Early structure formation with cold plus hot dark matter --- a success of strings plus inflation model

Quantum fluctuations created during inflation can account for the observed matter distribution in the linear regime if the universe has two components of dark matter, one which is cold and collisionless, and the other which is hot and free streams on small scales. However, this free streaming property of the hot component prevents early structure formation, and since objects, such as damped Lyman-$\alpha$ systems, have been observed at high redshift, it is necessary to produce more power on small scales. Here, we show that the situation can be improved substantially in models where cosmic strings are formed at the end of inflation, and in which both inflation and strings participate in the generation of structure.