue of the Hamiltonian constraint in Horava-Lifshits theory

In the framework of Horava-Lifshitz theory, we study the eigenvalues associated with the Wheeler-DeWitt equation representing the vacuum expectation values associated with the cosmological constant. The explicit calculation is performed with the help of a variational procedure with trial wave functionals of the Gaussian type. We analyze both the case with the detailed balanced condition and the case without it. In the case without the detailed balance, we find the existence of an eigenvalue depending on the set of coupling constants (g2,g3) and (g4,g5,g6), respectively, and on the physical scale.Comment: RevTeX,11 Pages, Substantial Improvements. References added. To appear in Phys.Rev.

Energy Extraction From Gravitational Collapse to Static Black Holes

The mass--energy formula of black holes implies that up to 50% of the energy can be extracted from a static black hole. Such a result is reexamined using the recently established analytic formulas for the collapse of a shell and expression for the irreducible mass of a static black hole. It is shown that the efficiency of energy extraction process during the formation of the black hole is linked in an essential way to the gravitational binding energy, the formation of the horizon and the reduction of the kinetic energy of implosion. Here a maximum efficiency of 50% in the extraction of the mass energy is shown to be generally attainable in the collapse of a spherically symmetric shell: surprisingly this result holds as well in the two limiting cases of the Schwarzschild and extreme Reissner-Nordstr\"{o}m space-times. Moreover, the analytic expression recently found for the implosion of a spherical shell onto an already formed black hole leads to a new exact analytic expression for the energy extraction which results in an efficiency strictly less than 100% for any physical implementable process. There appears to be no incompatibility between General Relativity and Thermodynamics at this classical level.Comment: 7 pages, 2 figures, to appear on Int. Journ. Mod. Phys.

Pengenalan Rumah Adat Indonesia Berbasis Augmented Reality dengan Memanfaatkan KTP sebagai Marker

Pada saat ini, pengenalan rumah tradisional yang masih menggunakan buku atau masih menggunakan pengenalan rumah tradisional dengan objek dua dimensi dianggap kurang efektif. Hal ini dikarenakan pengenalan objek rumah tradisional menggunakan dua dimensi hanya bisa dilihat di satu sisi. Augmented reality adalah kombinasi dari virtual reality ( benda virtual) dengan dunia realitas (dunia nyata). Augmented reality adalah pengganti media interaktif untuk gambar dua dimensi menjadi tiga dimensi. Seiring berkembangnya jaman augmented reality berkembang sangat pesat, sehingga memungkinkan pengembangan aplikasi ini di berbagai bidang seperti pendidikan. Salah satu aplikasi ini, dalam aplikasi ini terdapat rumah tradisional objek dan informasi terkait. Dengan aplikasi ini, pengguna dapat mengetahui keragaman rumah tradisional Indonesia melalui kamera smartphone android dengan menggunakan kartu KTP sebagai marker yang dapat memudahkan pengguna dalam mengakses aplikasi

Carrier thermal escape in families of InAs/InP self-assembled quantum dots

We investigate the thermal quenching of the multimodal photoluminescence from InAs/InP (001) self-assembled quantum dots. The temperature evolution of the photoluminescence spectra of two samples is followed from 10 K to 300 K. We develop a coupled rate-equation model that includes the effect of carrier thermal escape from a quantum dot to the wetting layer and to the InP matrix, followed by transport, recapture or non-radiative recombination. Our model reproduces the temperature dependence of the emission of each family of quantum dots with a single set of parameters. We find that the main escape mechanism of the carriers confined in the quantum dots is through thermal emission to the wetting layer. The activation energy for this process is found to be close to one-half the energy difference between that of a given family of quantum dots and that of the wetting layer as measured by photoluminescence excitation experiments. This indicates that electron and holes exit the InAs quantum dots as correlated pairs

Planet transit and stellar granulation detection with interferometry: Using the three-dimensional stellar atmosphere S tagger -grid simulations

Context. Stellar activity and, in particular, convection-related surface structures, potentially cause bias in planet detection and characterisation. In the latter, interferometry can help disentangle the signal of the transiting planet. Aims. We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger-grid and synthetic images computed with the radiative transfer code Optim3D to provide interferometric observables to extract the signature of stellar granulation and transiting planets. Methods. We computed intensity maps from RHD simulations and produced synthetic stellar disk images as a nearby observer would see, thereby accounting for the centre-to-limb variations. We did this for twelve interferometric instruments covering wavelengths ranging from optical to infrared. We chose an arbitrary date and arbitrary star with coordinates, and this ensures observability throughout the night. This optimisation of observability allows for a broad coverage of spatial frequencies. The stellar surface asymmetries in the brightness distribution mostly affect closure phases, because of either convection-related structures or a faint companion. We then computed closure phases for all images and compared the system star with a transiting planet and the star alone. We considered the impact of magnetic spots with the construction of a hypothetical starspot image and compared the resulting closure phases with the system star that has a transiting planet. Results. We analysed the impact of convection at different wavelengths. All the simulation depart from the axisymmetric case (closure phases not equal to 0 or ± π) at all wavelengths. The levels of asymmetry and inhomogeneity of stellar disk images reach high values with stronger effects from the 3rd visibility lobe on. We present two possible targets (Beta Com and Procyon) either in the visible or in the infrared and find that departures up to 16° can be detected on the 3rd lobe and higher. In particular, MIRC is the most appropriate instrument because it combines good UV coverage and long baselines. Moreover, we explored the impact of convection on interferometric planet signature for three prototypes of planets with sizes corresponding to one hot Jupiter, one hot Neptune, and a terrestrial planet. The signature of the transiting planet in the closure phase is mixed with the signal due to the convection-related surface structures, but it is possible to disentangle it at particular wavelengths (either in the infrared or in the optical) by comparing the closure phases of the star at difference phases of the planetary transit. It must be noted that starspots caused by the magnetic field may pollute the granulation and the transiting planet signals. However, it is possible to differentiate the transiting planet signal because the time scale of a planet crossing the stellar disk is much smaller than the typical rotational modulation of a star. Conclusions. Detection and characterisation of planets must be based on a comprehensive knowledge of the host star, and this includes the detailed study of the stellar surface convection with interferometric techniques. In this context, RHD simulations are crucial for this aim. We emphasise that interferometric observations should be pushed at high spatial frequencies by accumulating observations on closure phases at short and long baselines

The Cosmological Constant as an Eigenvalue of a Sturm-Liouville Problem and its Renormalization

We discuss the case of massive gravitons and their relation with the cosmological constant, considered as an eigenvalue of a Sturm-Liouville problem. A variational approach with Gaussian trial wave functionals is used as a method to study such a problem. We approximate the equation to one loop in a Schwarzschild background and a zeta function regularization is involved to handle with divergences. The regularization is closely related to the subtraction procedure appearing in the computation of Casimir energy in a curved background. A renormalization procedure is introduced to remove the infinities together with a renormalization group equation.Comment: 8 pages, Talk given at "QFEXT'05", the 7-th workshop on quantum field theory under the influence of external conditions, Barcelona, Spain, Sept. 5-9, 200

On the structure of the burst and afterglow of Gamma-Ray Bursts I: the radial approximation

We have proposed three paradigms for the theoretical interpretation of gamma-ray bursts (GRBs). (1) The relative space-time transformation (RSTT) paradigm emphasizes how the knowledge of the entire world-line of the source from the moment of gravitational collapse is a necessary condition to interpret GRB data. (2) The interpretation of the burst structure (IBS) paradigm differentiates in all GRBs between an injector phase and a beam-target phase. (3) The GRB-supernova time sequence (GSTS) paradigm introduces the concept of induced supernova explosion in the supernovae-GRB association. These three paradigms are illustrated using our theory based on the vacuum polarization process occurring around an electromagnetic black hole (EMBH theory) and using GRB 991216 as a prototype. We illustrate the five fundamental eras of the EMBH theory: the self acceleration of the $e^+e^-$ pair-electromagnetic plasma (PEM pulse), its interaction with the baryonic remnant of the progenitor star (PEMB pulse). We then study the approach of the PEMB pulse to transparency, the emission of the proper GRB (P-GRB) and its relation to the ``short GRBs''. Finally the three different regimes of the afterglow are described within the fully radiative and radial approximations. The best fit of the theory leads to an unequivocal identification of the ``long GRBs'' as extended emission occurring at the afterglow peak (E-APE). The relative intensities, the time separation and the hardness ratio of the P-GRB and the E-APE are used as distinctive observational test of the EMBH theory and the excellent agreement between our theoretical predictions and the observations are documented. The afterglow power-law indexes in the EMBH theory are compared and contrasted with the ones in the literature, and no beaming process is found for GRB 991216.Comment: 96 pages, 40 figures, to appear on Int. Journ. Mod. Phys.

Naked Singularity in a Modified Gravity Theory

The cosmological constant induced by quantum fluctuation of the graviton on a given background is considered as a tool for building a spectrum of different geometries. In particular, we apply the method to the Schwarzschild background with positive and negative mass parameter. In this way, we put on the same level of comparison the related naked singularity (-M) and the positive mass wormhole. We discuss how to extract information in the context of a f(R) theory. We use the Wheeler-De Witt equation as a basic equation to perform such an analysis regarded as a Sturm-Liouville problem . The application of the same procedure used for the ordinary theory, namely f(R)=R, reveals that to this approximation level, it is not possible to classify the Schwarzschild and its naked partner into a geometry spectrum.Comment: 8 Pages. Contribution given to DICE 2008. To appear in the proceeding

Self sustained traversable wormholes and the equation of state

We compute the graviton one loop contribution to a classical energy in a \textit{traversable} wormhole background. The form of the shape function considered is obtained by the equation of state $p=\omega\rho$. We investigate the size of the wormhole as a function of the parameter $\omega$. The investigation is evaluated by means of a variational approach with Gaussian trial wave functionals. A zeta function regularization is involved to handle with divergences. A renormalization procedure is introduced and the finite one loop energy is considered as a \textit{self-consistent} source for the traversable wormhole.The case of the phantom region is briefly discussed.Comment: Uses RevTeX 4. 21 pages. Submitted to Classical and Quantum Gravity. Extended version of the talk given at ERE2006 (Palma de Mallorca, September 4-8, 2006) and of the talk given at MG11-GT5, Berlin, 23-29 July, 200