Comment on "how the huge energy of quantum vacuum gravitates to drive the slow accelerating expansion of the Universe"

In a recent paper [Q. Wang, Z. Zhu, and W. G. Unruh, Phys. Rev. D 95, 103504 (2017)PRVDAQ2470-001010.1103/PhysRevD.95.103504] it was argued that, due to the fluctuations around its mean value, vacuum energy gravitates differently from what was previously assumed. As a consequence, the Universe would accelerate with a small Hubble expansion rate, solving the cosmological constant and dark energy problems. We point out here that the results depend on the type of cutoff used to evaluate the vacuum energy. In particular, they are not valid when one uses a covariant cutoff such that the zero-point energy density is positive definite.Fil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Trombetta, Leonardo Giuliano. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin

The infalling photon, the infalling particle, and the observer at rest near the horizon of a black hole

When a massive test particle or a photon fall radially into a black hole, their energy, as measured by a static observer located very close to the horizon, diverges. In introductory courses on general relativity, this fact gives rise to questions about the reality of this divergence and its eventual effect on the geometry of the black hole. We address these concerns and show that, eventually, it is the observer at rest who may induce corrections to the metric, unless its mass is crucially small when located near the horizon.Fil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Quantum corrections to the geodesic equation

In this talk we will argue that, when gravitons are taken into account, the solution to the semiclassical Einstein equations (SEE) is not physical. The reason is simple: any classical device used to measure the spacetime geometry will also feel the graviton fluctuations. As the coupling between the classical device and the metric is non linear, the device will not measure the `background geometry' (i.e. the geometry that solves the SEE). As a particular example we will show that a classical particle does not follow a geodesic of the background metric. Instead its motion is determined by a quantum corrected geodesic equation that takes into account its coupling to the gravitons. This analysis will also lead us to find a solution to the so-called gauge fixing problem: the quantum corrected geodesic equation is explicitly independent of any gauge fixing parameter.Comment: Revtex file, 6 pages, no figures. Talk presented at the meeting "Trends in Theoretical Physics II", Buenos Aires, Argentina, December 199

Casimir energy due to inhomogeneous thin plates

We study the Casimir energy due to a quantum real scalar field coupled to two planar, infinite, zerowidth, parallel mirrors with nonhomogeneous properties. These properties are represented, in the model we use, by scalar functions defined on each mirror’s plane. Using the Gelfand-Yaglom’s theorem, we construct a Lifshitz-like formula for the Casimir energy of such a system. Then we use it to evaluate the energy perturbatively, for the case of almost constant scalar functions, and also implementing a derivative expansion, under the assumption that the spatial dependence of the properties is sufficiently smooth. We point out that, in some particular cases, the Casimir interaction energy for nonplanar perfect mirrors can be reproduced by inhomogeneities on planar mirrors.Fil: Fosco, Cesar Daniel. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Cuyo; ArgentinaFil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Cuyo; Argentin

Casimir force between eccentric cylinders

We consider the Casimir interaction between a cylinder and a hollow cylinder, both conducting, with parallel axis and slightly different radii. The Casimir force, which vanishes in the coaxial situation, is evaluated for both small and large eccentricities using the proximity approximation. The cylindrical configuration offers various experimental advantages with respect to the parallel planes or the plane-sphere geometries, leading to favourable conditions for the search of extra-gravitational forces in the micrometer range and for the observation of finite temperature corrections.Comment: To be published in Europhysics Letters. 7 pages, 4 figure

EL PROYECTO ERATÓSTENES 2009 EN LA ARGENTINA

Observando cuidadosamente los fenómenos naturales que nos rodean, es posible llegar a conclusiones que, a veces, son sorprendentes. En el Siglo III antes de Cristo, Eratóstenes, un matemático, astrónomo, geógrafo y poeta griego, fue capaz de estimar el perímetro de la Tierra midiendo la sombra de una varilla durante el solsticio de verano (21 de junio, comienzo del verano en el hemisferio norte). Más de doscientas escuelas argentinas y de países limítrofes recrearon el método que usó Eratóstenes hace más de 2000 años para estimar el radio terrestre

Motion-induced radiation due to an atom in the presence of a graphene plane

We study the motion-induced radiation due to the non-relativistic motion of an atom, coupled to the vacuum electromagnetic field by an electric dipole term, in the presence of a static graphene plate. After computing the probability of emission for an accelerated atom in empty space, we evaluate the corrections due to the presence of the plate. We show that the effect of the plate is to increase the probability of emission when the atom is near the plate and oscillates along a direction perpendicular to it. On the contrary, for parallel oscillations, there is a suppression. We also evaluate the quantum friction on an atom moving at constant velocity parallel to the plate. We show that there is a threshold for quantum friction: friction occurs only when the velocity of the atom is larger than the Fermi velocity of the electrons in graphene.Fil: Fosco, Cesar Daniel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Lombardo, Fernando Cesar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Motion induced excitation and radiation from an atom facing a mirror

We study quantum dissipative effects due to the nonrelativistic, bounded, accelerated motion of a single neutral atom in the presence of a planar perfect mirror, i.e., a perfect conductor at all frequencies. We consider a simplified model whereby a moving “scalar atom” is coupled to a quantum real scalar field, subjected to either Dirichlet or Neumann boundary conditions on the plane. We use an expansion in powers of the departure of the atom with respect to a static average position to compute the vacuum persistence amplitude and the resulting vacuum decay probability. We evaluate transition amplitudes corresponding to the excitation of the atom plus the emission of a particle, and show explicitly that the vacuum decay probabilities match the results obtained by integrating the transition amplitudes over the directions of the emitted particle. We also compute the spontaneous emission rate of an oscillating atom that is initially in an excited state.Fil: Fosco, Cesar Daniel. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Lombardo, Fernando Cesar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Grupo de Física Teórica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Quantum vacuum fluctuations and the principle of virtual work in inhomogeneous backgrounds

We discuss several aspects of the stress-energy tensor for a quantum scalar field in an inhomogeneous background, the latter being modeled by a variable mass. Using a perturbative approach, dimensional regularization, and adiabatic subtraction, we present all-order formal expressions for the stress-energy tensor. Importantly, we provide an explicit proof of the principle of virtual work for Casimir forces, taking advantage of the conservation law for the renormalized stress-energy tensor. We discuss also discontinuity-induced divergences. For the particular case of planar inhomogeneities, we corroborate the perturbative results with a WKB-inspired expansion.Fil: Franchino Viñas, Sebastián Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mantiñan, M. N.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; ArgentinaFil: Mazzitelli, Francisco Diego. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin