Search results for "gravity"
showing 10 items of 537 documents
Oh, wait, O8 de Sitter may be unstable!
2021
We analyze the stability of four-dimensional de Sitter vacua constructed by compactifying massive Type IIA supergravity in the presence of two O8 sources [1]. When embedded in String Theory the first source has a clear interpretation as an O8$_-$ plane, but the second one could correspond to either an O8$_+$ plane or to an O8$_-$ plane with 16 D8-branes on top. We find that this latter solution has a tachyonic instability, corresponding to the D8-branes moving away from the O8$_-$ plane. We comment on the possible ways of distinguishing between these sources.
Induced-Gravity Inflation in Supergravity Confronted with Planck2013 and BICEP2
2015
Supersymmetric versions of induced-gravity inflation are f ormulated within Super- gravity (SUGRA) employing two gauge singlet chiral superfie lds. The proposed superpotential is uniquely determined by applying a continuous R and a discrete Z2 symmetry. We also employ a logarithmic Kahler potential respecting the symmetries above and including all the allowed terms up to fourth order in powers of the various fields. When the Kahle r manifold exhibits a no-scale-type symmetry, the model predicts spectral index ns ≃ 0.963 and tensor-to-scalar r ≃ 0.004. Beyond no-scale SUGRA, ns and r depend crucially on the coefficient kSΦ involved in the fourth order term, which mixes the inflaton Φ with th…
From hybrid to quadratic inflation with high-scale supersymmetry breaking
2014
Motivated by the reported discovery of inflationary gravity waves by the BICEP2 experiment, we propose an inflationary scenario in supergravity, based on the standard superpotential used in hybrid inflation. The new model yields a tensor-to-scalar ratio r ~ 0.14 and scalar spectral index ns ~ 0.964, corresponding to quadratic (chaotic) inflation. The important new ingredients are the high-scale, (1.6-10) x 10^13 GeV, soft supersymmetry breaking mass for the gauge singlet inflaton field and a shift symmetry imposed on the K\"ahler potential. The end of inflation is accompanied, as in the earlier hybrid inflation models, by the breaking of a gauge symmetry at (1.2-7.1) x 10^16 GeV, comparable…
Institutional Quality and International Competitiveness
2008
Cross-Border Higher Education : The Expansion of International Branch Campuses
2022
AbstractThe international expansion of higher education has intensified in recent decades with a rapidly growing number of international branch campuses appearing on the scene. This study investigates the economic, cultural and institutional, and educational determinants of transnational higher education on both the extensive margin (number of international branch campuses), and the intensive margin (the total number of educational programmes offered). Using the gravity equation, we applied fixed-effect empirical methods to a panel dataset that combined and extended the raw data from campuses and master’s programmes in 33 source countries and 76 host countries in the period from 1948 to 201…
Statistical Thermodynamics of Polymer Quantum Systems
2011
Polymer quantum systems are mechanical models quantized similarly as loop quantum gravity. It is actually in quantizing gravity that the polymer term holds proper as the quantum geometry excitations yield a reminiscent of a polymer material. In such an approach both non-singular cosmological models and a microscopic basis for the entropy of some black holes have arisen. Also important physical questions for these systems involve thermodynamics. With this motivation, in this work, we study the statistical thermody- namics of two one dimensional polymer quantum systems: an ensemble of oscillators that describe a solid and a bunch of non-interacting particles in a box, which thus form an ideal…
THE COST AS THE MAIN DETERMINANT OF THE LOCATION OF LOGSTICS CENTERS
2018
Apropriate location of the logistics center allows entrepreneurs to significantly reduce the costs of transport. On the other hand, it has a positive impact on the development of the transport infrastructure of the region.This paper presents the practical aspects of the localization problem of logistics center with the use of a geographic information system. It shows differences between theoretical models, the needs of decision-makers, and the data available to make the necessary calculations. The results of computational experiments were introduced to illustrate the effects of this approach.
On eleven-dimensional supergravity and chern?SIMONS Theory
2012
We probe in some depth into the structure of eleven-dimensional, osp(32|1)-based Chern-Simons supergravity, as put forward by Troncoso and Zanelli (TZ) in 1997. We find that the TZ Lagrangian may be cast as a polynomial in 1/l, where l is a length, and compute explicitly the first three dominant terms. The term proportional to 1/l^9 turns out to be essentially the Lagrangian of the standard 1978 supergravity theory of Cremmer, Julia and Scherk, thus establishing a previously unknown relation between the two theories. The computation is nontrivial because, when written in a sufficiently explicit way, the TZ Lagrangian has roughly one thousand non-explicitly Lorentz-covariant terms. Specially…
On the absence of BPS preonic solutions in IIA and IIB supergravities
2006
We consider the present absence of 31 out of 32 supersymmetric solutions in supergravity i.e., of solutions describing BPS preons. A recent result indicates that (bosonic) BPS preonic solutions do not exist in type IIB supergravity. We reconsider this analysis by using the G-frame method, extend it to the IIA supergravity case, and show that there are no (bosonic) preonic solutions for type IIA either. For the classical D=11 supergravity no conclusion can be drawn yet, although the negative IIA results permit establishing the conditions that preonic solutions would have to satisfy. For supergravities with `stringy' corrections, the existence of BPS preonic solutions remains fully open.
Two end-members of carbonate slope evolution during the Late Cretaceous in the peri-Tethyan domain (Western Sicily and Southern Albania)
2019
Climatic and tectonic processes are major mechanisms influencing tropical carbonate platform development, sediment production and sediment export. Mass transport deposits (including slides, slumps and debrites) and calciturbidites are some of the sediment export products resulting from the interplay of aforementioned redeposition mechanisms. They reflect distinct variations in both production and export of sediments from the carbonate factories. The gravitary export deposits provide information on their sediment source and result in sedimentary sequences with specific porosity / permeability properties prone to host hydrocarbon resources. Climate-controlled sea-level variations are well-con…