DF-strings fromD33 as cosmic strings

We study Dirac-Born-Infeld type effective field theory of a complex tachyonand U(1)$\times$U(1) gauge fields describing a D3${\bar {\rm D}}$3 system.Classical solutions of straight global and local DF-strings with quantizedvorticity are found and are classified into two types by the asymptoticbehavior of the tachyon amplitude. For sufficiently large radial distances, onehas linearly-growing tachyon amplitude and the other logarithmically-growingtachyon amplitude. A constant radial electric flux density denoting thefundamental-string background makes the obtained DF-strings thick. The otherelectric flux density parallel to the strings is localized, which representslocalization of fundamental strings in the D1-F1 bound states. Since theseDF-strings are formed in the coincidence limit of the D3${\bar {\rm D}}$3,these cosmic DF-strings are safe from inflation induced by the approach of theseparated D3 and ${\bar {\rm D}}3$.Comment: 23 pages, 5 eps figure