Spatially homogeneous black hole solutions in $$z=4$$ Hořava–Lifshitz gravity in $$(4+1)$$ dimensions with Nil geometry and $$H^2\times R$$ horizons

In this paper, we present two new families of spatially homogeneous black hole solution for $$z=4$$ z = 4 Hořava–Lifshitz Gravity equations in $$(4+1)$$ ( 4 + 1 ) dimensions with general coupling constant $$\lambda $$ λ and the especial case $$\lambda =1$$ λ = 1 , considering $$\beta =-1/3$$ β = - 1 / 3 . The three-dimensional horizons are considered to have Bianchi types II and III symmetries, and hence the horizons are modeled on two types of Thurston 3-geometries, namely the Nil geometry and $$H^2\times R$$ H 2 × R . Being foliated by compact 3-manifolds, the horizons are neither spherical, hyperbolic, nor toroidal, and therefore are not of the previously studied topological black hole solutions in Hořava–Lifshitz gravity. Using the Hamiltonian formalism, we establish the conventional thermodynamics of the solutions defining the mass and entropy of the black hole solutions for several classes of solutions. It turned out that for both horizon geometries the area term in the entropy receives two non-logarithmic negative corrections proportional to Hořava–Lifshitz parameters. Also, we show that choosing some proper set of parameters the solutions can exhibit locally stable or unstable behavior.

Maxwell-modified metric affine gravity

We present a gauge formulation of the special affine algebra extended to include an antisymmetric tensorial generator belonging to the tensor representation of the special linear group. We then obtain a Maxwell modified metric affine gravity action with a cosmological constant term. We find the field equations of the theory and show that the theory reduces to an Einstein-like equation for metric affine gravity with the source added to the gravity equations with cosmological constant $$\mu $$ μ contains linear contributions from the new gauge fields. The reduction of the Maxwell metric affine gravity to Riemann–Cartan one is discussed and the shear curvature tensor corresponding to the symmetric part of the special linear connection is identified with the dark energy. Furthermore, the new gauge fields are interpreted as geometrical inflaton vector fields which drive accelerated expansion.

Can e-commerce mitigate the negative impact of COVID-19 on international trade?

This study aims to empirically investigate the role of E-commerce (EC) on the trade impacts of COVID-19. To this end, we estimate gravity equations for bilateral trade among 34 reporting countries and their 145 partner countries during January–August in 2019 and 2020. Our major findings can be summarized as follows. A larger number of confirmed cases or deaths in both importing and exporting countries significantly decrease international trade. However, we found that EC development in importing countries contributes to mitigating this negative effect of COVID-19 on trade while that in exporting countries does not. These results are robust for our use of multiple measures of EC development.

From classical theory to spin 2 gravity

We consider here the simple derivation of the Einstein equations by Fock. Then, we approach the way from the spin 1 fields to the spin 2 fields for massive and massless particles and we derive the gravity equations from this base. In conclusion, we discuss the principle of equivalence in classical Einstein theory and in the Schwinger spin 2 gravity

US-China Tariff War: A Gravity Approach

Trade wars occur as a consequence of countries imposing tariffs and/or other trade barriers on one another. Such phenomenon is often a result of nationalism, unilateralism, and protectionism, and intensifies due to retaliation by different sides of the war. We use recent multinational trade data to measure the effects of single- and multi-sided tariffs on international trade. The methodology used in the paper is the structural Gravity model first introduced by Anderson and van Wincoop (2003). Theoretical implications and references of gravity equations are also presented throughout the article.

EVALUATING THE IMPACT OF SANITARY AND PHYTOSANITARY MEASURES ON AGRICULTURAL TRADE: EVIDENCE FROM THAI FRUIT EXPORTS TO CHINA

Food safety concerns have become increasingly important challenge for agricultural trade. Sanitary and phytosanitary (SPS) measures are often considered as major non-tariff trade barriers, which have surged rapidly over the recent decade. This study systematically investigates the impact of China’s SPS measures on Thai fruit exports. The panel dataset is constructed with 17 Thai fruit items for the sample period 2000–2018. Gravity equations are estimated to quantify the trade effects of SPS measures on the value of fruit exports from Thailand to China. The results from the sectoral analysis reveal that the restrictiveness of SPS measures has a positive and substantial effect on export volumes. This suggests that non-arbitrary and informative SPS requirements imposed by a large importing country would help facilitate the agricultural trade.

Triplets, quads and quints: Estimating disaggregate trade elasticities with different odds ratios

Trade elasticities are a crucial variable for research on international trade. Caliendo and Parro (2015) provide a novel method to estimate trade elasticities which is based on odds ratio triplets calculated from structural gravity equations. We find that these odds ratios can be set up not only as triplets, but also e. g. as quadruplets (quads) and quintuples (quints). We estimate trade elasticities from triplets, quads and quints for the two digit level of ISIC Rev.3. The corresponding estimates show certain differences, but the results are generally robust. Because the different odds ratios are all theoretically validated, we suggest using them for checking robustness. Benefits could also arise because larger odds ratios might be able to provide more reliable estimates.

Visualizing Spatial Economic Supply Chains to Enhance Sustainability and Resilience

This article presents a spatial supply network model for estimating and visualizing spatial commodity flows that used data on firm location and employment, an input–output table of inter-industry transactions, and material balance-type equations. Building on earlier work, we proposed a general method for visualizing detailed supply chains across geographic space, applying the preferential attachment rule to gravity equations in the network context; we then provided illustrations for U.S. extractive, manufacturing, and service industries, also highlighting differences in rural–urban interdependencies across these sectors. The resulting visualizations may be helpful for better understanding supply chain geographies, as well as business interconnections and interdependencies, and to anticipate and potentially address vulnerabilities to different types of shocks.

The effect of sanctions on Russian agricultural imports

This paper contributes to the methodology of trade policy analysis, specifically to the assessments of non -tariff measures. To quantifying the effects of these measures, the proportion between the variables of two gravity equations, describing the situation before and after the embargo is used. The ratio of imports per unit of the supplier’s GDP over the two compared periods (2013 and 2017) is different for two groups of trade partners, one of which includes free-trade partners while the other spans the rest of the world (with some exceptions). In the presence of the embargo the gap in the average imports per unit of the supplier’s GDP between the two groups is wider. This is a consequence of the emergence of a new trade barrier. This gap allows us to indirectly quantify the trade bans via their tariff equivalent. In this study the methodology is applied to the case of food and agricultural imports. Fish, as well as other products outside chapters 1–24 of Harmonized commodity description and coding system, are excluded. The hypothesis of the study is that the impact of the embargo on the food and agricultural imports does not exceed that of tariff and phytosanitary measures. The study rejects this hypothesis and concludes that the embargo establishes a prohibitive level of protection.