Vacuum Gravity Research Articles

Weighing the vacuum energy

We discuss the weight of vacuum energy in various contexts. First, we compute the vacuum energy for flat spacetimes of the form $\mathbb{T}^3 \times \mathbb{R}$, where $\mathbb{T}^3$ stands for a general 3-torus. We discover a quite simple relationship between energy at radius $R$ and energy at radius $\frac{l_s^2}{ R}$. Then we consider quantum gravity effects in the vacuum energy of a scalar field in $\mathbb{M}_3 \times S^1$ where $\mathbb{M}_3$ is a general curved spacetime, and the circle $S^1$ refers to a spacelike coordinate. We compute it for General Relativity and generic transverse {\em TDiff} theories. In the particular case of Unimodular Gravity vacuum energy does not gravitate.

High-bandwidth beam balance for vacuum-weight experiment and Newtonian noise subtraction

We report the experimental results of a prototype balance for the Archimedes experiment, devoted to measure the interaction between quantum vacuum energy and gravity. The prototype is a beam balance working at room temperature which shares with the final balance several mechanical and optical components. The balance sensitivity has been tested at the site of the Virgo gravitational wave detector in order to benefit from its quiet environment and control facilities. This allowed also the test of the coherence of the balance data with the Virgo interferometer signal and with the environmental data. In the low-frequency regime, the balance has shown a sensitivity of about 8times 10^{-12} {text {Nm}}/sqrt{text {Hz}}, which is among the best in the world, and it is very promising toward the final Archimedes measurement. In the high-frequency region, above a few Hz, relying on the behavior of the balance as a rotational sensor, the ground tilt has been measured in view of the next work devoted to Newtonian noise subtraction (NNS) in Virgo. The measured ground tilt reaches a minimum of about 8times 10^{-11} {text {rad}}/sqrt{{text {Hz}}} in the few Hz region and ranges from 10^{-10} to 10^{-9} {text {rad}}/sqrt{{text {Hz}}} in the 10–20 Hz region, where a very interesting coherence, at some frequencies, with the Virgo interferometer signal is shown.

General properties of f(R) gravity vacuum solutions

General properties of vacuum solutions of [Formula: see text] gravity are obtained by the condition that the divergence of the Weyl tensor is zero and [Formula: see text]. Specifically, a theorem states that the gradient of the curvature scalar, [Formula: see text], is an eigenvector of the Ricci tensor and, if it is timelike, the spacetime is a Generalized Friedman–Robertson–Walker metric; in dimension four, it is Friedman–Robertson–Walker.

Identification of Phenyl Propanoid Compound Isolated from Root Bark Datuan(Ficus vasculosa Wall. Ex Miq) and Antibacterial Activity Test on Escherichia coli

The purpose of this research was to identify phenyl propanoid compounds found in the root bark of Datuan (Ficus vasculosa Wall. Ex Miq) and to test the activity of Escherichia coli. Isolation was carried out by maceration method using methanol as a solvent. Then the extract was fractionated by Vacuum Liquid Chromatography and Gravity Column Chromatography methods using n-hexane, ethyl acetate, and methanol eluents. The result was obtained a yellow crystal needle orange weighing 20 mg with a melting point of 137°C - 140°C. Separation by TLC method showed that this compound had an Rf value of 0.56 with n-hexane: acetone eluent (6: 4). UV-Vis spectra showed three peaks on 310 nm, 228 nm and 200 nm. IR spectra showed that the isolated compound has unsaturated ester carbonyl groups conjugated with double bonds, aromatic substituted aromatic rings, and hydroxy groups. GC-MS analysis obtained molecular ions M+ = 178. The data of UV-Vis, IR and GC-MS analysis can be concluded that the isolated phenyl propanoid compound is a cinnamic derivative that is methyl p-hydroxycinamic. The results of bioactivity tests on E. Coli showed that the isolated compounds did not have antibacterial activity which was marked by the absence of a clear zone around the paper disk.

Routh Reduction of Palatini Gravity in Vacuum

An interpretation of Einstein-Hilbert gravity equations as Lagrangian reduction of Palatini gravity is made. The main technique involved in this task consists in representing the equations of motion as a set of differential forms on a suitable bundle. In this setting Einstein-Hilbert gravity can be considered as a kind of Routh reduction of the underlying field theory for Palatini gravity. As a byproduct of this approach, a novel set of conditions for the existence of a vielbein for a given metric is found.

Einstein-Maxwell-scalar black holes: The hot, the cold and the bald

The phenomenon of spontaneous scalarisation of charged black holes (BHs) has recently motivated studies of various Einstein-Maxwell-scalar models. Within these models, different classes of BH solutions are possible, depending on the non-minimal coupling function f(ϕ), between the scalar field and the Maxwell invariant. Here we consider the class wherein both the (bald) electrovacuum Reissner-Nordström (RN) BH and new scalarised BHs co-exist, and the former are never unstable against scalar perturbations. In particular we examine the model, within this subclass, with a quartic coupling function: f(Φ)=1+αΦ4. The domain of existence of the scalarised BHs, for fixed α, is composed of two branches. The first branch (cold scalarised BHs) is continuously connected to the extremal RN BH. The second branch (hot scalarised BHs) connects to the first one at the minimum value of the charge to mass ratio and it includes overcharged BHs. We then assess the perturbative stability of the scalarised solutions, focusing on spherical perturbations. On the one hand, cold scalarised BHs are shown to be unstable by explicitly computing growing modes. The instability is quenched at both endpoints of the first branch. On the other hand, hot scalarised BHs are shown to be stable by using the S-deformation method. Thus, in the spherical sector this model possesses two stable BH local ground states (RN and hot scalarised). We point out that the branch structure of BHs in this model parallels the one of BHs in five dimensional vacuum gravity, with [Myers-Perry BHs, fat rings, thin rings] playing the role of [RN, cold scalarised, hot scalarised] BHs.

The phase space of k-Essence f(R) gravity theory

Among the remaining viable theories that can successfully describe the late-time era is the k-Essence theory and in this work we study in detail the phase space of k-Essence f(R) gravity in vacuum. This theory can describe in a viable way the inflationary era too, so we shall study the phase space in detail, since this investigation may reveal general properties regarding the inflationary attractors. By appropriately choosing the dimensionless variables corresponding to the cosmological system, we shall construct an autonomous dynamical system, and we find the fixed points of the system. We focus on quasi-de Sitter attractors, but also to radiation and matter domination attractors, and study their stability. As we demonstrate, the phase space is mathematically rich since it contains stable and unstable manifolds. With regard to the inflationary attractors, these exist and become asymptotically unstable, a feature which we interpret as a strong hint that the theory has an inherent mechanism for graceful exit from inflation. We describe in full detail the underlying mathematical structures that control the instability of the inflationary attractors, and we also address the same problem for radiation and matter domination attractors. The whole study is performed for both canonical and phantom scalar fields, and as we demonstrate, the canonical scalar k-Essence theory is structurally more appealing in comparison to the phantom theory, a result also demonstrated in the related literature on k-Essence f(R) gravity.

Deformed General Relativity and Quantum Black Holes Interior

Effective models of black holes interior have led to several proposals for regular black holes. In the so-called polymer models, based on effective deformations of the phase space of spherically symmetric general relativity in vacuum, one considers a deformed Hamiltonian constraint while keeping a non-deformed vectorial constraint, leading under some conditions to a notion of deformed covariance. In this article, we revisit and study further the question of covariance in these deformed gravity models. In particular, we propose a Lagrangian formulation for these deformed gravity models where polymer-like deformations are introduced at the level of the full theory prior to the symmetry reduction and prior to the Legendre transformation. This enables us to test whether the concept of deformed covariance found in spherically symmetric vacuum gravity can be extended to the full theory, and we show that, in the large class of models we are considering, the deformed covariance cannot be realized beyond spherical symmetry in the sense that the only deformed theory which leads to a closed constraints algebra is general relativity. Hence, we focus on the spherically symmetric sector, where there exist non-trivial deformed but closed constraints algebras. We investigate the possibility to deform the vectorial constraint as well and we prove that non-trivial deformations of the vectorial constraint with the condition that the constraints algebra remains closed do not exist. Then, we compute the most general deformed Hamiltonian constraint which admits a closed constraints algebra and thus leads to a well-defined effective theory associated with a notion of deformed covariance. Finally, we study static solutions of these effective theories and, remarkably, we solve explicitly and in full generality the corresponding modified Einstein equations, even for the effective theories which do not satisfy the closeness condition. In particular, we give the expressions of the components of the effective metric (for spherically symmetric black holes interior) in terms of the functions that govern the deformations of the theory.

On Universal Black Holes

Recent results of arXiv:1907.08788 on universal black holes in $d$ dimensions are summarized. These are static metrics with an isotropy-irreducible homogeneous base space which can be consistently employed to construct solutions to virtually any metric theory of gravity in vacuum.

Progress in a Vacuum Weight Search Experiment

We present the status of the art of the Archimedes experiment, devoted to measuring the debated interaction of quantum vacuum fluctuations and gravity. The method is essentially the weighing of the transition energy of a layered superconductor where the contribution of vacuum energy to the transition energy is expected to be relevant. The transition is obtained by modulating the temperature of the superconducting sample at a frequency of about 10 mHz and the expected change of weight is measured with a suitably designed high sensitivity cryogenic beam balance. In this paper, we present an overview of the experiment, discussing the expected signal to be measured, and presenting in particular the result of a prototype balance operated in our present laboratory. In the frequency range of the measurement, the sensitivity is affected mainly by seismic, thermal, sensor, and control noise. We discuss these points showing in particular the design of the cryogenic apparatus, the final balance, and the quiet seismic site that will host the final measurement.

Revelation of New Compound from Ethanolic Extract of Fragaria x ananassa var. Lembang

Fragaria x ananassa (strawberry) is a subtropical plant that can adapt well in tropical highlands. Fragaria x ananassa have been widely used to cope with health problems. The active compound component of secondary metabolites contained in Fragaria x ananassa has the potential as an antioxidant. This research is done to isolate secondary metabolites from extract of Fragaria x ananassa fruits. Extract Fragaria x ananassa was produced by maceration using ethanol as the solvent. Separation and isolation compound were carried out using Vacuum Liquid Chromatography (VLC) and Gravity Column Chromatography (GCC) guided by Thin Layer Chromatography (TLC) using hexane: ethyl acetate (3:7) as the eluent. The flavonoid compound was determined by the total content of phenolic and flavonoid in extract of Fragaria x ananassa fruits. The results of total phenolic content and total flavonoid content were 0.1130 mg/g and 0.0112 mg/g, respectively. The alkaloid compound was determined by Dragendorff testing. The elucidation of the structure by Fourier Tansform Infrared (FTIR), Nuclear Magnetic Resonance (NMR), and Liquid Chromatography Mass Spectrometry (LCMS) showed that the active compound contained in the secondary metabolite of extract ethanol from Fragaria x ananassa is 3-Cyclopentyl-5-(1-hydroxyethyl)-1,6-dihydro-7H-pyrazolo[4,3- d]pyrimidin-7-one.Keywords: Fragaria x ananassa extract, flavonoid, alkaloid, total phenolic and flavonoid content, FTIR, NMR, LCMS.

Higgs potential from Wick rotation in conformal BSM

It is well known that in order to make the path integral of general relativity converge, one has to perform the Wick rotation over the conformal factor in addition to the more familiar Wick rotation of the time axis to pass to the spacetime with Euclidean signature. In this paper, we will apply this technique to a scalar field in the conformally invariant scalar–tensor gravity with a conformally invariant beyond-standard-model (BSM). It is then shown that a potential term in the conformally invariant potential, which corresponds to the Higgs mass term in the Higgs potential of the Standard Model (SM), can have a negative coefficient. The change of sign of the potential term naturally induces spontaneous symmetry breakdown of the electroweak gauge symmetry after symmetry breaking of conformal symmetry (local scale symmetry) via the Coleman–Weinberg mechanism around the Planck scale. This study might shed light on the fact that the existence of a stable vacuum in quantum gravity is relevant to that in the SM.

Mass in Lovelock unique vacuum gravity theories

We derive an expression for conserved charges in Lovelock AdS gravity for solutions having $k$-fold degenerate vacua, making manifest a link between the degeneracy of a given vacuum and the nonlinearity of the energy formula. We show for a black hole solution to the field equations on a branch of multiplicity $k$ that its mass comes from an expression that contains the product of $k$ Weyl tensors. We prove that all divergent contributions of the type (Weyl)$^q$, with $1\le q<k$, are suppressed. Our conserved charge definition is a natural generalization of the Conformal Mass by Ashtekar, Magnon and Das to the cases when $k>1$. Our results provide insight on the holographic properties of degenerate Lovelock theories.

Antioxidant activity of isolated compound from perepat roots (Sonneratia alba)

Perepat (Sonneratia alba) is one of the mangrove plants found in Tanjung Jabung Timur, Jambi Province. Research on perepat plants has been widely carried out on leaves, fruit and bark, but there is no research on perepat roots, so it is necessary to do research on perepat roots. This study aims to determine the compounds found in ethyl acetate extract from roots which have antioxidant activity. Extraction and fractionation of perepat roots were carried out in multilevel maceration. The isolation technique was carried out using vacuum column chromatography and gravity column chromatography. The isolated compound was identified using UV-Vis spectrophotometer, FT-IR and NMR. Antioxidant activity test of the isolated compound was carried out by DPPH method. Characterization using UV-Vis gives maximum absorption at wavelengths 268and 313 nm. While the characterization with FT-IR provide information that the isolate containing functional groups of OH, C=O, CH3 and CH2. Further identification using NMR suggests that isolate are a mixture of stigmasterol and ß-sitosterol compounds, known as phytosterols. Antioxidant activity testing of ethyl acetate extract and isolate gave IC50 values of 223.67 and 439.71 ppm, respectively, indicating that these compounds were classified as less active but still potential as antioxidants.

Taming Dirac strings and timelike loops in vacuum gravity

The problem of singularities associated with Dirac strings and closed timelike curves in classical solutions of pure gravity is analyzed here. A method to eliminate these is introduced and established first for the Taub-NUT geometry. This is superceded by a smooth solution of first order field equations, which is defined to be a unique extension of the Taub Universe to a degenerate metric phase. As an additional feature, this framework naturally provides a geometric interpretation of the magnetic charge in the context of gravity theory without matter. Finally, exploiting the two phases of the metric determinant, we find a (smooth and unique) continuation of the Misner geometry as well, ridding it of closed timelike worldlines which exist in its otherwise Einsteinian manifestation.

Nonlinear stability in nonlocal gravity

We address the stability issue of Ricci-flat and maximally symmetric spacetimes in nonlocal gravity to all perturbative orders in the gravitational perturbation. Assuming a potential at least cubic in curvature tensors but quadratic in the Ricci tensor, our proof consists on a mapping of the stability analysis in nonlocal gravity to the same problem in Einstein-Hilbert theory. One of the consequences is that only the graviton field can propagate and the theory is ghost-free at all perturbative orders. All the results known in Einstein gravity in vacuum with or without a cosmological constant can be exported to the case of nonlocal gravity: if a spacetime is stable at all perturbative orders in Einstein gravity, it is stable also in nonlocal gravity. Minkowski and de Sitter spacetimes are particular examples. We also study how the theory affects the propagation of gravitational waves in a cosmological background.

Effects of spatial curvature on the f (R) gravity phase space: no inflationary attractor?

In this paper we study the effects of spatial curvature of the metric on the phase space of vacuum gravity. Particularly, we appropriately choose the variables of the dynamical system, in order for this to be autonomous, and we study the phase space of the resulting theory, focusing on de Sitter, matter and radiation domination fixed points. Our analysis indicates that the effect of spatial curvature on the phase space is radical, since it destabilizes all the stable de Sitter vacua of the flat spacetime vacuum gravity phase space, making the phase space having non-trivial unstable submanifolds. This instability occurs regardless if the spacetime has elliptic or hyperbolic spatial sections, and it is also robust towards the choice of initial conditions. We investigate the source of the instability in the system, and also we discuss the stability of the matter and radiation domination vacua, which, as we demonstrate, are also highly unstable. Our results for de Sitter attractors indicate that the stable de Sitter attractors of the vacuum gravity theory for a flat Universe, are destabilized by the presence of curvature, and this shows that inflation for vacuum gravity in non-flat spacetime is problematic, at least at the phase space level. This result holds true for both elliptic and hyperbolic spacetimes.

The Poisson brackets of free null initial data for vacuum general relativity

A hypersurface composed of two null sheets, or ‘light fronts’, swept out by the two congruences of future null normal geodesics emerging from a spacelike 2-disk can serve as a Cauchy surface for a region of spacetime. Already in the 1960s free (unconstrained) initial data for vacuum general relativity were found for hypersurfaces of this type. Here the Poisson brackets of such free initial data are calculated from the Hilbert action. The brackets obtained can form the starting point for a constraint free canonical quantization of general relativity and may be relevant to holographic entropy bounds for vacuum gravity. Several of the results of the present work have been presented in abbreviated form in the letter (Reisenberger 2008 Phys. Rev. Lett. 101 211101).

Geometric phase of cosmological scalar and tensor perturbations in f(R) gravity

By using the conformal equivalence of f(R) gravity in vacuum and the usual Einstein theory with scalar-field matter, we derive the Hamiltonian of the linear cosmological scalar and tensor perturbations in f(R) gravity in the form of time-dependent harmonic oscillator Hamiltonians. We find the invariant operators of the resulting Hamiltonians and use their eigenstates to calculate the adiabatic Berry phase for sub-horizon modes as a Lewis–Riesenfeld phase.

Noether symmetry of Palatini F(ℜ) gravity

In metric formalism, Noether symmetry of [Formula: see text] theory of gravity in vacuum and in the presence of pressureless dust yields [Formula: see text] along with the conserved current [Formula: see text] in Robertson–Walker metric and nothing else. However, Roshan and Shojai have claimed in [Palatini [Formula: see text] gravity and Noether symmetry, Phys. Lett. B 668 (2008) 238–240] that Noether symmetry in the context of Palatini [Formula: see text] theory of gravity admits [Formula: see text], (where [Formula: see text] is arbitrary) in matter domain era in Friedmann–Robertson–Walker universe. But, it has been shown that the conserved current obtained under the process does not satisfy the field equations in general. Here, it is shown that Noether Symmetry admits [Formula: see text] along with a conserved current [Formula: see text] in Palatini gravity. Thus, their claim is not right.