Aspects of cosmological expansion inF(R) gravity models

The objective of this study is to analyze the determinants of Brazilian exports by levels of technological intensity in the period 2000-2015. Gravity models were estimated for total of the exports and for each type of exports by levels of technological intensity, using the PPML-estimator. The study indicates that there is a process of concentration of Brazilian exports in low technology and medium-low technology products, at the same period in which China's share of total Brazilian shipments abroad grew. Estimates of empirical gravity models have shown that the income and size of the consumer market of Brazil’s trading partners seem to have the greatest positive influence on the Brazilian exports. Indications of this study are that the Brazil should continue to diversify its trading partners to minimize the impacts of a possible reduction of the economic growth of large trading partners (such as China and the US) on its exports and increase its exports of products with greater technological intensity. The results also highlight the need for Brazil to make greater efforts to increase its competitiveness in the international market to reduce the negative impacts of transport costs on the final prices of products exported by the country.

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The Forgotten Discovery of Gravity Models and the Inefficiency of Early Railway Networks

SSRN Electronic Journal ◽

10.2139/ssrn.2490241 ◽

2014 ◽

Author(s):

Andrew Odlyzko

Keyword(s):

Gravity Models ◽

Railway Networks

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ON p – q DUALITY AND EXPLICIT SOLUTIONS IN c ≤ 1 2D GRAVITY MODELS

International Journal of Modern Physics A ◽

10.1142/s0217751x95000577 ◽

1995 ◽

Vol 10 (08) ◽

pp. 1219-1236 ◽

Cited By ~ 17

Author(s):

S. KHARCHEV ◽

A. MARSHAKOV

Keyword(s):

String Theory ◽

Exact Solutions ◽

2D Gravity ◽

Integral Formula ◽

Integral Representations ◽

Gravity Models ◽

Explicit Solutions ◽

String Equation ◽

Duality Transformation

We study the role of integral representations in the description of nonperturbative solutions to c ≤ 1 string theory. A generic solution is determined by two functions, W(x) and Q(x), which behave at infinity like xp and xq respectively. The integral formula for arbitrary (p, q) models is derived, which explicitly realizes a duality transformation between (p, q) and (q, p) 2D gravity solutions. We also discuss the exact solutions to the string equation and reduction condition and present several explicit examples.

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Constraining the Swiss-Cheese IR-Fixed Point Cosmology with Cosmic Expansion

Universe ◽

10.3390/universe7080263 ◽

2021 ◽

Vol 7 (8) ◽

pp. 263

Author(s):

Ayan Mitra ◽

Vasilios Zarikas ◽

Alfio Bonanno ◽

Michael Good ◽

Ertan Güdekli

Keyword(s):

Fixed Point ◽

Cosmological Constant ◽

Cosmic Acceleration ◽

Fine Tuning ◽

Clusters Of Galaxies ◽

Swiss Cheese ◽

Coincidence Problem ◽

Cosmological Expansion ◽

Cosmic Evolution ◽

Previous Assumption

A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a Swiss-cheese cosmology model, which relativistically integrates the contribution of all these anti-gravity sources on a galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides an explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals that, in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.

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Three-dimensional Maxwellian extended Newtonian gravity and flat limit

Journal of High Energy Physics ◽

10.1007/jhep10(2020)181 ◽

2020 ◽

Vol 2020 (10) ◽

Author(s):

Patrick Concha ◽

Lucrezia Ravera ◽

Evelyn Rodríguez ◽

Gustavo Rubio

Keyword(s):

Cosmological Constant ◽

Three Dimensional ◽

Expansion Method ◽

Gravity Models ◽

Newtonian Gravity ◽

Newtonian Theory ◽

Relativistic Limit ◽

Expansion Procedure ◽

Three Space ◽

Chern Simons

Abstract In the present work we find novel Newtonian gravity models in three space-time dimensions. We first present a Maxwellian version of the extended Newtonian gravity, which is obtained as the non-relativistic limit of a particular U(1)-enlargement of an enhanced Maxwell Chern-Simons gravity. We show that the extended Newtonian gravity appears as a particular sub-case. Then, the introduction of a cosmological constant to the Maxwellian extended Newtonian theory is also explored. To this purpose, we consider the non-relativistic limit of an enlarged symmetry. An alternative method to obtain our results is presented by applying the semigroup expansion method to the enhanced Nappi-Witten algebra. The advantages of considering the Lie algebra expansion procedure is also discussed.

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Characteristic cohomology and observables in higher spin gravity

Journal of High Energy Physics ◽

10.1007/jhep12(2020)190 ◽

2020 ◽

Vol 2020 (12) ◽

Author(s):

Alexey Sharapov ◽

Evgeny Skvortsov

Keyword(s):

Higher Spin Gravity ◽

Complete Classification ◽

Gravity Models ◽

Simons Theory ◽

Surface Charges ◽

Higher Spin ◽

Dynamical Invariants ◽

Chern Simons ◽

Conserved Currents

Abstract We give a complete classification of dynamical invariants in 3d and 4d Higher Spin Gravity models, with some comments on arbitrary d. These include holographic correlation functions, interaction vertices, on-shell actions, conserved currents, surface charges, and some others. Surprisingly, there are a good many conserved p-form currents with various p. The last fact, being in tension with ‘no nontrivial conserved currents in quantum gravity’ and similar statements, gives an indication of hidden integrability of the models. Our results rely on a systematic computation of Hochschild, cyclic, and Chevalley-Eilenberg cohomology for the corresponding higher spin algebras. A new invariant in Chern-Simons theory with the Weyl algebra as gauge algebra is also presented.

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Strategy for the realisation of the International Height Reference System (IHRS)

Journal of Geodesy ◽

10.1007/s00190-021-01481-0 ◽

2021 ◽

Vol 95 (3) ◽

Cited By ~ 4

Author(s):

Laura Sánchez ◽

Jonas Ågren ◽

Jianliang Huang ◽

Yan Ming Wang ◽

Jaakko Mäkinen ◽

...

Keyword(s):

Gravity Field ◽

Reference System ◽

International Association ◽

Accuracy Assessment ◽

Equipotential Surface ◽

Precise Determination ◽

Gravity Models ◽

Reference Network ◽

Global Gravity Models

AbstractIn 2015, the International Association of Geodesy defined the International Height Reference System (IHRS) as the conventional gravity field-related global height system. The IHRS is a geopotential reference system co-rotating with the Earth. Coordinates of points or objects close to or on the Earth’s surface are given by geopotential numbersC(P) referring to an equipotential surface defined by the conventional valueW0 = 62,636,853.4 m2 s−2, and geocentric Cartesian coordinatesXreferring to the International Terrestrial Reference System (ITRS). Current efforts concentrate on an accurate, consistent, and well-defined realisation of the IHRS to provide an international standard for the precise determination of physical coordinates worldwide. Accordingly, this study focuses on the strategy for the realisation of the IHRS; i.e. the establishment of the International Height Reference Frame (IHRF). Four main aspects are considered: (1) methods for the determination of IHRF physical coordinates; (2) standards and conventions needed to ensure consistency between the definition and the realisation of the reference system; (3) criteria for the IHRF reference network design and station selection; and (4) operational infrastructure to guarantee a reliable and long-term sustainability of the IHRF. A highlight of this work is the evaluation of different approaches for the determination and accuracy assessment of IHRF coordinates based on the existing resources, namely (1) global gravity models of high resolution, (2) precise regional gravity field modelling, and (3) vertical datum unification of the local height systems into the IHRF. After a detailed discussion of the advantages, current limitations, and possibilities of improvement in the coordinate determination using these options, we define a strategy for the establishment of the IHRF including data requirements, a set of minimum standards/conventions for the determination of potential coordinates, a first IHRF reference network configuration, and a proposal to create a component of the International Gravity Field Service (IGFS) dedicated to the maintenance and servicing of the IHRS/IHRF.

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Dwarf galaxies without dark matter: constraints on modified gravity

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3653 ◽

2020 ◽

Vol 501 (1) ◽

pp. 254-260

Author(s):

Ali Rida Khalifeh ◽

Raul Jimenez

Keyword(s):

Dark Matter ◽

Modified Gravity ◽

Virial Theorem ◽

Dwarf Galaxies ◽

Strong Support ◽

Gravity Models ◽

Birkhoff Theorem ◽

Astronomical Surveys ◽

Stringent Test ◽

Modified Gravity Models

ABSTRACT The discovery of 19 dwarf galaxies without dark matter (DM) provides, counterintuitively, strong support for the ΛCDM standard model of cosmology. Their presence is well accommodated in a scenario where the DM is in the form of cold dark particles. However, it is interesting to explore quantitatively what is needed from modified gravity models to accommodate the presence of these galaxies and what extra degree of freedom is needed in these models. To this end, we derive the dynamics at galaxy scales (Virial theorem) for a general class of modified gravity models. We distinguish between theories that satisfy the Jebsen–Birkhoff theorem, and those that do not. Our aim is to develop tests that can distinguish whether DM is part of the theory of gravity or a particle. The 19 dwarf galaxies discovered provide us with a stringent test for models of modified gravity. Our main finding is that there will always be an extra contribution to the Virial theorem coming from the modification of gravity, even if a certain galaxy shows very small, if not negligible, trace of DM, as has been reported recently. Thus, if these and more galaxies are confirmed as devoid (or negligible) of DM, while other similar galaxies have abundant DM, it seems interesting to find modifications of gravity to describe DM. Our result can be used by future astronomical surveys to put constraints on the parameters of modified gravity models at astrophysical scales where DM is described as such.

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Gravity Models in International Trade: An Exploration in Econo-Physics

South Asian Journal of Macroeconomics and Public Finance ◽

10.1177/2277978721989922 ◽

2021 ◽

pp. 227797872198992

Author(s):

Iman Pal ◽

Saibal Kar

Keyword(s):

Pattern Recognition ◽

International Trade ◽

Present Article ◽

Gravity Models ◽

Scientific Applications ◽

Physical Sciences ◽

Trade Patterns ◽

Pattern Recognition Techniques ◽

The Subject ◽

Jel Classifications

Several strands of the static and dynamic theoretical constructs and the empirical applications in the subject of economics owe substantially to the well-known principles of physical sciences. The present article explores as to how the development of the popular gravity models in international trade can be traced back to Newton’s law of gravitation, and to both Ohm’s Law and Kirchhoff’s Law of current electricity, as well as to the pattern recognition techniques commonly deployed in scientific applications. In addition to surveying these theoretical analogies, the article also offers numerical applications for observed trade patterns between India and a set of countries. JEL Classifications: F41, F42, C61, F47

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Does the Cosmological Expansion Change Local Dynamics?

Symmetry ◽

10.3390/sym13081417 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1417

Author(s):

Marcelo Schiffer

Keyword(s):

Dark Matter ◽

Modified Gravity ◽

Hubble Constant ◽

Matter Content ◽

Matter Distribution ◽

Present Value ◽

Field Equations ◽

Local Dynamics ◽

Cosmological Expansion ◽

Modified Gravity Theories

It is a well-known fact that the Newtonian description of dynamics within Galaxies for its known matter content is in disagreement with the observations as the acceleration approaches a0≈1.2×10−10 m/s2 (slighter larger for clusters). Both the Dark Matter scenario and Modified Gravity Theories (MGT) fail to explain the existence of such an acceleration scale. Motivated by the closeness of the acceleration scale and the Hubble constant cH0≈10−9 h m/s2, we are led to analyze whether this coincidence might have a Cosmological origin for scalar-tensor and spinor-tensor theories by performing detailed calculations for perturbations that represent the local matter distribution on the top of the cosmological background. Then, we solve the field equations for these perturbations in a power series in the present value of the Hubble constant. As we shall see, for both theories, the power expansion contains only even powers in the Hubble constant, a fact that renders the cosmological expansion irrelevant for the local dynamics.

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