Towards a measurement of the spectral runnings
2016
Single-field
slow-rollinflation predicts a nearly scale-free power spectrum of perturbations, as observed at the scales accessible to current cosmological experiments. This spectrum is slightly red, showing a tilt $(1-n_s)\sim 0.04$. A direct consequence of this tilt are nonvanishing runnings $\alpha_s=\mathrm d n_s/\mathrm d\log k$, and $\beta_s=\mathrm d\alpha_s/\mathrm d\log k$, which in the minimal inflationary scenario should reach absolute values of $10^{-3}$ and $10^{-5}$, respectively. In this work we calculate how well future surveys can measure these two runnings. We consider a Stage-4 (S4) CMB experiment and show that it will be able to detect significant deviations from the inflationary prediction for $\alpha_s$, although not for $\beta_s$. Adding to the S4 CMB experiment the information from a WFIRST-like, a
DESI-like, or a SKA-like galaxy survey improves the sensitivity to the runnings by $\sim$ 5\%, 15\%, and 25\%, respectively. A spectroscopic survey with a billion objects, such as
SKA2, will add enough information to the S4 measurements to allow a detection of $\alpha_s=10^{-3}$, required to probe the single-field
slow-rollinflationary paradigm. We show that a kilometer-long Epoch-of-
Reionizationinterferometric array can also reach this level of sensitivity to $\alpha_s$, although only a more
futuristic
dark-agesarray will be capable of measuring the minimal inflationary prediction for $\beta_s$. The results of other probes, such as a stochastic background of gravitational waves observable by
LIGO, the Ly-$\alpha$ forest, and spectral distortions, are shown for comparison. Finally, we study the claims that large values of $\beta_s$, if extrapolated to the smallest scales, can produce
primordial black holesof tens of
solar masses, which we show to be easily testable by the S4 CMB experiment.
Keywords:
-
Correction
-
Cite
-
Save
0
References
1
Citations
NaN
KQI