A model for multi-quark systems

As a step towards understanding multi-quark systems abundant in nature we construct a model that reproduces the binding energies of static four-quark systems. These energies have been calculated using SU(2) lattice gauge theory for a set of six different geometries representative of the general case. The model is based on ground and excited state two-body potentials and multi-quark interaction terms.Comment: 10 pages, one LaTeX figur

An interquark potential model for multi-quark systems

A potential model for four interacting quarks is constructed in SU(2) from six basis states -- the three partitions into quark pairs, where the gluon field is either in its ground state or first excited state. With four independent parameters to describe the interactions connecting these basis states, it is possible to fit 100 pieces of data -- the ground and first excited states of configurations from six different four-quark geometries calculated on a 16^3*32 lattice.Comment: 14 page

Four-quark flux distribution and binding in lattice SU(2)

The full spatial distribution of the color fields of two and four static quarks is measured in lattice SU(2) field theory at separations up to 1 fm at beta=2.4. The four-quark case is equivalent to a qbar q qbar q system in SU(2) and is relevant to meson-meson interactions. By subtracting two-body flux tubes from the four-quark distribution we isolate the flux contribution connected with the four-body binding energy. This contribution is further studied using a model for the binding energies. Lattice sum rules for two and four quarks are used to verify the results.Comment: 46 pages including 71 eps figures. 3D color figures are available at www.physics.helsinki.fi/~ppennane/pics

Decoupling between Lovelace’s checker server and main server

Abstract. Thesis provides an introduction to online learning environment Lovelace, defnes its coupling issues, and narrates the process of decoupling those issues. The tools that are used in the Lovelace system’s components main features and their role in the system are described and the term decoupling is explained to the reader. The system has a coupling issue between the main server and checker service; checker service has read and write access to the main server’s database and that needs to be revoked. In addition, Lovelace system utilizes network fle system to share fles between the checker service and the main server. For decoupling the system, a solution is designed and implemented that revokes those read and write rights and also strips the need for the network fle system. Solution for the issue has a three-step design where iterations are in order of importance. Iterations of the design are: revoking the write access; revoking the read access; and lastly the consideration regarding the use of network fle system. Implementation of the solution consist of creation of the development platform and each iteration of the implementation design. Evaluation is structured in a similar manner as the implementation. Each iteration of the implementation is evaluated as its own and evaluation is also given to the development platform. The evaluation itself consists of discussion and observations that are made from the implementations and its outcomes.Lovelacen tarkastinpalvelimen ja pääpalvelimen irtikytkentä. Tiivistelmä. Tutkielma esittelee verkko-oppimisympäristö Lovelacen, määrittelee oppimisympäristön kytkentäongelmat sekä kuvailee irtikytkennän vaiheet, että näiden vaiheiden ongelmat. Lovelace-järjestelmän komponentit ja niiden olennaisimmat ominaisuudet, sekä rooli järjestelmän toiminnassa on selitetty, ja termi irtikytkentä selitetään lukijalle. Järjestelmässä on kytkentäongelma pääpalvelimen sekä tarkistuspalvelimen välillä. Tarkistuspalvelimella on sekä luku- että kirjoitusoikeudet järjestelmän pääpalvelimen tietokantaan, jotka täytyy kumota. Järjestelmä jakaa myös tiedostoja lähiverkon yli palvelimelta toiselle, joka on osa palvelimien tiedonvaihtoa. Irtikytkentää varten suunnitellaan sekä toteutetaan ratkaisu, jolla tarkistinpalvelimen luku- ja kirjoitusoikeus pääpalvelimen tietokantaan evätään ja tiedostojen jaon tarve verkon yli lopetetaan. Toteutuksen ratkaisumalli on kolmeportainen, tärkeysjärjestykseen listattuna. Ratkaisumallin vaiheet ovat: tarkistuspalvelimen kirjoitusoikeuden kumoaminen, tarkistuspalvelimen tietokannan lukuoikeuden kumoaminen sekä tiedostojen verkon yli jakamisen tarpeellisuuden arviointi. Projektin toteutus koostuu kehitysympäristön rakentamisesta, sekä ratkaisumallin jokaisesta vaiheesta. Toteutuksen arviointi on jäsennelty alkuperäistä ratkaisumallia vastaavasti, arviointi tapahtuu erikseen jokaiselle vaiheelle sekä kehitysympäristö arvioidaan. Arviointi koostuu keskustelusta sekä havainnoista, joita toteutuksesta havaitaan

BB Potentials in Quenched Lattice QCD

The potentials between two B-mesons are computed in the heavy-quark limit using quenched lattice QCD at $m_\pi\sim 400~{\rm MeV}$. Non-zero central potentials are clearly evident in all four spin-isospin channels, (I,s_l) = (0,0) , (0,1) , (1,0) , (1,1), where s_l is the total spin of the light degrees of freedom. At short distance, we find repulsion in the $I\ne s_l$ channels and attraction in the I=s_l channels. Linear combinations of these potentials that have well-defined spin and isospin in the t-channel are found, in three of the four cases, to have substantially smaller uncertainties than the potentials defined with the s-channel (I,s_l), and allow quenching artifacts from single hairpin exchange to be isolated. The BB*\pi coupling extracted from the long-distance behavior of the finite-volume t-channel potential is found to be consistent with quenched calculations of the matrix element of the isovector axial-current. The tensor potentials in both of the s_l = 1 channels are found to be consistent with zero within calculational uncertainties.Comment: 30 page