Accessibility of the Pre-Big Bang Models to LIGO

The recent search for a stochastic background of gravitational waves with LIGO interferometers has produced a new upper bound on the amplitude of this background in the 100 Hz region. We investigate the implications of the current and future LIGO results on pre-Big-Bang models of the early Universe, determining the exclusion regions in the parameter space of the minimal pre-Big Bang scenario. Although the current LIGO reach is still weaker than the indirect bound from Big-Bang nucleosynthesis, future runs by LIGO, in the coming year, and by Advanced LIGO (∼2009) should further constrain the parameter space, and in some parts surpass the Big-Bang nucleosynthesis bound. It will be more difficult to constrain the parameter space in non-minimal pre-Big-Bang models, which are characterized by multiple cosmological phases in the yet not well understood stringy phase, and where the higher-order curvature and/or quantum-loop corrections in the string effective action should be included.