Induced Gravity Research Articles

One-loop effective action and emergent gravity on quantum spaces in the IKKT matrix model

A detailed derivation of 3 + 1 dimensional induced or emergent gravity in the IKKT matrix model at one loop is given, as announced in [1]. The mechanism requires a brane configuration with structure {mathcal{M}}^{3,1}times mathcal{K}subset {mathbb{R}}^{9,1} , where {mathcal{M}}^{3,1} is the noncommutative space-time brane, and mathcal{K} are compact fuzzy extra dimensions embedded in target space. The 3+1-dimensional Einstein-Hilbert action then arises in the one loop effective action of the maximally supersymmetric IIB or IKKT matrix model, with effective Newton constant determined by the Kaluza-Klein scale of mathcal{K} . At weak coupling, all physical modes are confined to the brane, leading to 3 + 1-dimensional low-energy physics. The Einstein-Hilbert action can be interpreted as interaction of mathcal{K} with the space-time brane via IIB supergravity. The vacuum energy does not act as cosmological constant, but stabilizes the brane structure at one loop.

A computational review of the line integral analytical formulation of the polyhedral gravity signal

ABSTRACTThe generally shaped polyhedron is a widely used model in gravity field modelling and interpretation. Its induced gravity signal – gravitational potential and its derivatives up to second order – has been studied extensively in the geophysical literature. The class of solutions with special interest is the one which leads to closed analytical expressions, as these offer an exact representation of the gravity signal of finite three‐dimensional distributions while being at the same time linked to a flexible means of geometric modelling. Of the several mathematical algorithms available, the line integral approach involves no approximations and is, however, connected with certain singularities, occurring for specific relative positions of the computation point with respect to the polyhedral source. The present contribution analyses the algorithmic details of the polyhedral line integral approach focusing on its geometric and computational aspects. Following the definitions of the individual coordinate systems and the two‐step application of the Gauss divergence theorem for each face and polygonal boundary of the source, the geometric insight of the algorithm is presented, which permits a deeper understanding of the significance of the involved numerical singular terms. An overview of the line integral analytical approach for the polyhedral gravity signal is presented with emphasis on its geometric and computational aspects. Matlab code and results for the two considered case studies, a prismatic source and asteroid Eros, are provided as electronic supplement.

Prone ventilation as treatment of acute respiratory distress syndrome related to COVID-19.

Prone ventilation refers to the delivery of mechanical ventilation with the patient lying in the prone position. The improvement of oxygenation during prone ventilation is multifactorial, but occurs mainly by reducing lung compression and improving lung perfusion. CT imaging modeling data demonstrated that the asymmetry of lung shape leads to a greater induced pleural pressure gravity gradient when supine as compared to prone positioning. Although proning is indicated in patients with severe ARDS who are not responding to other ventilator modalities, this technique has moved away from a salvage therapy for refractory hypoxemia to an upfront lung-protective strategy intended to improve survival in severe ARDS, especially due to the current COVID-19 pandemic. In view of different roles, we surgeons had to take during the COVID-19 pandemic, it is of importance to learn how to implement this therapeutic measure, especially in a surgical critical care unit setting. As such, this article aims to review the physiological principles and effects of the prone ventilation, positioning, as well as its contraindications and complications.

More on universal superconformal attractors

We define a general class of superconformal inflationary attractor models studied in our previous papers [1,2], which include, among others, inflationary models of 'induced gravity' which were argued to retain perturbative unitarity up to the Planck scale [3]. The choice of the function $f(\phi)$ in superconformal attractors for the models introduced in [3] is $f(\phi)= \phi^n - \xi^{-1}$. We present both superconformal and supergravity versions of these models, which were derived in [1,2] for arbitrary $f(\phi)$, together with the universal conditions required for stabilization of the extra three moduli present in the superconformal attractors, in addition to the inflaton.

Exact self-similar Bianchi II solutions for some scalar-tensor theories

We study how may behave the gravitational and the cosmological “constants”, (G and Λ) in several scalar-tensor theories with Bianchi II symmetries. By working under the hypothesis of self-similarity we find exact solutions for three different theoretical models, which are: the Jordan-Brans-Dicke (JBD) with Λ(ϕ), the usual JBD model with potential U(ϕ) (that mimics the behavior of Λ(ϕ)) and the induced gravity (IG) model proposed by Sakharov and Zee. After a careful study of the obtained solutions we may conclude that the solutions are quite similar although the IG model shows some peculiarities.

Brane induced gravity, its ghost and the cosmological constant problem

``Brane Induced Gravity'' is regarded as a promising framework for addressing the cosmological constant problem, but it also suffers from a ghost instability for parameter values that make it phenomenologically viable. We carry out a detailed analysis of codimension > 2 models employing gauge invariant variables in a flat background approximation. It is argued that using instead a curved background sourced by the brane would not resolve the ghost issue, unless a very specific condition is satisfied (if satisfiable at all). As for other properties of the model, from an explicit analysis of the 4-dimensional graviton propagator we extract a mass, a decay width and a momentum dependent modification of the gravitational coupling for the spin 2 mode. In the flat space approximation, the mass of the problematic spin 0 ghost is instrumental in filtering out a brane cosmological constant. The mass replaces a background curvature that would have had the same function. The optical theorem is used to demonstrate the suppression of graviton leakage into the uncompactified bulk. Then, we derive the 4-dimensional effective action for gravity and show that general covariance is spontaneously broken by the bulk-brane setup. This provides a natural realization of the gravitational Higgs mechanism. We also show that the addition of extrinsic curvature dependent terms has no bearing on linearized brane gravity.

Inflation and reheating in spontaneously generated gravity

Inflation is studied in the context of induced gravity (IG) $\gamma \sigma^2 R$, where $R$ is the Ricci scalar, $\sigma$ a scalar field and $\gamma$ a dimensionless constant, and diverse symmetry-breaking potentials $V(\sigma)$ are considered. In particular we compared the predictions for Landau-Ginzburg (LG) and Coleman-Weinberg (CW) type potentials and their possible generalizations with the most recent data. We find that large field inflation generally leads to fewer constraints on the parameters and the shape of the potential whereas small field inflation is more problematic and, if viable, implies more constraints, in particular on the parameter $\gamma$. We also examined the reheating phase and obtained an accurate analytical solution for the dynamics of inflaton and the Hubble parameter by using a multiple scale analysis (MSA). The solutions were then used to study the average expansion of the Universe, the average equation of state for the scalar field and both the perturbative and resonant decays of the inflaton field.

A Review About Invariance Induced Gravity: Gravity and Spin from Local Conformal-Affine Symmetry

In this review paper, we discuss how gravity and spin can be obtained as the realization of the local Conformal-Affine group of symmetry transformations. In particular, we show how gravitation is a gauge theory which can be obtained starting from local invariance as the Poincar\'{e} local symmetry.

Inflation and reheating in induced gravity

Inflation is studied in the context of induced gravity (IG) γσ2R, where R is the Ricci scalar, σ a scalar field and γ a dimensionless constant. We study in detail cosmological perturbations in IG and examine both a Landau–Ginzburg (LG) and a Coleman–Weinberg (CW) potential toy models for small field and large field (chaotic) inflation and find that small field inflationary models in IG are constrained to γ≲3×10−3 by WMAP 5-yrs data. Finally we describe the regime of coherent oscillations in induced gravity by an analytic approximation, showing how the homogeneous inflaton can decay in its short-scale fluctuations when it oscillates around a non-zero value σ0.

Cargèse Lectures on Brane Induced Gravity

A brief introduction is given to the subject of brane induced gravity. The 5D example is discussed in detail. The 4D laws of gravity are obtained on a brane embedded in an infinite volume extra space, where the problem of stabilization of the volume modulus is absent. The theory has two classically disjoint branches of solutions -- the conventional and self-accelerated one. The conventional branch gives a perturbatively stable model of a metastable graviton, with potentially testable predictions within the Solar system. The self-accelerated branch, on the other hand, provides an existence proof for an idea that the accelerated expansion of the Universe could be due to modified gravity. The issue of perturbative stability of the self-accelerated branch is obscured by a breakdown of the conventional perturbative expansion. However, a certain exact non-perturbative solution found in hep-th/0612016 exhibits a net negative gravitational mass, while this mass is positive on the conventional branch. This suggest that the self-accelerated solution must be non-perturbatively unstable. A proposal to overcome this problem in an extension of the original model, that also allows for the quantum gravity scale to be unrestricted, is briefly discussed.

Crossing w = −1 in Gauss–Bonnet Brane Worldwith Induced Gravity**The project supported in part bythe National Natural Science Foundation of China under Grant Nos. 10325525and 90403029, and by ``973" Project of the Ministryof Science and Technology of China under Grant No. TG1999075401

Recent type Ia supernovas data seemingly favor a dark energy modelwhose equation of state w(z) crosses −1 very recently, whichis a much more amazing problem than the acceleration of theuniverse. In this paper we show that it is possible to realizesuch a crossing without introducing any phantom component in aGauss–Bonnet brane world with induced gravity, where afour-dimensional curvature scalar on the brane and a five-dimensionalGauss–Bonnet term in the bulk are present. In this realization,the Gauss–Bonnet term and the mass parameter in the bulk play acrucial role.

Exact Seiberg–Witten map, induced gravity and topological invariants in non-commutative field theories

We revisit the exact Seiberg–Witten (SW) map on Dirac–Born–Infeld actions, making a connection with the deformation quantization scheme. The picture on field dependent induced gravity from non-commutativity becomes more transparent in the context of deformation quantization. We also find an exact SW map for an adjoint scalar field, consistent with that deduced from RR couplings of unstable non-BPS D-branes. The dual description via the exact SW map can again be interpreted as the ordinary field theory coupling to gravity induced by gauge fields. Using the exact SW maps, we further discuss several aspects of topological invariants in non-commutative (NC) gauge theory. Especially, it is shown that the K-theory class on NC instantons is mapped to the usual second Chern class via exact SW map and it leads to an exact SW map between commutative and NC Chern–Simons terms.

Brane-Cosmology Dynamics with Induced Gravity

The Friedmann equations for a brane with induced gravity are analyzed and compared with the standard general relativity and Randall-Sundrum cases. Randall-Sundrum gravity modifies the early universe dynamics, whereas induced gravity changes the late universe evolution. The early and late time limits are investigated. Induced gravity effects can contribute to late-universe acceleration. The conditions for this are found. Qualitative analysis is given for a range of scalar field potentials.

Effects of mantle flow law stress exponent on postglacial induced surface motion and gravity in Laurentia

SUMMARY Recent studies show that power-law rheology with stress exponent n = 3 in the lower mantle or in a thin zone just beneath the lithosphere are consistent with the sea level observations in and around Laurentia. In this study, the stress exponent n is varied from 2 to 4, and for each value of n, a range of creep parameter A ∗ is searched to find the earth model that gives the best fit to the sea level observations in and around Laurentia. The effects of stress exponent on other geophysical observables—namely present day uplift rate, horizontal velocity, free-air gravity and the rate of change in gravity are also studied. The model used to calculate the postglacial readjustment of the Earth is a 3-D finite element model that includes realistic ice histories and eustatic water loads on stratified incompressible viscoelastic Maxwell flat-earths. Three types of earth rheology models are considered—the first one has nonlinear rheology throughout the mantle and the second has a nonlinear zone at the top of the mantle below the elastic lithosphere and a linear mantle. The third one has nonlinear rheology restricted to lie in the lower mantle. It is found that the models with nonlinear rheology in the lower mantle give better fits to the sea level data in and around Laurentia than the first two types. However, sea level data, when taken as a whole, cannot clearly discriminate between the stress exponents 2, 3 or 4. Present day uplift rate, horizontal velocity and rate of gravity change however may be useful in further discriminating mantle rheology.

Can induced gravity isotropize Bianchi type I, V, or IX universes?

We analyze if Bianchi I, V, and IX models in the Induced Gravity (IG) theory can evolve to a Friedmann--Roberson--Walker (FRW) expansion due to the non--minimal coupling of gravity and the scalar field. The analytical results that we found for the Brans-Dicke (BD) theory are now applied to the IG theory which has $\omega \ll 1$ ($\omega$ being the square ratio of the Higgs to Planck mass) in a cosmological era in which the IG--potential is not significant. We find that the isotropization mechanism crucially depends on the value of $\omega$. Its smallness also permits inflationary solutions. For the Bianch V model inflation due to the Higgs potential takes place afterwads, and subsequently the spontaneous symmetry breaking (SSB) ends with an effective FRW evolution. The ordinary tests of successful cosmology are well satisfied.

SCHWINGER–DYSON EQUATIONS AND CHIRAL SYMMETRY BREAKING IN 2-D INDUCED GRAVITY

The Schwinger–Dyson equations in the ladder approximation for 2-D induced gravity coupled to fermions on a flat background are obtained in conformal gauge. A numerical study of these equations shows the possibility of chiral symmetry breaking in this theory.

On the potential of induced gravity

We investigate the potential of induced gravity in the Minkowski domain.

General overview of geophysical studies at Cerro Prieto

Geophysical investigations by the CFE in the Mexicali Valley near the Cerro Prieto volcano began nearly 20 years ago. Initially, gravity and seismic refraction methods were used for structural information related to faults and basement configuration. Geophysical emphasis shifted to d.c. resistivity surveys in the early 1970's after it was determined that a large area of low resistivity coincided with the thermal manifestations south of the volcano and the known high temperature zone at depth. Supplemented by ground magnetic and gravity measurements, the resistivity data are being interpreted to yield a detailed picture of the structure concealed by valley fill and to identify promising areas for future exploration. Under the DOE/CFE agreement, the LBL has been conducting various types of electrical, passive seismic and precision gravity surveys over the field. This work is less concerned with geothermal exploration than the CFE geophysical program. It involves applying exploration methods to reservoir-related questions; namely, can the reservoir area be delineated and can changes in reservoir characteristics be detected and monitored by means of surface measurements? As the second question involves a long time scale, repeated measurements and correlations to production data, only baseline information is presently being obtained. Dipole-dipole resistivity, magnetotelluric (MT) and self-potential (SP) surveys have been completed and results will be discussed. The large dipolar SP anomaly found over the field has encouraged further use of the method in the Mexicali Valley. Careful interpretation of dipole-dipole and Schlumberger data set yields a subsurface resistivity model which provides a surprising amount of useful detail. Permanent current electrodes have been emplaced and repeat measurements will be made at later times to determine whether changes in resistivity occurred within the reservoir area. Reference magnetic MT technique, developed recently at U.C. Berkeley, was applied at Cerro Prieto. Earlier tests have shown that in the presence of electro-magnetic noise, such as cultural noise, this technique yields more accurate subsurface information than conventional MT. Regional seismicity has been studied for many years. Recently, the CICESE has maintained a four station network in the Northern Mexicali Valley. The LBL passive seismic results show epicenters within the reservoir boundary associated with right-lateral strike-slip movement. V P/V S data from these events indicate a Poisson's ratio of 0.4 for the upper 2–3 km of the field. Although limited, P-wave velocity and attenuation data imply a local low near the western edge of the field superimposed upon a slight high for the entire production region. Beginning in the fall of 1978, continuous monitoring by the LBL and CICESE will provide more complete data on field characteristics. The first phase of precision gravity surveys at 60 monuments is nearly complete. Repeated gravity measurements coupled with repeated first-order leveling by the CFE will be needed to distinguish subsidence or tectonic induced gravity changes from the small changes (80–100 μgal) that might be associated with mass depletion due to fluid withdrawal. A five-station seismic array is being installed in shallow holes so that the long-term changes in seismic activity and relationship to subsidence and geothermal fluid production can be studied.