Abstract
The detection of Primordial Gravitational Waves (PGWs) is one of the most important goals of modern cosmology since PGWs can both provide substantial evidence for primordial inflation and shed light on its physical nature. Small scale experiments on gravitational waves such as LIGO/VIRGO and, in future, LISA and Einstein Telescope (ET), being sensitive to the stochastic background of gravitational waves, can be used together with the CMB data to constrain the inflationary parameters. In performing these analyses the primordial tensor spectrum is usually parametrized with a power law that includes only the amplitude and a scale independent tilt. In this paper, we investigate the robustness of assuming the tensor tilt as scale independent. We show that due to the huge difference in the scales probed by CMB and GWs data, even a small scale dependence can remarkably affect the shape of the primordial spectrum possibly breaking the power-law assumption. When the non-linear corrections are considered the final constraints can be significantly changed. We also study the scale dependence in two different physical models of inflation providing an example of negligible scale dependence and an example of non-negligible scale dependence.
Highlights
The search for primordial gravitational waves (PGWs) is one of the main goals of modern cosmology as they can both provide a substantial evidence for primordial inflation and shed light on its physical nature [1,2,3,4]
In particular from the LIGO/VIRGO bound on ΩGW, Eq(1), under the assumption of a scale independent tilt, an upper bound nt < 0.53 at 95% C.L. is derived combining the Cosmic Microwave Background (CMB) and GW data [18]
We have shown that when the assumption of scale independence is relaxed, the constraints may become very sensitive to the higher order corrections in the power law expansion and that even a tiny scale dependence can significantly change the above mentioned constraints
Summary
The search for primordial gravitational waves (PGWs) is one of the main goals of modern cosmology as they can both provide a substantial evidence for primordial inflation and shed light on its physical nature [1,2,3,4]. In the upcoming decade, a new generation of CMB experiments such as BICEP3 [19], CLASS [20] , SPT-3G [21], Advanced ACTPol [22], LBIRD [23] and CMB-S4 [24] are expected to bring the sensitivity to the tensor amplitude down to r ∼ 0.01 − 0.001 possibly leading to its first detection In deriving such bounds the slow roll consistency relation nt = −r/8 is usually assumed, basically leading to an almost scale independent slightly red tilted primordial tensor spectrum Pt(k).
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call