Moduli Redefinitions and Moduli Stabilisation

Field redefinitions occur in string compactifications at the one loop level. We review arguments for why such redefinitions occur and study their effect on moduli stabilisation and supersymmetry breaking in the LARGE volume scenario. For small moduli, although the effect of such redefinitions can be larger than that of the $\alpha'$ corrections in both the K\"ahler and scalar potentials, they do not alter the structure of the scalar potential. For the less well motivated case of large moduli, the redefinitions can dominate all other terms in the scalar potential. We also study the effect of redefinitions on the structure of supersymmetry breaking and soft terms.Comment: 21 pages, 3 figures; v2. references adde

Superpotential de-sequestering in string models

Non-perturbative superpotential cross-couplings between visible sector matter and K\"ahler moduli can lead to significant flavour-changing neutral currents in compactifications of type IIB string theory. Here, we compute corrections to Yukawa couplings in orbifold models with chiral matter localised on D3-branes and non-perturbative effects on distant D7-branes. By evaluating a threshold correction to the D7-brane gauge coupling, we determine conditions under which the non-perturbative corrections to the Yukawa couplings appear. The flavour structure of the induced Yukawa coupling generically fails to be aligned with the tree-flavour structure. We check our results by also evaluating a correlation function of two D7-brane gauginos and a D3-brane Yukawa coupling. Finally, by calculating a string amplitude between n hidden scalars and visible matter we show how non-vanishing vacuum expectation values of distant D7-brane scalars, if present, may correct visible Yukawa couplings with a flavour structure that differs from the tree-level flavour structure.Comment: 37 pages + appendices, 8 figure

Constraints on LVS Compactifications of IIB String Theory

We argue that once all theoretical and phenomenological constraints are imposed on the different versions of the Large Volume Scenario (LVS) compactifications of type IIB string theory, one particular version is favored. This is essentially a sequestered one in which the soft terms are generated by Weyl anomaly and RG running effects. We also show that arguments questioning sequestering in LVS models are not relevant in this case.Comment: 14 pages, additional discussion of D7 brane case and mSUGRA, reference adde

Collided path replanning in dynamic environments using RRT and Cell decomposition algorithms

The motion planning is an important part of robots’ models. It is responsible for robot’s movements. In this work, the cell decomposition algorithm is used to find a spatial path on preliminary static workspaces, and then, the rapidly exploring random tree algorithm (RRT) is used to validate this path on the actual workspace. Two methods have been proposed to enhance the omnidirectional robot’s navigation on partially changed workspace. First, the planner creates a RRT tree and biases its growth toward the path’s points in ordered form. The planner reduces the probability of choosing the next point when a collision is detected, which in turn increases the RRT’s expansion on the free space. The second method uses a straight planner to connect path’s points. If a collision is detected, the planner places RRTs on both sides of the collided segment. The proposed methods are compared with the others approaches, and the simulation shows better results in term of efficiency and completeness.Plánování pohybu robota je důležitou součástí modelování funkcí robotů. Plán řídí pohyby robota. V této práci se algoritmus rozkladu na buňky používá k nalezení cesty pracovní plochou a algoritmus prozkoumání náhodného stromu (RRT) k ověření cesty skutečným prostorem. Byly navrženy dvě metody ke zlepšení navigace všesměrové pohyblivého robota částečně změněnou pracovní plochou. Za prvé, plánovač vytvoří RRT strom a vychyluje jeho růst směrem k bodu na cestě. Plánovač snižuje pravděpodobnost výběru dalšího bodu, když je detekována kolize, což zase zvyšuje expanzi RRT na volném prostoru. Druhá metoda používá shodný plánovač pro napojení bodů cesty. Pokud je detekována kolize, plánovač upravuje RRT na obou stranách kolizního segmentu. Navrhované metody jsou porovnávány s dalšími používanými přístupy, přečemž simulace ukazuje lepší výsledky z hlediska účinnosti a úplnosti plánování cesty.The motion planning is an important part of robots’ models. It is responsible for robot’s movements. In this work, the cell decomposition algorithm is used to find a spatial path on preliminary static workspaces, and then, the rapidly exploring random tree algorithm (RRT) is used to validate this path on the actual workspace. Two methods have been proposed to enhance the omnidirectional robot’s navigation on partially changed workspace. First, the planner creates a RRT tree and biases its growth toward the path’s points in ordered form. The planner reduces the probability of choosing the next point when a collision is detected, which in turn increases the RRT’s expansion on the free space. The second method uses a straight planner to connect path’s points. If a collision is detected, the planner places RRTs on both sides of the collided segment. The proposed methods are compared with the others approaches, and the simulation shows better results in term of efficiency and completeness

Dark Radiation and Dark Matter in Large Volume Compactifications

We argue that dark radiation is naturally generated from the decay of the overall volume modulus in the LARGE volume scenario. We consider both sequestered and non-sequestered cases, and find that the axionic superpartner of the modulus is produced by the modulus decay and it can account for the dark radiation suggested by observations, while the modulus decay through the Giudice-Masiero term gives the dominant contribution to the total decay rate. In the sequestered case, the lightest supersymmetric particles produced by the modulus decay can naturally account for the observed dark matter density. In the non-sequestered case, on the other hand, the supersymmetric particles are not produced by the modulus decay, since the soft masses are of order the heavy gravitino mass. The QCD axion will then be a plausible dark matter candidate.Comment: 27 pages, 4 figures; version 3: version published in JHE

Moduli Stabilization and Inflationary Cosmology with Poly-Instantons in Type IIB Orientifolds

Equipped with concrete examples of Type IIB orientifolds featuring poly-instanton corrections to the superpotential, the effects on moduli stabilization and inflationary cosmology are analyzed. Working in the framework of the LARGE volume scenario, the Kaehler modulus related to the size of the four-cycle supporting the poly-instanton contributes sub-dominantly to the scalar potential. It is shown that this Kaehler modulus gets stabilized and, by displacing it from its minimum, can play the role of an inflaton. Subsequent cosmological implications are discussed and compared to experimental data.Comment: 38 pages, 7 figures, Reference added, Typo fixed, Published versio

Quantitative projections of a quality measure: Performance of a complex task

AbstractComplex data series that arise during interaction between humans (operators) and advanced technology in a controlled and realistic setting have been explored. The purpose is to obtain quantitative measures that reflect quality in task performance: on a ship simulator, nine crews have solved the same exercise, and detailed maneuvering histories have been logged. There are many degrees of freedom, some of them connected to the fact that the vessels may be freely moved in any direction. To compare maneuvering histories, several measures were used: the time needed to reach the position of operation, the integrated angle between the hull direction and the direction of motion, and the extent of movement when the vessel is to be manually kept in a fixed position. These measures are expected to reflect quality in performance. We have also obtained expert quality evaluations of the crews. The quantitative measures and the expert evaluations, taken together, allow a ranking of crew performance. However, except for time and integrated angle, there is no correlation between the individual measures. This may indicate that complex situations with social and man–machine interactions need complex measures of quality in task performance. In general terms, we have established a context-dependent and flexible framework with quantitative measures in contact with a social-science concept that is hard to define. This approach may be useful for other (qualitative) concepts in social science that contain important information on the society

Simulation-based analysis of micro-robots swimming at the center and near the wall of circular mini-channels

Swimming micro robots have great potential in biomedical applications such as targeted drug delivery, medical diagnosis, and destroying blood clots in arteries. Inspired by swimming micro organisms, micro robots can move in biofluids with helical tails attached to their bodies. In order to design and navigate micro robots, hydrodynamic characteristics of the flow field must be understood well. This work presents computational fluid dynamics (CFD) modeling and analysis of the flow due to the motion of micro robots that consist of magnetic heads and helical tails inside fluid-filled channels akin to bodily conduits; special emphasis is on the effects of the radial position of the robot. Time-averaged velocities, forces, torques, and efficiency of the micro robots placed in the channels are analyzed as functions of rotation frequency, helical pitch (wavelength) and helical radius (amplitude) of the tail. Results indicate that robots move faster and more efficiently near the wall than at the center of the channel. Forces acting on micro robots are asymmetrical due to the chirality of the robot’s tail and its motion. Moreover, robots placed near the wall have a different flow pattern around the head when compared to in-center and unbounded swimmers. According to simulation results, time-averaged for-ward velocity of the robot agrees well with the experimental values measured previously for a robot with almost the same dimensions