Ordinary Gravity Research Articles

Unimodular quadratic gravity and the cosmological constant

Unimodular gravity addresses the old cosmological constant (CC) problem, explaining why such constant is not at least as large as the largest particle mass scale, but classically it is indistinguishable from ordinary gravity. Conversely, quantum physics may give us a way to distinguish the two theories. Thus, here the unimodular constraint is imposed on a non-perturbative and background-independent quantum version of quadratic gravity, which was recently formulated. It is shown that unimodularity does lead to different predictions for some inflationary quantum observables. Unimodular gravity per se does not solve the new CC problem (why the CC has the observed value?) even in this realization. To address this issue a multiverse made by different eras in a single big bang is considered and the observed scale of dark energy is explained anthropically.

Infragravity waves and cross-shore motion–a conceptual study

It is widely known that Infragravity (IG) waves induce cross-shore fluid motion in the nearshore, and multiple recent observational studies have identified IG waves as the dominant factor for a range of nearshore processes such as particle drift in the surf zone, transport of suspended sediment and river plume oscillations. While it is clear that the underlying orbital motion linked to IG wave excursions correlates with IG wave periods, the exact relation between the IG wave amplitude and the strength of the cross-shore motion has not been investigated in great detail. In the present contribution, we aim to quantify the cross-shore motion as a function of the IG wave amplitude. Indeed, it is shown that IG waves of even the most minute amplitude induce a large horizontal movement of particles, and the cross-shore movement is often several orders of magnitude larger than the particle movement induced by ordinary gravity waves. The results hold across a number of situations including monochromatic waves, sea states given by a spectrum as well as nonlinear waves with and without strong bathymetric forcing.

CONSTRUCTIVE SOLUTIONS FOR EXPLOSION-RESISTANT BUILDINGS WITH CIVIL PROTECTION FACILITIES

In the conditions of the large-scale war led by russia in Ukraine, the issue of designingblast-resistant buildings with civil defense facilities that can withstand additional special loads and impacts has become crucial. These impacts include artillery and missile attacks, bomb explosions, blast waves, and the spread of fires, among others. An analysis of the consequences of building and structure destruction resulting from military operationsindicates that reinforced concrete structures of buildings have superior load-bearing capacity compared to traditional brick and steel frames of pavilion-type buildings.Reinforced concrete is a non-combustible material with significant mass, improving its inertialresistance. It possesses high strength and plasticity characteristics, allowing it to deform and redistribute forces between adjacent structures, thereby preventing progressive collapse – the cascading destruction of buildings.The main principles of designing blast-resistant reinforced concrete frames for high-rise buildings involve rational constructive systems and schemes with simple and compact configurations and symmetrical plans. The structural solution of the reinforced concrete frame must ensure the redistribution of gravity loads between adjacent structures. Therefore, the joints of vertical and horizontal structures must be plastic, capable of dissipating a significant amount of explosion energy. The load-bearing elements of buildingstructures must withstand cycles of large deformations in different directions, such aspressures from the lifting of floor slabs opposing ordinary gravity loads. For buildings classified with medium (CC2) and significant (CC3) consequences, where more than 50 individuals are constantly present or periodically more than 100 people, it is necessary to design civil protection premises. These premises should be strategically located below the planned ground level.The construction of civil protection premises located in the underground floors of an explosionproof building must withstand all types of main and episodic loads and impacts and resist the spread of fire. Building frames with monolithic reinforced concrete ribbed ceilings and systems of main and secondary beams or transversely located beams rigidly fixed to vertical supporting structures – columns, pylons, walls – can withstand such loadsbest. The article investigates the reasons for the destruction of reinforced concrete slabs in high-rise frame monolithic buildings when subjected to bending or pressure from explosive loads below. It also explores the potential twisting of the building as a result of reverse explosive effects.The article presents measures to strengthen sections of floor structures in high-rise framemonolithic buildings that may be destroyed due to reverse explosive loads and upward pressure from explosive forces. The expediency of reinforcing critical areas of monolithic reinforced concrete floor slabs with external reinforcement – adhering reinforcing mats in the form of fabrics, lamellas, or carbon fiber nets to the upper zones of slabs near vertical supports – is justified.

A New Efficient Hybrid Approach for Machine Learning-Based Firefly Optimization

Optimization is the task of minimizing or maximizing an objective function f(x) parameterized by x. A series of effective numerical optimization methods have become popular for improving the performance and efficiency of other methods characterized by high-quality solutions and high convergence speed. In recent years, there are a lot of interest in hybrid metaheuristics, where more than one method is ideally combined into one new method that has the ability to solve many problems rapidly and efficiently. The basic concept of the proposed method is based on the addition of the acceleration part of the Gravity Search Algorithm (GSA) model in the Firefly Algorithm (FA) model and creating new individuals. Some standard objective functions are used to compare the hybrid (FAGSA) method with FA and the traditional GSA to find the optimal solution. Simulation results obtained by MATLAB R2015a indicate that the hybrid algorithm has the ability to cross the local optimum limits with a faster convergence than the luminous Fireflies algorithm and the ordinary gravity search algorithm. Therefore, this paper proposes a new numerical optimization method based on integrating the properties of the two methods (luminous fireflies and gravity research). In most cases, the proposed method usually gives better results than the original methods individually.

Effect of yttrium content on microstructure and tensile properties of as-cast and as-solutionized Al-Zn-Mg-Cu alloys

Four kinds of 7xxx series aluminum alloys with different Y elementcontents were obtained by ordinary gravity casting. The effect of Y content on the microstructure and mechanical properties of as-cast and as-solutionized Al-7.9Zn-3Mg-2.4Cu-0.13Zr (wt%) alloys were investigated by means of x-ray diffraction (XRD), electron backscattering diffraction (EBSD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and room-temperature tensile tests. The results shows that, in as-cast condition, Y element can refine the grain and reduce the content of Mg(Zn, Cu, Al)2 lamellar phases at the interdendritic. (Al, Zn)8Cu4Y block-shaped phases form in interdendritic regions. After solution treatment, the undissolved Mg(Zn, Cu, Al)2 phases evolved from lamellar to bulk-like which distribution in interdendritic, but no obvious change in (Al, Zn)8Cu4Y phase. The tensile testing results shows that the optimal yttrium content is 0.45 wt%. At 0.45 wt% Y, the ultimate tensile strength and elongation are 267 MPa and 2.4% in as-cast condition and 420 MPa and 3.6% in as-solutionized condition.

Weak Interaction Dependent Super Gravity of Galactic Baryon Mass

Considering our light speed growing Planck scale universe, it seems possible to develop a practical model of Hubble-Hawking Universe by using which cosmic temperature and Hubble parameter can be correlated accurately. Without considering galactic dark matter, galactic flat rotation speeds can be addressed with ‘super gravity’ of galactic baryonic mass. In this context, (180 to 200) million solar masses can be considered as a characteristic upper mass limit of ordinary gravity. Considering the proposed current upper mass limit of ordinary gravity as a characteristic weak interaction mass unit, hypothecated galactic dark matter can be quantified. Clearly speaking, weak interaction boosts the gravity of galaxies in proportion to their virtual dark mass as (galactic baryonic mass)3/2 / (200 million solar masses)1/2. Based on cosmic recombination temperature and baryon acoustic bubble radius, upper mass limit of gravity can also be fitted. With further study, dark matter existence and physical properties can be explored.

A Matrix Model of Four-Dimensional Noncommutative Gravity

In this review, we revisit our latest works regarding the description of the gravitational interaction on noncommutative spaces as matrix models. Specifically, inspired by the gauge-theoretic approach of (ordinary) gravity, we make use of the suggested methodology, modified appropriately for the noncommutative framework, of the well-established formulation of gauge theories on them. Making use of a covariant four-dimensional fuzzy space, we formulate the gauge theory with an extended gauge group due to noncommutativity. In turn, in order to decrease the amount of symmetry we employ a symmetry breaking and result with an action which describes a theory that is a minimal noncommutative extension of the original.

Utilization of Gravity Satellite Data to Imaging Subsurface Conditions, Case Study: Lake Toba, North Sumatera

The purpose of this study is to utilize satellite gravity data for free to interpret subsurface conditions. The data can be obtained from the topex site with a latitude range is +/-80,738. The author tries to interpret the gravity data for Lake Toba, North Sumatra. The area is attractive because it has a sizeable geological object in the form of a large lake and a fault called the Sumatran fault. This gravity data is processed like ordinary gravity processing so that Complete Bouguer Anomaly (CBA) is obtained, then regional-residual separation is carried out using a moving average. From CBA, it can be seen that there are two closures just below Lake Toba. There are two possible chambers under Lake Toba, namely the central and southern parts. In addition, it is also clear that the lineament of the Sumatran fault is also visible, as well as three other lineaments which may be faults that are not identified from the surface. So, we can take advantage of this free gravity satellite data for interpretation of sizeable geological objects that can be applied to other areas. It is helpful to know the general picture of regional geology before conducting a more detailed survey.

Dynamic response analysis of blocks-combined dam under impact load

In order to reduce the damage of ordinary gravity dam impacted by boulders in debris flow, a blocks-combined dam based practical project is proposed. The dynamic response of the proposed dam under impact load is investigated by using ABAQUS finite element software. Considering the impact velocity and impact height, the anti-impact performance of blocks-combined dam is discussed in terms of deformation, displacement, impact force, acceleration, and energy, and is compared with that of ordinary dam. Results show that the displacement, impact force and acceleration of dam increase with the increase of impact velocity and height. The impact energy of blocks-combined dam is mainly absorbed and consumed by the friction between the component interfaces, which is related to the location of impact point. Compared with the ordinary gravity dam, the blocks-combined dam has better impact resistance to boulders in debris flow.

Influence of gravity on the frozen wave instability in immiscible liquids

Gravity is crucial to the frozen wave instability because it both sets the threshold of applied forcing and limits the growth of unstable perturbations. Through numerical simulations of immiscible liquids in finite containers we examine the transition from a supercritical pitchfork bifurcation in ordinary gravity, which is accompanied by stable finite-amplitude waves, to a degenerate bifurcation in weightlessness, which is followed by large columnar patterns. The vibroequilibria effect plays a symmetry-breaking role in the bifurcation, selecting frozen waves with the heavier fluid displaced upward along the lateral walls.

Support for two subglacial impact craters in northwest Greenland from Earth gravity model EIGEN 6C4 and other data

We support the very recent discovery of two impact craters under the ice of northwest Greenland (Hiawatha Glacier and Paterson). These discoveries are based mainly on geology and bedrock topography. We added an analysis of gravity field aspects (descriptors) in addition to the traditional gravity and magnetic anomalies. The gravity aspects (the Marussi tensor of the second derivatives, the gravity invariants and their special ratio, strike angles and virtual deformations) provide more complex and comprehensive information about the underground density variations due to a causative body than ordinary gravity anomalies. They show signals typical for the individual geological features like a mountain/volcano, fault, (river)valley, (paleo)lake, (ground)water, hydrocarbon/mineral deposits, etc., as well as for the targets known as impact craters. Our method has been tested on various geological features on the Earth and the Moon. The gravity aspects are, in our case, derived from the recent global static combined Earth gravity field model EIGEN 6C4 with a ground resolution ~9 km and a precision ~10 mGal. A further data come from the digital magnetic field database EMAG 2 with resolution ~5 km. Our method is novel and independent of anything which led to discoveries of these craters in Greenland.

Gravitational absorption lines

We consider the gravitational analogue of Lyman-alpha absorption lines in astronomical spectroscopy. If Einstein gravity with minimally coupled matter is valid up to the Planck scale, quantum bound states absorb gravitons of a specific frequency with Planckian cross section, $\sigma_{\text{abs}} \approx l_p^2$. Consequently, one can show that gravitational absorption by bound states is inefficient in ordinary gravity. If observed, gravitational absorption lines would therefore constitute a powerful smoking gun of new exotic astrophysical bound states (near extremal bound states) or new gravitational physics, as well as give direct evidence of the quantized nature of the gravitational field. We provide, as an example of new gravitational physics near the Planck scale, a non-minimal coupling of the matter fields which breaks the equivalence principle on-shell. We lay out a model in which absorption lines in the primordial gravitational wave spectrum are produced as a consequence of this coupling.

Constraining graviton non-Gaussianity through the CMB bispectra

Tensor non-Gaussianities are a key ingredient to test the symmetries and the presence of higher spin fields during the inflationary epoch. Indeed, the shape of the three point correlator of the graviton is totally fixed by the symmetries of the de Sitter stage and, in the case of parity conservation, gets contributions only from the ordinary gravity action plus a higher derivative term called the (Weyl)$^3$ action. We discuss current and future bounds on the three point tensor contribution from the (Weyl)$^3$ term using cosmic microwave background (CMB) bispectra. Our results indicate that forthcoming experiments, such as LiteBIRD, CMB-S4 and CORE, will detect the presence of the (Weyl)$^3$ term if $M_p^4 L^4 \sim 10^{17} r^{-4}$, where $L$ parametrizes the strength of the (Weyl)$^3$ term and $r$ is the tensor-to-scalar ratio, which corresponds to $L\gtrsim 3.2 \times 10^5 M_p^{-1}$, while the current upper limit is $M_p^4 L^4 = (1.1 \pm 4.0) \times 10^{19} r^{-4}$ (68%CL).

Stringy (Galilei) Newton-Hooke Chern-Simons gravities

We construct Chern-Simons gravities in (2 + 1)-dimensional space-time considering the Stringy Galilei algebra both with and without non-central extensions. In the first case, there is an invariant and non-degenerate bilinear form, however the field equations do not allow to express the spin connections in terms of the dreibeins. In the second case there is no invariant non-degenerate bilinear form. Therefore, in both cases we do not have an ordinary gravity theory. Instead, if we consider the stringy Newton-Hooke algebra with extensions as gauge group we have an invariant non-degenerate metric and from the field equations we express the spin connections in terms of the geometric fields.

Numerical damage evaluation assessment of blast loaded steel columns with similar section properties

In the last years, the increase of blast and terroristic attacks in the vicinity of critical structures and facilities highlighted the importance of appropriate simulation and design methods for blast loaded structures. Within a building exposed to blast, columns act as key components, being asked to sustain ordinary gravity and wind loads, but also possible additional exceptional loads like earthquakes or explosions. In this paper, the dynamic behavior of steel columns under blast pressures is numerically investigated. Careful consideration is spent – based on validated Finite Element (FE) models – for the blast performance of steel columns with different cross-sectional shapes but similar mechanical properties (i.e., total area, moment of inertia and elastic section modulus). Explicit FE analyses are carried out on a wide set of configurations, including variations in (a) cross-section properties, (b) boundary conditions and (c) explosions features. In doing so, the accuracy and reliability of different FE models (i.e., based on solid, shell and beam elements) are also investigated, both in terms of global/local results and computational cost of the dynamic simulations. As key damage parameters due to blast, the maximum displacement and the residual load carrying capacity of the examined columns are examined. The collected parametric results show that the cross-sectional shape only slightly affects the global dynamic behavior of steel columns, especially in terms of residual capacity. Moreover, compared to computationally expensive full solid models, the reliability and accuracy of geometrically simplified shell and beam is discussed, with respect to the observed responses and intrinsic computational efficiency.

Unimodular quantum gravity and the cosmological constant

It is shown that the one-loop effective action of unimodular gravity is the same as that of ordinary gravity, restricted to unimodular metrics. The only difference is in the treatment of the global scale degree of freedom and of the cosmological term. A constant vacuum energy does not gravitate, addressing one aspect of the cosmological constant problem.

Hidden conformal symmetry in tree-level graviton scattering

We argue that the scattering of gravitons in ordinary Einstein gravity possesses a hidden conformal symmetry at tree level in any number of dimensions. The presence of this conformal symmetry is indicated by the dilaton soft theorem in string theory, and it is reminiscent of the conformal invariance of gluon tree-level amplitudes in four dimensions. To motivate the underlying prescription, we demonstrate that formulating the conformal symmetry of gluon amplitudes in terms of momenta and polarization vectors requires manifest reversal and cyclic symmetry. Similarly, our formulation of the conformal symmetry of graviton amplitudes relies on a manifestly permutation symmetric form of the amplitude function.

Black hole merger estimates in Einstein-Maxwell and Einstein-Maxwell-dilaton gravity

The recent birth of gravitational wave astronomy invites a new generation of precision tests of general relativity. Signatures of black hole (BH) mergers must be systematically explored in a wide spectrum of modified gravity theories. Here, we turn to one such theory in which the initial value problem for BH mergers is well posed, the Einstein-Maxwell-dilaton system. We present conservative estimates for the merger parameters (final spins, quasinormal modes) based on techniques that have worked well for ordinary gravity mergers and utilize information extracted from test particle motion in the final BH metric. The computation is developed in parallel for the modified gravity BHs (we specifically focus on the Kaluza-Klein value of the dilaton coupling, for which analytic BH solutions are known) and ordinary Kerr-Newman BHs. We comment on the possibility of obtaining final BHs with spins consistent with current observations.

Effects of the distant population density on spatial patterns of demographic dynamics.

Spatio-temporal patterns of population changes within and across countries have various implications. Different geographical, demographic and econo-societal factors seem to contribute to migratory decisions made by individual inhabitants. Focusing on internal (i.e. domestic) migration, we ask whether individuals may take into account the information on the population density in distant locations to make migratory decisions. We analyse population census data in Japan recorded with a high spatial resolution (i.e. cells of size 500×500 m) for the entirety of the country, and simulate demographic dynamics induced by the gravity model and its variants. We show that, in the census data, the population growth rate in a cell is positively correlated with the population density in nearby cells up to a distance of 20 km as well as that of the focal cell. The ordinary gravity model does not capture this empirical observation. We then show that the empirical observation is better accounted for by extensions of the gravity model such that individuals are assumed to perceive the attractiveness, approximated by the population density, of the source or destination cell of migration as the spatial average over a circle of radius ≈1 km.

On feasibility to detect volcanoes hidden under the ice of Antarctica via their “gravitational signal”

<p class="Prosttext1">Many undiscovered volcanoes may be hidden under the thick layers of the ice of Antarctica. Hypothetic volcanoes were sought by means of the best present-day gravitational data (gravity field model EIGEN 6C4) and bedrock topography data (Bedmap2). A new previously unused method was tested. The analogy with the “gravitational signal” typical for volcanoes and other structures in other parts of the Earth is used. Various functions (not only ordinary gravity anomalies) of the disturbing geopotential were employed: Marussi tensor of the second derivatives, geopotential invariants, the strike angle and the virtual deformations. We attempted to discover if the best present-day gravitational and topographic data are of sufficient precision and resolution and how fast is the attenuation of the “gravitational signal” of a volcano with increasing depth under the ice. It is shown that there is no principal obstacle to detect volcanoes by our method. However, it appeared very quickly that our present-day attempts to discover such volcanoes could hardly be successful, mainly due to a low resolution of the existing gravity data and also due to a low resolution of the best bedrock topography of Antarctica currently available. Nevertheless, some examples of hypothetical volcanoes under the ice are given, but they are uncertain. However, the method, the main goal of this feasibility study, is ready and working. <strong></strong></p>