We present classical solutions for a D5 and NS5-branes in a pp-wave background. The worldvolume coordinates for these branes lie along a six dimensional pp-wave configuration obtained from AdS 3 × S 3 in a Penrose limit. One in addition has nontrivial R-R 3-form field strength as well as a dilaton background. Classical solutions for Dp-branes (p > 5), as well as their bound states, are then generated in both IIA and IIB string theories by using T -duality symmetries. We also briefly discuss the construction of Dp-branes in ppwave backgrounds, obtained from string theories on AdS m ×S m . Finally, the construction of the above D5-brane solution is presented from the point of view of the Green-Schwarz worldsheet string theory and its low lying spectrum is discussed.String theory in the presence of pp-wave backgrounds [1][2][3][4][5][6][7] has generated lots of excitement among physicists searching for a deep connection between quatum gravity and gauge theory dynamics. Such string backgrounds are technically tractable, and have direct applications to the four dimensional conformal theories from the point of view of a duality between string and gauge theories. The fact that pp-waves provide exact solutions of string theory, including in the presence of R − R fields [4], is now known for long time. It has now been realized [8,9] that in some special cases, they give rise to exactly solvable string theory with a quadratic action. As a result the spectrum of the theory can be explicitly obtained. Moreover, an interesting connection of pp-wave background with gauge field theories emerges by realizing that they can be obtained [10]

We study D-branes in a two-dimensional Lorentzian orbifold R 1,1 /Γ with a discrete boost Γ. This space is known as Misner or Milne space, and includes big crunch/big bang singularity. In this space, there are D0-branes in spiral orbits and D1-branes with or without flux on them. In particular, we observe imaginary parts of partition functions, and interpret them as the rates of open string pair creation for D0-branes and emission of winding closed strings for D1-branes. These phenomena occur due to the time-dependence of the background. Open string 2 → 2 scattering amplitude on a D1-brane is also computed and found to be less singular than closed string case. *

We study solutions for rigidly rotating strings on a two sphere. Among them we find two limiting cases that have a particular interest, one is the already known giant magnon and the other we call the single spike solution. The limiting behavior of this last solution is a string infinitely wrapped around the equator. It differs from that solution by the existence of a single spike of height ¯ θ that points toward the north pole. We study its properties and compute its energy E and angular momentum J as a function of ¯ θ. We further generalize the solution by adding one angular momentum to obtain a solution on S 3. We find a spin chain interpretation of these results in terms of free fermions and the Hubbard model but the exact relation with the same models derived from the field theory is not clear.

A class of time dependent pp-waves with NS-NS flux in type IIA string theory is considered. The background preserves 1/4 supersymmetry and may provide a toy model of Big Bang cosmology with non trivial flux. At the Big Bang singularity in early past, the string theory is strongly coupled and Matrix string model can be used to describe the dynamics. We also construct some time dependent supergravity solutions for D-branes and analyze their supersymmetry properties.Comment: 11 pages, a typo is fixed in eqn 20. To appear in Phys. Lett.

We study the giant magnon solutions in the near horizon geometry of the Neveu-Schwarz (NS) 5-brane background. In conformal gauge, we find magnon dispersion relation in the large angular momentum (J) limit. We further show that the giant magnon poses uniform distribution of the angular momentum along the string world-sheet as in case of AdS 5 × S 5 spacetime.